Patent Number: 
Section: description

The embodiments of the present invention will be described below with reference to the accompanying drawings. (First Embodiment) The present invention is applied to, e.g., a radiation imaging system 100 as shown in FIG. 1.  less than Arrangement of Radiation Imaging System 100 greater than  As shown in FIG. 1, the radiation imaging system 100 has an arrangement including an imaging device 110 for acquiring an image signal of an object (patient) 102 to be examined, a control device 111 for controlling the entire system 100, a storage device 112 for storing various data such as a control program for control processing by the control device 111 and the image, a display device 113 for displaying the image or the like, an image processing device 114 for executing arbitrary image processing for the image signal of the patient 102, which is obtained by the imaging device 110, an imaging condition instruction device 115 for instructing various imaging conditions in the imaging device 110, an imaging button 116 for instructing the system 100 to start imaging operation, and a radiation generator 117 for generating a radiation (e.g., X-rays) from a radiation tube 101 to the patient 102. The devices or components are connected to each other through a system bus 120 to exchange data. The imaging device 110 is located at a position where the radiation generated from the radiation tube 101 of the radiation generator 117 can be received through the patient 102. The imaging device 110 comprises a chest stand 103, grid 104, phosphor 105, sensor (two-dimensional solid-state image sensing element) 106, signal reading section 107, and grid moving section 108. The chest stand 103, grid 104, phosphor 105, and sensor 106 are arranged in this order from the side of the radiation tube 101 of the radiation generator 117.  less than Series of Operations of Radiation Imaging System 100 greater than  Outlines of the imaging procedure and radiation image generation process in the radiation imaging system 100 will be described here. The user (e.g., radiation technician) positions the patient 102 to the chest stand 103 and selectively inputs appropriate imaging conditions (e.g., tube voltage, tube current, irradiation time, type of sensor 106, and type of radiation tube 101) using the imaging condition instruction device 115. In this embodiment, the imaging conditions are manually inputted by the user through the imaging condition instruction device 115. However, the present invention is not limited to this. For example, the imaging conditions may be inputted through a network (not shown) connected to the imaging device 110. Next, the user presses the imaging button 116 to request the control device 111 to start imaging operation. After receiving the imaging operation start request from the user, the control device 111 performs initialization necessary in the system 100 and prompts the radiation generator 117 to irradiate the person with radiation. In accordance with the irradiation instruction from the control device 111, the radiation generator 117 generates radiation from the radiation tube 101. The radiation generated from the radiation tube 101 passes through the patient 102 and reaches chest stand 103. The chest stand 103 is exposed by the radiation transmitted through the patient 102 with a transmitted radiation distribution in accordance with the structure in the patient 102. Since the chest stand 103 is sufficiently transparent to the radiation, the radiation transmitted through the chest stand 103 reaches the grid 104. The grid 104 removes scattering ray components in the radiation transmitted through the chest stand 103 and sends only effective radiation components to the phosphor 185. The phosphor 105 converts the radiation (effective radiation) from the grid 104 into visible light in accordance with the spectral sensitivity of the sensor 106. The sensor 106 receives the radiation from the phosphor 105, converts the radiation light into an electrical signal (image signal) by two-dimensional photoelectric conversion, and accumulates it. The signal reading section 107 reads out the image signal accumulated in the sensor 106 and stores the signal in the storage device 112 as a radiation image signal. The image processing device 114 performs appropriate image processing for the radiation image signal stored in the storage device 112. The display device 113 displays the radiation image signal after processing by the image processing device 114.  