Patent Publication Number: US-2009218476-A1

Title: Radiation image pickup apparatus, its control method, and radiation image pickup system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a radiation image pickup apparatus, a radiation image pickup system, a control method of the radiation image pickup apparatus, and a program for allowing a computer to execute the control method. More particularly, the invention relates to a radiation image pickup apparatus having a sensor array constructed by two-dimensionally arranging pixels each including: a conversion element for converting a radiation from an object into an electric signal; and a transfer switching element for transferring the electric signal to an outside. 
     2. Description of the Related Art 
     In recent years, there has been known a radiation image pickup apparatus of flat panel type using a sensor array constructed by two-dimensionally arranging pixels each constructed by: a conversion element for converting a radiation into signal charges (electric signal); and a switching element such as a TFT or the like for transferring the electric signal to an outside. In such a flat panel type radiation image pickup apparatus, each of the conversion element and the switching element is made of a material such as amorphous silicon or polysilicon formed as a film on a glass substrate. In the radiation image pickup apparatus, generally, by performing matrix-driving using the switching elements such as TFTs or the like, the signal charges converted by the conversion elements are transferred to a reading circuit unit and read out. 
     The conventional radiation image pickup apparatus has pixels each including: a photodiode made of amorphous silicon as a conversion element; and a thin film transistor (TFT) as a switching element. The device has a sensor array constructed by two-dimensionally arranging those pixels and performs the matrix-driving. A bias voltage is applied from a power source to a common electrode side of the photodiode of each pixel through a bias line. 
     The conventional radiation image pickup apparatus in which the area sensor array constructed by two-dimensionally arranging the pixels each having the photodiode and the switching element is read out by the matrix-driving has simply been described above. The radiation image pickup apparatus with such a construction in which the area sensor array is read out by the matrix-driving has been disclosed in, for example, U.S. Pat. No. 6,330,303. 
     In the conventional radiation image pickup apparatus, there is a case where a technique called “pixel binning” in which the pixels (of a plurality of rows) connected to a same drive wiring are grouped and signals of the group pixels are added and read out is used. It is an object of the pixel adding to accomplish the improvement of a reading speed, adjustment of resolution, an increase in signal amount, and the like. The embodiment about the pixel binning in the horizontal scanning direction has also been disclosed in U.S. Pat. No. 6,330,303. 
     SUMMARY OF THE INVENTION 
     First, problems of the invention to be solved will be explained with reference to  FIGS. 10 and 11 .  FIG. 10  is a schematic constructional diagram in the conventional radiation image pickup apparatus for explaining the problems of the invention.  FIG. 11  is a timing chart showing the operation of the conventional radiation image pickup apparatus for explaining the problems of the invention. 
     As shown in  FIG. 10 , the conventional radiation image pickup apparatus has a sensor array  100  constructed by two-dimensionally arranging pixels  101  and performs matrix-driving. Each pixel  101  has: one of photodiodes (e.g. S 11 ) made of amorphous silicon serving as conversion elements; and one of thin film transistors (TFTs) (e.g. T 11 ) as switching elements. A bias voltage Vs has been applied from a power source  300  to common electrode sides of the PIN type photodiodes of each pixel  101  through a bias line  102 . 
     Gate electrodes of the switching elements of each pixel  101  in row direction are connected to common drive wirings Vg 1  to Vg 4 . The drive wirings Vg 1  to Vg 4  are connected to a gate driving device  400  constructed by a shift register or the like. Source electrodes of the switching elements in column direction are connected to common signal wirings Sig 1  to Sig 4 . Signal charges of each pixel  101  are converted into analog signals by a reading circuit unit  200  through the signal wirings Sig 1  to Sig 4 . The reading circuit unit  200  is constructed by amplifiers A 1  to A 4 , an analog multiplexer  201 , a buffer amplifier  202 , and the like. The analog signals converted by the reading circuit unit  200  are converted into digital signals by an A/D converter  500 . The digital signals are processed by an image processing unit  600  constructed by a memory, a processor, and the like and outputted to a monitor (not shown) or stored in a recording apparatus such as a hard disk or the like. 
     The operation of the conventional radiation image pickup apparatus will now be described with reference to  FIGS. 10 and 11 . 
     First, reset switches SW RC  provided for the amplifiers A 1  to A 4  are turned on by a reset signal RC which is generated from a timing generator (not shown). Thus, integration capacitors Cf of the amplifiers A 1  to A 4  and the signal wirings Sig 1  to Sig 4  are reset. 
     Subsequently, a pulse is applied to the drive wiring Vg 1  and the switching elements connected to the drive wiring Vg 1  are turned on. Thus, the signal charges generated in the photodiodes are transferred to the reading circuit unit  200  through the signal wirings Sig 1  to Sig 4 . The transferred signal charges are converted into voltages by the amplifiers A 1  to A 4  connected to the signal wirings Sig 1  to Sig 4 . 
