Patent Publication Number: US-2015085980-A1

Title: Radiological image-capturing device, radiological image-capturing system, radiological image-capturing method, and program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 14/267,192, filed on May 1, 2014, which is a continuation application of U.S. patent application Ser. No. 13/742,111, filed on Jan. 15, 2013, which issued as U.S. Pat. No. 8,841,628 on Sep. 23, 2014, which in turn is a continuation application of of International Application No. PCT/JP2011/062518 filed on May 31, 2011, which was published under PCT Article 21(2) in Japanese, which is based upon and claims the benefit of priority from Japanese Patent Applications No. 2010-161927 filed on Jul. 16, 2010, No. 2010-161925 filed on Jul. 16, 2010, No. 2010-161924 filed on Jul. 16, 2010, No. 2010-161922 filed on Jul. 16, 2010, No. 2010-161917 filed on Jul. 16, 2010, No. 2010-161915 filed on Jul. 16, 2010, No. 2010-164829 filed on Jul. 22, 2010, No. 2010-165981 filed on Jul. 23, 2010 and No. 2010-170055 filed on Jul. 29, 2010, the contents all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a radiographic (radiological) image capturing apparatus, a radiographic image capturing system, a radiographic image capturing method, and a program for forming an image from a radiation transmitted through a human body. 
     BACKGROUND ART 
     In the medical field, there have been used transportable radiographic image capturing apparatuses such as FPDs (Flat Panel Detectors), which detect intensity of a radiation transmitted through a human body to capture an image of an inside portion of the body. The FPD (hereinafter referred to as the electronic cassette) can capture the image while keeping a patient on a bed or the like, can be moved to adjust an area to be captured, and thereby can be flexibly used also for immobile patients. 
     In the electronic cassette, even if the radiation is not emitted, electric charges are generated by a dark current and stored in each pixel. The dark current appears as noise in the radiographic image. Therefore, in general, in the electronic cassette, a procedure of removing electric charges stored in each pixel is repeatedly carried out before a process of capturing a radiographic image. In a case where the radiographic image capturing process is performed, a control unit sends an image capturing instruction to the electronic cassette and a radiation apparatus for emitting the radiation. In a case where the radiation apparatus receives the image capturing instruction, the radiation apparatus starts to emit the radiation, and the electronic cassette starts to be exposed. When the radiation emission is completed, the electronic cassette reads the electric charges accumulated by the emission. In this process, the radiation emission timing of the radiation apparatus and the exposure timing of the electronic cassette are synchronized. Thus, the image capturing timings are synchronized. 
     Japanese Laid-Open Patent Publication No. 2010-081960 describes a first time measurement means disposed in a console (the control unit) and a second time measurement means disposed in the electronic cassette. The first and second time measurement means are synchronized with each other. At an exposure start predetermined by the console, the radiation is emitted from the radiation apparatus for a predetermined time. After the predetermined time has elapsed from the exposure start, the electronic cassette reads the electric charges generated in a radiation detector. 
     Various types and specifications of the electronic cassettes are used depending on the requirements of the image capturing conditions and the like. Also, the electronic cassettes are relatively costly. Therefore, as is often the case, a plurality of the electronic cassettes are not placed in each image capturing room, but are shared by a plurality of the image capturing rooms. In a case where a plurality of the electronic cassettes are shared by a plurality of the image capturing rooms, a user (such as a radiation technician) may make a mistake in selecting the electronic cassette. In the image capturing process, the electronic cassette has to be switched from a sleep mode to an image capturing mode in response to the instruction sent from the control unit (such as a console or a system controller). Therefore, in a case where the user makes the selection mistake, the image capturing process is performed while the electronic cassette remains in the sleep mode, thereby failing to obtain the radiographic image. Thus, Japanese Laid-Open Patent Publication No. 2009-219586 describes a technique, in which the image capturing process can be performed even if the user makes the selection mistake. 
     In Japanese Laid-Open Patent Publication No. 2009-219586, considering the possibility of the selection mistake, all the electronic cassettes (1) are switched from a standby mode to a capturing mode in the radiographic image capturing process. Thus, all the cassettes and their radiation detection means (22), located outside the subject area, are made ready for the radiation detection. Then, when the radiation detection means of one electronic cassette detects the radiation, the other electronic cassettes are returned to the standby mode (see, abstract, FIG. 8, and paragraphs 0054 to 0065 of the document). 
     SUMMARY OF INVENTION 
     To synchronize the image capturing timings, the control unit and the radiation apparatus have to be electrically connected. In this case, a manufacturer serviceman has to make the electrical connection between the control unit and the radiation apparatus at the system installation, resulting in high installation and maintenance costs. In addition, in a case where the control unit and the radiation apparatus are obtained from different manufacturers, they often cannot be electrically connected in view of safety. On the contrary, in a case where the control unit and the radiation apparatus are not electrically connected, the image capturing timings cannot be synchronized. In this case, the electronic cassette is exposed for a time longer than the irradiation time of the radiation, and the radiation is emitted while the electronic cassette is exposed, whereby the electronic cassette can be exposed to all the emitted radiation to capture the radiographic image. 
     In the case where the control unit and the radiation apparatus are not electrically connected, the image capturing timings cannot be synchronized as described above. Therefore, in this case, the electronic cassette is excessively exposed even in a period in which the radiation is not emitted, whereby the resultant radiographic image has a high noise content. Furthermore, the procedure of removing the unnecessary electric charges stored in the pixels cannot be carried out before the radiation emission, whereby the noise content of the resultant radiographic image is further increased. In addition, because the image capturing timings cannot be synchronized, the radiation cannot be emitted to the patient at a suitable timing. In a case where the radiation is emitted at an inaccurate timing, the resultant radiographic image often has a high noise content as described above, requiring the retaking of the radiographic image. 
     Assuming that the procedure of removing the unnecessary electric charges stored in the pixels can be carried out before the radiation emission, in a case where the radiation emission is not started even after a long time has elapsed from the start of the removal procedure, electric power used in the procedure is wasted. The unnecessary electric charges stored in the pixels before the radiation emission may contain electric charges corresponding to a residual image formed in a previous image capturing process (residual electric charges). When the residual electric charges cannot be reliably removed, the resultant radiographic image overlaps with the residual image. 
     In Japanese Laid-Open Patent Publication No. 2009-219586, the radiation detection means is located outside the subject area (paragraph 0038). Therefore, the electronic cassette is likely to have a large size. 
     Furthermore, Japanese Laid-Open Patent Publication No. 2009-219586 does not describes the structure of the radiation detection means. Thus, preferred structures and methods for detecting the radiation emission are not studied in this document. 
     Accordingly, in view of the above conventional problems, an object of the present invention is to provide a radiographic image capturing apparatus, a radiographic image capturing system, a radiographic image capturing method, and a program, capable of forming the radiographic image with a lowered noise content at low cost without synchronizing the image capturing timings. Another object of the present invention is to emit the radiation to the subject at the suitable timing without synchronizing the image capturing timings. A further object of the invention is to prevent the excessive electric power waste in the procedure of removing the unnecessary electric charges from the pixels before the radiation emission. A still further object of the invention is to reduce the overlap of the residual image with the radiographic image. A still further object of the invention is to form the radiographic image more appropriately even if the mistake is made in the selection of the radiographic image capturing apparatus such as the electronic cassette. A still further object of the invention is to improve the quality and S/N ratio of the radiographic image. 
     A radiographic image capturing apparatus according to a first aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously, and an irradiation start judgment part for judging start of the radiation emission from the radiation source to the image capturing panel in a case where a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value. In a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part acts to stop the reading of the electric signals and to switch the image capturing panel to an exposure state. 
     The first readout control part may read the electric signals stored in the pixels in the rows arranged at a predetermined row interval simultaneously. 
     In a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part may stop the reading of the electric signals stored in the pixels at a timing of completion of the reading. 
     In a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part may stop the reading of the electric signals at a timing of the judgment. 
     The radiographic image capturing apparatus may further have an elapsed time judgment part for judging whether a predetermined time has elapsed or not after the start of the radiation emission, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row. The second readout mode is executed if elapse of the predetermined time is judged by the elapsed time judgment part. 
     A number of images to be captured may be set beforehand, and the first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the setup number. 
     A radiographic image capturing system according to the first aspect has the above radiographic image capturing apparatus, a table storing irradiation times of the radiation corresponding to at least imaging areas, and an irradiation time setting part for setting an irradiation time corresponding to an imaging area selected by a user. 
     The elapsed time judgment part judges whether the irradiation time set by the irradiation time setting part has elapsed or not after the radiation emission is judged to be started. 
     The table may store the irradiation times of the radiation corresponding to at least the imaging areas and diagnostic sites, and the irradiation time setting part may set an irradiation time corresponding to an imaging area and a diagnostic site selected by the user. 
     The radiographic image capturing system may further have an image number setting part for setting a number of images to be captured selected by the user. The first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the number set by the image number setting part. 
     The table may store the irradiation times of the radiation and numbers of images to be captured corresponding to at least the imaging areas, and the first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the number of images corresponding to an imaging area selected by the user. 
     A method for capturing a radiographic image according to the first aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The method contains the steps of executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously, judging start of the radiation emission from the radiation source to the image capturing panel in a case where a value of the electric signals read in the first readout mode becomes larger than a threshold value, and stopping the reading of the electric signals to switch the image capturing panel to an exposure state in a case where the radiation emission is judged to be started. 
     A program according to the first aspect is for using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously and as an irradiation start judgment part for judging start of the radiation emission from the radiation source to the image capturing panel. In a case where a value of the electric signals read by the first readout control part becomes larger than a threshold value, the radiation emission is judged to be started. In a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part acts to stop the reading of the electric signals and to switch the image capturing panel to an exposure state. 
     In the first aspect, in the first readout mode, the electric charges stored in the pixels in a plurality of rows are read out as electric signals simultaneously, and the start of the radiation emission is detected based on the read electric signals. In a case where the radiation emission is judged to be started, the reading of the electric charges is stopped, and the image capturing panel is switched to an accumulation state. Therefore, in the first aspect, it is not necessary to synchronize the image capturing timings, resulting in low cost. Since the first readout mode is performed until the radiation emission is judged to be started, the unnecessary electric charges stored in the pixels can be removed to lower the noise content of the resultant radiographic image. 
     A radiographic image capturing apparatus according to a second aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric charges and storing the electric charges, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a predetermined row, an irradiation start judgment part for judging start of the radiation emission from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read by the first readout control part becomes larger than a threshold value, an elapsed time judgment part for judging whether a predetermined time has elapsed or not after the start of the radiation emission, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row, the second readout mode being executed in a case where elapse of the predetermined time is judged by the elapsed time judgment part. In a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part acts to stop the reading of the electric signals and to switch the image capturing panel to an exposure state. 
     The first readout control part may read the electric signals stored in the pixels in the predetermined row sequentially row by row in the first readout mode. 
     The pixels in the image capturing panel may include pixels for storing electric signals to be read in the first readout mode and pixels for storing electric signals to be read in the second readout mode. The pixels in the predetermined row may be the pixels for storing electric signals to be read in the first readout mode executed by the first readout control part. 
     The pixels in the predetermined row may be pixels in a row arbitrarily selected by a user. 
     A number of images to be captured may be set beforehand, and the first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the setup number. 
     A radiographic image capturing system according to the second aspect has the above radiographic image capturing apparatus, a table storing irradiation times of the radiation corresponding to at least imaging areas, and an irradiation time setting part for setting an irradiation time corresponding to an imaging area selected by a user. The elapsed time judgment part judges whether the irradiation time set by the irradiation time setting part has elapsed or not after the radiation emission is judged to be started. 
     The table may store the irradiation times of the radiation corresponding to at least the imaging areas and diagnostic sites, and the irradiation time setting part may set an irradiation time corresponding to an imaging area and a diagnostic site selected by the user. 
     The radiographic image capturing system may further have an image number setting part for setting a number of images to be captured selected by the user. The first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the number set by the image number setting part. 
     The table may store the irradiation times of the radiation and numbers of images to be captured corresponding to at least the imaging areas, and the first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the number corresponding to an imaging area selected by the user. 
     A method for capturing a radiographic image according to the second aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The method contains the steps of executing a first readout mode for reading the electric signals stored in the pixels in a predetermined row, judging start of the radiation emission from the radiation source to the image capturing panel in a case where a value of the electric signals read in the first readout mode becomes larger than a threshold value, stopping the reading of the electric signals to switch the image capturing panel to an exposure state in a case where the radiation emission is judged to be started, judging whether a predetermined time has elapsed or not after the start of the radiation emission, and executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row, the second readout mode being executed in a case where elapse of the predetermined time after the start of the radiation emission is judged. 
     A program according to the second aspect is for using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a predetermined row, an irradiation start judgment part for judging start of the radiation emission from the radiation source to the image capturing panel in a case where a value of the electric signals read by first readout control part becomes larger than a threshold value, an elapsed time judgment part for judging whether a predetermined time has elapsed or not after the start of the radiation emission, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row. The second readout mode is executed in a case where elapse of the predetermined time is judged by the elapsed time judgment part. In a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part acts to stop the reading of the electric signals and to switch the image capturing panel to an exposure state. 
     In the second aspect, the first readout mode for reading the electric signals stored in the predetermined pixels is performed until the radiation emission is judged to be started, and the start of the radiation emission is detected based on the read electric signals. In a case where the radiation emission is judged to be started, the image capturing panel is switched to the exposure state. After the predetermined time has elapsed, the second readout mode for reading the electric signals stored in the pixels sequentially row by row is performed. Therefore, in the second aspect, it is not necessary to synchronize the image capturing timings, resulting in low cost. Since the second readout mode is performed after the predetermined time has elapsed, considering the predetermined time as the irradiation time of the radiation, the image capturing panel can be prevented from being excessively exposed after the completion of the radiation emission, lowering the noise content of the resultant radiographic image. Furthermore, since the electric signals stored in the predetermined pixels are read out, the power consumption in the first readout mode can be reduced. In addition, the pixels other than the predetermined pixels are in the exposure state even during the first readout mode, so that the radiographic image can be captured without wasting the radiation. 
     A radiographic image capturing apparatus according to a third aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels, an irradiation start judgment part for judging start of the radiation emission from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value, and a first readout mode stop judgment part for stopping the first readout mode in a case where the values of the electric signals do not reach the threshold value even after a predetermined time has elapsed from the start of the first readout mode. 
     In the third aspect, the first readout control part preferably acts to switch the image capturing panel into the exposure state after the stop of the first readout mode. 
     In this case, it is preferred that the radiographic image capturing apparatus further has a transfer detection device for detecting the transfer of the radiographic image capturing apparatus, a light detection device for detecting a visible light for indicating an irradiation field of the radiation (which is emitted from an irradiation field lamp before the radiation emission from the radiation source), a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row, and an image acquirement judgment part for judging whether the second readout mode should be executed or not based on a detection result from the transfer detection device or the light detection device. In a case where the image acquirement judgment part judges that the second readout mode should be executed, the second readout control part preferably acts to read the electric signals in the pixels in the exposure state sequentially row by row. 
     In this case, in a case where a value of the electric signals read by the second readout control part reaches a predetermined value, the image acquirement judgment part may acquire the electric signals as a radiographic image of the subject. On the other hand, in a case where a value of the electric signals does not reach the predetermined value, the image acquirement judgment part may act to discharge the electric signals to the ground and to stop the second readout mode. 
     Alternatively, the radiographic image capturing apparatus may further have a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row, and the second readout control part may act to perform a reset operation for discharging the electric signals stored in the pixels to the ground after the stop of the first readout mode. 
     In this case, it is preferred that the radiographic image capturing apparatus further has a sleep state switch judgment part, which judges at least the operation stop of the image capturing panel and switches the radiographic image capturing apparatus to a sleep state in a case where the first readout mode is stopped or the reset operation is completed. 
     In this case, the radiographic image capturing apparatus may further have a transfer detection device for detecting the transfer of the apparatus, a light detection device for detecting a visible light for indicating an irradiation field of the radiation (which is emitted from an irradiation field lamp before the radiation emission from the radiation source), and a first readout mode restart judgment part for judging whether the first readout mode should be restarted or not based on a detection result from the transfer detection device or the light detection device. In a case where the first readout mode restart judgment part judges that the first readout mode should be restarted, the first readout control part may act to restart the first readout mode. 
     In the above described structures, the first readout control part may read the electric signals stored in the pixels in a plurality of rows simultaneously, or alternatively may read the electric signals stored in the pixels in a predetermined row. 
     In this case, the radiographic image capturing apparatus may further have a first announcement device for announcing the stop of the first readout mode to the outside. The first announcement device preferably includes at least one of a sound output device for outputting a sound indicating the stop of the first readout mode, a light output device for outputting a light indicating the stop of the first readout mode, and a first communication device for sending a communication signal indicating the stop of the first readout mode to the outside. 
     A radiographic image capturing system according to the third aspect has the above radiographic image capturing apparatus, a table storing image capturing conditions including at least irradiation times of the radiation, an image capturing menu setting unit for setting an image capturing menu associated with the radiation emission based on the image capturing conditions, a second communication device for sending at least the image capturing menu to the first communication device and receiving the communication signal from the first communication device, and a second announcement device for announcing the stop of the first readout mode based on the communication signal. 
     In this case, the radiographic image capturing system may further have an input device for receiving an input operation by a user to select image capturing conditions corresponding to an imaging area of the subject from the conditions stored in the table. The image capturing menu setting unit may set an image capturing menu including the image capturing conditions selected based on the input operation by the user. The second communication device may send the setup image capturing menu to the first communication device. 
     The radiographic image capturing system may further have an instruction signal generation unit, which generates an instruction signal for restarting the first readout mode in a case where the image capturing menu setting unit resets the image capturing menu or in a case where the user operates the input device, after the second communication device receives the communication signal. The second communication device sends the reset image capturing menu and the instruction signal or only the instruction signal to the first communication device. The radiographic image capturing apparatus may further have a first readout mode restart judgment part for judging whether the first readout mode should be restarted or not based on the instruction signal entered into the first communication device. The first readout control part may restart the first readout mode based on the reset image capturing menu entered into the first communication device and the judgment result from the first readout mode restart judgment part or only the judgment result. 
     In this case, the second announcement device preferably includes at least one of a display device for displaying a screen indicating the stop of the first readout mode, a sound output device for outputting a sound indicating the stop, and a light output device for outputting a light indicating the stop of the first readout mode. 
     A method for capturing a radiographic image according to the third aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The method contains the steps of executing a first readout mode for reading the electric signals stored in the pixels, judging whether or not a value of the electric signals read in the first readout mode becomes larger than an arbitrarily settable threshold value, and stopping the first readout mode in a case where the value of the electric signals does not reach the threshold value even after a predetermined time has elapsed from the start of the first readout mode, based on a judgment that the radiation emission from the radiation source to the image capturing panel is not started. 
     A program according to the third aspect is for using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels, an irradiation start judgment part for judging the start of the radiation emission from the radiation source to the image capturing panel in a case where a value of the electric signals read by first readout control part becomes larger than an arbitrarily settable threshold value, and a first readout mode stop judgment part for stopping the first readout mode in a case where the values of the electric signals do not reach the threshold value even after a predetermined time has elapsed from the start of the first readout mode. 
     In the third aspect, the start of the radiation emission is detected based on the read electric signals stored in the pixels in the first readout mode. Therefore, it is not necessary to synchronize the image capturing timings, resulting in low cost. Since the first readout mode is performed before the start of the radiation emission, the unnecessary electric charges stored in the pixels can be removed to lower the noise content of the resultant radiographic image. 
     Furthermore, in the third aspect, the first readout mode is stopped in a case where the values of the electric signals do not reach the threshold value even after the predetermined time has elapsed from the start of the first readout mode. Therefore, wasteful power consumption can be prevented in the first readout mode executed before the radiation emission. 
     A radiographic image capturing apparatus according to a fourth aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels based on an image capturing menu associated with the emission of the radiation, a mode switch judgment part for judging whether the first readout mode is started or not, and a first announcement device for announcing a judgment result from the mode switch judgment part to the outside in a case where the first readout mode is judged to be started by the mode switch judgment part. 
     In the fourth aspect, the first readout control part may read the electric signals stored in the pixels in a plurality of rows simultaneously, or alternatively may read the electric signals stored in the pixels in a predetermined row. 
     The radiographic image capturing apparatus may further have an irradiation start judgment part. In a case where a value of the electric signals read by first readout control part becomes larger than an arbitrarily settable threshold value, the irradiation start judgment part judges that the radiation emission from the radiation source to the image capturing panel is started, and sends an instruction to the first readout control part to stop the reading of the electric signals and switch the image capturing panel into the exposure state. 
     The first announcement device preferably includes at least one of a sound output device for outputting a sound indicating the judgment result, a light output device for outputting a light indicating the judgment result, and a first communication device for sending a communication signal indicating the judgment result to the outside. 
     A radiographic image capturing system according to the fourth aspect has the above radiographic image capturing apparatus, a table storing image capturing conditions including at least irradiation times of the radiation, an image capturing menu setting unit for setting an image capturing menu based on the image capturing conditions, a second communication device for sending the image capturing menu to the first communication device and receiving the communication signal from the first communication device, and a second announcement device for announcing start of the first readout mode based on the communication signal. 
     In this case, the radiographic image capturing system may further have an input device for receiving an input operation by a user to select image capturing conditions corresponding to an imaging area of the subject from the conditions stored in the table. The image capturing menu setting unit may set an image capturing menu including the image capturing conditions selected based on the input operation by the user. The second communication device may send the setup image capturing menu to the first communication device. In a case where the first communication device receives the image capturing menu, the first readout control part may execute the first readout mode based on the image capturing menu. 
     The radiographic image capturing apparatus may further have a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row, and an imaging control device for controlling the first readout control part to start the first readout mode or controlling the first and second readout control parts to switch from the second readout mode to the first readout mode in a case where the first communication device receives the image capturing menu. 
     In this case, the second readout control part preferably acts to execute the second readout mode for reading the electric signals stored in the pixels as offset signals sequentially row by row or to perform a reset operation for discharging the electric signals stored in the pixels to the ground, before the execution of the first readout mode by the first readout control part. 
     The second announcement device may include at least one of a display device for displaying a screen indicating the start of the first readout mode, a sound output device for outputting a sound indicating the start of the first readout mode, and a light output device for outputting a light indicating the start of the first readout mode. 
     The radiographic image capturing system preferably has the radiation source and a radiation switch, which is operated by a user to emit the radiation from the radiation source. The first announcement device and/or the second announcement device preferably announces that the user can operate the radiation switch. 
     A method for capturing a radiographic image according to the fourth aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The method contains the steps of executing a first readout mode for reading the electric signals stored in the pixels based on an image capturing menu associated with the radiation emission, judging the start of the start of the first readout mode, and announcing the judgment result from the first readout mode start to the outside. 
     A program according to the fourth aspect is for using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels based on an image capturing menu associated with the emission of the radiation, a mode switch judgment part for judging whether the first readout mode is started or not, and a first announcement device for announcing a judgment result from the mode switch judgment part to the outside in a case where the first readout mode is judged to be started by the mode switch judgment part. 
     In the fourth aspect, in a case where the first readout mode is started, the reading of the electric signals stored in the pixels are started, thus the procedure of removing the electric charges is started, and the radiographic image capturing apparatus is switched to a state in which the radiation can be emitted. Then, in the fourth aspect, the start of the first readout mode is judged, and the judgment result is announced to the outside, so that suitable radiation emission timing can be announced to the outside. Thus, the radiation is emitted to the subject after the announcement of the judgment result, whereby the radiographic image can be formed with high quality. The radiation can be emitted at a suitable timing to avoid retaking. 
     Consequently, in the fourth aspect, the radiation can be emitted to the subject at the suitable timing without synchronizing the image capturing timings, so that the radiographic image can be formed with a lowered noise content at low cost. 
     A radiographic image capturing apparatus according to a fifth aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels corresponding to an imaging region of the subject set in an image capturing menu associated with the emission of the radiation, an irradiation start judgment part for judging the start of the radiation emission from the radiation source to the image capturing panel and for sending an instruction to stop the reading of the electric signals and switch the image capturing panel to an exposure state to the first readout control part, the radiation emission being judged to be started in a case where a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels corresponding to the imaging region sequentially row by row, the second readout mode being executed after a predetermined time has elapsed from the start of the radiation emission. 
     In this case, the first readout control part may read the electric signals stored in the pixels corresponding to the imaging region at a predetermined row interval simultaneously, or alternatively may read the electric signals stored in the pixels corresponding to the imaging region in a predetermined row sequentially row by row. 
     In a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part may stop the reading of the electric signals stored in the pixels at a timing of completion of the reading or a timing of the judgment of the radiation emission as being started. 
     The first readout control part may read the electric signals stored in the pixels in rows and columns corresponding to the imaging region at a predetermined row interval simultaneously. Alternatively, the first readout control part may read the electric signals stored in the pixels in a predetermined row, among the rows and columns corresponding to the imaging region, sequentially row by row. The second readout control part may read the electric signals stored in the pixels in the rows and columns corresponding to the imaging region sequentially row by row. 
     In this case, before the first readout mode performed by the first readout control part, the second readout control part may act to execute an offset signal readout mode for reading the electric signals stored in the pixels in the rows and columns corresponding to the imaging region as offset signals sequentially row by row or a reset operation for discharging the electric signals stored in the pixels to the ground. 
     The radiographic image capturing apparatus may further have a communication device for sending signals to and receiving signals from the outside and an imaging control device for controlling the image capturing panel, the first readout control part, the irradiation start judgment part, the second readout control part, and the communication device. In a case where the communication device receives the image capturing menu from the outside, the imaging control device may, based on the imaging region set in the image capturing menu, detect the pixels in the rows and columns corresponding to the imaging region and send an instruction to the first and second readout control parts to read the electric signals stored in the pixels in the detected rows and columns. 
     In this case, the communication device may send signals to and receive signals from the outside via wireless communication. The radiographic image capturing apparatus may further have an electric power supply for supplying electric power to each component, and the electric power supply may be a battery. In addition, the radiographic image capturing apparatus is preferably a transportable image capturing apparatus. 
     A radiographic image capturing system according to the fifth aspect has the above radiographic image capturing apparatus, a table storing image capturing conditions including at least irradiation times of the radiation associated with imaging areas of the subject, an image capturing menu setting unit for setting an image capturing menu including the imaging region based on the image capturing conditions, and a transmission unit for sending the image capturing menu to the communication device. 
     A method for capturing a radiographic image according to the fifth aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The method contains the steps of executing a first readout mode for reading the electric signals stored in the pixels corresponding to an imaging region of the subject set in an image capturing menu associated with the radiation emission, judging the start of the radiation emission from the radiation source to the image capturing panel in a case where a value of the electric signals read in the first readout mode becomes larger than an arbitrarily settable threshold value, stopping the reading of the electric signals to switch the image capturing panel to an exposure state in a case where the radiation emission is judged to be started, and executing a second readout mode for reading the electric signals stored in the pixels corresponding to the imaging region sequentially row by row in a case where a predetermined time has elapsed from the start of the radiation emission. 
     A program according to the fifth aspect is for using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels corresponding to an imaging region of the subject set in an image capturing menu associated with the emission of the radiation, an irradiation start judgment part for judging start of the radiation emission from the radiation source to the image capturing panel and for sending an instruction to stop the reading of the electric signals and switch the image capturing panel to an exposure state to the first readout control part, the radiation emission being judged to be started when a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels corresponding to the imaging region sequentially row by row, the second readout mode being executed after a predetermined time has elapsed from the start of the radiation emission. 
     In the fifth aspect, the start of the radiation emission is judged based on the electric signals read from the pixels in the first readout mode. In a case where the radiation emission is judged to be started, the reading of the electric signals is stopped, and the image capturing panel is switched to an accumulation state. Therefore, it is not necessary to synchronize the image capturing timings, resulting in low cost. Since the first readout mode is performed until the radiation emission is judged to be started, the unnecessary electric charges stored in the pixels can be removed to lower the noise content of the resultant radiographic image. 
     Furthermore, in the fifth aspect, the electric signals stored in all the pixels in the image capturing panel are not read out, and only the electric signals stored in the pixels corresponding to the imaging region of the subject set in the image capturing menu are read out by the first or second readout control part. Therefore, the power consumption required for reading the electric signals can be lowered, and the radiographic image of the imaging region can be reliably acquired. 
     A radiographic image capturing apparatus according to a sixth aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously or reading the electric signals stored in the pixels in a predetermined row, a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row, and an imaging control device for deciding to execute the first or second readout mode with reference to an image capturing history contained in an image capturing menu associated with the emission of the radiation and making the first or second readout control part to read the electric signals in the decided mode. 
     With reference to the image capturing history, in a case where the last image capturing process is carried out using a relatively high radiation dose, the imaging control device may make the first and second readout control parts to read the electric signals in the pixels in the second readout mode, the first readout mode, and the second readout mode in this order. 
     Alternatively, with reference to the image capturing history, in a case where a predetermined time has elapsed from the last image capturing process, this image capturing process is carried out using a relatively low radiation dose, or this image capturing process is carried out using a relatively short irradiation time, the imaging control device may make the first and second readout control parts to read the electric signals in the pixels in the first readout mode and the second readout mode in this order. 
     In this case, with reference to the irradiation time and the image capturing history contained in the image capturing menu, the imaging control device may control the first readout control part to change a row interval at which the electric signals are read out simultaneously and use the changed row interval in the first readout mode. 
     Alternatively, the imaging control device may control the first readout control part to change the predetermined row and read the electric signals in the pixels in the changed row in the first readout mode. 
     The first readout control part may read the electric signals stored in the pixels in rows arranged at a predetermined row interval simultaneously, or read the electric signals stored in the pixels in the predetermined row sequentially row by row. The radiographic image capturing apparatus may further have an irradiation start judgment part. In a case where a value of the electric signals read by first readout control part becomes larger than an arbitrarily settable threshold value, the irradiation start judgment part judges that the radiation emission from the radiation source to the image capturing panel is started, and sends an instruction to the first readout control part to stop the reading of the electric signals and switch the image capturing panel into an exposure state. The second readout control part may act to execute the second readout mode for reading the electric signals stored in the pixels in a case where a predetermined time has elapsed from the start of the radiation emission. 
     In this case, in a case where the radiation emission is judged to be started by the irradiation start judgment part, the first readout control part may stop the reading of the electric signals stored in the pixels at a timing of completion of the reading or a timing of the judgment of the radiation emission as being started. 
     A radiographic image capturing system according to the sixth aspect has the above radiographic image capturing apparatus, a table storing image capturing conditions including at least irradiation times of the radiation associated with imaging areas of the subject, an image capturing history recording unit for recording the image capturing history, and an image capturing menu setting unit for setting the image capturing menu based on the image capturing conditions and the image capturing history. 