less than Most Characteristic Operation and Arrangement of Radiation Imaging System 100 greater than  FIG. 2 is a flow chart showing operation control processing executed by the control device 111 for the system 100. FIGS. 3A to 3F are timing charts showing the operation control timing. The processing shown in FIG. 2 corresponds to processing from the above-described imaging condition input by the user to image signal read from the sensor 106. Step S201: The control device 111 recognizes an irradiation time Texp, the type of sensor 106 used for imaging, and the type of radiation tube 101 on the basis of imaging conditions selectively input by the user through the imaging condition instruction device 115. In accordance with the recognized information, the control device 111 determines control until radiation irradiation and control after radiation irradiation by processing from step S202. Step S202: The control device 111 determines a sensor initialization time Tss in accordance with the type of sensor 106. The sensor initialization time Tss changes depending on the type of sensor 106. For example, when the sensor 106 requires predischarge of a dark current, the pre-read time is the sensor initialization time Tss. From this time, signal accumulation in the sensor 106 starts. Step S203: The control device 111 determines a grid initialization time Tgs and grid oscillation convergence time Tge from the irradiation time Texp. More specifically, to reduce stripe image formation on the object by the grid 104, for example, radiation must be transmitted through stripes of 10 or more cycles. However, the moving distance of the grid 104 is limited. Hence, the moving speed of the grid 104 must be optimized in accordance with the irradiation time Texp. In addition, since the grid 104 generally has a focal point, the irradiation central position of radiation and the central position of the grid 104 must be aligned to obtain an image with a satisfactory quality. Hence, a time required until the optimum moving speed (target moving speed) of the grid 104 is obtained, and the position of the grid 104 reaches the irradiation central position (target position) of radiation corresponds to the grid initialization time Tgs. In this embodiment, the grid initialization times Tgs until the target moving speed and position of the grid 104 are obtained and the grid oscillation convergence times Tge required to converge device oscillation caused by movement are obtained as a table by experiments in correspondence with, e.g., various patterns of irradiation time Texp and moving speed of the grid 104 and stored in the storage device 112 in advance. The grid initialization time Tgs and grid oscillation convergence time Tge corresponding to the actually obtained irradiation time Texp are determined from the table information in the storage device 112. Step S204: The control device 111 determines a pre-irradiation delay time Txs and post-irradiation delay time Txe on the basis of the type of radiation tube 101. The pre-irradiation delay time Txs is a time after the radiation generator 117 is instructed to permit radiation irradiation until the radiation generator 117 actually starts radiation irradiation, and is determined by the type of radiation generator 117 or radiation tube 101. In this embodiment, the pre-irradiation delay times Txs corresponding to, e.g., various types of radiation generator 117 or radiation tube 101 are prepared as a table in advance, and a corresponding pre-irradiation delay time Txs is determined from the table information. The post-irradiation delay time Txe is a delay time after the elapse of irradiation time Texp until the radiation generator 117 actually ends the radiation irradiation. The post-irradiation delay time Txe is also determined in accordance with the same procedure as that for the pre-irradiation delay time Txs. Step S205: The control device 111 determines an irradiation delay time T1. The irradiation delay time T1 is a delay time after an imaging request is input by the user through the imaging button 116 until the radiation generator 117 actually starts radiation irradiation. Of the sensor initialization time Tss determined in step S202, the grid initialization time Tgs determined in step S203, and the pre-irradiation delay time Txs determined in step S204, the longest time is determined as the irradiation delay time T1. Step S206: The control device 111 determines a time table before irradiation. This time table is determined from the sensor initialization time Tss determined in step S202, the grid initialization time Tgs determined in step S203, and the pre-irradiation delay time Txs determined in step S204. More specifically, the control sequence and times (timings) of initialization of the sensor 106, start of drive of the grid 104, and radiation irradiation instruction (irradiation permission) to the radiation generator 117 after the imaging request input by the user through the imaging button 116 is recognized are determined by subtracting each delay time from the irradiation delay time T1 determined in step S205. The initialization timing of the sensor 106 is determined as xe2x80x9cT1xe2x88x92Tssxe2x80x9d. The drive start timing