     Subsequently, sampling and holding signals SH are applied to the reading circuit unit  200  from the timing generator (not shown), so that the output voltages from the amplifiers A 1  to A 4  are sampled and held into sampling and holding capacitors C SH . After that, the voltages which have been sampled and held in the S/H capacitors C SH  are converted into serial voltages by the analog multiplexer  201  synchronously with a clock MUX_CLK from the timing generator (not shown). The converted serial voltages are inputted as analog signals to the A/D converter  500  through the buffer amplifier  202 . The analog signals inputted to the A/D converter  500  are A/D converted and supplied as digital signals to the image processing unit  600  in accordance with resolution of the A/D converter  500 . 
     Subsequently, a pulse is applied to the drive wiring Vg 2  and the switching elements (T 21  to T 24 ) connected to the drive wiring Vg 2  are turned on. Thus, the signal charges generated in the photodiodes S 21  to S 24  are read out to the reading circuit unit  200  through the signal wirings Sig 1  to Sig 4 . Operations similar to those mentioned above are also repetitively executed to the drive wiring Vg 3  and Vg 4  and the signal charges in the photodiodes of the whole sensor array  100  are read out. 
     Although irradiating timing of light (or X-ray) is not mentioned in the above description, either continuous light (or continuous X-ray) or pulse light (or pulse X-ray) may be used fundamentally. 
     In the conventional radiation image pickup apparatus, there is a case where the technique called “pixel binning” in which the pixels connected to a same drive wiring are grouped and signals of the group pixels are added and read out is used. It is an object of the pixel adding to accomplish the improvement of the reading speed, the adjustment of the resolution, the increase in signal amount, or the like. The embodiment about the pixel binning in the horizontal scanning direction has also been disclosed in U.S. Pat. No. 6,330,303. 
     That is, the following constructions (1) to (3) are specifically shown in U.S. Pat. No. 6,330,303. 
     (1) The signals derived after the amplifiers connected to the signal wirings are added by using an adding circuit of an operational amplifier.
 
(2) The digital signals which were A/D converted by the A/D converter are digitally added by the image processing unit.
 
(3) For the signals derived after the amplifiers connected to the signal wirings, an amplification factor is changed in accordance with a photographing mode.
 
     However, it should be noted that the addition of the signals is performed after the outputs of the amplifiers in U.S. Pat. No. 6,330,303. 
     In such a radiation image pickup apparatus, since the analog signals after the amplifiers are added, there is a fear that noises of the amplifiers, noises of the adding circuit (addition of thermal noises of resistors and amplifiers constructing the adding circuit), and the like are multiplexed to the added signal. There is also a fear of a case where a variation in gains of the amplifiers connected to the signal wirings and the like become noise components in the added signal. In the case where the digital signals which were A/D converted by the A/D converter are digitally added, there is also a fear that a quantization error of the A/D converter is added. 
     That is, U.S. Pat. No. 6,330,303 has such a problem that when the pixel signals are added, nothing is considered with respect to a deterioration in characteristics due to the noises in the amplifiers or the noises in the adding circuit or a deterioration in characteristics due to the quantization noises of the A/D converter. Therefore, U.S. Pat. No. 6,330,303 has such a problem that the noises are multiplexed and noise resistance characteristics cannot be improved. 
     According to the pixel addition in the radiation image pickup apparatus, as compared with a non-addition method, the improvement of the reading speed, the adjustment of the resolution, the increase in signal amount according to the radiation of a small dose, and the like can be accomplished. That is, it is very useful in a radiation image pickup apparatus which can perform a motion image photography such as a radioscopy or the like in which a high reading speed, the radiation of a small dose, and high sensitivity are required. However, according to U.S. Pat. No. 6,330,303, when the pixel signals are added, there is a deterioration in characteristics due to the noises in the amplifiers, the noises in the adding circuit, or the quantization noises of the A/D converter. Therefore, in the radiation image pickup apparatus which can perform the motion image photography, according to the pixel addition disclosed in U.S. Pat. No. 6,330,303, there is a fear that the advantage of the pixel addition is decreased by the deterioration in characteristics due to the noises as mentioned above. 
     It is, therefore, an object of the invention to provide a radiation image pickup apparatus, a radiation image pickup system, a control method of the radiation image pickup apparatus, and a program for such a control method, in which when pixel signals are added, the improvement of noise resistance characteristics is realized. 
     According to the invention, there is provided a radiation image pickup apparatus comprising: a sensor array constructed by two-dimensionally arranging a plurality of pixels each having a conversion element for converting a radiation into an electric signal and a transfer switching element for transferring the electric signal to an outside; a plurality of signal wirings each adapted to connect the transfer switching elements of the pixels of the sensor array in a column direction; a reading circuit unit including a plurality of amplifiers which are provided in correspondence to said signal wirings and each of which amplifies said electric signal transferred from each of said transfer switching elements and reads out the amplified signal; a mode setting unit adapted to set a mode in the radiation image pickup apparatus; and a switching unit which can switch electrical connection among the plurality of signal wirings and electrical connection between a predetermined one of the plurality of signal wirings and the amplifier corresponding thereto, wherein the switching unit is arranged between the signal wiring and the amplifier and, in accordance with the setting of the mode, the switching unit switches a first state where the plurality of signal wirings are electrically connected and the predetermined signal wiring and the amplifier corresponding thereto are electrically disconnected and a second state where the plurality of signal wirings are electrically disconnected and the predetermined signal wiring and the amplifier corresponding thereto are electrically connected. 