     A method for capturing a radiographic image according to the sixth aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The method contains the steps of deciding to execute one of first and second readout modes, and reading the electric signals stored in the pixels in the decided mode. In the first readout mode, the electric signals stored in the pixels in a plurality of rows are read out simultaneously, or alternatively the electric signals stored in the pixels in a predetermined row are read out. In the second readout mode, the electric signals stored in the pixels are read sequentially row by row. 
     A program according to the sixth aspect is for using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously or reading the electric signals stored in the pixels in a predetermined row, a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row, and an imaging control device for deciding to execute the first or second readout mode with reference to an image capturing history contained in an image capturing menu associated with the emission of the radiation and making the first or second readout control part to read the electric signals in the decided mode. 
     In the sixth aspect, the radiation emission is judged to be started based on the electric signals read from the pixels in the first readout mode. In a case where the radiation emission is judged to be started, the reading of the electric charges is stopped, and the image capturing panel is switched to an accumulation state. Therefore, in the sixth aspect, it is not necessary to synchronize the image capturing timings, resulting in low cost. Since the first readout mode is performed until the radiation emission is judged to be started, the unnecessary electric charges stored in the pixels can be removed to lower the noise content of the resultant radiographic image. 
     Furthermore, in the sixth aspect, the execution of the first or second readout mode is decided with reference to the image capturing history contained in the image capturing menu, and the first or second readout control means reads the electric charges (electric signals) in the decided mode. Therefore, residual electric charges stored in a previous image capturing process can be reliably removed before the radiation emission, and the radiographic image can be formed with a high quality without overlap of a residual image. 
     A radiographic image capturing apparatus according to a seventh aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously through an electric signal amplifier set at a first readout gain, an irradiation start judgment part for judging the start of the emission of the radiation from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value, and the first readout control part acting to stop the reading of the electric signals and to switch the image capturing panel to an exposure state in a case where the radiation emission is judged to be started by the irradiation start judgment part, an emission completion judgment part for judging the completion of the radiation emission, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row through the electric signal amplifier set at a second readout gain, the second readout mode being executed in a case where the radiation emission is judged to be completed by the emission completion judgment part. The first readout gain is set to be lower than the second readout gain. 
     The emission completion judgment part may be an elapsed time judgment part for judging whether a predetermined time has elapsed or not from the start of the radiation emission. In a case where the predetermined time is judged to have elapsed by the elapsed time judgment part, the second readout control part may act to execute the second readout mode for reading the electric signals stored in the pixels sequentially row by row through the electric signal amplifier at the second readout gain. 
     The emission completion judgment part may be a radiation detection sensor. In a case where the radiation emission is judged to be completed by the output of the radiation detection sensor, the second readout control part may act to execute the second readout mode for reading the electric signals stored in the pixels sequentially row by row through the electric signal amplifier at the second readout gain. 
     The first readout control part may simultaneously read the electric signals stored in the pixels in rows arranged at a predetermined row interval. 
     A radiation dose setting part may be used for setting a low or high radiation dose of the radiation to be emitted to the subject. The first readout control part may control the first readout gain based on information from the radiation dose setting part such that the gain for the high radiation dose is lower than that for the low radiation dose. 
     The first and second readout control parts may control the first and second readout gains depending on image capturing conditions. 
     With respect to the setup of the threshold value in the first readout mode executed by the first readout control part, the irradiation start judgment part may set a start threshold value at the start of the first readout mode, and may further set a normal threshold value smaller than the start threshold value. The normal threshold value is a sum of a predetermined value and a value of the electric signals in a plurality of the rows read at the start of the first readout mode. The setup normal threshold value may be used as the above threshold value in the following reading operation in the first readout mode. 
     The radiographic image capturing apparatus may further have a normal threshold value monitoring part for monitoring the normal threshold value. Then the monitored normal threshold value becomes larger than a predetermined value, the normal threshold value monitoring part may send a notice to the outside. 
     The first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on a number of images to be captured determined beforehand. 
     In a process of capturing the first image, the irradiation start judgment part may set the start threshold value and the normal threshold value in this order in the first readout mode. In processes of capturing the second and following images, the irradiation start judgment part may set the normal threshold value in first readout mode. 
     The electric signal amplifier may be a charge amplifier containing a capacitor and an operating amplifier. 
     A radiographic image capturing system according to the seventh aspect has at least the above radiographic image capturing apparatus and a radiation source. 
     A method for capturing a radiographic image according to the seventh aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The method contains a first readout control step of executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously through an electric signal amplifier set at a first readout gain, an irradiation start judgment step of judging the start of the emission of the radiation from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read by a first readout control part becomes larger than an arbitrarily settable threshold value, and the first readout control part acting to stop the reading of the electric signals and to switch the image capturing panel to an exposure state in a case where the radiation emission is judged to be started in the irradiation start judgment step, an emission completion judgment step of judging the completion of the radiation emission, and a second readout control step of executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row through the electric signal amplifier set at a second readout gain, the second readout mode being executed in a case where the radiation emission is judged to be completed by the emission completion judgment step. The first readout gain is set to be lower than the second readout gain. 
     A program according to the seventh aspect is for using a computer for controlling an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously through an electric signal amplifier set at a first readout gain, an irradiation start judgment part for judging the start of the emission of the radiation from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value, and the first readout control part acting to stop the reading of the electric signals and to switch the image capturing panel to an exposure state in a case where the radiation emission is judged to be started by the irradiation start judgment part, an emission completion judgment part for judging the completion of the radiation emission, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row through the electric signal amplifier set at a second readout gain, the second readout mode being executed in a case where the radiation emission is judged to be completed by the emission completion judgment part. The first readout gain is set to be lower than the second readout gain. 
     In the seventh aspect, the electric signals stored in the pixels in a plurality of the rows are simultaneously read out through the electric signal amplifier at the first readout gain in the first readout mode, and the start of the radiation emission is judged based on the read electric signals. In a case where the radiation emission is judged to be started, the reading of the electric signals is stopped, and the image capturing panel is switched to an accumulation state. Therefore, in the seventh aspect, it is not necessary to synchronize the image capturing timings, resulting in low cost. Since the first readout mode is performed until the radiation emission is judged to be started, unnecessary electric signals stored in the pixels can be removed, so that the noise content of the resultant radiographic image is lowered. Furthermore, in a case where the radiation emission is completed, the electric signals stored in the pixels are read sequentially row by row through the electric signal amplifier at the second readout gain higher than the first readout gain in the second readout mode. Therefore, even if a value of the electric signals read by the first readout control part becomes larger than the arbitrarily settable threshold value in the first readout mode, the output of the electric signal amplifier can be prevented from being excessively increased or saturated. In addition, the output value of the electric signal amplifier can be made within a suitable range in the second readout mode. 
     A radiographic image capturing apparatus according to an eighth aspect of the present invention has an image capturing panel containing a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject at least in an exposure period) into electric signals and storing the electric signals, a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously, an irradiation start judgment part for judging the start of the emission of the radiation from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value, and an all-pixel reset control part for performing an all-pixel reset process of discarding the electric signals stored in all the pixels in a case where the radiation emission is judged to be started by the irradiation start judgment part. The image capturing panel is switched to an exposure state in a case where the all-pixel reset process is completed. 
     After the radiation emission is judged to be started by the irradiation start judgment part, in a case where the first readout mode by the first readout control part is completed, the all-pixel reset control part may perform the all-pixel reset process. 
     The all-pixel reset control part may have an activation portion for activating all the rows of all the pixels simultaneously after the first readout mode by the first readout control is completed, and a switch control portion for connecting all the columns and drains over the activation period. 
     The all-pixel reset control part may perform the all-pixel reset process in a case where the radiation emission is judged to be started by the irradiation start judgment part. 
     The radiographic image capturing apparatus may further have a mask processing portion for disabling the first readout mode by the first readout control part in a case where the radiation emission is judged to be started. The all-pixel reset control part may have an activation portion for activating all the rows of all the pixels simultaneously in a case where the radiation emission is judged to be started by the irradiation start judgment part, and may further have a switch control portion for connecting all the columns and drains over the activation period. 
     In a case where the all-pixel reset process is completed, the image capturing panel may be switched to the exposure state to start the exposure period. 
     The radiographic image capturing apparatus may further have an elapsed time judgment part for judging whether a predetermined time has elapsed or not from the start of the exposure period, and a second readout control part for executing a second readout mode for reading the electric signals stored in the pixels sequentially row by row. The second readout mode is executed in a case where the elapsed time judgment part judges that the predetermined time has elapsed. 
     A number of images to be captured may be set beforehand, and the first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the setup number. 
     A radiographic image capturing system according to the eighth aspect has the above radiographic image capturing apparatus, a table storing irradiation times of the radiation associated with at least imaging areas, and an irradiation time setting part for setting an irradiation time corresponding to an imaging area selected by a user. 
     The elapsed time judgment part judges whether or not the irradiation time set by the irradiation time setting part has elapsed after the radiation emission is judged to be started. 
     The table may store the irradiation times of the radiation corresponding to at least the imaging areas and diagnostic sites, and the irradiation time setting part may set an irradiation time corresponding to an imaging area and a diagnostic site selected by the user. 
     The radiographic image capturing system may further have an image number setting part for setting a number of images to be captured selected by the user. The first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the number set by the image number setting part. 
     The table may store the irradiation times of the radiation and numbers of images to be captured corresponding to at least the imaging areas, and the first and second readout control parts may execute the first readout mode, the exposure state, and the second readout mode repeatedly based on the number corresponding to an imaging area selected by the user. 
     A method for capturing a radiographic image according to the eighth aspect is performed using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject in at least an exposure period) into electric signals and storing the electric signals. The method contains the steps of executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously, judging start of the emission of the radiation from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read in the first readout mode becomes larger than an arbitrarily settable threshold value, and discarding the electric signals stored in all the pixels to switch the image capturing panel to an exposure state in a case where the radiation emission is judged to be started. 
     A program according to the eighth aspect is for using a computer equipped with an image capturing panel. The image capturing panel contains a plurality of pixels arranged in a matrix for converting a radiation (which is emitted from a radiation source and transmitted through a subject in at least an exposure period) into electric signals and storing the electric signals. The computer is used as a first readout control part for executing a first readout mode for reading the electric signals stored in the pixels in a plurality of rows simultaneously, an irradiation start judgment part for judging start of the emission of the radiation from the radiation source to the image capturing panel, the radiation emission being judged to be started in a case where a value of the electric signals read by the first readout control part becomes larger than an arbitrarily settable threshold value, and an all-pixel reset control part for discarding the electric signals stored in all the pixels to switch the image capturing panel into an exposure state in a case where the radiation emission is judged to be started by the irradiation start judgment part. 
     In the eighth aspect, the radiation emission is judged to be started based on the electric signals read from the pixels in the first readout mode. In a case where the radiation emission is judged to be started, the reading of the electric charges is stopped, and the image capturing panel is switched to an accumulation state. Therefore, in the eighth aspect, it is not necessary to synchronize the image capturing timings, resulting in low cost. Since the first readout mode is performed until the radiation emission is judged to be started, the unnecessary electric charges stored in the pixels can be removed, lowering the noise content of the resultant radiographic image. 
     Furthermore, in the eighth aspect, the electric signals stored in all the pixels are discarded in a case where the radiation emission is judged to be started. Therefore, all the pixels can have approximately the same electric signals at the start of the exposure period, and the electric signal difference between the pixels can be mostly removed, to improve the quality and S/N ratio of the radiographic image. 
     A radiographic image capturing system according to a ninth aspect of the present invention has a radiation source for outputting a radiation, a plurality of radiographic image capturing apparatuses for acquiring a radiographic image, and a control unit for controlling the radiation source and the radiographic image capturing apparatuses. The radiographic image capturing apparatuses have an radiation conversion panel containing a plurality of pixels arranged in a matrix for converting the radiation, transmitted through a subject, into electric charges and storing the electric charges, and a readout control part for controlling the reading of the electric charges stored in the pixels and outputting radiographic image information based on the electric charges. The readout control part is capable of executing a first readout mode and a second readout mode. In the first readout mode, the electric charges stored in the pixels in a plurality of rows are simultaneously read out, and thus the electric charges stored in the pixels are read as first electric signals that are not used for forming the radiographic image. In the second readout mode, the electric charges stored in the pixels are read out row by row, and thus the electric charges stored in the pixels are read as second electric signals that are used for forming the radiographic image. 
     In a process of capturing the radiographic image, the control unit sends an instruction to execute the first readout mode to the readout control part in the radiographic image capturing apparatuses. The readout control part which receives the instruction to execute the first readout mode acts to execute the first readout mode. After that, in a case where the radiation conversion panel detects the radiation, the second readout mode is performed to output the radiographic image information. In this aspect, in the image capturing process, a plurality of the radiographic image capturing apparatuses can be used for forming the radiographic image. Therefore, the image capturing process can be performed even if a user (such as a radiation technician) makes a mistake in selecting the radiographic image capturing apparatus. In addition, the radiation is detected by using the radiation conversion panel for acquiring the radiographic image information. Therefore, a radiation detection means other than the radiation conversion panel is not required, and the radiographic image capturing apparatus can be reduced in size. 
     Furthermore, the electric charges stored in the pixels in a plurality of the rows are simultaneously read out in the first readout mode, whereby the start of the radiation emission can be judged rapidly and accurately. Thus, since the electric charges stored in the pixels are summed up and read out, a significantly larger value is obtained under the radiation emission than without the radiation emission, whereby the start of the radiation emission can be rapidly judged. Therefore, the radiation conversion panel can be readily switched from the first readout mode for reading the electric charges in a plurality of the rows to the second readout mode for reading the electric charges row by row. Consequently, the start of the radiation emission can be judged in a shorter irradiation time (using a smaller amount of the radiation), so that the energy of the radiation can be efficiently utilized. 
     Since a plurality of the rows are simultaneously read out in the first readout mode, each row can be controlled in a shorter cycle in the first readout mode than in a row-by-row reading mode. Therefore, at the start of acquiring the radiographic image information (which is practically used as the radiographic image), the electric charge difference between the pixels is smaller in a case where the radiation conversion panel is switched from the first readout mode to the second readout mode than in a case where the start of the radiation emission is detected in the second readout mode. Thus, in the ninth aspect, generation of artifacts can be reduced. 
     Consequently, in the ninth aspect, the radiographic image can be more appropriately captured even if the user makes a mistake in selecting the radiographic image capturing apparatus such as an electronic cassette. 
     After the readout control part receives the instruction to execute the first readout mode, in a case where the quantity of the electric charges stored in the pixels in the first readout mode exceeds a threshold value, the readout control part may judge that the radiation is emitted. 
     In a case where a plurality of the radiographic image capturing apparatuses execute the first readout mode and one of the apparatuses detects the radiation, the one apparatus may send the detection information to the other apparatuses directly or through the control unit. The other apparatuses may stop the first readout mode in a case where they receive the detection information. In this case, the radiographic image capturing apparatuses other than the one apparatus (which has detected the radiation) can stop the first readout mode, making it possible to reduce the subsequent power consumption. 
     The readout control part may read the electric charges only in a part of the pixels in the first readout mode. In this case, the power consumption or the calculation amount can be reduced in the first readout mode. 
     The control unit may receive radiographic image capturing conditions entered from the outside, and may select the radiographic image capturing apparatus suitable for the image capturing conditions from a plurality of the apparatuses. The control unit may send, to the radiographic image capturing apparatus suitable for the image capturing conditions, an instruction to execute the second readout mode in a case where the apparatus detects the radiation in the first readout mode. The control unit may send, to the radiographic image capturing apparatus unsuitable for the image capturing conditions, an instruction to send radiation detection information to the control unit without executing the second readout mode in a case where the apparatus detects the radiation in the first readout mode. In a case where the radiation detection information is sent from the apparatus unsuitable for the image capturing conditions to the control unit, the control unit may provide a warning to the user. In a case where the apparatus unsuitable for the image capturing conditions is selected by mistake, the control unit can encourage the user to restart the image capturing. 
     A radiographic image capturing apparatus according to the ninth aspect has an radiation conversion panel containing a plurality of pixels arranged in a matrix for converting a radiation, transmitted through a subject, into electric charges and storing the electric charges, and a readout control part for controlling the reading of the electric charges stored in the pixels and outputting radiographic image information based on the electric charges. The readout control part is capable of executing a first readout mode and a second readout mode. In the first readout mode, the electric charges stored in the pixels in a plurality of rows are simultaneously read out, and thus the electric charges stored in the pixels are read as first electric signals that are not used for forming the radiographic image. In the second readout mode, the electric charges stored in the pixels are read out row by row, and thus the electric charges stored in the pixels are read as second electric signals that are used for forming the radiographic image. In a case where the readout control part receives an instruction to perform a radiographic image capturing process from the outside, the readout control part acts to execute the first readout mode. Then, in a case where the radiation is detected, the readout control part acts to execute the second readout mode to output the radiographic image information. 
     A method for capturing a radiographic image according to the ninth aspect is performed using a radiographic image capturing system, which has a radiation source for outputting a radiation, a plurality of radiographic image capturing apparatuses for acquiring a radiographic image, and a control unit for controlling the radiation source and the radiographic image capturing apparatuses. The radiographic image capturing apparatuses have an radiation conversion panel containing a plurality of pixels arranged in a matrix for converting the radiation, transmitted through a subject, into electric charges and storing the electric charges, and a readout control part for controlling the reading of the electric charges stored in the pixels and outputting radiographic image information based on the electric charges. The readout control part is capable of executing a first readout mode and a second readout mode. In the first readout mode, the electric charges stored in the pixels in a plurality of rows are simultaneously read out, and thus the electric charges stored in the pixels are read as first electric signals that are not used for forming the radiographic image. In the second readout mode, the electric charges stored in the pixels are read out row by row, and thus the electric charges stored in the pixels are read as second electric signals that are used for forming the radiographic image. In a process of capturing the radiographic image, the control unit sends an instruction to execute the first readout mode to the radiographic image capturing apparatuses. The radiographic image capturing apparatuses receive the instruction to execute the first readout mode, and then act to execute the first readout mode. In a case where one of the radiographic image capturing apparatuses detects the radiation, the second readout mode is performed to output the radiographic image information. 
     A program according to the ninth aspect is used for a radiographic image capturing apparatus, which has an radiation conversion panel containing a plurality of pixels arranged in a matrix for converting the radiation, transmitted through a subject, into electric charges and storing the electric charges, and a readout control part for controlling the reading of the electric charges stored in the pixels and outputting radiographic image information based on the electric charges. The readout control part acts to execute a first readout mode and a second readout mode. In the first readout mode, the electric charges stored in the pixels in a plurality of rows are simultaneously read out, and thus the electric charges stored in the pixels are read as first electric signals that are not used for forming the radiographic image. In the second readout mode, the electric charges stored in the pixels are read out row by row, and thus the electric charges stored in the pixels are read as second electric signals that are used for forming the radiographic image. In a case where the radiographic image capturing apparatus receives an instruction to perform a radiographic image capturing process from the outside, the readout control part acts to execute the first readout mode. Then, in a case where the radiation is detected, the readout control part acts to execute the second readout mode to output the radiographic image information. 
     In the ninth aspect, the radiographic image can be more appropriately captured even if the user makes a mistake in selecting the radiographic image capturing apparatus such as an electronic cassette. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a radiographic image capturing system according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of an electronic cassette shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the electronic cassette taken along the line III-III of  FIG. 2 ; 
         FIG. 4  is a schematic view of a structure of three pixels in a radiation detector shown in  FIG. 3 ; 
         FIG. 5  is a schematic structural view of a TFT and a charge storage part shown in  FIG. 4 ; 
         FIG. 6  is a schematic structural view of the electric structure of the electronic cassette shown in  FIG. 1 ; 
         FIG. 7  is a detail view of a radiation conversion panel, a gate drive part, charge amplifiers, and a multiplexer part shown in  FIG. 6 ; 
         FIG. 8  is a time chart of input signals transferred from a cassette control device to the gate drive part and output signals transferred from the gate drive part to the cassette control device in a sequential readout mode; 
         FIG. 9  is a time chart of input signals transferred from the cassette control device to the gate drive part and output signals transferred from the gate drive part to the cassette control device in a scan mode; 
         FIG. 10  is a schematic structural view of the electric structures of a system controller and a console; 
         FIG. 11  is an example of a table shown in  FIG. 10 ; 
         FIG. 12  is a flowchart of the operation of the system controller and the console in the radiographic image capturing system; 
         FIG. 13  is a flowchart of the operation of the cassette control device; 
         FIG. 14  is a time chart of the operation of the electronic cassette; 
         FIG. 15  is a time chart of the operation of the electronic cassette in the case of setting the number of images to be captured to two; 
         FIG. 16  is a diagram for illustrating electric charges stored in the pixels in some rows in a case where the electronic cassette is switched into an accumulation state after a radiation is detected in a process of reading the electric charges in the 0th row and then one cycle of the scan mode is completed; 
         FIG. 17  is a diagram for illustrating electric charges stored in the pixels in some rows in a case where the electronic cassette is switched into the accumulation state after the radiation is detected in a process of reading the electric charges in the 238th row and then one cycle of the scan mode is completed; 
         FIG. 18  is a diagram for illustrating electric charges in the pixels in the rows in a case where the electronic cassette is switched into the accumulation state after the radiation is detected and then immediately the reading of the electric charges in the pixels in the scan mode is stopped; 
         FIG. 19  is a time chart of the operation of the electronic cassette of Modified Example 3; 
         FIG. 20  is a partial detail view of a radiation conversion panel according to Modified Example 4; 
         FIG. 21  is a partial detail view of a radiation conversion panel according to Modified Example 5; 
         FIG. 22  is a schematic view of a radiographic image capturing system according to Modified Example 7; 
         FIG. 23  is a schematic structural view of the electric structure of an electronic cassette shown in  FIG. 22 ; 
         FIG. 24  is a schematic structural view of the electric structures of a system controller and a console shown in  FIG. 22 ; 
         FIG. 25  is a flowchart for illustrating a part of the operation of Modified Example 7; 
         FIG. 26  is a flowchart for illustrating a part of the operation of Modified Example 7; 
         FIG. 27  is a flowchart for illustrating a part of the operation of Modified Example 7; 
         FIG. 28  is a schematic structural view of the electric structure of an electronic cassette according to Modified Example 8; 
         FIG. 29  is a schematic structural view of the electric structures of a system controller and a console according to Modified Example 8; 
         FIG. 30  is a flowchart of the operation of the system controller and the console in a radiographic image capturing system according to Modified Example 8; 
         FIG. 31  is a flowchart of the operation of a cassette control device according to Modified Example 8; 
         FIG. 32  is a schematic explanatory view of a radiation conversion panel according to Modified Example 9; 
         FIG. 33  is a schematic explanatory view of the radiation conversion panel of Modified Example 9; 
         FIG. 34  is a schematic explanatory view of the radiation conversion panel of Modified Example 9; 
         FIG. 35  is a schematic explanatory view of the radiation conversion panel of Modified Example 9; 
         FIG. 36  is a flowchart for illustrating the operation of Modified Example 10; 
         FIG. 37  is a flowchart for illustrating the operation of Modified Example 10; 
         FIG. 38  is a detail view of a radiation conversion panel, a gate drive part, charge amplifiers, and a multiplexer part according to Modified Example 11, wherein the gain of the charge amplifier can be modified; 
         FIG. 39A  is a circuit diagram of a charge amplifier with a two stage switchable gain; 
         FIG. 39B  is a circuit diagram of a charge amplifier with a three stage switchable gain; 
         FIG. 40  is a time chart for illustrating charge amplifier gain switching and threshold value setting in a process of capturing one image; 
         FIG. 41  is a time chart for illustrating charge amplifier gain switching and threshold value setting in a process of capturing two images; 
         FIG. 42  is an explanatory view of an electronic cassette having a normal threshold value monitoring part; 
         FIG. 43  is a detail view of a radiation conversion panel, a gate drive part, charge amplifiers, and a multiplexer part according to Modified Example 12, equipped with a radiation detection sensor as an emission completion judgment part; 
         FIG. 44  is a partial block diagram of an electronic cassette according to Modified Example 13; 
         FIG. 45  is a circuit diagram of an example of a mask processing portion; 
         FIG. 46  is a diagram for illustrating electric charges stored in pixels in some rows in a case where the electronic cassette is switched into an accumulation state after a radiation is detected and then immediately the reading of the electric charges in the pixels in the scan mode is stopped; 
         FIG. 47  is a partial block diagram of an electronic cassette according to Modified Example 14; 
         FIG. 48  is a circuit diagram of an example of an all-line activation circuit; 
         FIG. 49  is a diagram for illustrating electric charges stored in the pixels in some rows in a case where the electronic cassette is switched into an exposure state after a radiation is detected in a process of reading the electric charges in the 0th row, one cycle of the scan mode is completed, and then all pixels are reset; 
         FIG. 50  is a flowchart of the operation of a cassette control device in the electronic cassette according to Modified Example 14; 
         FIG. 51  is a partial block diagram of an electronic cassette according to Modified Example 15; 
         FIG. 52  is a circuit diagram of examples of a mask processing portion and an all-line activation circuit; 
         FIG. 53  is a diagram for illustrating electric charges stored in pixels in some rows in a case where the electronic cassette is switched into an exposure state after a radiation is detected, immediately the reading of the electric charges in the pixels in the scan mode is stopped, and all pixels are reset; 
         FIG. 54  is a flowchart of the operation of a cassette control device in the electronic cassette according to Modified Example 15; 
         FIG. 55  is a schematic view of a radiographic image capturing system according to Modified Example 16; 
         FIG. 56  is a flowchart of the operation of a system controller and a console in the radiographic image capturing system of Modified Example 16; 
         FIG. 57  is a flowchart of the operation of a cassette control device according to Modified Example 16; and 
         FIG. 58  is a flowchart of the operation of a cassette control device, which does not satisfy image capturing conditions, in an electronic cassette according to Modified Example 17. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Radiographic image capturing apparatuses and radiographic image capturing systems containing the apparatus according to preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 
       FIG. 1  is a schematic view of a radiographic image capturing system  10  according to an embodiment of the present invention. The radiographic image capturing system  10  has a radiation apparatus  18  for applying radiation  16  to a subject  14  of a patient lying on an image capturing base  12  such as a bed, an electronic cassette (radiographic image capturing apparatus)  20  for detecting the radiation  16  that has passed through the subject  14  and converting the detected radiation  16  into a radiographic image, a system controller  24  for controlling the entire radiographic image capturing system  10 , a console  26  for receiving operation input by a doctor, a technician, or the like (hereinafter referred to as the user), and a display device  28  for displaying the captured radiographic image and the like. 
     The system controller  24 , the electronic cassette  20 , and the display device  28  may send signals to and receive signals from each other via wireless communication using UWB (Ultra Wide Band), wireless LAN according to IEEE 802.11.a/b/g/n standard or the like, millimeter waves, etc. Alternatively, the components may send and receive signals via wired communication using cables. 
     The system controller  24  is connected to an RIS (radiology information system)  30 , which generally manages radiographic images and other information handled in the radiological department of a hospital. The RIS  30  is connected to an HIS (hospital information system)  32 , which generally manages medical information in the hospital. 
     The radiation apparatus  18  has a radiation source  34  for emitting the radiation  16 , a radiation control unit  36  for controlling the radiation source  34 , and a radiation switch  38 . The radiation source  34  applies the radiation  16  to the electronic cassette  20 . The radiation  16  emitted from the radiation source  34  may be X-ray, α-ray, β-ray, γ-ray, electron beam, or the like. The radiation switch  38  is of a two stage stroke type. When the radiation switch  38  is pressed halfway by the user, the radiation control unit  36  makes a preparation to emit the radiation  16 . When the radiation switch  38  is pressed completely, the radiation  16  is emitted from the radiation source  34 . The radiation control unit  36  has an input device (not shown), and the user can operate the input device to set an irradiation time for the radiation  16 , a tube voltage, a tube current, and the like. The radiation control unit  36  acts to emit the radiation  16  from the radiation source  34  based on the setup irradiation time and the like. 
       FIG. 2  is a perspective view of the electronic cassette  20  shown in  FIG. 1 , and  FIG. 3  is a cross-sectional view of the electronic cassette  20  taken along the line III-III of  FIG. 2 . The electronic cassette  20  has a panel unit  52  and a control unit  54  disposed thereon. The panel unit  52  is thinner than the control unit  54 . 
     The panel unit  52  has a substantially rectangular casing  56  composed of a material permeable to the radiation  16 . The panel unit  52  has an image capturing surface  42 , which is irradiated with the radiation  16 . The image capturing surface  42  has guide lines  58  substantially at the center as a reference for the image capturing range and position of the subject  14 . The outer frame of the guide lines  58  corresponds to an image capturable area  60  indicative of an irradiation field of the radiation  16 . The central position of the guide lines  58  (the crisscross intersection between the guide lines  58 ) corresponds to the center of the image capturable area  60 . 
     The panel unit  52  has a radiation detector (image capturing panel)  66  containing a scintillator  62  and a radiation conversion panel  64 , and further has a drive circuit device  106  for driving the radiation conversion panel  64  to be hereinafter described (see  FIG. 6 ). The scintillator  62  is for converting the radiation  16  transmitted through the subject  14  into a visible fluorescent light. The radiation conversion panel  64  is an indirect conversion panel for converting the fluorescence from the scintillator  62  into electric signals. The scintillator  62  and the radiation conversion panel  64  are arranged in the casing  56  in this order from the image capturing surface  42 , which is irradiated with the radiation  16 . The radiation conversion panel  64  may be a direct conversion panel for converting the radiation  16  directly into electric signals. In this case, the scintillator  62  is not required, so that the radiation conversion panel  64  corresponds to the radiation detector  66 . 
     The control unit  54  has a substantially rectangular casing  68  composed of a material impermeable to the radiation  16 . The casing  68  extends along one side of the image capturing surface  42 , and the control unit  54  is located outside of the image capturable area  60  on the image capturing surface  42 . In this case, the casing  68  contains a cassette control device (imaging control device)  122  for controlling the panel unit  52 , a buffer memory  124  for storing captured radiographic image data, a communication device (first announcement device or first communication device)  126  for sending signals to and receiving signals from the system controller  24  through a wireless communication link, and a power supply device (electric power supply)  128  such as a battery (see  FIG. 6 ). The power supply device  128  supplies electric power to the cassette control device  122  and the communication device  126 . 
       FIG. 4  is a schematic view of a structure of three pixels in the radiation detector  66 . In the radiation detector  66 , TFTs (field-effect-type thin film transistors)  72  and charge storage parts  74 , sensor parts  76 , and the scintillator  62  are stacked in this order on a board  70 . The pixels each contain the charge storage part  74  and the sensor part  76 , and are arranged in a matrix on the board  70 . Each TFT (switching element)  72  outputs electric charges in the charge storage part  74  of the pixel connected therewith. The scintillator  62  is disposed on the sensor parts  76  with a transparent insulating film  78  interposed therebetween. The scintillator  62  is formed as a film from a fluorescent material, which converts the radiation  16  injected from above (to the surface remote from the board  70 ) into a light. 