of the grid 104 is determined as xe2x80x9cT1xe2x88x92Tgsxe2x80x9d. The radiation irradiation instruction (irradiation permission) timing for the radiation generator 117 is determined as xe2x80x9cT1xe2x88x92Txsxe2x80x9d. Step S207: After control before radiation irradiation is determined in the above-described way, the control device 111 determines whether an imaging request is input by the user through the imaging button 116 and stands by until an imaging request is received. Step S208: Upon recognizing that an imaging request is input by the user through the imaging button 116, the control device 111 executes operation control according to the time table determined in step S206. Initialization of the sensor 106 is started after the elapse of xe2x80x9cT1xe2x88x92Tssxe2x80x9d, drive of the grid 104 is started after the elapse of xe2x80x9cT1xe2x88x92Tgsxe2x80x9d, and irradiation permission is executed after the elapse of xe2x80x9cT1xe2x88x92Txsxe2x80x9d. Step S209: The control device 111 stands by until the total time (T1+Texp+Txe) of the irradiation time (actual exposure time) Texp determined in step S201, the post-irradiation delay time Txe determined in step S204, and the irradiation delay time T1 determined in step S205 elapses. Step S210: When recognizing that the time (T1+Texp+Txe) has elapsed, the control device 111 stops driving the grid 104 through the grid moving section 108. Step S211: The control device 111 stands by until the grid oscillation convergence time Tge determined in step S203 elapses. Step S212: When recognizing that the grid oscillation convergence time Tge has elapsed, the control device 111 causes the signal reading section 107 to start reading out the signal accumulated in the sensor 106. In the operation control for the radiation imaging system 100 shown in the flow chart of FIG. 2, especially, since the operation stands by for the post-irradiation delay time Txe after the elapse of irradiation time Texp, stripe image formation on the object by the grid 104 can be prevented. In addition, since drive of the grid 104 is stopped, the influence of electromagnetic noise generated from the grid moving section 108 can be prevented. Furthermore, since the operation stands by for the grid oscillation convergence time Tge after the stop of drive of the grid 104, the influence of device oscillation can be prevented. Hence, after the imaging request from the user is recognized, the control device 111 controls the operation of the system 100 in accordance with the flow chart in FIG. 2, thereby acquiring a satisfactory image. The above operation control for the radiation imaging system 100 will be described below in more detail with reference to the timing charts shown in FIGS. 3A to 3F. The timing charts of FIGS. 3A to 3F explain timings after the imaging button 116 is pressed. In accordance with the imaging conditions input by the user, for example, Irradiation time Texp=100 ms Sensor initialization time Tss=200 ms Grid initialization time Tgs=300 ms Pre-irradiation delay time Txs=100 ms Grid oscillation convergence time Tge=300 ms Post-irradiation delay time Txe=100 ms are determined. In this case, the irradiation delay time T1 is the longest time of the sensor initialization time Tss, grid initialization time Tgs, and pre-irradiation delay time Txs and is determined by T1=max(Tss, Tgs, Txs)=Tgs=300 ms. Operation control until radiation irradiation is determined from these initial conditions. Next, control timings for sensor initialization, start of grid movement, and irradiation permission instruction after recognition of the imaging request are determined by subtracting a corresponding time required for operation from the irradiation delay time T1. Sensor initialization timing: T1xe2x88x92Tss 100 ms Grid movement start timing: T1xe2x88x92Tgs 0 ms Irradiation enable signal transmission timing: T1xe2x88x92Txsxe2x88x92200 ms Control timings after radiation irradiation are so determined that movement control for the grid 104 is stopped after the elapse of actual irradiation time obtained by adding the irradiation time Texp and post-irradiation delay time Txe to the irradiation delay T1, and the signal read from the sensor 106 is started after the elapse of grid oscillation convergence time Tge. That is, the grid control stop timing and signal read start timing are determined by Grid control stop timing: T1+Texp+Txe=500 ms Signal read start timing: T1+Texp+Txe+Tge=800 ms After the control timings are determined, an imaging request (FIG. 3A) input by the user by pressing the imaging button 116 is waited upon. When an imaging request is recognized, operation control for the radiation imaging system 100 is started on the basis of the determined control timings. First, movement (motion) of the grid 104 is started, as shown in FIG. 3B. The moving speed of the grid 104 acceleratingly increases