     According to the invention, there is provided a control method for a radiation image pickup apparatus, comprising: a first step of setting a mode in the radiation image pickup apparatus including a sensor array constructed by two-dimensionally arranging a plurality of pixels each having a conversion element for converting a radiation into an electric signal and a transfer switching element for transferring the electric signal to an outside, a plurality of signal wirings each adapted to connect the transfer switching elements of the pixels of the sensor array in a column direction, a reading circuit unit including a plurality of amplifiers which are provided in correspondence to said signal wirings and each of which amplifies said electric signal transferred from each of said transfer switching elements and reads out the amplified signal, and a switching unit which can switch electrical connection among the plurality of signal wirings and electrical connection between a predetermined one of the plurality of signal wirings and the amplifier corresponding thereto; and a second step of switching a state of the switching unit on the basis of the setting of the mode in the first step to either a first state where the plurality of signal wirings are electrically connected and the predetermined signal wiring and the amplifier corresponding thereto are electrically disconnected or a second state where the plurality of signal wirings are electrically disconnected and the predetermined signal wiring and the amplifier corresponding thereto are electrically connected. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments described with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic constructional diagram of a radiation image pickup apparatus according to the first embodiment of the invention. 
         FIG. 2  is a timing chart showing the operation of the radiation image pickup apparatus according to the first embodiment of the invention. 
         FIG. 3  is a schematic cross sectional view of a pixel in a sensor array. 
         FIG. 4  is a timing chart showing the operation of a radiation image pickup apparatus according to the second embodiment of the invention. 
         FIG. 5  is a schematic constructional diagram of a radiation image pickup apparatus according to the third embodiment of the invention. 
         FIG. 6  is a schematic constructional diagram of a radiation image pickup apparatus according to the fourth embodiment of the invention. 
         FIG. 7  is a timing chart showing the operation of the radiation image pickup apparatus according to the fourth embodiment of the invention. 
         FIG. 8  is a schematic constructional diagram of a radiation image pickup apparatus according to the fifth embodiment of the invention. 
         FIG. 9  shows the sixth embodiment of the invention and is a schematic diagram showing an example in which a radiation image pickup apparatus is applied to a radio-diagnostic system. 
         FIG. 10  is a schematic constructional diagram of a radiation image pickup apparatus for explaining problems in the invention. 
         FIG. 11  is a timing chart showing the operation of the radiation image pickup apparatus for explaining the problems in the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the invention will be described hereinbelow with reference to the drawings. Although examples in which an X-ray is used as a radiation are shown in the embodiments of the invention, the radiation in the invention is not limited to the X-ray but other electromagnetic waves such as α-ray, β-ray, γ-ray, and the like are also incorporated. 
     First Embodiment 
       FIG. 1  is a schematic constructional diagram of a radiation image pickup apparatus according to the first embodiment of the invention. 
     As shown in  FIG. 1 , the radiation image pickup apparatus according to the first embodiment has: the sensor array  100 ; a reading circuit unit  210 ; the power source  300 ; a gate driving device  410 ; the A/D converter  500 ; the image processing unit  600 ; a mode setting unit  700 ; and a control unit  800 . 
     The sensor array  100  is constructed by two-dimensionally arranging the pixels  101  and performs the matrix-driving. Each pixel  101  has: one of the photodiodes (e.g. S 11 ) made of amorphous silicon corresponding to the conversion elements each for converting the radiation into the electric signal; and one of the thin film transistors (TFTs) (e.g. T 11 ) corresponding to the transfer switching elements each for transferring the electric signal of each photodiode to the outside. The bias voltage Vs has been applied from the power source  300  to the common electrode sides of the photodiodes of each pixel  101  through the bias line  102 . 
     The gate electrodes of the TFTs of each pixel  101  are connected to the common drive wirings Vg 1  to Vg 4  every row of each pixel. The drive wirings Vg 1  to Vg 4  are connected to the gate driving device  410  constructed by the shift register or the like. The source electrodes of the TFTs of each pixel  101  are connected to the common signal wirings Sig 1  to Sig 4  every column of each pixel. The signal charges as an electric signal in each pixel  101  are converted into the analog signals by the reading circuit unit  210 . The reading circuit unit  210  has the amplifiers A 1  to A 4 , the analog multiplexer  201 , the buffer amplifier  202 , and the like. The analog signals converted by the reading circuit unit  210  are converted into the digital signals by the A/D converter  500 . The digital signals are processed by the image processing unit  600  constructed by the memory, the processor, and the like and outputted to the monitor (not shown) or stored in the recording apparatus such as a hard disk or the like. 