     The light emitted from the scintillator  62  preferably has a wavelength within the visible range (360 to 830 nm), and more preferably has a wavelength within the green range to form a monochrome image using the radiation detector  66 . In the case of using an X-ray as the radiation  16  for image capturing, the fluorescent material for the scintillator  62  preferably contains gadolinium oxide sulfur (GOS) or cesium iodide (CsI). The fluorescent material particularly preferably contains CsI(Tl) having an emission spectrum within a range of 420 to 700 nm under X-ray irradiation. The CsI(Tl) exhibits an emission peak wavelength of 565 nm in the visible range. 
     The sensor part  76  has an upper electrode  80 , a lower electrode  82 , and a photoelectric conversion film  84  disposed between the upper and lower electrodes  80  and  82 . The upper electrode  80  is preferably composed of an electrically conductive material transparent at least to the emission wavelength of the scintillator  62  to inject the light from the scintillator  62  into the photoelectric conversion film  84 . 
     The photoelectric conversion film  84  contains an organic photoconductor (OPC). The photoelectric conversion film  84  absorbs the light from the scintillator  62  to generate an electric charge corresponding to the absorbed light. The photoelectric conversion film  84  containing the organic photoconductor exhibits an absorption spectrum having a sharp peak in the visible range, and thereby hardly absorbs electromagnetic waves other than the light from the scintillator  62 . Thus, the photoelectric conversion film  84  can be effectively prevented from absorbing the radiation  16 , which otherwise generates noise. 
     The organic photoconductor in the photoelectric conversion film  84  preferably has an absorption peak wavelength closer to the emission peak wavelength of the scintillator  62  to absorb the light from the scintillator  62  more efficiently. It is ideal that the absorption peak wavelength of the organic photoconductor is equal to the emission peak wavelength of the scintillator  62 . When the difference between the peak wavelengths is small enough, the organic photoconductor can satisfactorily absorb the light from the scintillator  62 . Specifically, the difference between the absorption peak wavelength of the organic photoconductor and the emission peak wavelength of the scintillator  62  under the radiation  16  is preferably 10 nm or less, more preferably 5 nm or less. 
     Such organic photoconductors satisfying the above requirement include quinacridone-based organic compounds and phthalocyanine-based organic compounds. For example, quinacridone has an absorption peak wavelength of 560 nm in the visible range. Therefore, when the quinacridone is used as the organic photoconductor and CsI(Ti) is used as the material of the scintillator  62 , the difference between the above peak wavelengths can be 5 nm or less, whereby the amount of electric charges generated in the photoelectric conversion film  84  can be substantially maximized. 
     An electromagnetic wave absorption/photoelectric conversion region may be formed by a pair of the electrodes  80  and  82  and an organic layer containing the photoelectric conversion film  84  sandwiched therebetween. The organic layer may be formed by stacking or combining an electromagnetic wave absorption component, a photoelectric conversion component, an electron transport component, a hole transport component, an electron blocking component, a hole blocking component, a crystallization preventing component, an electrode, an interlayer contact improving component, etc. The organic layer preferably contains an organic p-type or n-type compound. 
     The organic p-type compound (semiconductor) is an organic donor compound (semiconductor) typified by an organic hole transport compound, which has an electron donating property. More specifically, in a case where two organic compounds are used in contact with each other, the organic donor compound is one compound having a lower ionization potential. Thus, any organic compounds having the electron donating property can be used as the organic donor compound. 
     The organic n-type compound (semiconductor) is an organic acceptor compound (semiconductor) typified by an organic electron transport compound, which has an electron accepting property. More specifically, in a case where two organic compounds are used in contact with each other, the organic acceptor compound is one compound having a higher electron affinity. Thus, any organic compounds having the electron accepting property can be used as the organic acceptor compound. Compounds usable as the organic p-type and n-type compounds and the structure of the photoelectric conversion film  84  are described in detail in Japanese Laid-Open Patent Publication No. 2009-032854, and therefore explanations thereof are omitted. 
     The lower electrode  82  contains a thin film divided for each pixel. The lower electrode  82  may be composed of a transparent or opaque conductive material, and preferred examples thereof include aluminum and silver. In the sensor part  76 , when a predetermined bias voltage is applied between the upper electrode  80  and the lower electrode  82 , one of the electric charges (holes and electrons) generated in the photoelectric conversion film  84  can be transferred to the upper electrode  80 , while the other can be transferred to the lower electrode  82 . In this embodiment, in the radiation detector  66 , a wire is connected to the upper electrode  80 , and the bias voltage is applied from the wire to the upper electrode  80 . The bias voltage has such a polarity that the electrons are transferred to the upper electrode  80  and the holes are transferred to the lower electrode  82  from the photoelectric conversion film  84 . The bias voltage may have a polarity opposite thereto. 
     The sensor part  76  in each pixel contains at least the lower electrode  82 , the photoelectric conversion film  84 , and the upper electrode  80 . Further, the sensor part  76  preferably contains at least one of an electron blocking film  86  and a hole blocking film  88 , and more preferably contains the both, to prevent dark current increase. 
     The electron blocking film  86  may be disposed between the lower electrode  82  and the photoelectric conversion film  84 . When the bias voltage is applied between the lower electrode  82  and the upper electrode  80 , the electron blocking film  86  can prevent electron injection from the lower electrode  82  into the photoelectric conversion film  84 , and thus can prevent the dark current increase. The electron blocking film  86  may be composed of an organic electron donating material. The material of the electron blocking film  86  may be practically selected depending on the materials of the adjacent lower electrode  82  and photoelectric conversion film  84 , etc. It is preferred that the material of the electron blocking film  86  has an electron affinity (Ea) larger by 1.3 eV or more than the work function (Wf) of the material of the adjacent lower electrode  82  and has an ionization potential (Ip) equal to or smaller than that of the material of the adjacent photoelectric conversion film  84 . Materials usable as the organic electron donating material are described in detail in Japanese Laid-Open Patent Publication No. 2009-032854, and therefore such materials will not be described in detail below. 
     The thickness of the electron blocking film  86  is preferably 10 to 200 nm, more preferably 30 to 150 nm, particularly preferably 50 to 100 nm, from the viewpoints of reliably achieving the dark current reducing effect and preventing reduction in the photoelectric conversion efficiency of the sensor part  76 . 
     The hole blocking film  88  may be disposed between the photoelectric conversion film  84  and the upper electrode  80 . When the bias voltage is applied between the lower electrode  82  and the upper electrode  80 , the hole blocking film  88  can prevent hole injection from the upper electrode  80  into the photoelectric conversion film  84 , and thus can prevent the dark current increase. 
     The hole blocking film  88  may be composed of an organic electron accepting material. The thickness of the hole blocking film  88  is preferably 10 to 200 nm, more preferably 30 to 150 nm, particularly preferably 50 to 100 nm, from the viewpoints of reliably achieving the dark current reducing effect and preventing reduction in the photoelectric conversion efficiency of the sensor part  76 . 
     The material of the hole blocking film  88  may be practically selected depending on the materials of the adjacent upper electrode  80  and photoelectric conversion film  84 , etc. It is preferred that the material of the hole blocking film  88  has an ionization potential (Ip) larger by 1.3 eV or more than the work function (Wf) of the material of the adjacent upper electrode  80  and has an electron affinity (Ea) equal to or larger than that of the material of the adjacent photoelectric conversion film  84 . Materials usable as the organic electron accepting material are described in detail in Japanese Laid-Open Patent Publication No. 2009-032854, and therefore such materials will not be described in detail below. 
       FIG. 5  is a schematic structural view of the TFT  72  and the charge storage part  74 . The electric charge transferred to the lower electrode  82  is stored in the charge storage part  74 , and the electric charge stored in the charge storage part  74  is converted to an electric signal and output by the TFT  72 . The region including the charge storage part  74  and the TFT  72  is partially overlapped with the lower electrode  82  as viewed in plan, so that the TFT  72  overlaps with the sensor part  76  in the thicknesswise direction in each pixel. It is preferred that the region including the charge storage part  74  and the TFT  72  is entirely covered with the lower electrode  82  to minimize the plane area of the radiation detector  66 . 
     The charge storage part  74  is electrically connected to the correspondent lower electrode  82  by a conductive material wire, which extends through an insulating film  90  formed between the board  70  and the lower electrode  82 . Thus, the electric charges collected in the lower electrode  82  can be transferred to the charge storage part  74 . 
     The TFT  72  contains a stack of a gate electrode  92 , a gate insulating film  94 , and an active layer (channel layer)  96 . A source electrode  98  and a drain electrode  100  are disposed on the active layer  96  at a predetermined distance. The active layer  96  contains an amorphous oxide. The amorphous oxide for the active layer  96  is preferably an oxide containing at least one of In, Ga, and Zn (such as In—O oxide), more preferably an oxide containing at least two of In, Ga, and Zn (such as In—Zn—O, In—Ga, or Ga—Zn—O oxide), particularly preferably an oxide containing all of In, Ga, and Zn. The amorphous In—Ga—Zn—O oxide is preferably an amorphous oxide having a composition of InGaO 3 (ZnO) m  (wherein m is a natural number of less than 6) in a crystalline state, particularly preferably InGaZnO 4 . 
     When the active layer  96  of the TFT  72  contains the amorphous oxide, the active layer  96  does not absorb the radiation  16  such as X-ray or absorbs only an extremely small amount of the radiation  16 , whereby noise generation can be effectively reduced in the TFT  72 . Both of the amorphous oxide for the active layer  96  of the TFT  72  and the organic photoconductor for the photoelectric conversion film  84  can be formed into a film at low temperature. Therefore, the board  70  is not limited to a highly heat-resistant substrate such as a semiconductor substrate, a quartz substrate, or a glass substrate, and may contain a flexible material (such as a plastic), an aramid, or a bionanofiber. Specifically, the board  70  may be a flexible substrate of a polyester (such as a polyethylene terephthalate, a polyethylene phthalate, or a polyethylene naphthalate), a polystyrene, a polycarbonate, a polyethersulfone, a polyarylate, a polyimide, a polycycloolefin, a norbornene resin, a poly(chlorotrifluoroethylene), or the like. In the case of using the flexible plastic substrate, the radiation detector  66  can be made lighter and easier to carry around. 
     The aramid can undergo a process at a high temperature of 200 degrees or higher. Therefore, in the case of using the aramid, a transparent electrode material can be hardened at a high temperature to lower the resistance, and a driver IC can be automatically mounted using a solder reflow process. Furthermore, the aramid has a thermal expansion coefficient close to those of ITO (Indium Tin Oxide) and glass, whereby the board  70  containing the aramid is less liable to warp and crack after fabrication thereof. In addition, the board  70  of the aramid can be made thinner as compared with glass substrates and the like. The board  70  may be formed by stacking the aramid on an ultrathin glass substrate. 
     The bionanofiber is prepared by combining a transparent resin with a cellulose microfibril bundle (bacteria cellulose) produced by bacteria (acetic acid bacteria,  Acetobacter Xylinum ). The cellulose microfibril bundle has a width of 50 nm, which is 1/10 of the visible light wavelength, and exhibits a high strength, a high elasticity, and a low thermal expansion. The bionanofiber can be produced with a light transmittance of about 90% at a wavelength of 500 nm even at a fibril content of 60% to 70% by impregnating the bacteria cellulose with the transparent resin such as an acrylic resin or an epoxy resin and then hardening the resin. The bionanofiber has a low thermal expansion coefficient (3 to 7 ppm) comparable to a silicon crystal, a high strength (460 MPa) comparable to a steel, a high elasticity (30 GPa), and a high flexibility, whereby the board  70  of the bionanofiber can be made thinner as compared with glass substrates and the like. 
     In this embodiment, the radiation detector  66  is formed by stacking the TFTs  72  and the charge storage parts  74 , the sensor parts  76 , and the transparent insulating film  78  in this order on the board  70  and by bonding the scintillator  62  to the stack with an adhesive resin having a low light absorbance or the like. The stack containing the board  70  to the transparent insulating film  78  is referred to as the radiation conversion panel  64 . 
     In the radiation detector  66 , the photoelectric conversion film  84  composed of the organic photoconductor hardly absorbs the radiation  16 . Therefore, in the radiation detector  66  of this embodiment, even in a case where the radiation  16  is transmitted through the radiation conversion panel  64  in a back side irradiation process, the amount of the radiation  16  absorbed by the photoelectric conversion film  84  can be reduced to prevent the deterioration of the sensitivity to the radiation  16 . In the back side irradiation process, the radiation  16  passes through the radiation conversion panel  64  and reaches the scintillator  62 . When the photoelectric conversion film  84  is composed of the organic photoconductor in the radiation conversion panel  64 , the photoelectric conversion film  84  hardly absorbs the radiation  16 , so that attenuation of the radiation  16  can be prevented. Therefore, the photoelectric conversion film  84  can be suitably used also in the back side irradiation process. 
       FIG. 6  is a schematic structural view of the electric structure of the electronic cassette  20  shown in  FIG. 1 . The electronic cassette  20  has the structure containing pixels  102  disposed on the TFTs  72  arranged in a matrix. The pixels  102  are arranged in a matrix and each have a photoelectric conversion element (not shown). The pixels  102 , which are supplied with a bias voltage from a bias supply  108  in the drive circuit device  106 , store electric charges generated by photoelectric conversion of a visible light. The TFTs  72  are turned on sequentially column by column, whereby the electric charge signals (electric signals) can be read from signal lines  112  as analog pixel signal values. Though the pixels  102  and the TFTs  72  are arranged vertically and horizontally in a 4×4 matrix in  FIG. 6  for the sake of convenience, they are practically arranged vertically and horizontally in a 2880×2304 matrix. 
     The TFTs  72 , connected to the pixels  102 , are connected with gate lines  110  extending in the row direction and the signal lines  112  extending in the column direction. The gate lines  110  are connected to a gate drive part  114  in the drive circuit device  106 , and the signal lines  112  are connected to a multiplexer part  118  in the drive circuit device  106  through a charge amplifier (electric signal amplifier)  116 . The multiplexer part  118  is connected to an AD conversion part  120  for converting the analog electric signals into digital electric signals. The AD conversion part  120  outputs the converted digital electric signals (digital pixel signal values, hereinafter referred to also as digital values) to the cassette control device  122 . 
     The cassette control device  122  is provided for controlling the entire electronic cassette  20 . The cassette control device  122  has a clock circuit (not shown) and acts also as a timer. An information processor such as a computer can be used as the cassette control device  122  of this embodiment by installing a predetermined program thereinto. 
     The cassette control device  122  is connected with the memory  124  and the communication device  126 . The memory  124  stores the digital pixel signal values, and the communication device  126  sends signals to and receives signals from the system controller  24 . The communication device  126  sends the pixel values sequentially row by row to the system controller  24 , and thus sends a packet of one image (one-frame image) containing the pixel values arranged in a matrix. The power supply device  128  supplies electric power to the cassette control device  122 , the memory  124 , and the communication device  126 . The electric power is transferred from the cassette control device  122  to the bias supply  108 , and is supplied to the pixels  102  by the bias supply  108 . 
     The cassette control device  122  has a first readout control part  130 , an irradiation start judgment part  132 , an elapsed time judgment part (emission completion judgment part or exposure completion judgment part)  134 , and a second readout control part  136 . The first readout control part  130  acts to read the electric charges stored in the pixels  102  in a plurality of the rows (lines) simultaneously in a scan mode (first readout mode). The first readout control part  130  controls the gate drive part  114 , the charge amplifiers  116 , the multiplexer part  118 , and the AD conversion part  120  to execute the scan mode. 
     The scan mode (first readout mode) is a fast readout mode capable of reading the one-frame image data in a shorter time as compared with a sequential readout mode (second readout mode) to be hereinafter described. 
     The outline of the scan mode will be described below. In the scan mode, for example, the gate drive part  114  outputs gate signals to the gate lines  110  in 0th and second rows, whereby the TFTs  72  in the 0th and second rows are turned on (the 0th and second rows are activated) to simultaneously read electric charges stored in the pixels  102  in the 0th and second rows through the signal lines  112 . The read electric charges in each column are output as electric charge signals (pixel values) to the charge amplifier  116  in each column. Since the electric charges stored in the pixels  102  in the 0th and second rows are simultaneously read out, the electric signals sent to the charge amplifier  116  are the sum of the electric signals stored in the pixels  102  in the 0th and second rows. Thus, the electric signals stored in the pixels  102  in the 0th and second rows are summed up in each column, and the sum of the electric signals is output to the charge amplifier  116  in each column. The electric charges in the pixels  102  in the 0th and second rows can be summed and read out in this manner. 
     The charge amplifiers  116  convert the entered electric charge signals into voltage signals, and output the voltage signals to the multiplexer part  118 . The multiplexer part  118  sequentially selects the entered voltage signals, and outputs the voltage signals to the AD conversion part  120 . The AD conversion part  120  converts the entered voltage signals into digital signals, and outputs the digital signals. Consequently, the electric signals (pixel values) stored in the pixels  102  in the 0th and second rows are summed up in each column, and are output from the AD conversion part  120  as the digital electric signals (pixel values). The digital electric signals (pixel values) are transferred from the AD conversion part  120  to the cassette control device  122 . In the cassette control device  122 , the transferred digital values are stored in the memory  124 . Thus, the memory  124  stores image data including the signals of the 0th and second rows summed up in each column. 
     After the electric charges stored in the pixels  102  in the 0th and second rows are read out as described above, the gate drive part  114  sends gate signals to the gate lines  110  in first and 3rd rows, whereby the TFTs  72  in the first and 3rd rows are turned on (the first and 3rd rows are activated) to simultaneously read electric charges (electric signals) stored in the pixels  102  in the first and 3rd rows through the signal lines  112 . The read electric signals are transferred to the cassette control device  122  and stored as digital signals in the memory  124  in the above manner. 
     When the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132  to be hereinafter described, the first readout control part  130  stops the scan mode. In a case where the reading of the one-frame image data is not completed at this time, the scan mode is stopped after the completion of the reading of the one-frame image data. 
     Since the electric charges stored in the pixels  102  are read out in the scan mode in this manner, the one-frame image data can be read out in a short time, and noise electric charges in the pixels  102  can be removed in a short time. Since the electric charges stored in the pixels  102  are read out in the scan mode in this manner, the electronic cassette  20  can be readily switched into an exposure state when the emission of the radiation  16  is judged to be started. Furthermore, the loss of the radiation  16  with image information can be reduced. On the contrary, in a case where the noise electric charges in the pixels  102  are removed in the sequential readout mode to be hereinafter described, it takes a long time to read the one-frame image data. In this case, the electronic cassette  20  cannot be readily switched into the exposure state when the emission of the radiation  16  is judged to be started during the process of reading the one-frame image data. Furthermore, the loss of the radiation  16  with image information is increased. 
     The irradiation start judgment part  132  judges whether or not the digital values, which are read by the first readout control part  130  and stored in the memory  124 , are larger than a threshold value. When the digital value becomes larger than the threshold value, the emission of the radiation  16  is judged to be started. Thus, the irradiation start judgment part  132  detects the radiation  16  based on the judgment on whether or not the obtained digital values are larger than the threshold value. In a case where the radiation  16  is not emitted, only a minute amount of the noise electric charges are stored in the pixels  102 . In a case where the radiation  16  is emitted and injected into the electronic cassette  20 , a larger amount of the electric charges are stored in the pixels  102  compared to the case where the radiation  16  is not emitted. Therefore, in a case where the digital signal converted from the electric signal read in the scan mode becomes larger than the threshold value, the emission of the radiation  16  can be judged to be started. 
     Since the electric charges stored in the pixels  102  in a plurality of the rows are simultaneously read out in the scan mode, the start of the emission of the radiation  16  can be judged rapidly and accurately. If the radiation  16  is emitted, the obtained digital electric signal has a significantly high intensity because the electric charges in the pixels  102  are summed up. Therefore, the start of the emission of the radiation  16  can be rapidly judged. Even in a case where the electric charges stored in the pixels  102  are not summed up, the start of the emission of the radiation  16  can be rapidly detected by using a smaller threshold value. However, in this case, the ratio of the noise electric signals to the threshold value is increased, whereby the start of the emission of the radiation  16  cannot be accurately detected. The threshold value may be arbitrarily set by the user. 
     The elapsed time judgment part  134  judges whether a predetermined time has elapsed or not after the start of the emission of the radiation  16 . The predetermined time may be a time for which the radiation  16  is emitted from the radiation source  34 , and may be a time for which the electronic cassette  20  is exposed to the radiation  16  to form the radiographic image. The predetermined time is stored in the memory  124 . 
     The second readout control part  136  acts to read the electric charges stored in the pixels  102  sequentially row by row in the sequential readout mode (second readout mode). The second readout control part  136  controls the gate drive part  114 , the charge amplifiers  116 , the multiplexer part  118 , and the AD conversion part  120  to perform the sequential readout mode. 
     The outline of the sequential readout mode will be described below. In the sequential readout mode, the gate drive part  114  outputs a gate signal to the gate line  110  in the 0th row, whereby the TFTs  72  in the 0th row are turned on (the 0th row is activated) to read the electric charges stored in the pixels  102  in the 0th row through the signal lines  112 . The read electric charges in each column are output as electric charge signals (pixel values) to the charge amplifier  116  in each column. The charge amplifier  116  converts the entered electric charge signals into voltage signals, and outputs the voltage signals to the multiplexer part  118 . The AD conversion part  120  converts the electric signals (pixel values) in the pixels  102  in the 0th row into digital signals, and sends the digital signals to the cassette control device  122 . The sent digital signals are stored in the memory  124 . Thus, the memory  124  stores image data of the 0th row. 
     After the electric charges stored in the pixels  102  in the 0th row are read out as described above, the gate drive part  114  sends a gate signal to the gate line  110  in the first row, whereby the TFTs  72  in the first row are turned on (the first row is activated) to read electric charges (electric signals) stored in the pixels  102  in the first row through the signal lines  112 . The read electric signals are transferred to the cassette control device  122  and stored as digital signals in the memory  124 . 
     After the electric charges stored in the pixels  102  in the first row are read out, the gate drive part  114  acts to read electric charges stored in the pixels  102  in the second row and then read electric charges stored in the pixels  102  in the 3rd row. 
     The cassette control device  122  sends image data of each row stored in the memory  124  sequentially to the system controller  24  through the communication device  126 . Thus, the one-row image data of the rows are sequentially sent row by row. Alternatively, the one-row image data of the rows may be collectively sent as a one-frame image data. 
       FIG. 7  is a detail view of the radiation conversion panel  64 , the gate drive part  114 , the charge amplifiers  116 , and the multiplexer part  118  shown in  FIG. 6 . The gate drive part  114  has 12 gate drive circuits  150  (first to twelfth gate drive circuits  150 ), which are each connected with 240 gate lines  110 . The 240 gate lines  110  are connected to the pixels  102  through the TFTs  72 , and each gate drive circuit  150  reads electric charges stored in the pixels  102  connected therewith. Thus, each gate drive circuit  150  has an associated readout region (0th to 239th rows), and reads the electric charges stored in the pixels  102  in the region. The first to twelfth gate drive circuits  150  are generally referred to as the gate drive circuits  150 . 
     The multiplexer part  118  contains 9 multiplexers  152  (first to ninth multiplexers  152 ), which are each connected with 256 signal lines  112 . Each multiplexer  152  has an associated readout region (0th to 255th columns), and the electric charge signals in the pixels  102  in the region are input through the charge amplifiers  116  into the multiplexer  152 . The first to ninth multiplexers  152  are generally referred to as the multiplexers  152 . Consequently, the radiation conversion panel  64  has 2880 (240×12)×2304 (256×9) pixels  102  and TFTs  72  arranged vertically and horizontally. 
     The AD conversion part  120  contains 9 A/D converters  154  (first to ninth A/D converters  154 ). The voltage signals are output from the multiplexers  152  to the A/D converters  154 . Specifically, the voltage signals output from the first multiplexer  152  are sent to the first A/D converter  154 , and the voltage signals output from the second multiplexer  152  are sent to the second A/D converter  154 . Thus, the voltage signals output from each multiplexer  152  are sent to the correspondent A/D converter  154  in this manner. The A/D converters  154  convert the entered voltage signals to digital voltage signals. The first to ninth A/D converters  154  are generally referred to as the A/D converters  154 . 
     The TFTs  72  are sequentially turned on row by row by the gate drive circuits  150 . Thus, the electric charges stored in the pixels  102  are read sequentially row by row, and are output as charge signals to the charge amplifiers  116  through the signal lines  112 . Specifically, each gate drive circuit  150  selects the gate line  110  in the 0th row (to be read in the first procedure) from a plurality of the gate lines  110  connected therewith, and outputs a gate signal to the selected gate line  110 , whereby the TFTs  72  in the 0th row are turned on to read the electric charges stored in the pixels  102  in the 0th row. After the electric charges stored in the pixels  102  in the 0th row are read out, the gate drive circuit  150  selects the gate line  110  in the first row (to be read in the second procedure) and outputs a gate signal to the selected gate line  110 , whereby the TFTs  72  in the first row are turned on to read the electric charges stored in the pixels  102  in the first row. Then, the gate drive circuit  150  selects the gate lines  110  in the second row, the 3rd row, . . . , and the 239th row (to be read in the final procedure) sequentially, and outputs gate signals to the selected gate lines  110  sequentially, whereby the TFTs  72  in the rows are turned on sequentially row by row to read the electric charges stored in the pixels  102  in the rows. 
     The read electric charges in each column are input through the signal line  112  into the charge amplifier  116  in the column. The charge amplifier  116  has an operational amplifier (OA)  156 , a capacitor  158 , and a switch  160 . In a case where the switch  160  is in the off state, the charge amplifier  116  converts the electric charge signals entered to the operational amplifier  156  into voltage signals, and outputs the voltage signals. The charge amplifier  116  amplifies the electric signals with a gain set by the cassette control device  122  and outputs the amplified signals. In a case where the switch  160  is in the on state, the electric charges stored in the capacitor  158  are emitted by a closed circuit of the capacitor  158  and the switch  160 , and the electric charges stored in the pixels  102  are emitted through the closed switch  160  and the operational amplifier  156  to GND (ground potential). This operation, which contains turning on the switch  160  to emit the electric charges stored in the pixels  102  to the GND (ground potential), is referred to as a reset operation (empty reading operation). Thus, in the reset operation, the voltage signals corresponding to the electric charge signals stored in the pixels  102  are not output to the multiplexer part  118  and the AD conversion part  120 , but are discarded. In this embodiment, “the electric charges stored in the pixels  102  are read” means that the voltage signals corresponding to the electric charges stored in the pixels  102  are output to the multiplexer part  118  and the AD conversion part  120 . 
     The voltage signals converted by the charge amplifier  116  are output to the multiplexer  152 . The multiplexer  152  selects and outputs the entered voltage signals sequentially based on control signals from the cassette control device  122 . The A/D converter  154  converts the voltage signals transferred from the multiplexer  152  into digital signals, and outputs the converted digital signals to the cassette control device  122 . 
       FIG. 8  is a time chart of input signals transferred from the cassette control device  122  to the gate drive part  114  and output signals transferred from the gate drive part  114  to the cassette control device  122  in the sequential readout mode. In the normal readout mode, the cassette control device  122  sends an input signal (drive signal) a 1  to the first gate drive circuit  150 . When the drive signal a 1  is entered, the first gate drive circuit  150  selects the associated gate line  110  in the 0th row and then selects those in the other rows sequentially, and outputs the gate signals to the selected gate lines  110  sequentially row by row. Then, the TFTs  72  are turned on sequentially, and the electric charges stored in the pixels  102  are read out row by row. In a case where the final row (the 239th row) is selected, the first gate drive circuit  150  sends an output signal (end signal) b 1  to the cassette control device  122 . When the cassette control device  122  receives the end signal b 1 , the cassette control device  122  sends an input signal (drive signal) a 2  to the second gate drive circuit  150 . 
     In a case where the input signal a 2  is entered, the second gate drive circuit  150  selects the associated gate line  110  in the 0th row and then selects those in the other rows sequentially, and outputs the gate signals to the selected gate lines  110  sequentially row by row. Then, the TFTs  72  are turned on sequentially, and the electric charges stored in the pixels  102  are read out row by row. When the final row (the 239th row) is selected, the second gate drive circuit  150  sends an output signal (end signal) b 2  to the cassette control device  122 . When the cassette control device  122  receives the end signal b 2 , the cassette control device  122  sends an input signal (drive signal) a 3  to the third gate drive circuit  150 . Such a procedure is repeated in the first to twelfth gate drive circuits  150 . 
     Thus, the drive signals a 1  to a 12  are entered into the first to twelfth gate drive circuits  150  to drive the circuits  150  sequentially, and the electric charges stored in the pixels  102  are read out sequentially row by row. Consequently, the electric charges stored in the pixels  102  in the 0th to 2879th rows on the radiation conversion panel  64  are read out sequentially row by row. In this sequential readout mode, considering the quality of the captured radiographic image, it takes a time of about 173 μsec to read the electric charges stored in the pixels  102  in one row. Therefore, in the sequential readout mode, it takes a time of about 500 msec (173 μsec/l×2880 lines) to read the electric charges in all rows (2880 rows). 
       FIG. 9  is a time chart of input signals transferred from the cassette control device  122  to the gate drive part  114  and output signals transferred from the gate drive part  114  to the cassette control device  122  in the scan mode. In the scan mode, the cassette control device  122  sends input signals c 1  to c 12  to the first to twelfth gate drive circuits  150  simultaneously. When the drive signals c 1  to c 12  are entered, the first to twelfth gate drive circuits  150  each select the associated gate line  110  in the 0th row and then select those in the other rows sequentially, and outputs the gate signals to the selected gate lines  110 . Then, in the associated readout region of each gate drive circuit  150 , the TFTs  72  are turned on sequentially row by row, and the electric charges stored in the pixels  102  are read out sequentially row by row. 
     Specifically, in the associated readout regions of the gate drive circuits  150 , the electric charges stored in the pixels  102  in the 0th rows are simultaneously read out, and then the electric charges stored in the pixels  102  in the first rows are simultaneously read out. Thus, the procedure of reading the electric charges stored in the pixels  102  sequentially row by row in the associated readout region is performed in the gate drive circuits  150  simultaneously. Consequently, the electric charges in the pixels  102  read by the gate drive circuits  150  are summed up in each column. For example, in a case where the gate drive circuits  150  read the electric charges stored in the pixels  102  in the 0th rows simultaneously, the read electric charges of the 0th rows are summed up in each column. The sum of the electric charges in each column is input to the charge amplifier  116  in each column. When the final row (the 239th row) is selected, the gate drive circuits  150  send output signals (end signals) d 1  to d 12  to the cassette control device  122 . 