and reaches an irradiation enable state after the elapse of 300 ms (grid initialization time Tgs=300 ms), as shown in FIG. 3C. Next, as shown in FIG. 3F, after the elapse of 100 ms (sensor initialization timing: T1xe2x88x92Tss=100 ms) from imaging request recognition, initialization of the sensor 106 is started. After the elapse of 200 ms (sensor initialization time Tss=200 ms), initialization of the sensor 106 is ended. As shown in FIG. 3D, after the elapse of 200 ms (irradiation enable signal transmission timing: T1xe2x88x92Txs=200 ms) from imaging request recognition, the radiation generator 117 is instructed to start irradiation. The radiation generator 117 starts actual irradiation after the elapse of 100 ms (preirradiation delay time Txs=100 ms), as shown in FIG. 3E. The end timing of sensor initialization (end timing of the sensor initialization time Tss), the end timing of grid movement (end timing of the grid initialization time Tgs), and the end timing of irradiation enable signal transmission (end timing of the pre-irradiation delay time Txs) match the end timing of the irradiation delay time T1 from the imaging request to actual irradiation. After the elapse of 500 ms (grid control stop timing: T1+Texp+Txe=500 ms) from imaging request recognition, actual irradiation by the radiation generator 117 is ended. At this time, movement control for the grid 104 is stopped, as shown in FIG. 3B, and the moving speed of the grid 104 gradually decreases. Along with this deceleration, the oscillation of the imaging device 110, that is generated by moving the grid 104, starts converging. After that, as shown in FIG. 3F, after the elapse of 800 ms (signal read start timing: T1+Texp+Txe+Tge=800 ms) from imaging request recognition, the signal reading section 107 is instructed to end signal accumulation in the sensor 106 and start reading the signal. At this time, the oscillation of the imaging device 110 has become so small that it does not affect the image quality. As a result, a satisfactory image can be obtained. (Second Embodiment) The present invention is applied to, e.g., a radiation imaging system 300 as shown in FIG. 4. This radiation imaging system 300 has the same arrangement as that of the radiation imaging system 100 shown in FIG. 1 except that a radiation detector 302 for detecting a radiation irradiation state and an oscillation measurement device 301 for measuring the oscillation state of a grid 104 are prepared in an imaging device 110. The same reference numerals as in the radiation imaging system 100 shown in FIG. 1 denote the same parts in the radiation imaging system 300 shown in FIG. 4, and a detailed description thereof will be omitted. Only parts different from the radiation imaging system 100 in FIG. 1 will be described in detail. FIG. 5 is a flow chart showing operation control processing executed by a control device 111 of this embodiment for the system 300. FIGS. 6A to 6H are timing charts showing the operation control timing. The same step numbers as in the flow chart of FIG. 2 denote the same processing steps in the flow chart of FIG. 5, and a detailed description thereof will be omitted. Step S201: The control device 111 recognizes an irradiation time Texp, the type of sensor 106 used for imaging, and the type of radiation tube 101 on the basis of imaging conditions selectively input by the user through an imaging condition instruction device 115. In accordance with the recognized information, the control device 111 determines control until radiation irradiation and control after radiation irradiation by processing from step S202. Step S202: The control device 111 determines a sensor initialization time Tss in accordance with the type of sensor 106. Step S203xe2x80x2: The control device 111 determines a grid initialization time Tgs (time until the grid 104 reaches the target moving speed and position) from the irradiation time Texp. Step S204xe2x80x2: The control device 111 determines a pre-irradiation delay time Txs (time after radiation irradiation permission is instructed to a radiation generator 117 until the radiation generator 117 actually starts radiation irradiation) on the basis of the type of radiation tube 101. Step S205: The control device 111 determines an irradiation delay time T1 (the longest time of the sensor initialization time Tss, grid initialization time Tgs, and pre-irradiation delay time Txs). Step S206: The control device 111 determines, as a time table before irradiation, the initialization timing of the sensor 106 as xe2x80x9cT1xe2x88x92Tssxe2x80x9d, the drive start timing of the grid 104 as xe2x80x9cT1xe2x88x92Tgsxe2x80x9d, and the radiation irradiation instruction (irradiation permission) timing for the radiation generator 117 as xe2x80x9cT1xe2x88x92Txsxe2x80x9d. Step S207: After control before radiation irradiation is determined in the above-described