     The amplifiers A 1  to A 4  are provided in correspondence to the signal wirings Sig 1  to Sig 4 , amplify the signal charges transferred from the TFTs, and read out the amplified signal charges. The gate driving device  410  drives the drive wirings Vg 1  to Vg 4  under the control of the control unit  800  in order to read out the signal charges of each pixel  101  connected to the drive wirings Vg 1  to Vg 4 . 
     As compared with the general device shown in  FIG. 10 , the radiation image pickup apparatus according to the first embodiment further has first switches SW 1 , second switches SW 2 , and an inverter  203  in the reading circuit unit  210 . Each switching unit is constructed by the first switch SW 1 , the second switch SW 2 , and the inverter  203 . Further, the radiation image pickup apparatus has the mode setting unit  700  and the control unit  800 . 
     The first switch SW 1  switches the electrical connection and the electrical disconnection between the signal wiring and the amplifier provided in correspondence to the signal wiring. In the embodiment, the first switches SW 1  are provided between the signal wirings Sig 2  and Sig 4  of the even-number columns and the amplifiers A 2  and A 4 , respectively. 
     The second switch SW 2  switches the electrical connection and the electrical disconnection among the plurality of (in the embodiment, two) different signal wirings. In the embodiment, as second switches SW 2 , there are provided switches for switching the electrical connection and the electrical disconnection between the signal wiring Sig 1  of the odd-number column and the signal wiring Sig 2  of the even-number column and between the signal wiring Sig 3  of the odd-number column and the signal wiring Sig 4  of the even-number column. The second switch SW 2  is arranged so as to be connected between the signal wiring and the amplifier. That is, it is arranged so as to connect the input stages of the amplifiers of a plurality of different signal wirings. Further, the second switch SW 2  is arranged at a position (the input stage of the first switch SW 1 ) closer to the pixel than that to the first switch SW 1 . Although the second switch SW 2  is constructed by the switch adapted to switch the electrical connection and the electrical disconnection between the two different signal wirings in the embodiment, in the invention, it is sufficient to use the switch which can switch the electrical connection and the electrical disconnection among a plurality of different signal wirings. For example, the second switch SW 2  may be constructed so as to switch the electrical connection and the electrical disconnection among four signal wirings. 
     A switch unit switches the electrical connection and the electrical disconnection between the first switch SW 1  and the second switch SW 2  on the basis of a control signal from the control unit  800 . 
     The mode setting unit  700  sets the mode in the radiation image pickup apparatus by switching a “normal reading mode” for reading out the electric signal from one pixel by the amplifier corresponding to the pixel and a “pixel binning mode” for adding the electric signals from a plurality of pixels and reading out the added electric signal by one of a plurality of amplifiers corresponding to each pixel. The mode setting unit  700  outputs a mode signal indicative of the set mode to the control unit  800 . 
     The control unit  800  is connected to the mode setting unit  700 , the reading circuit unit  210 , and the gate driving device  410 . On the basis of the setting of the mode by the mode setting unit  700 , the control unit  800  controls the switch unit, thereby controlling the change-over of the first switch SW 1  and the second switch SW 2 . 
     Specifically speaking, if the mode signal indicative of the setting of the “normal reading mode” is received from the mode setting unit  700 , the control unit  800  controls the inverter  203  so as to electrically connect the first switch SW 1  and electrically disconnect the second switch SW 2 . If the mode signal indicative of the setting of the “pixel binning mode” is received from the mode setting unit  700 , the control unit  800  controls the inverter  203  so as to electrically disconnect the first switch SW 1  and electrically connect the second switch SW 2 . 
     When the signal charges of each pixel  101  connected to the drive wirings Vg 1  to Vg 4  are read out, the control unit  800  controls the gate driving device  410  so as to drive the drive wirings Vg 1  to Vg 4  and scan. 
     The operation of the radiation image pickup apparatus according to the embodiment will now be described. 
       FIG. 2  is a timing chart showing the operation of the radiation image pickup apparatus according to the first embodiment of the invention. 
     First, the reset switches SW RC  provided for the amplifiers A 1  to A 4  are turned on by the reset signal RC which is generated from the timing generator (not shown) and the integration capacitors Cf of the amplifiers A 1  to A 4  and the signal wirings Sig 1  to Sig 4  are reset. 
     When the “normal reading mode” is set by the mode setting unit  700 , the control unit  800  outputs a control signal CTRL (specifically speaking, an “L” signal in the embodiment) regarding the “normal reading mode” to the switch unit. The switch unit which received the control signal CTRL electrically connects the first switch SW 1  and electrical disconnects the second switch SW 2 . The operation in the “normal reading mode” is similar to that shown in  FIG. 11 . That is, the signal charges of each pixel  101  are sent to the amplifiers A 1  to A 4  provided in correspondence to the signal wirings through the signal wirings Sig 1  to Sig 4  and converted into voltages here. 