     In the scan mode, it is necessary to shorten the time required to read the electric charges stored in the pixels  102 . However, when the time for reading the electric charges is excessively shortened, excess electric charges stored in the pixels  102  cannot be removed, and the radiographic image cannot be captured with excellent quality. To satisfy both the requirements, the electric charges stored in the pixels  102  in one row are read out in a time of 21 μsec. Therefore, in the scan mode, it takes a time of about 5 msec (21 μsec×2880 lines×( 1/12)) to read the electric charges in all rows (2880 rows). Thus, the time required to read the electric charges stored in the pixels  102  in all rows in the scan mode is approximately 1/100 of that in the sequential readout mode. It should be noted that (21 vec×2880 lines) is multiplied by ( 1/12) because the electric charges stored in the pixels  102  in 12 rows are simultaneously read out in the scan mode. 
     The electronic cassette  20  has at least a plurality of the pixels  102 , which are arranged in matrix, a plurality of the TFTs  72 , which are arranged in matrix to read the electric signals stored in the pixels  102 , a plurality of the gate lines  110 , which extend parallel to the row direction and are each connected to the TFTs  72  in one row, a plurality of the gate drive circuits  150 , which are arranged in parallel in the column direction and are each connected with a plurality of the gate lines  110  to send the gate signals to the TFTs  72  row by row, and a plurality of the signal lines  112 , which extend parallel to the column direction to read the electric signals stored in the pixels  102 . 
     The TFT  72  has a gate connected to the gate line  110 , a source connected to the pixel  102 , and a drain connected to the signal line  112 . When the drive signal a or c is entered, the gate drive circuit  150  selects the gate lines  110  connected therewith sequentially, sends the gate signals to the selected gate lines  110  to turn on the TFTs  72  sequentially, and reads the electric signals stored in the pixels  102  connected therewith sequentially row by row through the signal lines  112 . 
     In the scan mode, the first readout control part  130  sends the drive signals c to the gate drive circuits  150  simultaneously, and reads the electric signals stored in the pixels  102  in a plurality of the rows simultaneously. 
     In the sequential readout mode, the second readout control part  136  in the cassette control device  122  sequentially sends the drive signals a to the gate drive circuits  150  to sequentially drive the gate drive circuits  150 , and reads the electric signals stored in the pixels  102  sequentially row by row. 
       FIG. 10  is a schematic structural view of the electric structures of the system controller  24  and the console  26 . The console  26  has an input unit  200  for receiving an input operation by the user, a control unit  202  for controlling the entire console  26 , a display unit (second announcement device)  204  for displaying an image to help the input operation by the user, and an interface I/F  206  for sending signals to and receiving signals from the system controller  24 . 
     The system controller  24  has an interface I/F  210  for sending signals to and receiving signals from the console  26 , a control unit (image capturing menu setting unit, instruction signal generation unit, control unit)  212  for controlling the entire radiographic image capturing system  10 , a communication unit (second communication device, transmission unit)  214  for sending signals to and receiving signals from the electronic cassette  20  and the display device  28  through a wireless communication link, a recording unit (image capturing history recording unit)  216  for recording the image data transferred from the electronic cassette  20  through the communication unit  214 , a program, and the like, and a database  220  having a table  218 , which stores image capturing conditions including irradiation times of the radiation  16  associated with imaging areas and diagnostic sites. The interface I/F  206  and the interface I/F  210  are connected by a cable  230 . The input unit  200  has a mouse, a keyboard, or the like (not shown), and sends operation signals entered by the user to the control unit  202 . 
     The control unit  202  acts to display a screen (containing an image capturing menu), to which the user inputs the imaging area (imaging region) and the diagnostic site (region of interest) and the number of images to be captured, on the display unit  204 , so that the display unit  204  is utilized as a GUI (Graphical User Interface). A doctor operates the input unit  200  while watching the screen (containing the image capturing menu) on the display unit  204 , to select the imaging area, the diagnostic site, and the number of images to be captured. The imaging area (imaging region) is a body area of a patient that undergoes the radiographic image capturing process, such as a chest, lower abdomen, or leg. The diagnostic site (the region of interest) is a body site to be examined using an image obtained by the radiographic image capturing process. Even if the imaging area is a chest, the diagnostic site may be different, e.g., circulatory organs, rib bones, the heart, etc. 
     The control unit  202  sends (the image capturing menu containing) the imaging area, the diagnostic site, and the number of images to be captured, selected by the user, through the interfaces I/F  206  and  210  to the control unit  212  in the system controller  24 . In the control unit  212 , an image capturing condition setting part (irradiation time setting part)  222  acts to set image capturing conditions corresponding to the imaging area and the diagnostic site sent from the console  26  (selected by the user). Specifically, the image capturing condition setting part  222  reads the image capturing conditions corresponding to the imaging area and the diagnostic site (selected by the user) from the table  218 , and sets the read image capturing conditions as conditions for the following radiographic image capturing process. The image capturing condition setting part  222  sends at least the irradiation time condition included in the setup image capturing conditions through the communication unit  214  to the electronic cassette  20 . In the electronic cassette  20 , the sent irradiation time is stored in the memory  124 . The stored irradiation time is used as the above-described predetermined time. 
     In the control unit  212 , an image number setting part  224  acts to set the number of images to be captured, sent from the console  26  (selected by the user). The image number setting part  224  sends the setup number of images through the communication unit  214  to the electronic cassette  20 . In the electronic cassette  20 , the sent number of images is stored in the memory  124 . In the control unit  212 , an image record control part  226  acts to record the one-frame image data (sent from the electronic cassette  20  through the communication unit  214 ) in the recording unit  216 . 
       FIG. 11  is an example of the table  218 . In the table  218 , the image capturing conditions including the irradiation times, tube voltages, and tube currents are recorded in association with the imaging areas and the diagnostic sites. The imaging areas include a plurality of the diagnostic sites, and the image capturing conditions are recorded in association with the sites. For example, in a case where the imaging area is a chest, it includes a plurality of diagnostic sites such as circulatory organs, rib bones, and the heart, and the image capturing conditions are recorded in association with the sites. If the imaging area is a chest and the diagnostic site is circulatory organs, the irradiation time is 200 msec, the tube voltage is 100 kV, and the tube current is 10 mA. The user may operate the input unit  200  in the console  26  to modify the information recorded on the table  218 . 
     Operations of the radiographic image capturing system  10  will be described below with reference to the flowcharts of  FIGS. 12 and 13 .  FIG. 12  is a flowchart of the operation of the system controller  24  and the console  26  in the radiographic image capturing system  10 , and  FIG. 13  is a flowchart of the operation of the cassette control device  122 . The operation of the system controller  24  and the console  26  will be described first, and then the operation of the cassette control device  122  will be described below. 
     In the console  26 , the control unit  202  judges whether or not the user operates the input unit  200  to select the imaging area, the diagnostic site, and the number of images to be captured (step S 1 ). In this step, the control unit  202  acts to display an image on the display unit  204 , which is used by the user for selecting the imaging area, the diagnostic site, and the number of images. The user can select, while watching the displayed image, the imaging area and the diagnostic site of a patient that undergoes the radiographic image capturing process. 
     In a case where the imaging area, the diagnostic site, and the number of images are judged to be not selected in step S 1 , the radiographic image capturing system  10  remains in step S 1  until they are selected. 
     When the imaging area, the diagnostic site, and the number of images are judged to be selected by the user in step S 1 , the image capturing condition setting part  222  reads the image capturing conditions corresponding to the imaging area and the diagnostic site selected by the user from the table  218 , and sets the read image capturing conditions as conditions for the following radiographic image capturing process, and the image number setting part  224  sets the number of images selected by the user (step S 2 ). Specifically, when the user operates the input unit  200  to select the imaging area and the like, the control unit  202  outputs the selected imaging area and the like to the control unit  212  in the system controller  24  through the interfaces I/F  206  and  210 . Then, in the control unit  212 , the image capturing condition setting part  222  sets the image capturing conditions corresponding to the imaging area and the diagnostic site sent from the console  26  and sets the number of images sent from the console  26 . The system controller  24  may output the setup image capturing conditions to the control unit  202  through the interfaces I/F  210  and  206 , and the control unit  202  may act to display the setup image capturing conditions and the setup number of images on the display unit  204 . In this case, the user can visually recognize the contents of the setup image capturing conditions. 
     To emit the radiation  16  from the radiation source  34  under the setup image capturing conditions, the user operates the input device in the radiation control unit  36 , so that the radiation control unit  36  sets image capturing conditions equal to the conditions set in the system controller  24 . For example, the radiation apparatus  18  may have a table equal to the table  218 , and the user may select the imaging area and the diagnostic site from the table to set the equal image capturing conditions. Alternatively, the user may enter the irradiation time, the tube voltage, the tube current, and the like directly. 
     After the image capturing conditions are set, the control unit  212  sends a startup signal to the electronic cassette  20  through the communication unit  214 , whereby the electronic cassette  20  is started up (step S 3 ). The electronic cassette  20  is in the sleep state until the startup signal is sent. The sleep state is such a state that electric power is not supplied to at least the radiation conversion panel  64  and the drive circuit device  106 . When the electronic cassette  20  is started up, the electronic cassette  20  acts to execute the scan mode. After the start up, the electronic cassette  20  may act to perform the reset operation before the scan mode. 
     The image capturing condition setting part  222  and the image number setting part  224  send the setup irradiation time and the setup number of images to the electronic cassette  20  through the communication unit  214  (step S 4 ). 
     The control unit  212  judges whether a readout start signal from the electronic cassette  20  is received or not (step S 5 ). The readout start signal includes an instruction to start the reading of the electric charges stored in the pixels  102  in the sequential readout mode. 
     If the readout start signal is judged to be not received in step S 5 , the radiographic image capturing system  10  remains in step S 5  until it is received. When the readout start signal is judged to be received, the image record control part  226  judges whether the one-row image data are sent or not (step S 6 ). The one-row image data are sequentially read out row by row, and the electronic cassette  20  sequentially outputs the one-row image data to the system controller  24 . Thus, the one-row image data are sequentially sent to the system controller  24 . 
     If the one-row image data are judged to be sent in step S 6 , the image record control part  226  acts to store the sent one-row image data in a buffer memory (not shown) in the control unit  212  (step S 7 ). 
     The image record control part  226  judges whether the readout of the one-frame image data is completed or not (step S 8 ). If the readout of the one-frame image data is completed, the electronic cassette  20  outputs a readout end signal to the system controller  24 . In a case where the image record control part  226  receives the readout end signal, the readout of the one-frame image data is judged to be completed. 
     If the reading of the one-frame image data is judged to be not completed in step S 8 , the radiographic image capturing system  10  is returned to step S 6 , and the above steps are repeated. 
     If the readout of the one-frame image data is judged to be completed in step S 8 , an image file is created from the one-frame image data stored in the buffer memory, and is recorded in the recording unit  216  (step S 9 ). 
     The image record control part  226  judges whether or not the sent image data satisfy the required number of images set in step S 2  (step S 10 ). If the sent image data are judged to be in short of the set number of images in step S 10 , the radiographic image capturing system  10  is returned to step S 6 . When the sent image data are judged to satisfy the set number of images, the process is completed. 
     The operation of the electronic cassette  20  will be described below with reference to the flowchart of  FIG. 13  and the time chart of  FIG. 14 . When the startup signal is sent from the system controller  24 , the electronic cassette  20  is started up, and the cassette control device  122  acts to store the irradiation time and the number of images sent from the system controller  24  in the memory  124  (step S 21 ). 
     Then, the first readout control part  130  in the cassette control device  122  acts to start the execution of the scan mode (step S 22 ). When the scan mode is started, the first readout control part  130  outputs the drive signals c to the gate drive circuits  150 . When the drive signal c is received, each gate drive circuit  150  selects the gate lines  110  connected therewith in the 0th to final rows sequentially, and outputs the gate signals to the selected gate lines  110 . Thus, each gate drive circuit  150  reads the electric charges stored in the pixels  102  in the 0th to final rows in the associated readout region sequentially row by row. Consequently, the procedure of reading the electric charges stored in the pixels  102  sequentially row by row in the associated readout region is performed in a plurality of the gate drive circuits  150  simultaneously. The read electric charges are summed up in each column. 
     Specifically, the electric charges stored in the pixels  102  in the 0th rows in the associated readout regions of the gate drive circuits  150  are simultaneously read out, summed up in each column, and output to the charge amplifier  116  in each column. Then, the electric charges stored in the pixels  102  in the first rows in the associated readout regions of the gate drive circuits  150  are simultaneously read out, summed up in each column, and output to the charge amplifier  116  in each column. The steps are repeated also in the second to 239th rows. 
     The one-row electric charges, which are read out sequentially row by row and summed up in each column, are send to the charge amplifiers  116 , transferred through the multiplexer part  118  and the AD conversion part  120 , and stored as the digital electric signals in the memory  124 . Thus, the summed one-row image data are sequentially stored in the memory  124 . When the electric charges stored in the pixels  102  in the 239th rows are read out, the gate drive circuits  150  sends the end signals d to the cassette control device  122 . 
     The first readout control part  130  controls the switches  160  of the charge amplifiers  116  in the off states while implementing the scan mode. Thus, the charge amplifiers  116  can output the sent electric charge signals as the voltage signals. After the start up, the cassette control device  122  may act to perform the reset operation before the start of the scan mode. The first readout control part  130  may start the scan mode when a predetermined time (e.g. 10 seconds) has elapsed after the start up. 
     The irradiation start judgment part  132  judges whether or not the digital electric signals stored in the memory  124  are larger than the threshold value (step S 23 ). When the radiation  16  is emitted from the radiation source  34  to the electronic cassette  20 , the digital electric signals stored in the memory  124  become larger than the threshold value. Thus, whether the radiation  16  is emitted or not is detected based on whether or not the digital electric signals are larger than the threshold value. When the electric signals are judged to be not larger than the threshold value in step S 23 , the electronic cassette  20  remains in step S 23  until the signal is judged to be larger than the threshold value. When the end signals d 1  to d 12  are sent from the gate drive circuits  150  to the cassette control device  122  (the one-frame electric charges are read out), the first readout control part  130  outputs the drive signals c 1  to c 12  to the gate drive circuits  150  again. One cycle of the scan mode include the steps from the input of the drive signals c 1  to c 12  into the gate drive circuits  150  to the output of the end signals d 1  to d 12 . The end signals d 1  to d 12  are sent from the gate drive circuits  150  at the same timing. 
     When the digital electric signal stored in the memory  124  is judged to be larger than the threshold value in step S 23 , the emission of the radiation  16  from the radiation source  34  is judged to be started by the irradiation start judgment part  132  (step S 24 ). 
     When the radiation switch  38  is pressed halfway by the user in the scan mode, the radiation control unit  36  makes a preparation to apply the radiation  16 . Then, when the radiation switch  38  is pressed completely by the user, the radiation control unit  36  acts to emit the radiation  16  from the radiation source  34  for the predetermined time. Since the radiation control unit  36  acts to emit the radiation  16  under the image capturing conditions corresponding to the imaging area and the diagnostic site selected by the user as described above, the predetermined time is the irradiation time corresponding to the imaging area and the diagnostic site selected by the user. In the case of capturing a plurality of images, the user operates the radiation switch  38  at a certain time interval to apply the radiation  16  from the radiation source  34 . 
     When the emission of the radiation  16  is judged to be started in step S 24 , the cassette control device  122  acts to start a timer (step S 25 ), and the first readout control part  130  judges whether the electric charges stored in all the pixels  102  are read out completely or not (whether the reading of the one-frame electric charges is completely or not) in the scan mode (step S 26 ). Thus, after the emission of the radiation  16  is judged to be started, the first readout control part  130  judges whether one cycle of the scan mode is completed or not. Specifically, after the emission of the radiation  16  is judged to be started, the first readout control part  130  judges whether or not the end signals d 1  to d 12  are sent from the gate drive circuits  150 . 
     If the electric charges stored in all the pixels  102  are judged to be not completely read out in step S 26 , the electronic cassette  20  remains in step S 26  until the electric charges are completely read out. In a case where the electric charges stored in all the pixels  102  are judged to be completely read out, the radiographic image capturing process is carried out, and thus the radiation  16  is applied, and the electric charges stored in the pixels  102  by the radiation  16  exposure are read out. Specifically, the first readout control part  130  stops the scan mode to start the exposure, and the electronic cassette  20  is switched to the exposure state (step S 27 ). After this step, the first readout control part  130  does not output the drive signals c 1  to c 12  to the gate drive circuits  150  even if the end signals d 1  to d 12  are sent to the cassette control device  122 . At the same time as the stop of the scan mode, the first readout control part  130  acts to turn on the switches  160  of the charge amplifiers  116 . Consequently, unnecessary electric charges stored in the capacitors  158  can be discarded to improve the radiographic image quality. 
     As shown in  FIG. 14 , until the emission of the radiation  16  from the radiation source  34  is judged to be started, the scan mode is repeated. A timing t1 represents a point at which the emission of the radiation  16  is judged to be started, and an arrow A represents one cycle of the scan mode, which is carried out in about 5 msec. After the emission of the radiation  16  is judged to be started, when the ongoing cycle of the scan mode is completed, the scan mode is stopped, so that the electronic cassette  20  is switched to the exposure state. 
     After the scan mode is stopped in step S 27 , the elapsed time judgment part  134  judges whether the predetermined time has elapsed or not from the judgment of the emission start of the radiation  16  (step S 28 ). When the elapsed time judgment part  134  judges that the predetermined time has not elapsed from the start of the emission of the radiation  16  in step S 28 , the electronic cassette  20  remains in step S 28  until the predetermined time elapses. The predetermined time is the irradiation time corresponding to the imaging area and diagnosis purpose selected by the user, and therefore the elapsed time judgment part  134  judges whether the emission of the radiation  16  is completed or not in step S 28 . Thus, after the scan mode is stopped, the exposure for the radiographic image capturing process is continued until the predetermined time elapses. 
     In a case where elapse of the predetermined time from the start of the emission of the radiation  16  is judged in step S 28 , the exposure is stopped, and the second readout control part  136  acts to start the sequential readout mode for reading the electric charges generated by the exposure with the radiation  16  (step S 29 ). In this step, the second readout control part  136  outputs the readout start signal to the system controller  24  through the communication device  126  before, at, or after the start of the sequential readout mode. Consequently, the system controller  24  detects that the radiographic image data will be sent from the electronic cassette  20 , and makes a preparation to receive the image data. 
     In the sequential readout mode, the second readout control part  136  outputs the drive signal a 1  to the first gate drive circuit  150 . When the drive signal a 1  is entered, the first gate drive circuit  150  selects the associated gate lines  110  in the 0th to final rows sequentially, outputs the gate signals to the selected gate lines  110 , and reads the electric charges stored in the pixels  102  in the 0th to final rows in the associated region sequentially row by row. Thus, the first gate drive circuit  150  reads the electric charges stored in the pixels  102  in the 0th to 239th rows in the associated region sequentially row by row. When the 239th row is selected, the first gate drive circuit  150  sends the end signal b 1  to the cassette control device  122 . 
     When the end signal b 1  is entered, the second readout control part  136  sends the drive signal a 2  to the second gate drive circuit  150 . Such a procedure is repeated in the first to twelfth gate drive circuits  150 . Consequently, the electric charges stored in the pixels  102  in the 0th to 2879th rows on the radiation conversion panel  64  are read out sequentially row by row. The electric charges, read out sequentially row by row, are input into the charge amplifier  116  in each column, transferred through the multiplexer part  118  and the AD conversion part  120 , and stored as the digital electric signals in the memory  124 . Thus, the one-row image data, obtained row by row, are sequentially stored in the memory  124 . 
     In  FIG. 14 , a timing t3 represents a point at which the predetermined time is judged to have elapsed in step S 28 , and the sequential readout mode is started at approximately the same time as the timing t3 or immediately after the timing t3. The second readout control part  136  outputs the readout start signal to the system controller  24  at the same time as the start of the sequential readout mode. An arrow B represents one cycle of the sequential readout mode, which is carried out in about 500 msec. After the drive signal a 1  is entered into the first gate drive circuit  150 , one cycle of the sequential readout mode is carried out until the twelfth gate drive circuit  150  outputs the end signal b 12 . 
     The cassette control device  122  controls the switches  160  of the charge amplifiers  116  in the off states during implementing the sequential readout mode. Thus, the charge amplifiers  116  can output the sent electric charge signals as voltage signals. 
     After the start of the sequential readout mode, the cassette control device  122  starts to sequentially send the one-row image data (obtained row by row) to the system controller  24  (step S 30 ). Thus, the one-row image data are stored in the memory  124 , and sent to the system controller  24  through the communication device  126 . 
     The second readout control part  136  judges whether the electric charges stored in all the pixels  102  are read out completely or not (whether the one-frame of electric charges are read out completely or not) in the sequential readout mode (step S 31 ). Thus, the second readout control part  136  judges whether one cycle of the sequential readout mode is completed or not. Specifically, the second readout control part  136  judges whether or not the end signal b 12  is sent from the twelfth gate drive circuit  150 . 
     In a case where the electric charges stored in all the pixels  102  are judged to be not completely read out in step S 31 , the electronic cassette  20  remains in step S 31  until the electric charges are completely read out. In a case where the electric charges stored in all the pixels  102  are judged to be completely read out, the second readout control part  136  stops the sequential readout mode (step S 32 ). In this step, the second readout control part  136  outputs the readout end signal to the system controller  24  through the communication device  126 . 
     The cassette control device  122  judges whether or not the number of the captured images reaches the setup number of images stored (set by the user) in step S 21 , thus whether or not the performed exposure and sequential readout procedures satisfy the condition of the setup number of images stored in step S 21  (step S 33 ). When the number of the captured images is judged to be in short of the setup number of images in step S 33 , the electronic cassette  20  is returned to step S 22 , and the above steps are repeated. When the number of the captured images is judged to reach the setup number of images, the process is completed and stopped. 
       FIG. 15  is a time chart of the operation of the electronic cassette  20  in a case where the setup number of images is 2. In the electronic cassette  20 , the first readout control part  130  acts to repeatedly execute the scan mode until the first emission of the radiation  16  is carried out. When the emission of the radiation  16  from the radiation source  34  is started, the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132 , and the ongoing cycle of the scan mode is completed, the electronic cassette  20  is switched to the exposure state. When the predetermined time has elapsed (the emission of the radiation  16  is completed), the second readout control part  136  acts to execute the sequential readout mode, and the electric charges stored by the emission of the radiation  16  in the pixels  102  are read out. Then, the first readout control part  130  acts to repeatedly execute the scan mode again. When the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132 , and the ongoing cycle of the scan mode is completed, the electronic cassette  20  is switched to the exposure state. When the predetermined time has elapsed (the emission of the radiation  16  is completed), the electric charges stored in the pixels  102  are read out, and thus the process is completed. In this case, the user may operate the radiation switch  38  twice at a certain time interval to apply the radiation  16  twice to the subject  14 . 
     In this manner, before the emission of the radiation  16 , the electric charges stored in the pixels  102  are read out in the scan mode, which is capable of more rapid reading than the sequential readout mode. When the digital value obtained by reading the electric charge becomes larger than the threshold value, the emission of the radiation  16  is judged to be started, and the exposure is started. Therefore, it is not necessary to synchronize the image capturing timings (an emission timing of the radiation  16  and an exposure timing of the electronic cassette  20 ), and the radiographic image can be readily captured. 
     Since the electric charges stored in the pixels  102  in a plurality of the rows are simultaneously read out in the scan mode, the start of the emission of the radiation  16  can be judged rapidly and accurately. Thus, since the electric charges in the pixels  102  are summed up, the obtained digital electric signal has a significantly higher intensity under the emission of the radiation  16  than without the emission, so that the start of the emission of the radiation  16  can be rapidly judged. Even in a case where the electric charges stored in the pixels  102  are not summed up, the start of the emission of the radiation  16  can be rapidly detected by using a smaller threshold value. However, in this case, the ratio of the noise electric signals to the threshold value is increased, whereby the start of the emission of the radiation  16  cannot be accurately detected. 
     Since the electric charges in a plurality of the rows are read simultaneously in the scan mode, the one-frame image can be read out at high speed (the one cycle of the scan mode can be shortened). Therefore, when the emission of the radiation  16  is judged to be started, the electronic cassette  20  can be switched to the exposure state in a shorter time. 
     In the scan mode, the procedure of reading the electric charges stored in the pixels  102  in the 0th to final rows sequentially row by row in the associated readout region is performed in a plurality of the gate drive circuits  150  simultaneously. Therefore, the start of the emission of the radiation  16  can be rapidly detected regardless of area in the radiation conversion panel  64  to which the radiation  16  is emitted. In a case where the electric charges stored in the pixels  102  are read to detect the start of the emission of the radiation  16  in the sequential readout mode, if the radiation  16  is emitted to an area of the 2000th to 2879th rows, the emission of the radiation  16  cannot be detected while the electric charges stored in the pixels  102  in the 0th to 1999th rows are read out. In contrast, since each gate drive circuits  150  read the electric charges stored in the pixels  102  in the 0th to 239th rows row by row in the scan mode, and thus the electric charges stored in the pixels  102  in the rows located at an interval of 240 rows are simultaneously read out in the scan mode, the start of the emission of the radiation  16  can be rapidly detected regardless of the area to which the radiation  16  is emitted. 
     The electronic cassette  20  perform the scan mode until the emission of the radiation  16  is judged to be started, and is switched to the exposure state when the start of the emission of the radiation  16  is detected. Therefore, it is not necessary to synchronize the image capturing timings, and thus it is not necessary to electrically connect the radiation apparatus  18  and the system controller  24 , resulting in lowered cost. Since the scan mode is executed until the emission of the radiation  16  is judged to be started, the unnecessary electric charges stored in the pixels  102  can be removed to reduce the noise content of the radiographic image. 
     When the emission of the radiation  16  is judged to be started, the scan mode is stopped and switched by the exposure state. Therefore, the loss of the radiation  16  with the image information can be reduced. When the irradiation time (the predetermined time) has elapsed from the start of the emission of the radiation  16 , the sequential readout mode is executed. Therefore, the exposure period of the pixels can be shortened to the minimum to further reduce the noise content of the radiographic image. Furthermore, it is not necessary to add another radiation detection sensor, thereby resulting in low cost. 
     The above embodiment can be modified as follows. Components of the following modified examples, which are identical to those of the above embodiment, are denoted by identical reference characters, and explanations thereof are omitted. 
     Modified Example 1 
     In the above embodiment, even when the emission of the radiation  16  is judged to be started in the scan mode, the electronic cassette  20  is not switched into the exposure state until the one cycle is completed. The electronic cassette  20  may be switched into the exposure state immediately after the judgment of the emission of the radiation  16 . 
       FIGS. 16 and 17  are diagrams for illustrating the electric charges in the pixels  102  in some rows in a case where the electronic cassette  20  is switched into the accumulation state after the radiation  16  is detected and then the one cycle of the scan mode is completed. In the scan mode, each of the gate drive circuits  150  reads the electric charges stored in the pixels  102  in the 0th to final rows sequentially row by row. In this case, for example, even if a digital value obtained by reading the electric charges stored in the pixels  102  in the 0th row is judged to be larger than the threshold value and thus the radiation  16  is detected, the scan mode is not switched into the exposure state until the reading of the electric charges stored in the pixels  102  in the 239th row is completed. 
     Therefore, even after the detection of the radiation  16  in the scan mode, the electric charges stored in the pixels  102  under the radiation  16  are read out (discarded), whereby the loss of the radiation  16  with the image information is increased. The loss is increased significantly when the radiation  16  is detected at an early stage of the one cycle of the scan mode. Thus, as the timing of the detection of the emission of the radiation  16  is closer to the timing of reading the electric charges stored in the pixels  102  in the 239th row, the loss of the radiation  16  is reduced. 
     Specifically, even when the radiation  16  is detected in the step of reading the electric charges in the pixels  102  in the 0th row as shown in  FIG. 16 , the electric charges stored in the pixels  102  in the following first to 239th rows are read out sequentially row by row in the scan mode. The electric charges stored in the pixels  102  in the first to 239th rows under the radiation  16  are discarded. Therefore, the electric charges accumulated by the emission of the radiation  16  are wasted. The amount Q0 of the electric charges stored in the pixels  102  in the 0th row by the exposure for capturing the radiographic image and the amount Q239 of the electric charges stored in the pixels  102  in the 239th row satisfy the relation of Q0&gt;Q239, and the difference between the amounts is large. The rows exhibit large variations in the amounts of the electric charges stored in the pixels  102 . An amount Qn represents an amount of the electric charges stored in the pixels  102  in the n-th row. For example, the amount of the electric charges stored in the pixels  102  in the 3rd row is represented by Q3, and the amount of the electric charges stored in the pixels  102  in the 200th row is represented by Q200. 
     When the radiation  16  is detected in the step of reading the electric charges in the 238th row as shown in  FIG. 17 , the electric charges stored in the pixels  102  only in the following 239th row are read out in the scan mode. Therefore, only the electric charges stored in the pixels  102  in the 239th row under the radiation  16  are discarded. In this case, the amount Q0 of the electric charges stored in the pixels  102  in the 0th row by the exposure for capturing the radiographic image, the amount Q238 of the electric charges stored in the pixels  102  in the 238th row, and the amount Q239 of the electric charges stored in the pixels  102  in the 239th row satisfy the relation of Q0&gt;Q238&gt;Q239, but the difference between the amounts is not large. The rows exhibit small variations in the amounts of the electric charges stored in the pixels  102 . 
     Consequently, the amounts of the electric charges, which are stored in the pixels  102  in the rows by the exposure for capturing the radiographic image, are varied depending on the timing of the emission of the radiation  16 . 
     Accordingly, in Modified Example 1, the electric charges stored in the pixels  102  are not read out after the emission of the radiation  16  is detected, and the electronic cassette  20  is switched into the accumulation state. Specifically, when the start of the emission of the radiation  16  is detected, the cassette control device  122  sends readout stop signals to the gate drive circuits  150 . When the drive signals c 1  to c 12  are sent, each of the gate drive circuits  150  selects the gate lines  110 , outputs the gate signals to the selected gate lines  110 , and reads the electric charges stored in the pixels  102  sequentially row by row. When the stop signals are sent, a mask processing is carried out, and the gate drive circuits  150  do not output the gate signals. Thus, the first readout control part  130  stops the reading of the electric charges stored in the pixels  102  in the scan mode. In this case, even when the stop signals are sent, each of the gate drive circuits  150  continues to sequentially select the gate lines  110  (the scan mode is continued). However, since the mask processing is carried out, the gate signals are not sent to the selected gate lines  110 . Therefore, the electronic cassette  20  can be switched into the exposure state after the detection of the radiation  16 . 
     For example, even in a case where the stop signals are sent after the gate signal is sent to the gate line  110  of the 0th row, each of the gate drive circuits  150  continues to sequentially select the gate lines  110  of the first, second, . . . , and final rows, but does not output the gate signals to the selected gate lines  110 . In this case, even if the stop signals are sent, the gate drive circuits  150  sequentially select the gate lines  110 , and thereby output the end signals d 1  to d 12  after the gate lines  110  of the 239th rows are selected. When the end signals d 1  to d 12  are sent from the gate drive circuits  150 , the first readout control part  130  acts to stop the scan mode. 