way, the control device 111 determines whether an imaging request is input by the user through an imaging button 116 and stands by until an imaging request is received. Step S208: Upon recognizing that an imaging request is input by the user through the imaging button 116, the control device 111 executes operation control according to the time table determined in step S206. Initialization of the sensor 106 is started after the elapse of xe2x80x9cT1xe2x88x92Tssxe2x80x9d. Drive of the grid 104 is started after the elapse of xe2x80x9cT1xe2x88x92Tgsxe2x80x9d. Irradiation permission is executed after the elapse of xe2x80x9cT1xe2x88x92Txsxe2x80x9d. Step S209xe2x80x2: The control device 111 determines on the basis of a detection signal output from the radiation detector 302 whether radiation irradiation by the radiation generator 117 is ended. Step S210: Upon recognizing that radiation irradiation by the radiation generator 117 is ended, the control device 111 stops driving the grid 104 through a grid moving section 108. Step S211xe2x80x2: The control device 111 determines on the basis of a measurement result from the oscillation measurement device 301 whether the oscillation of the grid 104 has converged. Step S212: When recognizing that the oscillation of the grid 104 has converged, the control device 111 causes a signal reading section 107 to start reading out the signal accumulated in the sensor 106. In the operation control for the radiation imaging system 300 shown in the flow chart of FIG. 5, especially when the end of radiation irradiation is recognized in accordance with the detection result from the radiation detector 302, drive of the grid 104 is stopped. For this reason, the influence of electromagnetic noise generated from the grid moving section 108 can be prevented. Furthermore, since the operation stands until it is determined on the basis of the measurement result from the oscillation measurement device 301 that the oscillation of the grid 104 has converged after the stop of drive of the grid 104, the influence of device oscillation can be prevented. Hence, after the imaging request from the user is recognized, the control device 111 controls the operation of the system 300 in accordance with the flow chart in FIG. 5, thereby acquiring a satisfactory image. The above operation control for the radiation imaging system 300 will be described below in more detail with reference to the timing charts shown in FIGS. 6A to 6H. The timing charts of FIGS. 6A to 6H explain timings after the imaging button 116 is pressed. In accordance with the imaging conditions input by the user, for example, Irradiation time Texp=100 ms Sensor initialization time Tss=200 ms Grid initialization time Tgs=300 ms Pre-irradiation delay time Txs=100 ms are determined. In this case, the irradiation delay time T1 is the longest time of the sensor initialization time Tss, grid initialization time Tgs, and pre-irradiation delay time Txs and is determined by T1=max(Tss, Tgs, Txs)=Tgs=300 ms. Operation control until radiation irradiation is determined from these initial conditions. Next, control timings for sensor initialization, start of grid movement, and irradiation permission instruction after recognition of the imaging request are determined by subtracting a corresponding time required for operation from the irradiation delay time T1. Sensor initialization timing: T1 Tss=100 ms Grid movement start timing: T1 Tgs=0 ms Irradiation enable signal transmission timing: T1xe2x88x92Txs=200 ms After the control timings are determined, an imaging request (FIG. 6A) input by the user by pressing the imaging button 116 is waited upon. When an imaging request is recognized, operation control for the radiation imaging system 300 is started on the basis of the determined control timings. First, movement (motion) of the grid 104 is started, as shown in FIG. 6B. Simultaneously, the oscillation detection signal representing that the grid 104 is in a moving state is set at High level, as shown in FIG. 6G. The moving speed of the grid 104 acceleratingly increases and reaches an irradiation enable state after the elapse of 300 ms (grid initialization time Tgs=300 ms), as shown in FIG. 6C. Next, as shown in FIG. 6H, after the elapse of 100 ms (sensor initialization timing: T1xe2x88x92Tss=100 ms) from imaging request recognition, initialization of the sensor 106 is started. After the elapse of 200 ms (sensor initialization time Tss=200 ms), initialization of the sensor 106 is ended. As shown in FIG. 6D, after the elapse of 200 ms (irradiation enable signal transmission timing: T1xe2x88x92Txs=200 ms) from imaging request recognition, the radiation generator 117 is instructed to start irradiation. The radiation generator 117 starts actual irradiation after the elapse of 100 ms (pre-irradiation delay time Txs=100 ms), as shown in FIG. 6E. Simultaneously, the