     Subsequently, when the “pixel binning mode” is set by the mode setting unit  700 , the control unit  800  outputs the control signal CTRL (specifically speaking, an “H” signal in the embodiment) regarding the “pixel binning mode” to the switch unit. The s switch unit which received the control signal CTRL electrically disconnects the first switch SW 1  and electrical connects the second switch SW 2 . In this instance, the signal charges in the pixels connected to the signal wirings Sig 2  and Sig 4  of the even-number columns are added to the signal charges in the pixels connected to the signal wirings Sig 1  and Sig 3  of the odd-number columns by the second switches SW 2 , respectively. The added signal charges are converted into voltages by the amplifiers A 1  and A 3  of the odd-number columns, respectively. 
     In the first embodiment, in the “pixel binning mode”, the signal charges in the pixels of the even-number columns and the signal charges in the pixels of the odd-number columns are added in front of the amplifiers A 1  to A 4  (before the input stage) and the added signal charges are read out by the amplifiers A 1  and A 3  of the odd-number columns. Thus, when the pixel signals are added, as compared with the case where the adding circuit is provided after the amplifiers A 1  to A 4  or the case where the they are A/D converted by the A/D converter  500  and, thereafter, digitally added, the occurrence of the noise multiplex due to the noises in the amplifiers A 1  to A 4 , the noises in the adding circuit, the quantization noises of the A/D converter, or the like can be prevented. As compared with the general radiation image pickup apparatus, the improvement of the noise resistance characteristics can be realized. Particularly, in the radiation image pickup apparatus which can perform the motion image photography in which the high reading speed, the radiation of a small dose, and the high sensitivity are required, since the reduction in advantage of the pixel addition can be prevented, the effect of the invention becomes more typical. 
     Since it is sufficient that the reading circuit unit  210  executes the scan in the horizontal direction, that is the scan of the analog multiplexer  201  only to the signal wirings Sig 1  and Sig 3  of the odd-number columns, the reading speed can be also improved. Such an effect is particularly remarkable in the case where an ON time in each of the switching elements of each pixel  101  is shorter than the time necessary for the horizontal scan, in other words, in the case where the reading speed of the radiation image pickup apparatus is rate limited by the horizontal scan. 
     A cross sectional structure of the radiation image pickup apparatus according to the embodiment will now be described. 
       FIG. 3  is a schematic cross sectional view of the pixel in the sensor array. As shown in  FIG. 3 , each pixel  101  is constructed by forming the photodiode as a conversion element, the TFT as a switching element, and a wiring unit onto a glass substrate  10  as an insulating substrate. 
     The TFT is constructed by laminating the following layers onto the glass substrate  10 : a first metal thin film layer  11  serving as a gate electrode; an insulating layer  12  made of an amorphous silicon nitride film formed on the first metal thin film layer  11 ; a semiconductor layer  13  made of amorphous silicon formed on the insulating layer  12 ; n-type impurity semiconductor layers (n-layers)  14  separately formed in a source forming region and a drain forming region on the semiconductor layer  13 , respectively; and second metal thin film layers  15  formed in a source forming region and a drain forming region on the n-layers  14  and serving as a source electrode and a drain electrode, respectively. 
     The photodiode is constructed by laminating the following layers onto the glass substrate  10 : the second metal thin film layer  15  connected to the drain electrode of the TFT and serving as a lower electrode layer; a p-type impurity semiconductor layer (p-layer)  16  formed on the second metal thin film layer  15 ; a semiconductor layer  17  made of amorphous silicon formed on the p-layer  16 ; an n-type impurity semiconductor layer (n-layer)  18  formed on the semiconductor layer  17 ; and a third metal thin film layer  19  formed on the n-layer  18  and serving as an upper electrode layer. 
     The wiring unit is constructed by laminating the following layers: the insulating layer  12  made of the amorphous silicon nitride film formed on the glass substrate  10 ; the semiconductor layer  13  made of amorphous silicon formed on the insulating layer  12 ; the n-type impurity semiconductor layer (n-layer)  14  formed on the semiconductor layer  13 ; and the second metal thin film layer  15  formed on the n-layer  14  and serving as a wiring layer. 
     A protecting layer  20  made of the amorphous silicon nitride film or the like is provided over the photodiode, TFT, and wiring unit formed as films on the glass substrate  10  and the whole portions are covered with the protecting layer  20 . Since  FIG. 3  shows an example in the case of constructing an X-ray image pickup device using the X-ray as a radiation, a phosphor layer  22  as a wavelength converter is further arranged over the protecting layer  20  through an adhesive layer  21 . 