       FIG. 18  is a diagram for illustrating the electric charges in the pixels  102  in some rows in a case where the electronic cassette  20  is switched into the accumulation state after the radiation  16  is detected and then immediately the reading of the electric charges in the pixels  102  in the scan mode is stopped. 
     The electric charges in the pixels  102  in the some rows, stored in a case where the radiation  16  is detected in a process of reading the electric charges stored in the 0th row, are shown in  FIG. 18 . When the radiation  16  is detected, the cassette control device  122  sends the stop signals to the gate drive circuits  150 . Therefore, the electric charges stored in the pixels  102  in the second to final rows under the emission of the radiation  16  are not read out and remain in the rows. In this case, the amount Q0 of the electric charges stored in the pixels  102  in the 0th row by the exposure for capturing the radiographic image, the amount Q1 of the electric charges stored in the pixels  102  in the first row, and the amount Q239 of the electric charges stored in the pixels  102  in the 239th row satisfy the relation of Q0&lt;Q1=Q239, and the difference between the amounts is not large. Thus, the exposure can be performed without wasting the radiation  16  with the image information, and the rows exhibit only small variations in the amounts of the electric charges. 
     The operation of the cassette control device  122  in Modified Example 1 is approximately equal to that shown in the flowchart of  FIG. 13 . However, in Modified Example 1, in a case where the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132  in step S 24  of  FIG. 13 , the first readout control part  130  sends the stop signals to the gate drive circuits  150  to perform step S 25 , so that the electronic cassette  20  can be switched into the exposure state. Then, the first readout control part  130  judges whether or not the end signals d 1  to d 12  are sent from the gate drive circuits  150  in step S 26 . When the end signals d 1  to d 12  are judged to be sent, the scan mode is stopped in step S 27 . 
     In this manner, when the emission of the radiation  16  is judged to be started, the electronic cassette  20  outputs the stop signals to the gate drive circuits  150 . Though the scan mode is continued until the one cycle is completed, the electric charges stored in the pixels  102  are not read out, whereby the radiation  16  with the image information are not wasted and are utilized for capturing the radiographic image. 
     Modified Example 2 
     In the above embodiment and Modified Example 1, the user operates the input unit  200  to input the number of images to be captured, and the image number setting part  224  in the system controller  24  sets the number of images to be captured and sends the number of images to the electronic cassette  20 . The numbers of images may be recorded on the table  218  in association with the imaging areas and the diagnosis purposes. In this case, the image capturing condition setting part  222  reads from the table  218  the number of images corresponding to the imaging area and the diagnosis purpose selected by the user, sets the number of images, and sends the setup number of images to the electronic cassette  20 . 
     Modified Example 3 
     In the above embodiment and Modified Examples 1 and 2, in a case where the radiographic image capturing process is performed multiple times, the user operates the radiation switch  38  to emit the radiation  16  from the radiation source  34  multiple times. In this case, the radiation  16  may be continuously emitted from the radiation source  34  over a predetermined time, and the electronic cassette  20  may act to perform the radiographic image capturing process multiple times in the predetermined time. The user can operate the input device of the radiation control unit  36  to set the predetermined time. The radiation control unit  36  controls the radiation source  34  to emit the radiation  16  for the setup predetermined time. 
       FIG. 19  is a time chart of the operation of the electronic cassette  20  in Modified Example 3. In the electronic cassette  20 , the first readout control part  130  repeatedly executes the scan mode until the emission of the radiation  16 . When the emission of the radiation  16  from the radiation source  34  is started, the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132 , and the electronic cassette  20  is switched into the exposure state. When the predetermined time has elapsed, the second readout control part  136  acts to execute the sequential readout mode to read the electric charges stored in the pixels  102  under the emission of the radiation  16 . Then, the first readout control part  130  acts to execute the scan mode again. However, since the radiation  16  is continuously emitted, the emission of the radiation  16  is immediately detected by the irradiation start judgment part  132 , and the electronic cassette  20  is rapidly switched into the exposure state. When the predetermined time has elapsed, the second readout control part  136  acts to execute the sequential readout mode to read the electric charges stored in the pixels  102  under the emission of the radiation  16 . The radiographic image capturing process can be performed multiple times while emitting the radiation  16  in this manner. The predetermined time may be an irradiation time corresponding to the imaging area and the diagnosis purpose selected by the user, a default value, or an irradiation time set independently by the user. 
     Modified Example 4 
     In the above embodiment and Modified Examples 1 to 3, in the scan mode, the procedures of simultaneously reading a plurality of the rows are sequentially performed to read the electric charges stored in all pixels  102 . However, only the pixels in a predetermined row may be read out. Modified Example 4 will be described in detail below. 
       FIG. 20  is a partial detail view of a radiation conversion panel  64  according to Modified Example 4. The radiation conversion panel  64  has a gate line  250 , which is directly connected to the cassette control device  122 . The gate line  250  is connected to pixels  254  through the TFTs  252 . When the TFTs  252  are turned on, electric charges stored in the pixels  254  are read out through the signal lines  112 . A gate signal for reading the electric charges stored in the pixels  254  in the scan mode is supplied to the TFTs  252  through the gate line  250 . Thus, the gate line  250 , the TFTs  252 , and the pixels  254  are formed to execute the scan mode in addition to the gate lines  110 , the TFTs  72 , and the pixels  102 . The radiation conversion panel  64  may have one gate line  250  or a plurality of the gate lines  250 , which are each located between the gate drive circuits  150  or arranged at regular intervals over the entire radiation conversion panel  64 . For example, the gate lines  250  may be formed between the first and second gate drive circuits  150 , between the sixth and seventh gate drive circuits  150 , and between the eleventh and twelfth gate drive circuits  150 . In this case, at least one of the pixels  254  can receive the radiation  16  regardless of area in the radiation conversion panel  64  to which the radiation  16  is emitted. The pixels  254  connected to the gate line  250  correspond to the pixels in the predetermined row. 
     Though not shown in the drawing, each of the gate drive circuits  150  is connected with 240 gate lines  110 , and each of the gate lines  110  is connected with the pixels  102  through the TFTs  72 . 
     In Modified Example 4, in the scan mode, the first readout control part  130  outputs the gate signal directly to the gate line  250  to repeatedly read the electric charges stored in the pixels  254  row by row. For example, in the case of forming only one gate line  250 , the gate signal is sent to the gate line  250  in the one cycle of the scan mode, and the gate signal is sent again to the gate line  250  in the next cycle of the scan mode after the completion of the one cycle, so that the electric charges stored in the pixels  254  are repeatedly read out. 
     In the case of forming a plurality of the gate lines  250 , the first readout control part  130  sequentially outputs the gate signals directly to the gate lines  250 , so that the procedure of sequentially reading the electric charges stored in the pixels  254  row by row is repeatedly performed. For example, in the case of forming three gate lines  250 , the gate signal is sent to the gate line  250  of the 0th row, and the electric charges stored in the pixels  254  connected to the gate line  250  of the 0th row are read out. Then, the gate signal is sent to the gate line  250  of the first row, and the electric charges stored in the pixels  254  connected to the gate line  250  of the first row are read out. 
     Finally, the gate signal is sent to the gate line  250  of the second row, and the electric charges stored in the pixels  254  connected to the gate line  250  of the second row are read out. After the gate signal is sent to the gate line  250  of the second row, the one cycle of the scan mode is completed. Then, in the next cycle, the gate signal is sent again to the gate line  250  of the 0th row. 
     In a case where the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132 , the scan mode is immediately stopped, and the electronic cassette  20  is switched into the exposure state. After the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132 , the gate drive circuits  150  do not send the gate signal to the gate line  250 . For example, in the case of forming three gate lines  250 , when the digital value obtained by outputting the gate signal to the gate line  250  of the 0th row is judged to be larger than the threshold value, the scan mode is immediately stopped without sending the gate signals to the gate lines  250  of the first and second rows. Thus, the electric power consumption in the scan mode can be reduced. 
     In a case where the predetermined time has elapsed from the detection of the radiation  16  (the judgment of the emission start of the radiation  16 ), i.e. when the emission of the radiation  16  is completed, the second readout control part  136  acts to execute the sequential readout mode. 
     The electronic cassette  20  has at least a plurality of the pixels (first pixels)  102 , which are arranged in the matrix, a plurality of the TFTs (first switching elements)  72 , which are arranged in the matrix to read the electric signals stored in the pixels  102 , a plurality of the gate lines (first gate lines)  110 , which extend parallel to the row direction and are each connected to the TFTs  72  in one row, a plurality of the gate drive circuits  150 , which are arranged in parallel in the column direction and are each connected with a plurality of the gate lines  110  to send the gate signals to the TFTs  72  row by row, and a plurality of the signal lines  112 , which extend parallel to the column direction to read the electric signals stored in the pixels  102 . 
     The electronic cassette  20  further has a plurality of the pixels (second pixels)  254 , which are arranged in the row direction on the surface having the pixels  102 , a plurality of the TFTs (second switching elements)  252 , which are arranged in the row direction to read the electric signals stored in the pixels  254 , and at least one gate line  250 , which extends parallel to the row direction and is connected to the TFTs  252 . 
     The TFTs  72  and  252  each have a gate connected to the gate line  110  or  250 , a source connected to the pixel  102  or  254 , and a drain connected to the signal line  112 . When the drive signal a is entered, each gate drive circuit  150  selects the gate lines  110  connected therewith sequentially, sends the gate signals to the selected gate lines  110  to turn on the TFTs  72  sequentially, and reads the electric signals stored in the pixels  102  connected therewith sequentially row by row through the signal lines  112 . 
     The first readout control part  130  sends the gate signal to the gate line  250  sequentially, and thereby acts to execute the scan mode for reading the electric signals stored in the pixels  254  sequentially row by row. The second readout control part  136  sends the drive signals a to the gate drive circuits  150  sequentially to operate the gate drive circuits  150  sequentially, and thereby acts to execute the sequential readout mode for reading the electric signals in the pixels  102  sequentially row by row. 
     The operation of the cassette control device  122  in Modified Example 4 is approximately equal to that shown in the flowchart of  FIG. 13 . However, in Modified Example 4, when the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132  in step S 24  of  FIG. 13 , the first readout control part  130  immediately acts to stop the output of the gate signal to the gate line  250  (to stop the scan mode), and step S 25  is carried out. The timer is started in step S 25 , and then step S 28  is carried out without performing steps S 26  and S 27 . 
     In Modified Example 4, the electric charges in the pixels  102  are not read out in the scan mode, whereby the pixels  102  are in the exposure state in the scan mode. Therefore, the radiation  16  with the image information is not wasted, and the electric charges corresponding to the emitted radiation  16  can be stored. Since the start of the emission of the radiation  16  is judged by reading the electric charges stored in the pixels  254 , the timing of the emission start of the radiation  16  can be detected. Furthermore, the electronic cassette  20  is switched into the sequential readout mode when the irradiation time has elapsed from the emission start of the radiation  16 . Therefore, the electronic cassette  20  is not exposed excessively after the completion of the emission of the radiation  16 , whereby the noise content of the radiographic image can be lowered. In addition, since the start of the emission of the radiation  16  is judged by reading the electric charges stored in the pixels  254 , the electric power consumption in the scan mode can be reduced. 
     In Modified Example 4, in the scan mode, the electric charges stored in the pixels  254  in one row may be read out in a time of 173 μsec in the same manner as the sequential mode. Because the electric charges stored in the pixels  254  are read out within 173 μsec in this manner, the emission start of the radiation  16  can be judged with high accuracy without summing the electric charges stored in the pixels  254 . The number of the gate lines  250  for the scan mode is smaller than that of the gate lines  110  for the radiographic image capturing process. Therefore, even when the electric charges stored in the pixels  102  in one row are read in the time in the same manner as the sequential readout mode, the one cycle of the scan mode can be performed in a short time. For example, when the number of the gate lines  250  is 29, the one cycle of the scan mode can be performed in a time of about 5 msec in the same manner as the above embodiment. 
     In the case of forming a plurality of the gate lines  250 , the user may operates the input unit  200  of the console  26  to select one, two, or more gate lines  250  for use in the scan mode. The user can expect an area in the electronic cassette  20 , which is irradiated with the radiation  16  from the radiation source  34 . Therefore, the user may select the gate line  250  corresponding to the area to be irradiated with the radiation  16 . The information of the selected gate line  250  is transferred from the console  26  through the system controller  24  to the electronic cassette  20 . The first readout control part  130  sends the gate signal only to the selected gate line  250  in the scan mode. 
     Consequently, the start of the emission of the radiation  16  can be judged rapidly and reliably by the irradiation start judgment part  132 . The gate signal is not sent to the gate line  250  in an area, which is not irradiated with the radiation  16 . Therefore, the electric power consumption in the scan mode can be further reduced. 
     Furthermore, in the case of forming a plurality of the gate lines  250 , a larger number of the gate lines  250  may be selected in an area, which is likely to be irradiated or is irradiated with the radiation  16 . Meanwhile, a smaller number of the gate lines  250  may be selected in an area, which is unlikely to be irradiated or is not irradiated with the radiation  16 . In the scan mode, the gate signal is sent only to the selected gate line  250 . The user can operate the input unit  200  of the console  26  to specify the area, which is likely to be irradiated or is irradiated with the radiation  16 . In this case, the area, which is likely to be irradiated or is irradiated with the radiation  16 , may be directly specified by the user. Alternatively, the control unit  212  of the system controller  24  may read from the table  218  and specify the area corresponding to the imaging area and the diagnosis purpose selected by the user. The control unit  212  of the system controller  24  selects the gate line  250  to be used in the scan mode based on the specified area, and sends the information of the selected gate line  250  to the electronic cassette  20 . 
     Modified Example 5 
     In Modified Example 4, the gate line  250 , the TFTs  252 , and the pixels  254  for the scan mode are formed independently from the gate lines  110 , the TFTs  72 , and the pixels  102 . However, some of the gate lines  110 , the TFTs  72 , and the pixels  102  may be predetermined as components to be used also in the scan mode. 
       FIG. 21  is a partial detail view of a radiation conversion panel  64  according to Modified Example 5. Though not shown in the drawing, each of the gate drive circuits  150  is connected with 240 gate lines  110 , and each of the gate lines  110  is connected with the pixels  102  through the TFTs  72 . One of the 240 gate lines  110  extending from each gate drive circuit  150  is connected to the cassette control device  122  through a bypass line  260 . The bypass line  260  has a switching element  262 . 
     The bypass line  260  connected to the gate line  110  of the first gate drive circuit  150  is referred to as the first bypass line  260 , and the bypass line  260  connected to the gate line  110  of the second gate drive circuit  150  is referred to as the second bypass line  260 . Similarly, the bypass lines  260  connected to the gate lines  110  of the third to twelfth gate drive circuits  150  are referred to as the third to twelfth bypass lines  260 . Furthermore, for the sake of convenience, the gate line  110  connected with the first bypass line  260  is referred to as the first scanning gate line  110 , and the gate line  110  connected with the second bypass line  260  is referred to as the second scanning gate line  110 . Similarly, the gate lines  110  connected with the third to twelfth bypass lines  260  are referred to as the third to twelfth scanning gate lines  110 . Though one of the 240 gate lines  110  connected to each of the gate drive circuits  150  is used as the scanning gate lines  110  for the sake of convenience in Modified Example 5, some of the gate drive circuits  150  may have no scanning gate lines  110  and may have a plurality of the scanning gate lines  110 . 
     In Modified Example 5, in the scan mode, all or part of the switching elements  262  are turned on, and the first readout control part  130  sequentially sends gate signals to the bypass lines  260  with the switching elements  262  turned on, to read the electric charges stored in the pixels  102  sequentially row by row. When the gate signals are sent to all the bypass lines  260  with the switching elements  262  turned on, the one cycle of the scan mode is completed, and the next cycle is performed. 
     For example, in a case where the switching elements  262  of all the bypass lines  260  are turned on, the first readout control part  130  sends the gate signal to the first bypass line  260  to read the electric charges stored in the pixels  102  connected with the first scanning gate line  110  row by row. Then, the first readout control part  130  sends the gate signal to the second bypass line  260  to read the electric charges stored in the pixels  102  connected with the second scanning gate line  110  row by row. In this manner, the first readout control part  130  sequentially sends the gate signals to the first to twelfth bypass lines  260  to sequentially read the electric charges stored in the pixels  102  connected with the first to twelfth scanning gate lines  110  row by row. When the gate signal is sent to the twelfth bypass line  260 , the one cycle of the scan mode is completed, and the gate signal is sent to the first bypass line  260  in the next cycle. 
     Thus, the electronic cassette  20  has at least a plurality of the pixels  102 , which are arranged in the matrix, a plurality of the TFTs  72 , which are arranged in the matrix to read the electric signals stored in the pixels  102 , a plurality of the gate lines  110 , which extend parallel to the row direction and are each connected to the TFTs  72  in one row, a plurality of the gate drive circuits  150 , which are arranged in parallel in the column direction and are each connected with a plurality of the gate lines  110  to send the gate signals to the TFTs  72  row by row, and a plurality of the signal lines  112 , which extend parallel to the column direction to read the electric signals stored in the pixels  102 . 
     At least one of the gate lines  110  is connected with the bypass line  260  having the switching element  262 . Thus, the electronic cassette  20  further has at least one bypass line  260  having the switching element  262  connected to the at least one gate line  110 . 
     The TFTs  72  each have a gate connected to the gate line  110 , a source connected to the pixel  102 , and a drain connected to the signal line  112 . When the drive signal a is entered, each gate drive circuit  150  selects the gate lines  110  connected therewith sequentially, sends the gate signals to the selected gate lines  110  to turn on the TFTs  72  sequentially, and reads the electric signals stored in the pixels  102  connected therewith sequentially row by row through the signal lines  112 . 
     The first readout control part  130  turns on the switching element  262  of the bypass line  260  connected to the predetermined gate line (scanning gate line)  110  and sends the gate signal, and thereby acts to execute the scan mode for reading the electric signals stored in the pixels  102  connected with the predetermined gate line  110  sequentially row by row. The second readout control part  136  sends the drive signals a to the gate drive circuits  150  sequentially to operate the gate drive circuits  150  sequentially, and thereby acts to execute the sequential readout mode for reading the electric signals in the pixels  102  sequentially row by row. 
     The user operates the input unit  200  of the console  26  to select the scanning gate line  110  to be used in the scan mode. The selected scanning gate line  110  is used as the predetermined gate line  110 , and the pixels  102  connected with the selected scanning gate line  110  are used as the pixels  102  in the predetermined row. The user can expect an area in the electronic cassette  20 , which is irradiated with the radiation  16  from the radiation source  34 . Therefore, the user can select the scanning gate line  110  corresponding to the area to be irradiated with the radiation  16 . The information of the selected scanning gate line  110  is transferred from the console  26  through the system controller  24  to the electronic cassette  20 . The first readout control part  130  turns on the switching element  262  of the bypass line  260  connected to the scanning gate line  110  selected by the user, while the scan mode is executed. The first readout control part  130  turns off all the switching elements  262  to stop the execution of the scan mode. 
     In Modified Example 5, the gate signal is sent only to the selected scanning gate line  110  in the scan mode, whereby the pixels  102 , other than the predetermined pixels  102  connected with the selected scanning gate line  110 , are in the exposure state even in the scan mode. Therefore, the radiation  16  with the image information is not wasted, and the electric charges corresponding to the emitted radiation  16  can be stored. Furthermore, the electronic cassette  20  is switched into the sequential readout mode when the irradiation time has elapsed from the emission start of the radiation  16 . Therefore, the electronic cassette  20  is not exposed excessively after the completion of the emission of the radiation  16 , whereby the noise content of the radiographic image can be lowered. 
     The user selects the scanning gate line  110  in the area to be irradiated with the radiation  16 . Therefore, the start of the emission of the radiation  16  can be judged rapidly and reliably by the irradiation start judgment part  132 . In addition, since the gate signal is sent only to the selected scanning gate line  110 , the electric power consumption in the scan mode can be reduced. 
     In Modified Example 5, in the scan mode, the electric charges stored in the pixels  102  in one row may be read out in a time of 173 μsec in the same manner as the sequential mode. When the electric charges stored in the pixels  102  are read out in 173 μsec in this manner, the emission start of the radiation  16  can be judged with high accuracy without summing the electric charges stored in the pixels  102 . Only a small number of the scanning gate lines  110  are used in the scan mode. Therefore, even when the electric charges stored in the pixels  102  in one row are read in the time in the same manner as the sequential readout mode, the one cycle of the scan mode can be performed in a short time. 
     A larger number of the scanning gate lines  110  may be selected in an area, which is likely to be irradiated or is irradiated with the radiation  16 . Meanwhile, a smaller number of the scanning gate lines  110  may be selected in an area, which is unlikely to be irradiated or is not irradiated with the radiation  16 . In the scan mode, the gate signal is sent only to the selected scanning gate line  110 . The user can operate the input unit  200  of the console  26  to specify the area, which is likely to be irradiated or is irradiated with the radiation  16 . In this case, the area, which is likely to be irradiated or is irradiated with the radiation  16 , may be directly specified by the user. Alternatively, the control unit  212  of the system controller  24  may read from the table  218  and specify the area corresponding to the imaging area and the diagnosis purpose selected by the user. The control unit  212  of system controller  24  selects the scanning gate line  110  to be used in the scan mode based on the specified area, and sends the information of the selected scanning gate line  110  to the electronic cassette  20 . 
     Modified Example 6 
     In Modified Example 4, the gate line  250 , the TFTs  252 , and the pixels  254  for the scan mode are formed independently from the gate lines  110 , the TFTs  72 , and the pixels  102 . However, a predetermined gate drive circuit  150  may be used in the scan mode, so that the gate line  110 , the TFTs  72 , and the pixels  102  in the associated readout region of the gate drive circuit  150  may be used in the scan mode. 
     In the scan mode, the first readout control part  130  sends the drive signal c to one predetermined gate drive circuit  150 . When the drive signal c is entered, the gate drive circuit  150  reads the electric charges stored in the pixels  102  in the 0th to 239th rows of the associated readout region sequentially row by row. Consequently, the digital electric signals are obtained sequentially row by row. When the digital electric signal is judged to be larger than the threshold value by the irradiation start judgment part  132 , the first readout control part  130  stops the scan mode. The first readout control part  130  repeatedly executes the scan mode until the emission is judged to be started. Thus, when the end signal d is sent from the gate drive circuit  150 , the drive signal c is sent again to the predetermined gate drive circuit  150 . In this case, the electric charges stored in the pixels  102  in one row may be read out in a time of 173 μsec in the same manner as the sequential readout mode or in a time of 21 μsec in the same manner as the scan mode in the above embodiment. 
     The user can operate the input unit  200  of the console  26  to select the gate drive circuit  150  to be used in the scan mode. The user can expect an area in the electronic cassette  20 , which is irradiated with the radiation  16  from the radiation source  34 . Therefore, the user can select the gate drive circuit  150  for reading the pixels  102  corresponding to the area to be irradiated with the radiation  16 . The information of the gate drive circuit  150  selected by the user is transferred from the console  26  through the system controller  24  to the electronic cassette  20 . The first readout control part  130  sends the drive signal c in the scan mode to the gate drive circuit  150  selected by the user, which is used as the predetermined gate drive circuit  150 . 
     The user may select a plurality of the gate drive circuits  150  to be used in the scan mode. In this case, the first readout control part  130  may simultaneously send the drive signals c to the selected gate drive circuits  150 . Thus, the gate drive circuits  150  may be simultaneously operated. Furthermore, the first readout control part  130  may sequentially actuate the predetermined gate drive circuits  150 . For example, the end signal d is sent from one of the gate drive circuits  150 , and then the drive signal c is sent to the next gate drive circuit  150 . 
     In Modified Example 6, the gate drive circuits  150  other than the selected gate drive circuit  150  do not send the gate signals during the execution of the scan mode, whereby the pixels  102 , other than the pixels  102  in the associated readout region of the selected gate drive circuit  150 , are in the exposure state even in the scan mode. Therefore, the radiation  16  with the image information is not wasted, and the electric charges corresponding to the emitted radiation  16  can be stored. Furthermore, the electronic cassette  20  is switched into the sequential readout mode when the irradiation time has elapsed from the emission start of the radiation  16 . Therefore, the electronic cassette  20  is not exposed excessively after the completion of the emission of the radiation  16 , whereby the noise content of the radiographic image can be lowered. 
     The user selects the gate drive circuit  150  for reading the electric charges stored in the pixels  102  in the area to be irradiated with the radiation  16 . Therefore, the start of the emission of the radiation  16  can be judged rapidly and reliably by the irradiation start judgment part  132 . In addition, since only the selected gate drive circuit  150  acts to read the electric charges stored in the pixels  102 , the electric power consumption in the scan mode can be reduced. 
     Modified Example 7 
     In Modified Example 7, as described below with reference to  FIGS. 22 to 27 , when the emission of the radiation  16  cannot be detected even after the predetermined time has elapsed from the start of the scan mode (step S 22  of  FIG. 13 ), the scan mode is stopped to avoid wasteful electric power consumption. The scan mode in Modified Example 7 includes those in the above embodiment and Modified Examples 1 to 6. 
     The components of Modified Example 7 will be described below with reference to  FIGS. 22 to 24 . 
     In Modified Example 7, the radiation apparatus  18  further has an irradiation field lamp  300  and a mirror  302 . The irradiation field lamp  300  emits an illuminating light before the emission of the radiation  16  according to an instruction from the radiation control unit  36 . The illuminating light from the irradiation field lamp  300  is reflected toward the electronic cassette  20  by the mirror  302  composed of a material transmissive to the radiation  16 , and is directed onto the image capturing surface  42  of the panel unit  52  (see  FIGS. 2 and 22 ). In this case, when the distance between the radiation source  34  and the radiation conversion panel  64  is controlled at a source to image receptor distance (SID), the emission area of the illuminating light is approximately equal to the image capturable area  60  on the image capturing surface  42 . Thus, the illuminating light incident onto the image capturing surface  42  indicates the irradiation field of the radiation  16 . When the radiation switch  38  is pressed halfway by the user, the radiation control unit  36  makes a preparation to emit the radiation  16  while the output of the illuminating light from the irradiation field lamp  300  is stopped. 
     The electronic cassette  20  further has a light sensor (light detection device)  304  for detecting the illuminating light incident onto the image capturing surface  42 , an acceleration sensor (transfer detection device)  306  for detecting an acceleration in the transfer of the electronic cassette  20 , a speaker (first announcement device, sound output device)  308  for outputting sound corresponding to signals from the cassette control device  122  to the outside, and an LED (first announcement device, light output device)  310  for emitting a light depending on signals from the cassette control device  122 . In this case, for example, the light sensor  304  may be disposed in an arbitrary position on the image capturing surface  42  to detect the illuminating light. The acceleration sensor  306  may be disposed in an arbitrary position in the casing  56 . The speaker  308  and the LED  310  may be disposed in, for example, the control unit  54  such that the user can recognize the sound and the light. 
     The cassette control device  122  further has a scan mode stop judgment part (first readout mode stop judgment part)  312 , a sleep state switch judgment part  314 , a scan mode restart judgment part (first readout mode restart judgment part)  316 , and an image acquirement judgment part  318 . The scan mode stop judgment part  312  judges whether the scan mode should be halted or not. The sleep state switch judgment part  314  judges after the stop of the scan mode whether or not the electric power supplied from the power supply device  128  to the components in the electronic cassette  20  should be stopped to switch the electronic cassette  20  into the sleep state. The scan mode restart judgment part  316  judges whether or not the halted scan mode should be restarted. The image acquirement judgment part  318  judges, after the scan mode is halted and the pixels  102  are switched into the exposure states, whether or not the second readout control part  136  should act to read the electric signals in the pixels  102  in the sequential readout mode. 
     The system controller  24  further has an LED (second announcement device, light output device)  322  for emitting a light depending on signals from the control unit  212 , and a speaker (second announcement device, sound output device)  320  for outputting sound corresponding to signals from the control unit  212  to the outside (see  FIG. 24 ). Also the console  26  further has a speaker (second announcement device, sound output device)  324  for outputting sound corresponding to signals from the control unit  202  to the outside (see  FIG. 24 ). 
     Operations of the radiographic image capturing system  10  of Modified Example 7 having the above structure will be described below with reference to the flowcharts of  FIGS. 25 to 27 . The operations are described using the flowcharts of  FIGS. 12 and 13  and  FIGS. 22 to 24  if necessary. 
     The scan mode is started in step S 22  of  FIG. 13 , and the irradiation start judgment part  132  judges whether or not the digital electric signals stored in the memory  124  are larger than the threshold value in next step S 23 . When the electric signals do not reach the threshold value (step S 23 : NO), step S 41  of  FIG. 25  is carried out. 
     In step S 41 , the scan mode stop judgment part  312  judges whether the predetermined time has elapsed or not from the start of the execution of the scan mode. When the predetermined time is judged to have elapsed (step S 41 : YES), then the scan mode stop judgment part  312  judges whether or not the cassette control device  122  receives a signal from the system controller  24  or the console  26  (step S 42 ). The signal from the system controller  24  or the console  26  is an instruction signal including an image capturing menu reset (re-entered) by the control unit  212  of the system controller  24 , an operation of the input unit  200  by the user, or the like as hereinafter described. 
     When the cassette control device  122  does not receive the signal from the system controller  24  or the console  26  (step S 42 : NO), the scan mode stop judgment part  312  judges that the emission of the radiation  16  is not started even after the predetermined time has elapsed from the start of the scan mode, and the electric power will be wasted if the scan mode is further continued. Thus, the scan mode stop judgment part  312  decides to stop the scan mode, and controls the first readout control part  130  to stop the scan mode based on the judgment result (step S 43 ). 
     After the scan mode is stopped, the scan mode stop judgment part  312  controls the first readout control part  130  to turn off all the TFTs  252 , so that all the pixels  102  are switched into the exposure states (step S 44 ). A communication signal, which indicates that the scan mode is stopped and all the pixels  102  are switched into the exposure states, is sent from the communication device  126  to the system controller  24  via wireless communication (step S 45 ), and then step S 61  of  FIG. 27  is carried out. The scan mode stop judgment part  312  further acts to output a sound (such as a beep sound) corresponding to the communication signal from the speaker  308  to the outside and to emit the light from the LED  310 . The user can hear the sound from the speaker  308  or visually recognize the light from the LED  310  to understand that the scan mode is stopped and the pixels  102  are put into the exposure states. 
     In a case where the predetermined time has not elapsed in step S 41  of  FIG. 25  (step S 41 : NO), the irradiation start judgment part  132  continues to perform the judgment of step S 23 . 