radiation detection signal representing radiation irradiation is set at High level, as shown in FIG. 6F. When radiation irradiation is ended, and the output from the radiation detector 302 becomes smaller than a predetermined threshold value, it is determined that irradiation is ended. As shown in FIG. 6F, the radiation detection signal is set at Low level. Along with this processing, movement control for the grid 104 is stopped, as shown in FIG. 6B. The moving speed of the grid 104 gradually decreases. The oscillation state of the grid 104 at this time is observed by the oscillation measurement device 301. When the oscillation of the imaging device 110, that is generated by moving the grid 104, starts converging, and it is recognized that the output from the oscillation measurement device 301 becomes smaller than a predetermined oscillation amount, the oscillation detection signal is set at Low level, as shown in FIG. 6G. As shown in FIG. 6F, the signal reading section 107 is instructed to end signal accumulation in the sensor 106 and start reading the signal. At this time, the oscillation of the imaging device 110 has become so small that it does not affect the image quality. As a result, a satisfactory image can be obtained. The object of the present invention is achieved even by supplying a storage medium which stores software program codes for implementing the functions of the first and second embodiments in a system or apparatus and causing the computer (or a CPU or MPU) of the system or apparatus to read out and execute the program codes stored in the storage medium. In this case, the program codes read out from the storage medium implement the functions of the first and second embodiments by themselves, and the storage medium which stores the program codes constitutes the present invention. As a storage medium for supplying the program codes, for example, a ROM, a floppy disk, hard disk, optical disk, magnetooptical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card or the like can be used. The functions of the first and second embodiments are implemented not only when the readout program codes are executed by the computer, but also when the operating system (OS) running on the computer performs part or all of actual processing on the basis of the instructions of the program codes. The functions of the first and second embodiments are also implemented when the program codes read out from the storage medium are written in the memory of a function expansion board inserted into the computer or a function expansion unit connected to the computer. The CPU of the function expansion board or function expansion unit performs part or all of actual processing on the basis of the instructions of the program codes. As has been described above, in the above embodiments, the timing when the irradiation means is permitted to perform irradiation is determined from the initialization time of the image sensing means (e.g., two-dimensional solid-state image sensing element) and the irradiation delay time (delay time after irradiation execution instruction, i.e., irradiation permission is issued until actual irradiation is performed) of the irradiation means (e.g., radiation generation means). Therefore, imaging operation control for an imaging request and initialization of the image sensing element can be parallelly executed. Accordingly, the time delay from the imaging request to actual irradiation can be shortened. Additionally, the timing when the irradiation means is permitted to perform irradiation is determined from the initialization time of the image sensing means and the initialization time of grid movement (delay time until the grid moves to an appropriate target position), or the initialization time of the image sensing means, the irradiation delay time of the irradiation means, and the initialization time of grid movement. Therefore, imaging operation control for an imaging request and initialization of the image sensing element and/or grid movement can be parallelly executed. Accordingly, the time delay from the imaging request to actual irradiation can be shortened. Furthermore, since grid movement such as the grid position or speed can be controlled in consideration of the irradiation delay time corresponding to the irradiation means used for imaging, a satisfactory image without any grid stripe image formation on the object can be obtained. Hence, according to the above embodiments, a satisfactory image can be obtained at a desired imaging timing. For example, when the present invention is applied to radiation imaging, a satisfactory radiation image without any grid stripe image formation on the object can be provided, and any diagnostic error in image diagnosis can be reliably prevented. The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention, the following claims are made.