     Generally, the photodiode made of amorphous silicon as a main material is hardly sensitive to the X-ray. Therefore, as shown in  FIG. 3 , it is necessary that the photodiode is provided with the phosphor layer  22  as a wavelength converter to convert the X-ray into visible light is provided over the protecting layer  20  through the adhesive layer  21 . As a phosphor layer  22 , a layer made of gadolinium system or CsI (cesium iodide) as a main material is grown to a columnar crystal and such a crystal or the like is used. 
     When the X-ray transmitted through the object enters the phosphor layer  22 , the X-ray is converted into the visible light in the phosphor layer  22  and enters the photodiode. The signal charges generated in the semiconductor layer  17  of the photodiode are sequentially transferred to the reading circuit unit  210  by the TFT and read out. 
     Although the embodiment has been described with respect to the example in which the PIN-type photodiode made of amorphous silicon as a main material is used as a photoelectric conversion element, the invention is not limited to such an example. For instance, an MIS-type sensor or an element made of polysilicon as a main material can be also used as a photoelectric conversion element. A conversion element of what is called a direct converting type for absorbing the radiation such as an X-ray or the like and directly converting it into charges can be also used as a photoelectric conversion element. As a conversion element of the direct converting type in this case, there can be mentioned an element made of at least one of amorphous selenium, gallium arsenide, gallium phosphide, lead iodide, mercury iodide, CdTe, and CdZnTe as a main material. 
     Although the embodiment has been described with respect to the example in which a transistor obtained by forming amorphous silicon as a main material onto the glass substrate  10  is used as a TFT, the invention is not limited to such an example. For instance, a transistor made of polysilicon or an organic material as a main material can be also used. 
     Each device of the reading circuit unit  210  is generally constructed by an integrated circuit (IC) made of polysilicon as a main material. That is, together with the amplifiers A 1  to A 4 , the analog multiplexer  201 , and the like, the first switch SW 1 , the second switch SW 2 , and the switch change-over unit  203  are constructed on the insulating substrate in the integrated circuit made of polysilicon as a main material. Although each device of the reading circuit unit  210  is made of polysilicon as a main material in the embodiment, the invention is not limited to such an example. For instance, it may be made of amorphous silicon as a main material. It may be formed on a monocrystalline semiconductor substrate. 
     In the embodiment, the gate driving device  410  may be constructed by a shift register including the TFT made of amorphous silicon or polysilicon as a main material on the same glass substrate  10  as that of the TFT of the sensor array  100 . According to such a construction, since there is no need to separately provide the gate driving device  410 , such an effect is particularly remarkable for the cost reduction of the radiation image pickup apparatus. 
     Second Embodiment 
     A schematic construction of a radiation image pickup apparatus according to the second embodiment of the invention is similar to that of the radiation image pickup apparatus according to the first embodiment shown in  FIG. 1 . 
     In addition to the functions described in the first embodiment, if the mode signal indicative of the setting of the “pixel binning mode” is received from the mode setting unit  700 , the control unit  800  in the second embodiment controls the gate driving device  410  so as to simultaneously drive some of the drive wirings Vg 1  to Vg 4  and scan. That is, in the “pixel binning mode”, not only the addition of the pixel signals in the horizontal scanning direction but also the addition of the pixel signals in the vertical scanning direction is simultaneously executed. 
       FIG. 4  is a timing chart showing the operation of the radiation image pickup apparatus according to the second embodiment of the invention. A control signal CTRL 1  shown in  FIG. 4  is a control signal which is supplied from the control unit  800  shown in  FIG. 1  to the gate driving device  410 . A control signal CTRL 2  shown in  FIG. 4  is a control signal (control signal CTRL shown in  FIG. 1 ) which is supplied from the control unit  800  to the switch change-over unit  203 .  FIG. 4  shows the state where the gate driving device  410  has simultaneously driven the drive wirings Vg 1  and Vg 2  and has simultaneously driven the drive wirings Vg 3  and Vg 4  by the control signal CTRL 1 . 
     In the second embodiment, resolution in the horizontal direction and resolution in the vertical direction can be made coincide. In the example shown in  FIG. 4 , the signal charges of four pixels are added at the front stage of the amplifiers A 1  to A 4 . Therefore, as compared with the case where the adding circuit is provided after the amplifiers A 1  to A 4  or the case where the signal charges are A/D converted by the A/D converter  500  and, thereafter, digitally added, the occurrence of the noise multiplex due to the noises in the amplifiers A 1  to A 4 , the noises in the adding circuit, the quantization noises of the A/D converter, or the like can be prevented. Thus, the noise resistance characteristics can improved and, further, not only the horizontal scanning time but also the vertical scanning time can be shortened. Therefore, the reading speed can be raised. 
     The embodiment has been described with respect to the example in which the gate driving device  410  simultaneously drives the drive wirings Vg 1  and Vg 2  and simultaneously drives the drive wirings Vg 3  and Vg 4  by the control of the control unit  800 . However, in the invention, it is sufficient to use a construction in which some of the drive wirings Vg 1  to Vg 4  are simultaneously driven, for example, the four drive wirings Vg 1  to Vg 4  may be simultaneously driven. 