     In the above description, steps S 41  to S 43  are performed by the scan mode stop judgment part  312 . Modified Example 7 is not limited to the description, the judgment of step S 41  may be performed by the elapsed time judgment part  134 . The elapsed time judgment part  134  judges whether the predetermined time has elapsed or not from the start of the emission of the radiation  16  in step S 28 . Therefore, the elapsed time judgment part  134  may perform this judgment in step S 41 , and may send the judgment result to the irradiation start judgment part  132  and the scan mode stop judgment part  312 . 
     When the cassette control device  122  receives the signal from the system controller  24  or the console  26  in step S 42 , the scan mode stop judgment part  312  recognizes that another instruction (re-entered image capturing menu or instruction signal) is sent, and controls the first readout control part  130  to stop the scan mode (step S 48 ). Then, step S 21  of  FIG. 13  is performed in the cassette control device  122 . 
     Furthermore, after the judgment of step S 41 , the scan mode stop judgment part  312  may perform step S 43  without step S 42  as shown by a dashed line in  FIG. 25 . 
     In addition, after step S 43 , steps S 46  and S 47  to be hereinafter described may be performed instead of the switching to the exposure state (the accumulation state) of step S 44  as shown by a dashed-dotted line in  FIG. 25 . 
     Thus, after step S 43 , the scan mode stop judgment part  312  may control the second readout control part  136  to carry out a reset operation (step S 46 ). In this case, the reset operation is performed in the sequential readout mode. It is to be understood that the scan mode stop judgment part  312  may control the first readout control part  130  to carry out a reset operation in the scan mode. 
     When the sleep state switch judgment part  314  detects the completion of the reset operation, the sleep state switch judgment part  314  acts to stop the electric power supply from the power supply device  128  to the components in the electronic cassette  20 , so that the electronic cassette  20  is switched into the sleep state (step S 47 ). Alternatively, after step S 43 , step S 47  may be carried out without the reset operation of step S 46  as shown by a dashed-two dotted line in  FIG. 25 . 
     Consequently, in step S 45  after the operation of step S 47 , the scan mode stop judgment part  312  acts to send a communication signal, which indicates that the scan mode is stopped and the electronic cassette  20  is switched into the sleep state, from the communication device  126  to the communication unit  214  via wireless communication. Also in this case, the sound is output from the speaker  308  to the outside and the light is emitted from the LED  310 . Therefore, the user can hear the sound from the speaker  308  or visually recognize the light from the LED  310  to understand that the scan mode is stopped and the electronic cassette  20  is put into the sleep state. 
     The switching of the electronic cassette  20  into the sleep state is carried out in order to avoid wasteful electric power consumption before the emission of the radiation  16 . Therefore, in the sleep state, power supply to at least the radiation conversion panel  64  and the drive circuit device  106  is stopped, while power supply to the cassette control device  122  and the communication device  126  may be continued. In this case, the electronic cassette  20  and the system controller  24  can send signals to and receive signals from each other also in the sleep state. Furthermore, the electronic cassette  20  can be rapidly switched from the sleep state into the active state based on a signal from the system controller  24 . 
     After step S 4  of  FIG. 12 , step S 51  of  FIG. 26  is carried out. The control unit  212  of the system controller  24  judges whether or not the communication signal can be received from the electronic cassette  20  through the communication unit  214 . When the communication signal can be received (step S 51 : YES), in step S 52 , the control unit  212  acts to emit a light from the LED  322  and to output a sound (such as a beep sound) from the speaker  320  to the outside. Furthermore, the control unit  212  sends the communication signal to the console  26 . Then, the control unit  202  of the console  26  acts to display the contents of the communication signal as an image (such as a screen-saver display) on the display unit  204 , and to output a sound (such as a beep sound) from the speaker  324  to the outside. 
     Consequently, the user can visually recognize the light emission of the LED  322  and the image on the display unit  204  and can hear the sounds from the speakers  320  and  324  to understand that the scan mode is stopped and that all the pixels  102  are switched into the exposure states or the electronic cassette  20  is switched into the sleep state. 
     Next, when the user operates the input unit  200  (step S 53 : YES), the control unit  202  acts to switch the display unit  204  from the screen-saver display to the normal screen, and to send information of the operation to the control unit  212  of the system controller  24 . 
     When the communication signal from the electronic cassette  20  indicates that the scan mode is stopped and all the pixels  102  are switched into the exposure states, the control unit  212  generates, based on the information sent from the control unit  202 , an instruction signal for instructing to restart the scan mode or read the electric signals in all the pixels  102  in the sequential scan mode. The control unit  212  sends the generated instruction signal to the electronic cassette  20  through the communication unit  214  via wireless communication (step S 54 ), and then step S 5  of  FIG. 12  is carried out. 
     Alternatively, when the communication signal from the electronic cassette  20  indicates that the scan mode is stopped and the electronic cassette  20  is switched into the sleep state, the control unit  212  generates, based on the information sent from the control unit  202 , an instruction signal for instructing transition from the sleep state into the active state (startup state) and restart of the scan mode. The control unit  212  sends the generated instruction signal to the electronic cassette  20  through the communication unit  214  via wireless communication (step S 54 ). 
     When the user operates the input unit  200  to reset the image capturing menu (step S 53 : YES), as shown by a dashed line in  FIG. 26 , the control unit  202  sends the image capturing menu reset by the user to the control unit  212 . The control unit  212  acts to re-enter the image capturing menu sent from the control unit  202  as a renewed image capturing menu instead of the ongoing image capturing menu that has been sent to the electronic cassette  20 . The re-entered image capturing menu is sent to the electronic cassette  20  through the communication unit  214  via wireless communication (step S 55 ). In this case, in addition to image capturing menu, the control unit  212  sends also the instruction signal to the electronic cassette  20  through the communication unit  214  (step S 54 ), and then step S 5  of  FIG. 12  is carried out. 
     In step S 61  of  FIG. 27 , the scan mode restart judgment part  316  and/or the image acquirement judgment part  318  sequentially judge whether or not the instruction signal and/or the image capturing menu are sent from the system controller  24  to the communication device  126  (step S 61 ), whether the detection signal corresponding to the illuminating light is entered or not from the light sensor  304  (step S 62 ), and whether the detection signal corresponding to the transfer of the electronic cassette  20  is entered or not from the acceleration sensor  306  (step S 63 ). 
     In the judgments of steps S 61  to S 63 , when a signal (the image capturing menu, the instruction signal) can be received from the system controller  24  (step S 61 : YES), when the detection signal is entered from the light sensor  304  (step S 62 : YES), or when the detection signal is entered from the acceleration sensor  306  (step S 63 : YES), the scan mode restart judgment part  316  decides to restart the scan mode, and the image acquirement judgment part  318  decides to read the electric signals from all the pixels  102  in the exposure states in the sequential readout mode (step S 64 ). 
     Then, when the instruction signal includes the instruction to restart the scan mode or the scan mode has to be executed under the new image capturing menu (step S 65 : YES), the scan mode restart judgment part  316  acts to perform step S 22  of  FIG. 13 , so that the first readout control part  130  acts to restart the scan mode. 
     In a case where the instruction signal does not include the instruction to restart the scan mode and the new image capturing menu is not received (step S 65 : NO), and the instruction signal includes the instruction to read the electric signals from all the pixels  102  in the exposure states in the sequential readout mode (step S 66 : YES), the image acquirement judgment part  318  controls the second readout control part  136  to execute the sequential readout mode in the same manner as steps S 29  and S 30  of  FIG. 13  (step S 67 ). 
     In a case where the value of the obtained electric signals (digital signal pixel value) becomes larger than the predetermined value (the predetermined threshold value) (step S 68 : YES), the image acquirement judgment part  318  judges that the radiation  16  is injected from the radiation source  34  through the subject  14  into the electronic cassette  20  in the exposure state and that the electric signals correspond to the radiographic image of the subject  14 , and thereby stores the pixel values in the memory  124  (step S 69 ). Thus, the radiographic image of the subject  14  can be reliably acquired without retaking. Thereafter, the cassette control device  122  acts to perform step S 32  of  FIG. 13 . 
     If the obtained pixel values do not reach the predetermined value (step S 68 : NO), the radiation  16  is judged to be not emitted during the exposure state. The pixel values are discarded (the electric signals with the pixel values are discharged to the ground) (step S 70 ) to stop the sequential readout mode (step S 71 ). Then, the cassette control device  122  acts to perform step S 44 , S 46 , or S 47  of  FIG. 25 . 
     When the instruction signal includes not the instruction to read the electric signal from all the pixels  102  in the exposure states in the sequential readout mode but the instruction to startup the electronic cassette  20  (step S 66 : NO), the scan mode restart judgment part  316  acts to restart the electric power supply from the power supply device  128  to each component in the electronic cassette  20 , so that the electronic cassette  20  is switched from the sleep state into the active state (step S 72 ). Then, the cassette control device  122  acts to perform step S 22  of  FIG. 13 , whereby the scan mode is restarted. 
     In Modified Example 7, as described above, the scan mode is stopped when the electric signal values do not reach the threshold value even after the predetermined time has elapsed from the start of the scan mode. Therefore, the wasteful electric power consumption in the scan mode before the emission of the radiation  16  can be reduced. The scan mode is stopped even when the instruction signal or the image capturing menu is not received from the system controller  24 . Therefore, the electric power consumption before the emission of the radiation  16  can be efficiently reduced. Thus, the above steps of Modified Example 7 can be performed to reduce the electric power consumption before the emission of the radiation  16  also in the above embodiment and Modified Examples 1 to 6. 
     After the stop of the scan mode, all the pixels  102  may be switched into the exposure states (the accumulation states). When the radiation  16  is emitted to the subject  14  and the electronic cassette  20  in the exposure state, the electric charges (electric signals) corresponding to the radiographic image of the subject  14  can be reliably stored in the pixels  102 . 
     After the stop of the scan mode, the electronic cassette  20  may be switched into the sleep state after the reset operation or immediately. In this case, the electric power consumption before the emission of the radiation  16  can be further reduced. 
     In Modified Example 7, the speaker  308  outputs a sound and the LED  310  emits a light depending on the communication signal indicating the stop of the scan mode or the switch into the exposure state or the sleep state. The communication signal is sent from the electronic cassette  20  to the system controller  24 . Then, in the system controller  24 , the speaker  320  outputs a sound and the LED  322  emits a light depending on the received communication signal. Furthermore, in the console  26 , the display unit  204  displays an image and the speaker  324  outputs a sound depending on the communication signal from the system controller  24 . Thus, the user can hear the sounds from the speakers  308 ,  320 ,  324  and can visually recognize the image on the display unit  204  and the lights from the LEDs  310 ,  322  to easily understand the stop of the scan mode and the like. 
     In a case where the image capturing menu is re-entered by the control unit  212  of the system controller  24  or in a case where the user operates the input unit  200  to generate the instruction signal in the control unit  212 , the system controller  24  sends the image capturing menu or the instruction signal to the electronic cassette  20 . In a case where the illuminating light is emitted from the irradiation field lamp  300  onto the image capturing surface  42  in the preparation for the image capturing process, the light sensor  304  detects the illuminating light and outputs the detection signal to the cassette control device  122 . Furthermore, in a case where the user transfers the electronic cassette  20  in the preparation for the image capturing process, the acceleration sensor  306  detects the acceleration in the movement of the electronic cassette  20  and outputs the detection signal to the cassette control device  122 . 
     Thus, based on the entered image capturing menu, instruction signal, and detection signals, the scan mode restart judgment part  316  and the image acquirement judgment part  318  can efficiently and reliably perform the restart of the scan mode, the reading of the electric signals from the pixels  102  in the exposure states in the sequential readout mode, the switch of the electronic cassette  20  from the sleep state into the active state, and the judgment associated with the restart of the scan mode. 
     The electric signals in all the pixels  102  in the exposure states are read out in the sequential readout mode before the restart of the scan mode. Therefore, in a case where the radiation  16  is emitted to the subject  14  and the electronic cassette  20  during the period of the exposure state, the electric signals corresponding to the radiographic image of the subject  14  can be reliably read out. Since the electric signals corresponding to the radiographic image are read out in this manner, the user can avoid retaking the subject  14 . 
     In this case, the image acquirement judgment part  318  judges whether or not the read electric signals reach the predetermined value. Therefore, the radiographic image can be efficiently acquired. In a case where the electric signals do not reach the predetermined value, the electric signals may be discarded to the ground. Therefore, the memory  124  can be prevented from storing unnecessary data by mistake. 
     In Modified Example 7, when the radiation  16  cannot be detected even after the predetermined time has elapsed from the switch into the exposure state in step S 44 , as shown by a thick dashed line in  FIG. 25 , step S 47  may be carried out to switch the electronic cassette  20  into the sleep state. Also in this case, the electric power consumption can be reduced before the emission of the radiation  16 . 
     In Modified Example 7, before the scan mode performed by the first readout control part  130 , the second readout control part  136  may act to execute the reset operation or an offset signal readout mode for reading the electric signals stored in the pixels  102  as image correction offset signals (non-exposure signals) sequentially row by row. Also in this case, the electric charges can be reliably removed from the pixels  102  before the emission of the radiation  16 , whereby the radiographic image can be obtained with high quality. In addition, the quality of the radiographic image can be further improved by performing an image correction processing using the offset signals. 
     Modified Example 8 
       FIG. 28  is a schematic structural view of the electric structure of an electronic cassette  20  according to Modified Example 8. The control unit  54  has the cassette control device  122 , the memory  124 , the communication device  126 , and the power supply device  128 , and further has the speaker (the first announcement device, the sound output device)  308  for outputting sound corresponding to signals from the cassette control device  122  to the outside, and the LED (the first announcement device, the light output device)  310  for emitting a light depending on signals from the cassette control device  122 . The speaker  308  and the LED  310  are disposed in the casing  68  of the control unit  54 . 
     The cassette control device  122  has the first readout control part  130 , the irradiation start judgment part  132 , the elapsed time judgment part  134 , and the second readout control part  136 , and further has a mode switch judgment part  330 . The mode switch judgment part  330  judges whether the readout mode for reading the electric charges stored in the pixels  102  is switched into the scan mode or not. Specifically, in a case where the first readout control part  130  acts to start the scan mode, the mode switch judgment part  330  judges that the electronic cassette  20  is switched into the first readout mode, and sends a scan mode switch signal (communication signal) including the judgment result to the speaker  308 , the LED  310 , and the communication device  126 . The speaker  308  outputs a sound (such as a beep sound) corresponding to the scan mode switch signal to the outside, the LED  310  emits a light corresponding to the scan mode switch signal, and the communication device  126  sends the scan mode switch signal to the system controller  24  via wireless communication. 
     As described above, the readout mode may be the scan mode or the sequential readout mode. Before the emission of the radiation  16 , not only the scan mode but also the sequential readout mode may be performed in some cases. 
     In the electronic cassette  20 , for example, the scan mode may be started when the image capturing menu is received from the system controller  24 . Alternatively, the sequential readout mode is executed before the image capturing menu is received, and then the sequential readout mode may be switched into the scan mode when the image capturing menu is received. The sequential readout mode executed before the scan mode may be the reset operation or the offset signal readout mode for reading the electric signals stored in the pixels  102  as image correction offset signals (non-exposure signals) sequentially row by row. 
     Thus, to handle these cases, the mode switch judgment part  330  detects the start of the scan mode executed by the first readout control part  130  for judging that the electronic cassette  20  is switched into the scan mode (from the sequential readout mode). 
       FIG. 29  is a schematic structural view of the electric structures of the system controller  24  and the console  26  of Modified Example 8. 
     The console  26  has the input unit  200 , the control unit  202 , the display unit  204 , and the interface I/F  206 , and further has the speaker (the second announcement device, the sound output device)  324  for outputting sound corresponding to signals from the control unit  202 . 
     The system controller  24  has the interface I/F  210 , the control unit  212 , the communication unit  214 , the recording unit  216 , and the database  220  containing the table  218 , and further has the speaker (the second announcement device, the sound output device)  320  for outputting sound corresponding to signals from the control unit  212  to the outside and the LED (the second announcement device, the light output device)  322  for emitting a light depending on signals from the control unit  212 . 
     When the communication unit  214  receives the scan mode switch signal from the electronic cassette  20 , the control unit  212  sends the scan mode switch signal to the control unit  202  of the console  26 , the speaker  320 , and the LED  322 . The speaker  320  outputs a sound (such as a beep sound) corresponding to the scan mode switch signal to the outside, and the LED  322  emits a light corresponding to the scan mode switch signal. The control unit  202  acts to display an image corresponding to the scan mode switch signal from the control unit  212  on the display unit  204 , and to output a sound (such as a beep sound) corresponding to the scan mode switch signal from the speaker  324  to the outside. 
     Operations of the radiographic image capturing system  10  of Modified Example 8 will be described below with reference to the flowcharts of  FIGS. 30 and 31 .  FIG. 30  is a flowchart of the operation of the system controller  24  and the console  26 , and  FIG. 31  is a flowchart of the operation of the cassette control device  122  in the radiographic image capturing system  10 . The operation of the system controller  24  and the console  26  will be described first, and then the operation of the cassette control device  122  will be described below. 
     In the console  26 , the control unit  202  judges whether or not the user operates the input unit  200  to select the imaging area, the diagnostic site, and the number of images to be captured (step SA 1 ). In this step, the control unit  202  acts to display, on the display unit  204 , an image (image capturing menu), which is used by the user for selecting the imaging area, the diagnostic site, and the number of images. The user can select, while watching the displayed image, the imaging area and the diagnostic site of a patient that undergoes the radiographic image capturing process. 
     In a case where the imaging area, the diagnostic site, and the number of images are judged to be not selected in step SA 1 , the radiographic image capturing system  10  remains in step SA 1  until they are selected. 
     In a case where the imaging area, the diagnostic site, and the number of images are judged to be selected by the user in step SA 1 , the image capturing condition setting part  222  reads the image capturing conditions corresponding to the imaging area and the diagnostic site selected by the user from the table  218 , and sets the read image capturing conditions as conditions for the following radiographic image capturing process, and the image number setting part  224  sets the number of images selected by the user (step SA 2 ). Specifically, when the user operates the input unit  200  to select the imaging area and the like, the control unit  202  outputs (the image capturing menu containing) the selected imaging area and the like to the control unit  212  in the system controller  24  through the interfaces I/F  206 ,  210 . Then, in the control unit  212 , the image capturing condition setting part  222  sets the image capturing conditions corresponding to the imaging area and the diagnostic site sent from the console  26 , and sets the number of images sent from the console  26 . The system controller  24  may output the setup image capturing conditions to the control unit  202  through the interfaces I/F  210 ,  206 , and the control unit  202  may act to display the setup image capturing conditions and the setup number of images on the display unit  204 . In this case, the user can visually recognize the contents of the setup image capturing conditions. 
     To emit the radiation  16  from the radiation source  34  under the setup image capturing conditions, the user operates the input device in the radiation control unit  36 , so that the radiation control unit  36  sets image capturing conditions equal to the conditions set in the system controller  24 . For example, the radiation apparatus  18  may have a table equal to the table  218 , and the user may select the imaging area and the diagnostic site from the table to set the equal image capturing conditions. Alternatively, the user may enter the irradiation time, the tube voltage, the tube current, and the like directly. 
     After the image capturing conditions are set, the control unit  212  sends a startup signal to the electronic cassette  20  through the communication unit  214 , whereby the electronic cassette  20  is started up (step SA 3 ). The electronic cassette  20  is in the sleep state until the startup signal is sent. The sleep state is such a state that electric power is not supplied to at least the radiation conversion panel  64  and the drive circuit device  106 . In a case where the electronic cassette  20  is started up, the electronic cassette  20  acts to execute the scan mode, and the mode switch judgment part  330  judges the execution of the scan mode and generates a scan mode switch signal including the judgment result. After the start up, the electronic cassette  20  may act to perform the reset operation before the scan mode. 
     The image capturing condition setting part  222  and the image number setting part  224  send the setup irradiation time and the setup number of images to the electronic cassette  20  through the communication unit  214  (step SA 4 ). 
     The control unit  212  judges whether or not the communication unit  214  receives the scan mode switch signal from the electronic cassette  20  (step SA 5 ). 
     If the scan mode switch signal is received in step SA 5 , the control unit  212  acts to output the sound (the beep sound) for indicating the scan mode switch signal from the speaker  320  to the outside and to emit the light from the LED  322 . Furthermore, the control unit  212  sends the scan mode switch signal to the control unit  202  of the console  26 . The control unit  202  acts to display an image corresponding to the received scan mode switch signal on the display unit  204  and to output the sound (the beep sound) for indicating the scan mode switch signal from the speaker  324  to the outside (step SA 6 ). The user can understand that the scan mode is started and the electronic cassette  20  is switched into a state, in which the radiation  16  can be emitted (the image capturing process is allowed) by at least one of hearing the sound from the speaker  320  or  324  and visually recognizing the light from the LED  322  or the image on the display unit  204 . If the control unit  212  judges that the scan mode switch signal is not received in step SA 5 , the radiographic image capturing system  10  remains in step SA 5  until it is received. 
     The control unit  212  judges whether a readout start signal from the electronic cassette  20  is received or not (step SA 7 ). The readout start signal includes an instruction to start the reading of the electric charges stored in the pixels  102  in the sequential readout mode. 
     IF the readout start signal is judged to be not received in step SA 7 , the radiographic image capturing system  10  remains in step SA 7  until it is received. If the readout start signal is judged to be received, the image record control part  226  judges whether the one-row image data are sent or not (step SA 8 ). The one-row image data are sequentially read out row by row, and the electronic cassette  20  sequentially outputs the one-row image data to the system controller  24 . Thus, the one-row image data are sequentially sent to the system controller  24 . 
     When the one-row image data are judged to be sent in step SA 8 , the image record control part  226  acts to store the sent one-row image data in a buffer memory (not shown) in the control unit  212  (step SA 9 ). 
     The image record control part  226  judges whether the readout of the one-frame image data is completed or not (step SA 10 ). If the readout of the one-frame image data is completed, the electronic cassette  20  outputs a readout end signal to the system controller  24 . When the image record control part  226  receives the readout end signal, the readout of the one-frame image data is judged to be completed. 
     If the reading of the one-frame image data is judged to be not completed in step SA 10 , the radiographic image capturing system  10  is returned to step SA 8 , and the above steps are repeated. 
     If the readout of the one-frame image data is judged to be completed in step SA 10 , an image file is created from the one-frame image data stored in the buffer memory, and is recorded in the recording unit  216  (step SA 11 ). 
     The image record control part  226  judges whether or not the sent image data satisfy the condition of the number of images set in step SA 2  (step SA 12 ). In a case where it is judged that the sent image data are not sufficient to meet the condition of the setup number of images in step SA 12 , the radiographic image capturing system  10  is returned to step SA 8 . If the sent image data are judged to be sufficient to meet the condition of the setup number of images, the process is completed. 
     The operation of the electronic cassette  20  will be described below with reference to the flowchart of  FIG. 31 . When the startup signal is sent from the system controller  24 , the electronic cassette  20  is started up, and the cassette control device  122  acts to store the irradiation time and the number of images sent from the system controller  24  in the memory  124  (step SA 21 ). 
     Then, the first readout control part  130  in the cassette control device  122  acts to start the execution of the scan mode (step SA 22 ). Consequently, the mode switch judgment part  330  judges that the scan mode is started, and sends the scan mode switch signal including the judgment result to the communication device  126 , the speaker  308 , and the LED  310 . The communication device  126  sends the scan mode switch signal to the system controller  24  via wireless communication. The speaker  308  outputs the sound (the beep sound) corresponding to the scan mode switch signal to the outside, and the LED  310  emits the light corresponding to the scan mode switch signal (step SA 23 ). In the same manner as step SA 6  described above, the user can understand that the scan mode is started and the electronic cassette  20  is switched into a state, in which the radiation  16  can be emitted (the image capturing process is allowed) by at least one of hearing the sound from the speaker  308  and visually recognizing the light from the LED  310 . 
     When the scan mode is started, the first readout control part  130  outputs the drive signals c to the gate drive circuits  150 . When the drive signal c is received, each gate drive circuit  150  selects the gate lines  110  connected therewith in the 0th to final rows sequentially, and outputs the gate signals to the selected gate lines  110 . Thus, each gate drive circuit  150  reads the electric charges stored in the pixels  102  in the 0th to final rows in the associated readout region sequentially row by row. Consequently, the procedure of reading the electric charges stored in the pixels  102  sequentially row by row in the associated readout region is performed in a plurality of the gate drive circuits  150  simultaneously. The read electric charges are summed up in each column. 
     Specifically, the electric charges stored in the pixels  102  in the 0th rows in the associated readout regions of the gate drive circuits  150  are simultaneously read out, summed up in each column, and output to the charge amplifier  116  in each column. Then, the electric charges stored in the pixels  102  in the first rows in the associated readout regions of the gate drive circuits  150  are simultaneously read out, summed up in each column, and output to the charge amplifier  116  in each column. The steps are repeated also in the second to 239th rows. 
     The one-row electric charges, which are read out sequentially row by row and summed up in each column, are send to the charge amplifiers  116 , transferred through the multiplexer part  118  and the AD conversion part  120 , and stored as the digital electric signals in the memory  124 . Thus, the summed one-row image data are sequentially stored in the memory  124 . When the electric charges stored in the pixels  102  in the 239th rows are read out, the gate drive circuits  150  send the end signals d to the cassette control device  122 . 
     The first readout control part  130  controls the switches  160  of the charge amplifiers  116  in the off states in the scan mode. Thus, the charge amplifiers  116  can output the sent electric charge signals as the voltage signals. After the start up, the cassette control device  122  may act to perform the reset operation before the start of the scan mode. The first readout control part  130  may start the scan mode when a predetermined time (e.g. 10 seconds) has elapsed after the start up. 
     The irradiation start judgment part  132  judges whether or not the digital electric signals stored in the memory  124  are larger than the threshold value (step SA 24 ). If the radiation  16  is emitted from the radiation source  34  to the electronic cassette  20 , the digital electric signals stored in the memory  124  become larger than the threshold value. Thus, whether the radiation  16  is emitted or not is detected based on whether the digital electric signals are larger or not than the threshold value. In a case where the electric signals are judged to be not larger than the threshold value in step SA 24 , the electronic cassette  20  remains in step SA 24  until the signal is judged to be larger than the threshold value. When the end signals d 1  to d 12  are sent from the gate drive circuits  150  to the cassette control device  122  (the one-frame electric charges are read out), the first readout control part  130  outputs the drive signals c 1  to c 12  to the gate drive circuits  150  again. One cycle of the scan mode include the steps from the input of the drive signals c 1  to c 12  into the gate drive circuits  150  to the output of the end signals d 1  to d 12 . The end signals d 1  to d 12  are sent from the gate drive circuits  150  at the same timing. 
     If the digital electric signal stored in the memory  124  is judged to be larger than the threshold value in step SA 24 , the emission of the radiation  16  from the radiation source  34  is judged to be started by the irradiation start judgment part  132  (step SA 25 ). 
     Thus, the user confirms at least one of the beep sound from one of the speakers  308 ,  320 ,  324 , the light from one of the LEDs  310 ,  322 , and the image on the display unit  204 , and thereby understands that the scan mode is started (the image capturing process is allowed). When the radiation switch  38  is pressed halfway by the user in the scan mode, the radiation control unit  36  makes preparations to emit the radiation  16 . Then, when the radiation switch  38  is pressed completely by the user, the radiation control unit  36  acts to emit the radiation  16  from the radiation source  34  for the predetermined time. Since the radiation control unit  36  acts to emit the radiation  16  under the image capturing conditions corresponding to the imaging area and the diagnostic site selected by the user as described above, the predetermined time is the irradiation time corresponding to the imaging area and the diagnostic site selected by the user. In the case of capturing a plurality of images, the user operates the radiation switch  38  at a certain time interval to apply the radiation  16  from the radiation source  34 . 
     If the emission of the radiation  16  is judged to be started in step SA 25 , the cassette control device  122  acts to start a timer (step SA 26 ), and the first readout control part  130  judges whether the electric charges stored in all the pixels  102  are read out completely or not (whether the one-frame electric charges are read out completely or not) in the scan mode (step SA 27 ). Thus, after the emission of the radiation  16  is judged to be started, the first readout control part  130  judges whether the one cycle of the scan mode is completed or not. Specifically, after the emission of the radiation  16  is judged to be started, the first readout control part  130  judges whether or not the end signals d 1  to d 12  are sent from the gate drive circuits  150 . 
     If the electric charges stored in all the pixels  102  are judged to be not completely read out in step SA 27 , the electronic cassette  20  remains in step SA 27  until the electric charges are judged to be completely read out. If the electric charges stored in all the pixels  102  are judged to be completely read out, the radiographic image capturing process is carried out, and thus the radiation  16  is applied, and the electric charges stored in the pixels  102  by the radiation  16  exposure are read out. Specifically, the first readout control part  130  stops the scan mode to start the exposure, and the electronic cassette  20  is switched to the exposure state (step SA 28 ). After this step, the first readout control part  130  does not output the drive signals c 1  to c 12  to the gate drive circuits  150  when the end signals d 1  to d 12  are sent to the cassette control device  122 . At the same time as the stop of the scan mode, the first readout control part  130  acts to turn on the switches  160  of the charge amplifiers  116 . Consequently, unnecessary electric charges stored in the capacitors  158  can be discarded to improve the radiographic image quality. 
     After the scan mode is stopped in step SA 28 , the elapsed time judgment part  134  judges whether the predetermined time has elapsed or not from the judgment of the emission start of the radiation  16  (step SA 29 ). If the elapsed time judgment part  134  judges that the predetermined time has not elapsed from the start of the emission of the radiation  16  in step SA 29 , the electronic cassette  20  remains in step SA 29  until the predetermined time elapses. The predetermined time is the irradiation time corresponding to the imaging area and diagnosis purpose selected by the user, and therefore the elapsed time judgment part  134  judges whether the emission of the radiation  16  is completed or not in step SA 29 . Thus, after the scan mode is stopped, the exposure for the radiographic image capturing process is continued until the predetermined time elapses. 
     In a case where the predetermined time is judged to have elapsed from the start of the emission of the radiation  16  in step SA 29 , the exposure is stopped, and the second readout control part  136  acts to start the sequential readout mode for reading the electric charges generated by the exposure with the radiation  16  (step SA 30 ). In this step, the second readout control part  136  outputs the readout start signal to the system controller  24  through the communication device  126  before, at, or after the start of the sequential readout mode. Consequently, the system controller  24  detects that the radiographic image data will be sent from the electronic cassette  20 , and makes preparations to receive the image data. 
     In the sequential readout mode, the second readout control part  136  outputs the drive signal a 1  to the first gate drive circuit  150 . When the drive signal a 1  is entered, the first gate drive circuit  150  selects the associated gate lines  110  in the 0th to final rows sequentially, outputs the gate signals to the selected gate lines  110 , and reads the electric charges stored in the pixels  102  in the 0th to final rows in the associated region sequentially row by row. Thus, the first gate drive circuit  150  reads the electric charges stored in the pixels  102  in the 0th to 239th rows in the associated region sequentially row by row. When the 239th row is selected, the first gate drive circuit  150  sends the end signal b 1  to the cassette control device  122 . 