     A cross sectional structure of the radiation image pickup apparatus according to the second embodiment is similar to that of the first embodiment. The gate driving device  410  in the embodiment which can simultaneously scan a plurality of drive wirings may be constructed by a TFT or the like made of amorphous silicon or polysilicon as a main material on the same glass substrate  10  as that of the TFT of the sensor array  100 . For example, in the case of forming the gate driving device  410  by the TFT made of polysilicon as a main material, it is possible to form the gate driving device  410  by a method whereby after amorphous silicon was deposited, a process such as laser annealing or the like is performed to amorphous silicon so that it is converted into polysilicon. By forming the gate driving device  410  onto the same glass substrate  10  as that of the TFT of the sensor array  100  as mentioned above, there is no need to separately provide the gate driving device. Therefore, such an effect is particularly remarkable for the cost reduction of the radiation image pickup apparatus. 
     Third Embodiment 
       FIG. 5  is a schematic constructional diagram of a radiation image pickup apparatus according to the third embodiment of the invention. 
     As compared with the radiation image pickup apparatus according to the first embodiment of the invention shown in  FIG. 1 , in the radiation image pickup apparatus according to the third embodiment, the first switches SW 1  and the second switches SW 2  are formed on the same insulating substrate (glass substrate  10 ) as that of the pixels  101  having the photodiodes and the TFTs. 
     Each of the first switch SW 1  and the second switch SW 2  is made of amorphous silicon or polysilicon as a main material in a manner similar to each of the TFTs of a sensor array  110 . For example, in the case of forming the first switch SW 1  and the second switch SW 2  by polysilicon as a main material, it is also possible to use a method whereby after amorphous silicon was deposited, a process such as laser annealing or the like is performed to amorphous silicon so that it is converted into polysilicon. The operation of the radiation image pickup apparatus according to the third embodiment is similar to that of the radiation image pickup apparatus according to the first embodiment or the second embodiment. 
     Fourth Embodiment 
       FIG. 6  is a schematic constructional diagram of a radiation image pickup apparatus according to the fourth embodiment of the invention. 
     As compared with the integration capacitors Cf of the amplifiers A 1  to A 4  of the radiation image pickup apparatus according to the first embodiment shown in  FIG. 1 , the radiation image pickup apparatus according to the fourth embodiment of the invention has two integration capacitors Cf 1  and Cf 2  of different capacitance values (it is assumed that Cf 1 &lt;Cf 2 ). In accordance with the setting of the mode by the mode setting unit, the control unit  800  changes the integration capacitors Cf 1  and Cf 2  for accumulating the signal charges of the pixel  101 . 
     In the “pixel binning mode”, a larger amount of signal charges than that in the “normal reading mode” are transferred to the amplifiers A 1  to A 4 . A dynamic range of each of the amplifiers depends on the integration capacitor Cf. In order to prevent the saturation of the amplifier in the “pixel binning mode” and assure the dynamic range characteristics of the radiation image pickup apparatus, it is desirable to use the construction in which the integration capacitors Cf of the amplifiers can be switched in accordance with the mode. 
     For this purpose, if the “normal reading mode” is set by the mode setting unit  700 , the control unit  800  controls so as to accumulate the signal charges of the pixel  101  into the integration capacitor Cf 1 . If the “pixel binning mode” is set by the mode setting unit  700 , the control unit  800  controls so as to accumulate the signal charges of the pixel  101  into the integration capacitor Cf 2  whose capacitance is larger than that of the integration capacitor Cf 1 . 
       FIG. 7  is a timing chart showing the operation of the radiation image pickup apparatus according to the fourth embodiment of the invention.  FIG. 7  shows the case where the gate driving device  410  simultaneously drives the drive wirings Vg 1  and Vg 2  and simultaneously drives the drive wirings Vg 3  and Vg 4  by the control of the control unit  800 . The analog signals which are outputted from the amplifiers A 1  to A 4  are shown in  FIG. 7 . In addition to the analog signals in the case where integration capacitors Cf of the amplifiers have been switched (the integration capacitor Cf 1  in the “normal reading mode”; the integration capacitor Cf 2  in the “pixel binning mode”), the analog signals in the case where integration capacitors Cf of the amplifiers are not switched irrespective of the mode (the integration capacitor Cf 1  is fixedly used irrespective of the mode) are also shown in  FIG. 7  for the purpose of comparison. 
     As shown in  FIG. 7 , in the case of the construction in which the integration capacitors Cf are not switched, the saturation of the amplifier occurs for the dynamic range of the amplifier in the “pixel binning mode”. On the other hand, in the case of the construction in which the integration capacitors Cf are switched, it will be understood that the saturation of the amplifier for the dynamic range of the amplifier can be avoided even in the “pixel binning mode”. 
     In the embodiment, in addition to the effect in the first embodiment, the saturation of the amplifier in the “pixel binning mode” can be prevented and the dynamic range characteristics of the radiation image pickup apparatus can be assured. Thus, the improvement of the noise resistance characteristics, the reading speed characteristics, and the dynamic range characteristics of the radiation image pickup apparatus can be realized. Although the fourth embodiment has the construction in which the two kinds of integration capacitors in the amplifiers are provided, many kinds of integration capacitors may be provided. 
     Fifth Embodiment 
       FIG. 8  is a schematic constructional diagram of a radiation image pickup apparatus according to the fifth embodiment of the invention. In order to explain the radiation image pickup apparatus according to the fifth embodiment, 36 (6×6) pixels  101  in total are shown in a sensor array  120  shown in  FIG. 8 . 
     In the embodiment, in addition to in the “normal reading (1×1) mode”, a “(2×2) pixel binning mode” and a “(3×3) pixel binning mode” are set as modes which are set by the mode setting unit  700 . When those modes are set by the mode setting unit  700 , in the case of the “normal reading (1×1) mode”, the control unit  800  outputs the control signal CTRL 1  shown in  FIG. 8  and controls so as to drive the first switch SW 1 . In the case of the “(2×2) pixel binning mode”, the control unit  800  outputs the control signal CTRL 2  shown in  FIG. 8  and controls so as to drive a second switch SW 2 - 2  for adding the (2×2) pixel signals. Further, in the case of the “(3×3) pixel binning mode”, the control unit  800  outputs a control signal CTRL 3  shown in  FIG. 8  and controls so as to drive a second switch SW 2 - 3  for adding the (3×3) pixel signals. 
     Sixth Embodiment 
       FIG. 9  shows the sixth embodiment of the invention and is a schematic diagram showing an example in which a radiation image pickup apparatus is applied to a radio-diagnostic (image pickup) system. An X-ray diagnostic system in which the X-ray is used as a radiation will now be described. 
     An X-ray  6060  generated by an X-ray tube  6050  as an X-ray generating unit is transmitted through a chest region  5071  of an object (patient)  507  and enters an image sensor  6040 . Information showing the inside of a body of the object  507  is included in the X-ray which has entered the image sensor  6040 . In the image sensor  6040 , the incident X-ray is converted into visible light in a phosphor layer and the light is further photoelectrically converted, thereby obtaining signal charges (electric signal). The electric signal is converted into a digital signal, image-processed by an image processor  6070 , displayed as an image onto a display  6080  in a control room, and observed. 
     The radiation image pickup apparatus according to each of the foregoing embodiments corresponds to, for example, the image sensor  6040 . For instance, the mode setting unit  700 , the control unit  800 , the A/D converter  500 , the image processing unit  600 , and the like may be provided for the image processor  6070 . 
     The image data formed by the image process by the image processor  6070  can be transferred to a remote place by transmitting means such as a telephone line  6090  or the like, can be displayed onto a display  6081  or stored into storing means such as an optical disk or the like at another place such as a doctor room or the like or a doctor at a remote place can diagnose such image data. The image data can be also recorded as a film  6110  by a film processor  6100 . 
     Since the radiation image pickup apparatus according to each of the foregoing embodiments of the invention can accomplish both of the improvement of the noise resistance characteristics and the improvement of the reading speed, it is suitable for the X-ray image pickup system shown in  FIG. 9 . 
     The respective units shown in  FIGS. 1 ,  5 ,  6 , and  8  constructing the radiation image pickup apparatus according to each of the foregoing embodiments of the invention and the control method for the radiation image pickup apparatus can be realized by a method whereby a program stored in a RAM, a ROM, or the like of a computer operates. Such a program and a computer-readable storing medium in which the program has been stored are incorporated in the invention. 
     Specifically speaking, the program is recorded into the storing medium such as a CD-ROM and provided for the computer or it is provided thereto through various transmitting media. As a storing medium to record the program, besides the CD-ROM, a flexible disk, a hard disk, a magnetic tape, a magnetooptic disk, a non-volatile memory card, or the like can be used. As a transmitting medium of the program, it is possible to use a communicating medium (a wired line such as an optical fiber or the like, a wireless line, or the like) in a computer network (LAN, WAN such as Internet or the like, wireless communication network, or the like) system for propagating the program information as a carrier and supplying it. 
     The program is incorporated in the invention not only the case where the computer executes the supplied program, so that the functions of the radiation image pickup apparatus according to each of the foregoing embodiments of the invention are realized but also in the case where the program operates in cooperation with an OS (Operating System) which is operating in the computer, another application software, or the like and the functions of the radiation image pickup apparatus according to each of the foregoing embodiments of the invention are realized or the case where the all or a part of the processes of the supplied program are executed by a function expanding board or a function expanding unit of the computer and the functions of the radiation image pickup apparatus according to each of the foregoing embodiments of the invention are realized. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2005-236038, filed Aug. 16, 2005, which is hereby incorporated by reference herein in its entirety.