     When the end signal b 1  is entered, the second readout control part  136  sends the drive signal a 2  to the second gate drive circuit  150 . Such a procedure is repeated in the first to twelfth gate drive circuits  150 . Consequently, the electric charges stored in the pixels  102  in the 0th to 2879th rows on the radiation conversion panel  64  are read out sequentially row by row. The electric charges, read out sequentially row by row, are input into the charge amplifier  116  in each column, transferred through the multiplexer part  118  and the AD conversion part  120 , and stored as the digital electric signals in the memory  124 . Thus, the one-row image data, obtained row by row, are sequentially stored in the memory  124 . 
     The cassette control device  122  controls the switches  160  of the charge amplifiers  116  in the off states during the sequential readout mode. Thus, the charge amplifiers  116  can output the sent electric charge signals as voltage signals. 
     After the start of the sequential readout mode, the cassette control device  122  starts to sequentially send the one-row image data (obtained row by row) to the system controller  24  (step SA 31 ). Thus, the one-row image data are stored in the memory  124 , and sent to the system controller  24  through the communication device  126 . 
     The second readout control part  136  judges whether the electric charges stored in all the pixels  102  are read out completely or not (whether the one-frame electric charges are read out completely or not) in the sequential readout mode (step SA 32 ). Thus, the second readout control part  136  judges whether the one cycle of the sequential readout mode is completed or not. Specifically, the second readout control part  136  judges whether or not the end signal b 12  is sent from the twelfth gate drive circuit  150 . 
     If the electric charges stored in all the pixels  102  are judged to be not completely read out in step SA 32 , the electronic cassette  20  remains in step SA 32  until the electric charges are judged to be completely read out. If the electric charges stored in all the pixels  102  are judged to be completely read out, the second readout control part  136  stops the sequential readout mode (step SA 33 ). In this step, the second readout control part  136  outputs the readout end signal to the system controller  24  through the communication device  126 . 
     The cassette control device  122  judges whether or not the number of the captured images reaches the setup number of images stored (set by the user) in step SA 21 , thus whether or not the performed exposure and sequential readout procedures satisfy the condition of the setup number of images stored in step SA 34  (step SA 34 ). In a case where it is judged that the number of the captured images does not reach the setup number of images in step SA 34 , the electronic cassette  20  is returned to step SA 22 , and the above steps are repeated. In a case where it is judged that the number of the captured images reaches the setup number of images, the process is completed and stopped. 
     In Modified Example 8, the mode switch judgment part  330  acts to judge the start of the scan mode and to announce the judgment result to the outside from the speakers  308 ,  320 ,  324 , the LEDs  310 ,  322 , and the display unit  204 . Therefore, the user can receive the information of the start of the scan mode (the information of the image capturing allowance including the suitable timing of the emission of the radiation  16 ). Thus, after the announcement, the user can operate the radiation switch  38  to start the emission of the radiation  16  to the subject  14 , whereby the radiographic image can be obtained with high quality. Since the radiation  16  can be emitted at the suitable timing, the user can avoid retaking of the image. Consequently, in Modified Example 8, the radiation  16  can be emitted at the suitable timing without synchronizing the image capturing timings, so that the radiographic image can be formed with a lowered noise content at low cost. 
     In Modified Example 8, before the scan mode performed by the first readout control part  130 , the second readout control part  136  may act to execute the reset operation or the offset signal readout mode for reading the electric signals stored in the pixels  102  as image correction offset signals (non-exposure signals) sequentially row by row. Also in this case, the electric charges can be reliably removed from the pixels  102  before the emission of the radiation  16 , whereby the radiographic image can be obtained with high quality. In addition, the quality of the radiographic image can be further improved by performing the image correction processing using the offset signals. 
     In Modified Example 8, the sound, light, image, and the like are used as described above, whereby the user can receive, through the eye or ear, the information of the scan mode start (the image capturing allowance). Therefore, for example, a speaker or a display device may be connected to a wireless access point, which can be connected to the electronic cassette  20  via wireless communication. In this case, when the wireless access point receives the scan mode switch signal, the speaker or the display device performs a predetermined announcement processing (e.g. of outputting a beep sound or an image capturing allowance screen). It is to be understood that Modified Examples 1 to 7 can be modified as Modified Example 8. 
     Modified Example 9 
     In Modified Example 9, as shown in  FIGS. 32 to 35 , in a case where an imaging area (imaging region)  352 ,  356  of the subject  14 , included in the image capturing menu, is smaller than the plane area of the radiation conversion panel  64 , the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed only in the pixels  102  corresponding to the imaging area  352 ,  356 , to reduce the electric power consumption in the reading and the judgment. 
     First, an example of  FIG. 32  will be described below. As described above, the gate drive circuits  150  and the multiplexers  152  (see  FIG. 7 ) each have predetermined readout subject pixels  102  (a predetermined associated readout region). Thus, with respect to all the pixels  102  on the radiation conversion panel  64 , one gate drive circuit  150  and one multiplexer  152  have an associated pixel region  350  containing a plurality of the pixels  102  (in 240 rows×256 columns) and read the electric signals from the pixels  102  in the associated pixel region  350 . Thus, the radiation conversion panel  64  is divided into the pixel regions  350  each containing a plurality of the pixels  102 , and each combination of the gate drive circuit  150  and the multiplexer  152  is responsible for one pixel region  350 . 
     In the case of  FIG. 32 , the user operates the input unit  200  to select the chest of the subject  14  as the imaging area  352 , and the control unit  212  of the system controller  24  (see  FIG. 10 ) registers (sets) the image capturing menu corresponding to the imaging area  352  and sends the setup image capturing menu to the electronic cassette  20  (see  FIG. 6 ). The cassette control device  122  of the electronic cassette  20  detects the imaging area  352  in the received image capturing menu and sets a thick frame  354  corresponding to a matrix of the pixels  102  containing the imaging area  352  as viewed in plan. Thus, the cassette control device  122  sets the associated pixel regions  350  in the thick frame  354 . 
     The cassette control device  122  acts to actuate the first to eighth gate drive circuits  150  and the second to eighth multiplexers  152  corresponding to the associated pixel regions  350  in the thick frame  354 . Thus, the cassette control device  122  controls the first readout control part  130  and the second readout control part  136  to read the electric charges from the pixels  102  in the associated pixel regions  350  in the thick frame  354 , and controls the irradiation start judgment part  132  to judge the start of the emission of the radiation  16  only in the pixels  102  in the associated pixel regions  350  in the thick frame  354 . 
     Consequently, on the radiation conversion panel  64 , the reading of the electric signals and the judgment of the emission start of the radiation  16  are not performed in the pixels  102  in the pixel regions  350  located outside the thick frame  354 . Therefore, the electric power consumption can be lowered in this case as compared with a case where the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed in all the pixels  102 . The electronic cassette  20  is a transportable apparatus, which is driven by the electric power supply from the battery of the power supply device  128 . The communication device  126  sends signals to and receives signals from the outside (the system controller  24 ) via wireless communication. Therefore, it is desirable to reduce wasteful electric power consumption. Thus, the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed only in the pixels  102  in the thick frame  354 , which are necessary for acquiring the radiographic image of the imaging area  352 . The electric power is not supplied to the ninth to twelfth gate drive circuits  150  and the first and ninth multiplexers  152 , other than the first to eighth gate drive circuits  150  and the second to eighth multiplexers  152 , so that electric power saving can be achieved in the entire electronic cassette  20 . 
     Furthermore, since the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed only in the pixels  102  in the associated pixel regions  350  in the thick frame  354  corresponding to the imaging area  352 , the radiographic image of the imaging area  352  can be reliably formed, and the time required to read the electric charges (electric signals) can be shortened. 
     Modified Example 9 is similar to the above embodiment and Modified Examples 1 to 8 except that the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed only in the pixels  102  in the associated pixel regions  350  in the thick frame  354 . Therefore, the reading and the judgment in each pixel  102  may be carried out in the same manner as the above embodiment and Modified Examples 1 to 8. 
     In the case of  FIG. 33 , the ankle of the subject  14  is selected as the imaging area  356 . The imaging area  356  is smaller than the imaging area  352  of the chest shown in  FIG. 32 . In this case, the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed in the pixels  102  in the associated pixel regions  350  in a thick frame  358  surrounding the imaging area  356  as viewed in plan, so that the radiographic image of the imaging area  356  can be reliably formed, and the above effects can be achieved in the same manner as  FIG. 32 . 
     In  FIGS. 34 and 35 , unlike  FIGS. 32 and 33  utilizing the associated pixel regions  350  for capturing the image of the imaging area  352 ,  356 , the cassette control device  122  acts to set (detect) two gate lines  110  and two signal lines  112  surrounding the imaging area  352 ,  356  as viewed in plan. The reading of the electric signals and the judgment of the emission start of the radiation  16  are performed only in the pixels  102  connectable with a plurality of the gate lines  110  between the two gate lines  110  and a plurality of the signal lines  112  between the two signal lines  112 . 
     In  FIG. 34 , the cassette control device  122  (see  FIG. 6 ) specifies two gate lines  110  and two signal lines  112  surrounding the imaging area  352  as viewed in plan based on the image capturing menu. Then, a plurality of the gate lines  110  between the specified two gate lines  110  are set as lines to which the gate drive circuits  150  should output the gate signals, and a plurality of the signal lines  112  between the specified two signal lines  112  are set as lines from which the multiplexers  152  should read the electric signals. 
     The cassette control device  122  acts to actuate the first to eighth gate drive circuits  150  corresponding to the setup gate lines  110  and the second to eighth multiplexers  152  corresponding to the setup signal lines  112  respectively. The cassette control device  122  controls the first readout control part  130  and the second readout control part  136  to read the electric signals only from the pixels  102  connected with the setup gate lines  110  and the setup signal lines  112 , and controls the irradiation start judgment part  132  to judge the start of the emission of the radiation  16  only in these pixels  102 . 
     Thus, in  FIG. 34 , the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed only in the pixels  102  in the region surrounded by the two gate lines  110  and the two signal lines  112 , and are not performed in the pixels  102  located outside the region. Therefore, the electric power consumption can be lowered in this case, like the cases of  FIGS. 32 and 33 , as compared with a case where the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed in all the pixels  102 . Furthermore, the radiographic image of the imaging area  352  can be reliably formed, and the time required to read the electric signals can be shortened. 
     In the case of  FIG. 35 , the ankle of the subject  14  is selected as the imaging area  356 . The region surrounded by the two gate lines  110  and the two signal lines  112  is smaller than that for the imaging area  352  of the chest shown in  FIG. 34 . Also in this case, the reading of the electric signals and the judgment of the emission start of the radiation  16  are performed only in the pixels  102  in the above region, so that the radiographic image of the imaging area  356  can be reliably formed, and the above effects can be achieved in the same manner as  FIG. 34 . 
     In Modified Example 9, before the scan mode performed by the first readout control part  130 , the second readout control part  136  may act to execute the reset operation or the offset signal readout mode for reading the electric signals stored in the pixels  102  in rows and columns corresponding to the imaging area  352 ,  356  as image correction offset signals (non-exposure signals) sequentially row by row. Also in this case, the electric charges can be reliably removed from the pixels  102  before the emission of the radiation  16 , whereby the radiographic image can be obtained with high quality. In addition, the quality of the radiographic image can be further improved by performing the image correction processing using the offset signals. 
     Modified Example 10 
     In Modified Example 10, the image capturing menu also includes the image capturing history recorded in the recording unit  216  (see  FIG. 10 ). The cassette control device  122  decides an electric charge readout mode to be performed before the emission of the radiation  16  based on the image capturing history and the like in the image capturing menu. Then, the cassette control device  122  controls the first readout control part  130  and the second readout control part  136  based on the decided readout mode, to read the electric charges from the pixels  102 . 
     After step S 1  of  FIG. 12 , in step S 81  of  FIG. 36 , the control unit  202  acts to display an image indicating also the image capturing history recorded in the recording unit  216  on the display unit  204 . While watching the displayed image (image capturing history), when the last image capturing process is carried out using a relatively high radiation dose (step S 82 : YES) and only a short time has elapsed from the last image capturing process (step S 83 : NO), the user judges that residual electric charges generated in the last image capturing process may be stored in the pixels  102 . Therefore, the user can decide to execute the sequential readout mode before the scan mode, and can operate the input unit  200  to enter the decision (step S 84 ). 
     While watching the displayed image capturing history, when the last image capturing process is carried out using a relatively high radiation dose (step S 82 : YES) and a long time has elapsed from the last image capturing process (step S 83 : YES), the user judges that the residual electric charges to affect the next radiographic image are not stored in the pixels  102 . Therefore, the user can decide to execute only the scan mode before the emission of the radiation  16 , and can operate the input unit  200  to enter the decision (step S 85 ). 
     While watching the displayed image capturing history, when the last image capturing process is carried out using a low radiation dose (step S 82 : NO), the user judges that the residual electric charges to affect the next radiographic image are not stored in the pixels  102 . Therefore, the step S 85  is carried out. 
     Furthermore, in Modified Example 10, after step S 1 , step S 83  may be carried out without step S 82  as shown by a dashed line in  FIG. 36 . 
     After step S 84  or S 85  is carried out in this manner, step S 2  and following steps of  FIG. 12  are performed. In this case, in step S 4 , the control unit  212  of the system controller  24  (see  FIG. 10 ) sends the image capturing menu including the decision of step S 84  or S 85  and the image capturing history to the electronic cassette  20 . 
     In the electronic cassette  20 , after the image capturing menu (including the image capturing conditions, the number of images, the decision, and the image capturing history) is received in step S 21  of  FIG. 13 , the cassette control device  122  judges whether the sequential readout mode should be executed or not before the scan mode based on the image capturing menu (the image capturing history and the decision included therein) in step S 86  of  FIG. 37 . 
     When the sequential readout mode should be executed (step S 86 : YES), the cassette control device  122  controls the second readout control part  136  to execute the sequential readout mode (step S 87 ). If the sequential readout mode executed by the second readout control part  136  is completed in the pixels  102  (step S 88 : YES), the cassette control device  122  controls the first readout control part  130  to execute the scan mode in step S 22  of  FIG. 13 , and the following steps are carried out. When the sequential readout mode is not completed, the cassette control device  122  remains in step S 88 . 
     On the other hand, when the sequential readout mode does not have to be executed (step S 86 : NO), the cassette control device  122  acts to perform step S 22  and the following steps of  FIG. 13 . 
     In Modified Example 10, the electric charge readout mode (the scan mode or the sequential readout mode) to be executed before the emission of the radiation  16  is selected by the system controller  24  and the console  26  based on the image capturing history in the image capturing menu. The image capturing menu including the decision and the image capturing history are sent to the electronic cassette  20 . The cassette control device  122  of the electronic cassette  20  controls the first readout control part  130  and the second readout control part  136  to execute the selected electric charge (electric signal) readout mode before the emission of the radiation  16  based on the decision and the image capturing history in the image capturing menu. 
     Consequently, the residual electric charges generated in the last image capturing process can be reliably removed from the pixels  102  before the emission of the radiation  16 , and the radiographic image can be formed with a high quality without overlap of a residual image. Since the electric charge readout mode to be executed before the emission start of the radiation  16  can be selected based on the image capturing history including the condition (the high or low radiation dose) of the last image capturing process and the time from the last image capturing process, the residual electric charges in the pixels  102  can be efficiently removed. 
     In Modified Example 10, step S 84  or S 85  may be carried out depending on the conditions of the ongoing image capturing process. For example, when this image capturing process is carried out using a low radiation dose, the execution of the scan mode in a short time may be decided to increase the response speed for detecting the radiation  16  in the pixels  102  (step S 85 ). When this image capturing process is carried out using a short irradiation time of the radiation  16 , the execution of only the scan mode in a short time may be decided to avoid waste of time (step S 85 ). In this case, the scan mode in a short time may be performed in all or part of the pixels  102  in the same manner as Modified Examples 4 to 6. 
     In Modified Example 10, the cassette control device  122  may change the interval between the rows, which are simultaneously read out in the scan mode, based on the radiation  16  irradiation time, the decision, and the image capturing history in the image capturing menu. For example, when this image capturing process is carried out under a short irradiation time of the radiation  16  to avoid waste of time, the cassette control device  122  may set a wide row interval and then control the first readout control part  130  to execute the scan mode. In this case, the scan mode can be completed in a short time. 
     In a case where only the pixels  102  in the predetermined rows are read out in the scan mode in the same manner as Modified Example 4, the cassette control device  122  may change the rows, which are read out in the scan mode, based on the radiation  16  irradiation time, the decision, and the image capturing history in the image capturing menu. In this case, the scan mode can be completed in a short time e.g. by increasing the interval between the predetermined rows. 
     Furthermore, in Modified Example 10, in step S 84  or S 85 , the scan mode or the sequential readout mode may be decided to be executed only in the pixels  102  corresponding to the imaging area  352  or  356  in the same manner as Modified Example 9. 
     As described above, in steps S 81  to S 85 , the user may decide the electric charge readout mode to be executed before the emission of the radiation  16  while watching the image on the display unit  204 . Modified Example 10 is not limited thereto. The electric charge readout mode to be executed before the emission of the radiation  16  may be automatically decided by the control unit  212  based on the image capturing history recorded in the recording unit  216 . Of course, the above effects can be achieved also in this case. It is to be understood that Modified Examples 1 to 9 may be further modified like Modified Example 10. 
     Modified Example 11 
     In the above embodiment and Modified Examples, the electric charges stored in the pixels  102  in a plurality of the rows (e.g. 12 rows) are simultaneously read out in the scan mode (the first readout mode). Therefore, the start of the emission of the radiation  16  can be rapidly and accurately judged. 
     In the scan mode, the irradiation start judgment part  132  judges whether or not the digital electric signals stored in the memory  124  are larger than the arbitrary settable threshold value (hereinafter referred to as the threshold value Th) (step S 23 ). A significantly larger signal value is output from the charge amplifier  116  under the emission of the radiation  16  from the radiation source  34  to the electronic cassette  20  than without the emission of the radiation  16 . Therefore, the digital electric signal stored in the memory  124  becomes larger than the threshold value Th under the emission of the radiation  16 , whereby the start of the emission of the radiation  16  can be rapidly judged. 
     For example, the gains of the charge amplifiers  116  (hereinafter referred to as the gains G) may be controlled at a second readout gain G2 in the sequential readout mode. In a case where the charge amplifiers  116  are controlled at the second readout gain G2 in the simultaneous readout mode, 12 pixels  102  are simultaneously read out, the charge amplifiers  116  exhibit 12-fold signal values, and 12-fold digital electric signals are sent from the A/D converters  154  and stored in the memory  124 . If the 12-fold digital electric signal becomes larger than the threshold value Th, the emission of the radiation  16  is judged to be started. 
     The gains G of the charge amplifiers  116  are designed such that the signals output from the charge amplifiers  116  have magnitudes within and closer to input dynamic ranges of the A/D converters  154  to improve the readout resolution (readout accuracy) in the sequential readout mode. Therefore, in a case where the gains G are not changed in the scan mode, the charge amplifiers  116  may be saturated, failing to ensure the high-speed operation. 
     In Modified Example 11, the charge amplifiers  116  are controlled at a first readout gain G1 by the first readout control part  130  in the scan mode, and are controlled at the second readout gain G2 by the second readout control part  136  in the sequential readout mode. The first readout gain G1 used in the scan mode is lower than the second readout gain G2 used in the sequential readout mode (G1&lt;G2). For example, when 12 pixels in 12 rows are simultaneously read out in the scan mode, the first readout gain G1 may be 1/12 of the second readout gain G2 (G1=G2/12) to prevent the saturation of the charge amplifiers  116 . 
       FIG. 38  is a detail view of the radiation conversion panel  64 , the gate drive part  114 , and the multiplexer part  118 , equipped with the charge amplifiers  116 . In each charge amplifier  116 , the capacitor  158  connected to the input and output terminals of the operational amplifier  156  is replaced by a variable capacitor  158 A to modify the gain G of the charge amplifier  116 . 
     As shown in  FIG. 39A , the capacitance of the variable capacitor  158 A can be switched by a switch  161   b , which is controlled by the first readout control part  130  or the second readout control part  136 . In a case where the switch  161   b  is in the off state and only the capacitor  158  is used as the feedback capacitor, the gain G of the charge amplifier  116  is controlled at the second readout gain G2 for the sequential readout mode. When the switch  161   b  is in the on state and the capacitors  158  and  158   a  are used in combination as the feedback capacitor, the gain G of the charge amplifier  116  is controlled at the first readout gain G1 for the scan mode (G1&lt;G2). A voltage generated between terminals of a capacitor under an electric charge amount is inversely proportional to the capacitance value of the capacitor. Therefore, it should be noted that, as the capacitance value of the feedback capacitor is reduced, the terminal voltage under an electric charge amount is increased, resulting in a higher gain G of the charge amplifier  116 . Thus, assuming a lossless condition to facilitate understanding, the gain G of the charge amplifier  116  satisfies the relation of G=Ca/Cf, in which Ca represents the equivalent capacitance value of the charge storage part  74  and Cf represents the capacitance value of the feedback capacitor of the charge amplifier  116 . 
     As shown in  FIG. 40 , the gain G is controlled at the first readout gain G1 or a first readout gain G1′ (to be hereinafter described) in the scan mode and is controlled at the second readout gain G2 in the sequential readout mode (G1′&lt;G1&lt;G2). 
     In the above embodiment and Modified Examples 1 to 10, among the setup image capturing conditions (including the irradiation time, the tube voltage, the tube current, and the like, stored in association with the imaging area and the diagnostic site in the table  218 ), at least the irradiation time is sent from the image capturing condition setting part  222  through the communication unit  214  to the electronic cassette  20 . In Modified Example 11, at least the irradiation time and the tube current are sent to the electronic cassette  20 . In Modified Example 11, the tube current is considered proportional to the radiation dose. In this sense, the image capturing condition setting part  222  acts as a radiation dose setting part. 
     In  FIG. 40 , the first readout gain G1′, lower than the first readout gain G1, is used when a high radiation dose (a radiation dose higher than a predetermined value) of the emission of the radiation  16  is set by the image capturing condition setting part  222  (the radiation dose setting part). Thus, the first readout control part  130  can set the first readout gain G1′ for the high radiation dose or the first readout gain G1 for the low radiation dose, the first readout gain G1′ being lower than the first readout gain G1, so that the output saturation of the charge amplifier  116  can be prevented under both the high and low radiation doses. 
     In Modified Example 11, the first readout gain G is changed depending on the radiation dose in this manner. Therefore, as described above, among the image capturing conditions, the image capturing condition setting part  222  sends the irradiation time and further sends at least the tube current value corresponding to the radiation dose to the electronic cassette  20 . 
     The electronic cassette  20  acts to store the sent irradiation time and tube current value corresponding to the radiation dose in the memory  124 . The first readout control part  130  sets the scan mode gain (first readout gain) G1 or G1′, based on the tube current value stored in the memory  124 . 
       FIG. 39B  is a structural view of the charge amplifier  116  capable of switching the gain G into the second readout gain G2 for the sequential readout mode or the first readout gain (scan mode gain) G1 or G1′. When both of switches  161   a  and  161   b  are in the on states, the capacitor  158  can be connected in parallel to capacitors  158   a  and  158   b  to set the lowest scan mode gain G1′ (G1′&lt;G1&lt;G2). 
     The first readout control part  130  and the second readout control part  136  may set the first readout gain G1 or G1′ or the second readout gain G2 depending on the image capturing conditions (the imaging area and the diagnostic site) such as those of  FIG. 11 . In this case, when the user operates the input unit  200  of the console  26  to select the imaging area and the diagnostic site, the image capturing condition setting part  222  sends all the image capturing conditions corresponding thereto to the electronic cassette  20  through the communication unit  214 . 
     With respect to the setting of the threshold value Th in the scan mode executed by the first readout control part  130 , as shown in  FIG. 40 , a start threshold value Thi is set at the start of the scan mode and is used between timings t0 and t0′ in the first cycle. In the first cycle, each plurality of the rows (e.g. 12 rows) is simultaneously read to obtain electric signal values Si. Furthermore, a normal threshold value Tha is set in the following cycles of the scan mode (after the timing t0′). The normal threshold value Tha is represented by Si+α, obtained by adding a predetermined value (small value) α to the electric signal value Si. The normal threshold value Tha is smaller than the start threshold value Thi (Si+α=Tha&lt;Thi). 
     In this manner, the normal threshold value Tha set in the following cycles of the scan mode can be larger than but close to the noise level. Therefore, the emission of the radiation  16  can be detected more rapidly. 
     In this case, the setup number of images may be 2 or more similarly to  FIG. 15 . As shown by a solid line in the bottom of  FIG. 41 , in the first image capturing process, the threshold value Th in the scan mode (first readout mode) is controlled such that the irradiation start judgment part  132  sets the start threshold value Thi between timings t10 and t10′ and then sets the normal threshold value Tha between timings t10′ to t12. In the second and following image capturing processes, the normal threshold value Tha is continuously used in the scan mode (first readout mode) as in the example of the timings t20 to t22. Thus, the emission of the radiation  16  can be rapidly detected even in the first cycle of the scan mode in the second and following image capturing processes. 
     As shown in  FIG. 42 , the cassette control device  122  has a normal threshold value monitoring part  131  for monitoring (logging) the normal threshold value Tha, which is set depending on the read noise level. If the monitored normal threshold value Tha (Si+α) based on the readout noise level becomes larger than a predetermined value (warning value), the normal threshold value monitoring part  131  sends a notice to at least one of a warning lamp (not shown) disposed on the electronic cassette  20  and the console  26  or the display device  28  through the communication device  126  and the system controller  24  (thereby providing a warning image or sound). Furthermore, the normal threshold value monitoring part  131  may send the notice directly from the console  26  or the electronic cassette  20  to a server in a maintenance center or the like through a communication link (not shown). In this case, at least one of the user and the outside maintenance center can predict a failure of the electronic cassette  20  containing the radiation conversion panel  64  via so-called remote maintenance. 
     As described above, in Modified Example 11, the electronic cassette  20  used as the radiographic image capturing apparatus has the image capturing panel having the radiation conversion panel  64  containing a plurality of the pixels  102  arranged in a matrix for converting the radiation  16  (which is emitted from the radiation source  34  and transmitted through the subject  14 ) into the electric signals and storing the electric signals, the first readout control part  130  for executing the first readout mode for reading the electric signals stored in the pixels  102  in a plurality of the rows simultaneously through the electric signal amplifiers of the charge amplifiers  116  set at the first readout gain G1, the irradiation start judgment part  132  for judging the start of the emission of the radiation  16  from the radiation source  34  to the image capturing panel having the radiation conversion panel  64 , the emission of the radiation  16  being judged to be started in a case where a value of the electric signals read by the first readout control part  130  becomes larger than the arbitrarily settable threshold value Th, and the first readout control part  130  acting to stop the reading of the electric signals and to switch the image capturing panel having the radiation conversion panel  64  to the exposure state in a case where the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132 , the elapsed time judgment part  134  for judging whether the predetermined time has elapsed or not from the start of the emission of the radiation  16 , and the second readout control part  136  for executing the second readout mode for reading the electric signals stored in the pixels sequentially row by row through the charge amplifiers  116  set at the second readout gain G2, the second readout mode being executed in a case where the predetermined time is judged to have elapsed by the elapsed time judgment part  134 . The first readout gain G1 is lower than the second readout gain G2. 
     The charge amplifiers  116  are controlled at the lower gains in the first readout mode (scan mode). Therefore, even if the electric charges in a plurality of the pixels are simultaneously read out and the electric signal value becomes larger than the threshold value Th for detecting the start of the emission of the radiation  16 , the output values of the charge amplifiers  116  are not excessively increased and are not saturated. 
     It should be noted that the first readout control part  130  can simultaneously read the electric signals stored in the pixels  102  in a plurality of the rows arranged at a predetermined row interval. 
     In addition, the image capturing condition setting part  222  is used as the radiation dose setting part for setting a low or high radiation dose of the radiation  16  to be emitted to the subject  14 . The first readout control part  130  controls the first readout gain G based on information from the image capturing condition setting part  222  such that the first readout gain G1′ for the high radiation dose is lower than the first readout gain G1 for the low radiation dose. Therefore, the output signals of the charge amplifiers  116  are not saturated under the high radiation dose and are sufficiently increased under the low radiation dose. Consequently, the emission of the radiation  16  can be rapidly detected. 
     The first readout control part  130  and the second readout control part  136  may set the first readout gain G1 (G1′) and the second readout gain G2 based on the image capturing conditions (the imaging area and the diagnostic site). 
     Modified Example 12 
     In the above embodiment and Modified Examples 1 to 11, the elapsed time judgment part  134  is used for judging the completion of the emission of the radiation  16 . 
     Alternatively, as shown in  FIG. 43 , a radiation detection sensor (an emission completion judgment part or an exposure completion judgment part)  103  may be used for the judgment in the drive circuit device  106 . The radiation detection sensor  103  may be a semiconductor sensor such as a photodiode, which outputs a signal only under the emission of the radiation  16 . 
     In this case, if the radiation detection sensor  103  exhibits an output value of approximately zero, the emission of the radiation  16  is judged to be completed. If the emission of the radiation  16  is judged to be completed, the second readout control part  136  acts to execute the second readout mode for reading the electric signals stored in the pixels  102  sequentially row by row through the charge amplifiers  116  set at the second readout gain G2. 
     The radiation detection sensor  103  may be disposed on the image capturing surface  42  (see  FIG. 2 ) of the panel unit  52 , and may be located on each corner of the image capturable area  60 . 
     Other than the semiconductor sensor such as the photodiode, the radiation detection sensor  103  may be such that another pixel and another TFT are formed in the radiation conversion panel  64 , another charge amplifier (an operating amplifier, a feedback capacitor, and a reset switch) and another A/D converter are formed in the drive circuit device  106 , and the second readout control part  136  directly controls the TFT, charge amplifier, and A/D converter. When the exposure is started, the reset switch is opened, the output of the charge amplifier is increased, and the increase is stopped (the output becomes constant), the emission of the radiation  16  can be judged to be completed. When the emission of the radiation  16  is judged to be completed, the reset switch is closed, so that the feedback capacitor in the charge amplifier is discharged. 
     Modified Example 13 
     Modified Examples 1 to 12 may be further modified as follows. An electronic cassette  20   a  according to Modified Example 13 will be described below with reference to  FIGS. 44 to 46 . 
     As shown in  FIG. 44 , the cassette control device  122  has a stop signal output part  600  for outputting a stop signal Sb based on a detection signal Sa from the irradiation start judgment part  132  (indicating the detection of the emission start of the radiation  16 ), and a return signal output part  602  for outputting a return signal Sd based on a scan end signal Sc from the first readout control part  130  (indicating the completion of the scan mode). The stop signal Sb and the return signal Sd are supplied to the gate drive part  114 . 
     The gate drive part  114  has a mask processing portion  604  for each of the gate drive circuits  150 . As shown in  FIG. 45 , the mask processing portion  604  has a first switch circuit  606 , and further has AND circuits  608  corresponding to output terminals of the gate drive circuit  150 . 
     The first switch circuit  606  outputs a high-level signal (Vh) at an early stage, outputs a low-level signal (Vss) based on the entered stop signal Sb, and outputs the high-level signal (Vh) based on the entered return signal Sd. 
     Each of the AND circuits  608  receives two types of signals from the gate drive circuit  150  and the first switch circuit  606 , and outputs the logical product of the entered signals. The AND circuit  608  has an output line corresponding to the gate line  110 . At the early stage and in a case where the return signal Sd is entered, the first switch circuit  606  outputs the high-level signal (Vh) to the AND circuit  608 , so that the output from the gate drive circuit  150  is made effective, and the gate signal is sent to the selected gate line  110 . In a case where the stop signal Sb is entered into the first switch circuit  606 , until the return signal Sd is entered, the first switch circuit  606  outputs the low-level signal (Vss) to the AND circuit  608 , so that the output from the gate drive circuit  150  is made ineffective, and the gate signal is not sent to the gate line  110 . 
     When the start of the emission of the radiation  16  is detected, the cassette control device  122  sends the stop signal Sb to the gate drive circuits  150  to stop the reading. When the drive signals c 1  to c 12  are sent, the gate drive circuits  150  select the gate lines  110  sequentially, and output the gate signals to the selected gate lines  110  sequentially, to read the electric charges stored in the pixels  102  sequentially row by row. When the stop signal Sb is entered, the mask processing portions  604  act to perform a mask processing, and the gate drive circuits  150  do not output the gate signals. Thus, the first readout control part  130  stops the reading of the electric charges stored in the pixels  102  in the scan mode. In this case, when the stop signal Sb is sent, each of the gate drive circuits  150  continues to sequentially select the gate lines  110  (the scan mode is continued). However, since the mask processing is carried out, the gate signals are not sent to the selected gate lines  110 . Therefore, the electronic cassette  20   a  can be switched into the exposure state at the timing of the detection of the radiation  16  (the judgment of the emission of the radiation  16  in the scan mode). 
     For example, even if the stop signal Sb is sent after the gate signal is sent to the gate line  110  of the 0th row, each of the gate drive circuits  150  continues to sequentially select the gate lines  110  of the first, second, . . . , and final rows, but does not output the gate signals to the selected gate lines  110 . In this case, even if the stop signal Sb is sent, the gate drive circuits  150  sequentially select the gate lines  110 , and thereby output the end signals d 1  to d 12  after the gate lines  110  of the 239th rows are selected. When the end signals d 1  to d 12  are sent from the gate drive circuits  150 , the first readout control part  130  acts to stop the scan mode. 
       FIG. 46  is a diagram for illustrating the electric charges stored in the pixels  102  in some rows in a case where the electronic cassette  20   a  is switched into the accumulation state after the radiation  16  is detected and then immediately the reading of the electric charges in the pixels  102  in the scan mode is stopped. 
     The electric charges in the pixels  102  in the some rows, stored in a case where the radiation  16  is detected in a process of reading the electric charges stored in the 0th row, are shown in  FIG. 46 . When the radiation  16  is detected, the cassette control device  122  sends the stop signal Sb to the gate drive circuits  150 . Therefore, the electric charges stored in the pixels  102  in the second to final rows under the emission of the radiation  16  are not read out and remain in the rows. In this case, the amount Q0 of the electric charges stored in the pixels  102  is the 0th row by the exposure for capturing the radiographic image, the amount Q1 of the electric charges stored in the pixels  102  in the first row, and the amount Q239 of the electric charges stored in the pixels  102  in the 239th row satisfy the relation of Q0&lt;Q1=Q239, and the difference between the amounts is not large. Thus, the exposure can be performed without wasting the radiation  16  with the image information, and the rows exhibit only small variations in the amounts of the electric charges. 
     The operation of the cassette control device  122  in Modified Example 13 is approximately equal to that shown in the flowchart of  FIG. 13 . However, in Modified Example 13, when the emission of the radiation  16  is judged to be started by the irradiation start judgment part  132  in step S 24  of  FIG. 13 , the stop signal output part  600  sends the stop signal Sb to the gate drive circuits  150  to perform step S 25 , so that the electronic cassette  20   a  can be switched into the exposure state. Then, the first readout control part  130  judges whether the end signals d 1  to d 12  are sent or not from the gate drive circuits  150  in step S 26 . In a case where the end signals d 1  to d 12  are judged to be sent, the scan mode is stopped in step S 27 . At this time, the return signal output part  602  outputs the return signal Sd, and the mask processing by the mask processing portion  604  is stopped. 
     In this manner, when the emission of the radiation  16  is judged to be started, the electronic cassette  20   a  outputs the stop signal Sb to the gate drive circuits  150 . Though the scan mode is continued until the one cycle is completed, the electric charges stored in the pixels  102  are not read out, whereby the radiation  16  with the image information are not wasted and are utilized for capturing the radiographic image. 
     In the above described example, the mask processing portion  604  for each gate drive circuit  150  is hardware containing the first switch circuit  606  and a plurality of the AND circuits  608 . When the gate drive circuit  150  has a CPU, software (such as bit mask processing program) having the same function as the mask processing portion  604  may be embedded. 
     Modified Example 14 
     In an electronic cassette  20   b  according to Modified Example 14, in a case where the emission of the radiation  16  is detected and then the one cycle is completed in the scan mode, an all-line activation processing (all-pixel reset mode) for discarding excess charges in all the pixels  102  is carried out. In the all-line activation processing, the gate signals are sent to all the gate lines  110  to turn on all the TFTs  72  connected therewith. 
     The electronic cassette  20   b  of Modified Example 14 will be described specifically below with reference to  FIGS. 47 to 50 . 
     As shown in  FIG. 47 , the cassette control device  122  has an all-pixel reset control part  610 . The all-pixel reset control part  610  has an all-line activation portion  612 , which outputs a reset signal Se for activating all lines based on a signal indicating the completion of the scan mode (the scan end signal Sc) sent from the first readout control part  130 . The all-pixel reset control part  610  further has a switch control portion  614 , which controls the switches  160  of the charge amplifiers  116  (see  FIG. 7 ) in the on states over a predetermined time (hereinafter referred to as the reset time) based on the scan end signal Sc. 
     The gate drive part  114  has an all-line activation circuit  616  for each of the gate drive circuits  150 . As shown in  FIG. 48 , the all-line activation circuit  616  has a second switch circuit  618 , and further has OR circuits  620  corresponding to the output terminals of the gate drive circuit  150 . 
     The second switch circuit  618  outputs a low-level signal (Vss) at an early stage, and outputs a high-level signal (Vh) over the reset time based on the entered reset signal Se. The output of the high-level signal (Vh) is synchronized with the control of the switches  160  of the charge amplifiers  116  in the on states by the switch control portion  614 . 
     Each of the OR circuits  620  receives two types of signals from the gate drive circuit  150  and the second switch circuit  618 , and outputs the logical sum of the entered signals. The OR circuit  620  has an output line corresponding to the gate line  110 . When the scan mode is completed, the second switch circuit  618  outputs the high-level signal (Vh) to each OR circuit  620  over the reset time, so that the gate signals are sent to all the gate lines  110  (all the gate lines  110  are activated). At this time, the switches  160  of the charge amplifiers  116  are turned on. Consequently, the residual electric charges (excess charges) in all the pixels  102  are emitted through the switches  160  and the operational amplifiers  156  to GND (ground potential). The electric charges in the pixels  102  may be discarded onto the GND without modification, it being not necessary to convert the electric charges into the electric signals. Therefore, the reset time may be the sum of the one-row pixel readout time (e.g. 21 μsec) and a retardation time, and for example is 30 to 40 μsec. 
     On the other hand, when the second switch circuit  618  outputs the low-level signal (Vss), the output from the gate drive circuit  150  is effective, and the gate signal is sent to the selected gate line  110 . It should be noted that the gate signals are not sent to the gate lines  110  in the exposure period. 
       FIG. 49  is a diagram for illustrating the electric charges stored in the pixels  102  in some rows in a case where the electronic cassette  20   b  is switched into the exposure state after the radiation  16  is detected in a process of reading the electric charges in the 0th row, the one cycle of the scan mode is completed, and then all the pixels  102  are reset. In the scan mode, each of the gate drive circuits  150  reads the electric charges stored in the pixels  102  in the 0th to final rows sequentially row by row. In this case, for example, even after a digital value obtained by reading the electric charges stored in the pixels  102  in the 0th row is judged to be larger than the threshold value to detect the radiation  16 , the electric charges stored in the pixels  102  in the first to 239th rows are read sequentially row by row in the scan mode. When the electric charges stored in the pixels  102  in the 239th row are read out, the scan mode is completed. The electric charges remaining in all the pixels  102  are emitted to the GND (ground potential) in the reset time Ta after the completion, so that the electronic cassette  20   b  is switched into the exposure state after the reset time Ta. Thus, the all-pixel reset control part  610  acts to switch the radiation conversion panel  64  into the exposure state at the end of the all-pixel reset process. Consequently, at the start of the exposure period Tb, the amounts Q0, . . . , Q238, and Q239 of the electric charges in the pixels  102  can be approximately the same, and the difference between the amounts can be almost eliminated. 
     The operation of the cassette control device  122  in Modified Example 14 is approximately equal to that shown in the flowchart of  FIG. 13 . As shown in  FIG. 50 , in Modified Example 14, steps S 201  to S 204  are carried out first in the same manner as steps S 21  to S 24  of  FIG. 13 . After the emission of the radiation  16  is judged to be started in step S 204 , the first readout control part  130  is in the standby state until the one cycle of the scan mode is completed (step S 205 ). When the scan mode is completed, the first readout control part  130  outputs the scan end signal Sc, the all-line activation portion  612  outputs the reset signal Se to the all-line activation circuits  616  in the gate drive part  114 , and the switch control portion  614  controls the switches  160  of the charge amplifiers  116  in the on states over the reset time Ta (see  FIG. 7 ). Thus, the excess charges in all the pixels  102  are emitted to the GND to reset the pixels  102  (step S 207 ). Then, when the reset time Ta has elapsed, the electronic cassette  20   b  is switched into the exposure state to start the exposure period Tb (step S 208 ). At the start of the exposure period Tb, the cassette control device  122  acts to start a timer (step S 209 ). In next step S 210 , the elapsed time judgment part  134  judges whether or not a predetermined time (equal to the exposure period Tb in this case) has elapsed from the start of the exposure period Tb. In a case where the predetermined time is judged to have elapsed in step S 210 , the exposure is completed (the exposure period Tb is stopped), and the second readout control part  136  acts to start the sequential readout mode to read the electric charges generated by the exposure with the radiation  16  (step S 211 ). Steps S 211  to S 215  are carried out in the same manner as steps S 29  to S 33  of  FIG. 13 , and therefore explanations thereof are omitted. 
     In the electronic cassette  20   b  of Modified Example 14, the electric charge amount difference between the pixels  102  can be almost eliminated at the start of the exposure period Tb. Therefore, the image quality and the S/N ratio of the radiographic image can be improved. 
     In the above described example, the all-line activation circuit  616  for each gate drive circuit  150  is hardware containing the second switch circuit  618  and a plurality of the OR circuits  620 . When the gate drive circuit  150  has a CPU, software having the same function as the all-line activation circuit  616  may be embedded. 
     Modified Example 15 
     In Modified Example 14, after the emission of the radiation  16  is detected in the scan mode, the step of discarding the excess charges in all the pixels  102  is not carried out until the one cycle is completed. 
     Alternatively, the step of discarding the excess charges in all the pixels  102  may be carried out immediately after the detection of the emission of the radiation  16  in the scan mode. 
     An electronic cassette  20   c  according to Modified Example 15 will be described specifically below with reference to  FIGS. 51 to 54 . 
     As shown in  FIG. 51 , the cassette control device  122  has the stop signal output part  600  and the return signal output part  602  as in Modified Example 13, and further has the all-pixel reset control part  610  (the all-line activation portion  612  and the switch control portion  614 ) as in Modified Example 14. In Modified Example 15, the all-line activation portion  612  outputs the reset signal Se for activating all lines based on the detection signal Sa from the irradiation start judgment part  132  (indicating the detection of the emission start of the radiation  16 ). 
     The gate drive part  114  has the mask processing portion  604  and the all-line activation circuit  616  for each of the gate drive circuits  150 . As shown in  FIG. 52 , the mask processing portion  604  has the first switch circuit  606 , and further has the AND circuits  608  corresponding to the output terminals of the gate drive circuit  150 , as in Modified Example 13. The all-line activation circuit  616  has the second switch circuit  618 , and further has the OR circuits  620  corresponding to the output terminals of the gate drive circuit  150 , as in Modified Example 14. 
     Each of the AND circuits  608  receives the two types of signals from the gate drive circuit  150  and the first switch circuit  606 , and outputs the logical product of the entered signals. Each of the OR circuits  620  receives the two types of signals from the associated AND circuit  608  and the second switch circuit  618 , and outputs the logical sum of the entered signals. The OR circuit  620  has the output line corresponding to the gate line  110 . 
     When the start of the emission of the radiation  16  is detected, the stop signal Sb is entered into the first switch circuit  606 . Then, until the return signal Sd is entered, each AND circuit  608  outputs the low-level signals (Vss). Meanwhile, when the start of the emission of the radiation  16  is detected, the reset signal Se is entered into the second switch circuit  618 . Then, the second switch circuit  618  outputs the high-level signal (Vh) over the reset time Ta, so that the gate signals are sent to all the gate lines  110  (all the gate lines  110  are activated). At this time, the switches  160  of the charge amplifiers  116  are turned on. Consequently, the residual electric charges (excess charges) in all the pixels  102  are emitted through the switches  160  and the operational amplifiers  156  to the GND (ground potential). 
     Modified Example 15 will be described below with reference to  FIG. 53 . In the scan mode, each of the gate drive circuits  150  reads the electric charges stored in the pixels  102  in the 0th to final rows sequentially row by row. In this case, for example, when a digital value obtained by reading the electric charges stored in the pixels  102  in the 0th row is judged to be larger than the threshold value to detect the radiation  16 , the electric charges remaining in all the pixels  102  are emitted to the GND (ground potential) in the reset time Ta immediately after the judgment. After the reset time Ta has elapsed, though the scan mode is continued until the one cycle is completed, the electric charges stored in the pixels  102  are not read out. Therefore, when the reset time Ta has elapsed from the detection of the radiation  16  (the judgment of the emission of the radiation  16  in the scan mode), before the completion of the one cycle of the scan mode, the electronic cassette  20   c  can be switched into the exposure state. 
     The operation of the cassette control device  122  in Modified Example 15 is approximately equal to that shown in the flowchart of  FIG. 13 . As shown in  FIG. 54 , in Modified Example 15, steps S 221  to S 224  are carried out first in the same manner as steps S 21  to S 24  of  FIG. 13 . If the emission of the radiation  16  is judged to be started in step S 224 , the stop signal output part  600  sends the stop signal Sb to the gate drive circuits  150  to start the mask processing using the mask processing portion  604  (to stop the output from the gate drive circuits  150 ). Furthermore, as described above, when the emission of the radiation  16  is judged to be started, the all-line activation portion  612  outputs the reset signal Se to the all-line activation circuits  616  in the gate drive part  114 , and the switch control portion  614  controls the switches  160  of the charge amplifiers  116  in the on states over the reset time Ta (see  FIG. 7 ). Thus, the excess charges in all the pixels  102  are emitted to the GND to reset the pixels  102  (step S 225 ). Then, when the reset time Ta has elapsed, the electronic cassette  20   c  is switched into the exposure state to start the exposure period Tb (step S 226 ). At the start of the exposure period Tb, the cassette control device  122  acts to start a timer (step S 227 ). The cassette control device  122  is in the standby state until the scan mode is completed in step S 228 . When the scan mode is completed, the return signal output part  602  outputs the return signal Sd, so that the mask processing using the mask processing portion  604  is completed. In next step S 229 , the elapsed time judgment part  134  judges whether a predetermined time (equal to the exposure period Tb also in this case) has elapsed or not from the start of the exposure period Tb. If the predetermined time is judged to have elapsed in step S 229 , the exposure is completed (the exposure period Tb is stopped), and the second readout control part  136  acts to start the sequential readout mode to read the electric charges generated by the exposure with the radiation  16  (step S 230 ). Steps  230  to  5234  are carried out in the same manner as steps S 29  to S 33  of  FIG. 13 , and therefore explanations thereof are omitted. 
     In Modified Example 15, the advantageous effects of both of Modified Examples 13 and 14 can be achieved. Thus, at the start of the exposure period Tb, the amounts Q0, . . . , Q238, and Q239 of the electric charges in the pixels  102  can be approximately the same, and the difference between the amounts can be almost eliminated. Therefore, the image quality and the S/N ratio of the radiographic image can be improved. Furthermore, the radiation  16  with the image information is not wasted and is utilized for capturing the radiographic image. 
     In the above described example, the mask processing portion  604  and the all-line activation circuit  616  for each gate drive circuit  150  are hardware containing the first switch circuit  606  and a plurality of the AND circuits  608  and hardware containing the second switch circuit  618  and a plurality of the OR circuits  620  respectively. When the gate drive circuit  150  has a CPU, software having the same functions as the mask processing portion  604  and the all-line activation circuit  616  may be embedded. 
     Modified Example 16 
     In the above embodiment and Modified Examples 1 to 15, one electronic cassette  20  is used and described. In general, various types and specifications of the electronic cassettes  20  are used depending on the requirements of the image capturing conditions and the like. For example, in a case where the electronic cassette  20  is a so-called indirect type apparatus using a scintillator, its specification depends on the sensitivity, the pixel size, and the like of the scintillator. Furthermore, the electronic cassettes  20  are relatively costly. Therefore, as is often the case, a plurality of the electronic cassettes  20  are not placed in each of a plurality of image capturing rooms, but are shared by the image capturing rooms. When a plurality of the electronic cassettes  20  are shared by a plurality of the image capturing rooms, a radiation technician may make a mistake in selecting the electronic cassette  20 . 
     Thus, a radiographic image capturing system  10  according to Modified Example 16 has a structure containing a plurality of the electronic cassettes  20 , which can be appropriately used even if the mistake is made in the selection of the electronic cassette  20 . 
       FIG. 55  is a schematic view of the radiographic image capturing system  10  of Modified Example 16. As shown in  FIG. 55 , the radiographic image capturing system  10  has the electronic cassette  20  that is practically used in the image capturing process, and further has a plurality of the electronic cassettes  20  arranged on a cradle  700 . The electronic cassettes  20  may have the same or different specifications. The electronic cassettes  20  arranged on the cradle  700  can be charged up by the cradle  700 . 
       FIG. 56  is a flowchart of the operation of the system controller  24  and the console  26  in the radiographic image capturing system  10  of Modified Example 16, and  FIG. 57  is a flowchart of the operation of the cassette control device  122  of Modified Example 16 (see  FIG. 6 ). 
     The operation of each component in Modified Example 16 is substantially equal to that in the above embodiment ( FIGS. 12 and 13 ). However, Modified Example 16 is different from the above embodiment in that any one of a plurality of the electronic cassettes  20  can be used in the image capturing process. 
     In the operation of the system controller  24  and the console  26  in the radiographic image capturing system  10 , steps S 301  and S 302  of  FIG. 56  are carried out in the same manner as steps S 1  and S 2  of  FIG. 12 . After the image capturing conditions are set, in next step S 303 , the control unit  212  sends the startup signal to a plurality of the electronic cassettes  20  through the communication unit  214 , whereby the electronic cassettes  20  are started up. The electronic cassettes  20  are in the sleep states until the startup signal is sent. Furthermore, the control unit  212  acts to send identification information of one or more electronic cassettes  20  usable in this image capturing process to the console  26 , and to display the identification information on the display unit  204 . 
     Though the one or more electronic cassettes  20  usable in this image capturing process are identified as described above, all the electronic cassettes  20  in the radiographic image capturing system  10  are started up. Alternatively, the control unit  212  may select the electronic cassettes  20  depending on the setup image capturing conditions, and may send the startup signal only to the selected electronic cassettes  20 . 
     When the startup signal is received, a plurality of the electronic cassettes  20  are switched from the sleep mode to the scan mode. The electronic cassettes  20  may act to perform the reset operation before the scan mode. In the sleep mode, electric power is supplied only to essential components (such as the cassette control device  122  and the communication device  126 ), and is not supplied to the other components. 
     The image capturing condition setting part  222  and the image number setting part  224  in the control unit  212  (see  FIG. 10 ) send the setup irradiation time and the setup number of images to the started electronic cassettes  20  through the communication unit  214  (step S 304 ). 
     The control unit  212  judges whether a radiation detection information signal is received or not from any one of the electronic cassettes  20  (step S 305 ). The radiation detection information signal includes a notice of the detection of the radiation  16  in the electronic cassette  20 , and includes identification information for identifying the electronic cassette  20 . 
     If the radiation detection information signal is judged to be not received in step S 305 , the radiographic image capturing system  10  remains in step S 305  until it is received. If the radiation detection information signal is judged to be received, the control unit  212  acts to switch the electronic cassettes  20 , other than the electronic cassette  20  sending the radiation detection information signal, into the sleep mode, thereby stopping the other electronic cassettes  20  (step S 306 ). Thus, the control unit  212  outputs a stop signal to the electronic cassettes  20 , other than the electronic cassette  20  sending the radiation detection information signal. The stop signal includes an instruction to stop the scan mode and switch into the sleep mode. When the stop signal is received, the other electronic cassettes  20  are switched from the scan mode into the sleep mode. Alternatively, the other electronic cassettes  20  may be shut down or switched into a standby mode. In the standby mode, electric power is supplied only to components (such as the memory  124  and the pixels  102 ) other than the essential components. In a case where the electric power is supplied from the bias supply  108  to the pixels  102  in the standby mode, the electric charges are stored in the pixels  102  but do not read out. 
     Steps S 308  to S 312  are carried out in the same manner as steps S 6  to S 10  of  FIG. 12 . To judge whether or not the data are sent to the electronic cassette  20 , from which the radiation detection information signal is sent, the data may include the identification information of the electronic cassette  20 . 
     The operation of the cassette control device  122  is shown in  FIG. 57  as described above. It should be noted that, in Modified Example 16, not one but a plurality of the cassette control devices  122  in all the electronic cassettes  20  that received the startup signal act to perform the operation of  FIG. 57 . 
     Steps S 321  to S 324  of  FIG. 57  are carried out in the same manner as steps S 21  to S 24  of  FIG. 13 . One cassette control device  122  detects the emission of the radiation  16 , and then sends the radiation detection information signal to the control unit  212  in the system controller  24  and the other cassette control devices  122  in the other electronic cassettes  20  in next step S 325 . The one cassette control device  122  may send the radiation detection information signal only to the control unit  212  or the other cassette control devices  122 . 
     Steps S 326  to S 334  are carried out in the same manner as steps S 25  to S 33  of  FIG. 13 . 
     When the irradiation start judgment part  132  judges in step S 323  that the digital electric signals stored in the memory  124  are not larger than the threshold value (S 323 : NO), the other cassette control devices  122  judge whether the radiation  16  is detected or not in the other electronic cassettes  20  (step S 335 ). This judgment is made based on the stop signal from the system controller  24  or the radiation detection information signal from the other electronic cassette  20 . Thus, in a case where the stop signal or the radiation detection information signal is received, the cassette control device  122  judges that the radiation  16  is detected in the other electronic cassette  20 . On the other hand, in a case where the stop signal and the radiation detection information signal are not received, the cassette control device  122  judges that the radiation  16  is not detected in the other electronic cassettes  20 . 
     When the radiation  16  is not detected in the other electronic cassettes  20  (S 335 : NO), the radiographic image capturing system  10  is returned to step S 323 . When the radiation  16  is detected in the other electronic cassette  20  (S 335 : YES), the cassette control devices  122  act to stop the scan mode and are switched into the sleep mode (step S 336 ). Alternatively, as described above, the cassette control devices  122  may be shut down or switched into the standby mode. 
     As described above, in Modified Example 16, a plurality of the electronic cassettes  20  can be used in the radiographic image capturing process. Therefore, the radiographic image can be obtained even if the user (such as the radiation technician) makes the mistake in selecting the electronic cassette  20 . Since the radiation  16  is detected by the radiation conversion panel  64 , a radiation detection means other than the radiation conversion panel  64  is not required, and the electronic cassette  20  can be reduced in size. 
     Furthermore, the electric charges stored in the pixels in a plurality of the rows are simultaneously read out in the scan mode, whereby the start of the emission of the radiation  16  can be judged rapidly and accurately. Since the electric charges stored in the pixels are summed up and read out, a significantly larger value is obtained under the emission of the radiation  16  than without the emission of the radiation  16 , whereby the start of the emission of the radiation  16  can be rapidly judged. Therefore, the electronic cassette  20  can be readily switched from the scan mode for simultaneously reading the electric charges in a plurality of the rows to the sequential readout mode for reading the electric charges row by row. Consequently, the start of the emission of the radiation  16  can be judged in a shorter irradiation time (using a smaller amount of the radiation  16 ), so that the energy of the radiation  16  can be efficiently utilized. 
     Since a plurality of the rows are simultaneously read out in the scan mode, each row can be controlled in a shorter period in the scan mode than in a row-by-row reading mode. At the start of acquiring the radiographic image information (which is practically used as the radiographic image), the electric charge difference between the pixels is smaller in a case where the electronic cassette  20  is switched from the scan mode to the sequential readout mode than in a case where the start of the emission of the radiation  16  is detected in the second readout mode. Thus, in Modified Example 16, generation of artifacts can be reduced. 
     Consequently, in Modified Example 16, the radiographic image can be more appropriately captured even if the user makes the mistake in selecting the electronic cassette  20 . 
     In Modified Example 16, when a plurality of the electronic cassettes  20  execute the scan mode and one electronic cassette  20  detects the radiation  16 , the one electronic cassette  20  sends the detection information to the other electronic cassettes  20  directly or through the system controller  24 . The other electronic cassettes  20  act to stop the scan mode in a case where they receive the detection information. In this case, the electronic cassettes  20  other than the one electronic cassette  20  (which has detected the radiation  16 ) can reduce the subsequent power consumption. 
     Though the other electronic cassettes  20  act to stop the scan mode and are switched into the sleep mode based on the stop signal from the system controller  24  or the radiation detection information signal from the one electronic cassette  20  in the above example, Modified Example 16 is not limited thereto. For example, only one of the stop signal and the radiation detection information signal may be utilized. Alternatively, the readout start signal from the electronic cassette  20  may be used instead of the radiation detection information signal. In addition, the system controller  24  may send the stop signal to the other electronic cassettes  20  depending on the readout start signal. In this case, the readout start signal is used also as the radiation detection information signal, so that the processing of the electronic cassette  20  can be simplified. 
     The contents of Modified Example 16 may be used in combination with Modified Examples 1 to 15. For example, in Modified Example 16, the electric charges may be read only from part of the pixels in the scan mode in the same manner as Modified Example 4. In this case, the electric power consumption or the calculation amount in the scan mode can be reduced. 
     Modified Example 17 
     In Modified Example 16, the radiographic image capturing process is performed in all the electronic cassettes  20  that receive the startup signal. However, in some cases, the electronic cassette  20  selected by mistake by the radiation technician do not satisfy the image capturing conditions at all. 
     Thus, in Modified Example 17, the electronic cassettes  20 , which satisfy the image capturing conditions, act to perform the image capturing process after the scan mode. On the other hand, the electronic cassettes  20 , which do not satisfy the image capturing conditions, do not perform the image capturing process, though they are switched into the scan mode. 
     The radiographic image capturing system  10  of Modified Example 17 has the same structure as that of Modified Example 16 ( FIG. 55 ). The operation of the system controller  24  and the console  26  in the radiographic image capturing system  10  in Modified Example 17 is substantially equal to that in Modified Example 16 ( FIG. 56 ). However, in step S 302  of  FIG. 56 , the control unit  212  acts to identify a plurality of the electronic cassettes  20  corresponding to the image capturing conditions and the number of images (the electronic cassettes  20  usable for the image capturing process). Then, in step S 303 , the control unit  212  sends, to the usable electronic cassettes  20 , a startup signal (first startup signal) for instructing the execution of the sequential readout mode after the scan mode. Meanwhile, the control unit  212  sends, to the unusable electronic cassettes  20 , a startup signal (second startup signal) for instructing the execution of the sleep mode after the scan mode. 
     In Modified Example 17, the operation of each cassette control device  122 , to which the first startup signal is sent from the control unit  212 , is performed in the same manner as Modified Example 16 ( FIG. 57 ). Meanwhile, the operation of each cassette control device  122 , to which the second startup signal is sent from the control unit  212 , is performed as shown in  FIG. 58 . 
     Steps S 341  to S 345 , S 347 , and S 348  of  FIG. 58  are carried out in the same manner as steps S 321  to S 325 , S 335 , and S 336  of  FIG. 57 . 
     The cassette control device  122  sends the radiation detection information signal in step S 345 , and is switched from the scan mode into the sleep mode in next step S 346 . The cassette control device  122  may be switched into the sleep mode after it receives a radiation detection information signal receipt acknowledgment from the system controller  24  or the other electronic cassette  20 . 
     In Modified Example 17, the following effect can be achieved in addition to the advantageous effects of Modified Example 16. In Modified Example 17, the system controller  24  receives the entered radiographic image capturing conditions, and selects the electronic cassettes  20  suitable for the image capturing conditions from a plurality of the electronic cassettes  20 . Then, if the radiation  16  is detected in the scan mode, the system controller  24  sends, to the selected electronic cassette  20  suitable for the image capturing conditions, an instruction to execute the sequential readout mode. Meanwhile, if the radiation  16  is detected in the scan mode, the system controller  24  sends, to the electronic cassettes  20  unsuitable for the image capturing conditions, an instruction not to execute the sequential readout mode but to send the radiation  16  detection information to the system controller  24 . If the radiation  16  detection information is sent from the electronic cassette  20  unsuitable for the image capturing conditions, the system controller  24  provides a warning to the user (such as the radiation technician) through the display device  28 . 
     Consequently, in a case where the electronic cassette  20  unsuitable for the image capturing conditions is selected by mistake, the system controller  24  can encourage the user to restart the image capturing process. 
     The contents of Modified Example 17 may be used in combination with Modified Examples 1 to 15. For example, in Modified Example 17, the electric charges may be read only from part of the pixels in the scan mode in the same manner as Modified Example 4. In this case, the electric power consumption or the calculation amount in the scan mode can be reduced. 
     The technical scope of the present invention is not limited to the above description of the embodiment. It will be apparent to those skilled in the art that various changes and modifications may be made therein. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims.