Radiographic apparatus, radiographic system, radiographic apparatus control method, and program

Abstract

To provide a radiographic apparatus that can highly accurately perform irradiation stop control of radiation from a radiation generator and reduce deterioration of image quality due to detected pixels.SOLUTION: Provided is a radiographic apparatus, including: an imaging unit in which are arranged a plurality of pixels including an imaging pixel that generates a signal used for generation of a radiographic image and a detection pixel that generates a signal indicating a dose of irradiated radiation; a control unit for stopping reading of a signal indicating a radiation dose from the detection pixel when a detected radiation dose based on the signal indicating the radiation dose is equal to or greater than one of a first threshold value that changes with time and a second threshold value that is different from the first threshold value; an output unit for outputting a stop signal for stopping irradiation of radiation when the detected dose is equal to or greater than the first threshold value or when the detected dose is equal to or greater than the second threshold value and a standby time has elapsed; and a generation unit for generating a radiographic image using signals stored in the imaging pixels and the detection pixels.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a radiation imaging apparatus, a radiation imaging system, a control method for a radiation imaging apparatus, and a program. [Background technology]

[0002] 2. Description of the Related Art Currently, radiation imaging devices equipped with flat panel detectors (FPDs) made of semiconductor materials are in widespread use as radiation imaging devices used for medical image diagnosis and non-destructive testing using radiation such as X-rays.

[0003] Some radiography devices monitor the dose of irradiated radiation (accumulated dose) and, when the accumulated dose reaches a threshold, stop irradiating radiation by, for example, outputting an irradiation stop signal to a radiation generating device to stop irradiation of radiation. This operation is called automatic exposure control (AEC), and can, for example, prevent overirradiation of radiation.

[0004] As such a radiation imaging apparatus, for example, a radiation imaging apparatus that includes a dose detection unit that detects the dose of radiation reaching the imaging area within the imaging area of ​​an FPD has been proposed. Patent Document 1 describes a technology for stopping irradiation with high accuracy by transmitting an irradiation stop timing notification before the irradiation stop timing arrives, taking into account the delay time until the radiation from a radiation generating device stops.

[0005] Furthermore, Patent Document 2 describes a technology that suppresses degradation of image quality by comparing the read-out dose detection signal with a preset threshold value, turning off a switch element when the comparison result is obtained, and leaving dose information in the detection pixel and performing correction. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2023-70098 A [Patent Document 2] JP 2013-135390 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the technology described in Patent Document 1, since no signal remains in the detection pixel, dose information of the detection pixel is lost, and the image quality of the generated radiographic image may be degraded. In addition, in the technology described in Patent Document 2, since no signal remains in the detection pixel in a case where irradiation is stopped before the comparison result is obtained, dose information of the detection pixel is lost, and the image quality of the generated radiographic image may be degraded. In addition, Patent Document 2 does not state anything about the delay time until irradiation is stopped.

[0008] In consideration of such problems, one embodiment of the present disclosure has an object to provide a radiation imaging device that can control the stop of radiation irradiation from a radiation generating device with high accuracy and reduce degradation of image quality due to detection pixels. [Means for solving the problem]

[0009] A radiographic imaging apparatus according to one embodiment of the present disclosure includes an imaging unit having a plurality of pixels arranged to detect radiation, the plurality of pixels including imaging pixels that generate signals used to generate a radiographic image, and detection pixels that generate signals indicative of the dose of the irradiated radiation; a control unit that controls the plurality of pixels, the control unit stopping reading of the signal indicative of the dose from the detection pixel when a detected dose based on the signal indicative of the dose of radiation is equal to or greater than either a first threshold that changes with time or a second threshold different from the first threshold; an output unit that outputs a stop signal to stop the irradiation of the radiation when the detected dose is equal to or greater than the first threshold, or when the detected dose is equal to or greater than the second threshold and a waiting time has elapsed; and a generation unit that generates a radiographic image using signals accumulated in the imaging pixels and the detection pixels. Effect of the Invention

[0010] According to an embodiment of the present disclosure, it is possible to perform highly accurate control of stopping irradiation of radiation from a radiation generating device, and to reduce degradation of image quality due to detection pixels. [Brief description of the drawings]

[0011] [Figure 1A] 1 shows an example of a schematic configuration of a radiation imaging apparatus according to a first embodiment. [Figure 1B] 3 shows an example of a circuit configuration of an amplifier unit according to the first embodiment. [Diagram 2] 1 shows an example of a schematic configuration of a radiation imaging system according to a first embodiment. [Figure 3A] 5 is a flowchart showing an example of a series of control methods for photographing a subject according to the first embodiment. [Figure 3B] 10 is a flowchart showing another example of a series of control methods for photographing a subject according to the first embodiment. [Figure 4] 4 shows an example of the relationship between the dose and the change over time of a threshold set by a threshold change control unit according to the first embodiment. [Diagram 5] 4 shows the operation of the radiation imaging apparatus according to the first embodiment. [Figure 6] 10 is a flowchart showing an example of a series of control methods for photographing a subject according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, exemplary embodiments for carrying out the present disclosure will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of components described in the following embodiments are arbitrary and can be changed according to the configuration of an apparatus to which the present disclosure is applied or various conditions. In addition, in the drawings, the same reference numerals are used between the drawings to indicate elements that are the same or functionally similar.

[0013] In the following embodiments, a radiography system using X-rays as an example of radiation will be described, but the radiography system according to the present disclosure may use other types of radiation. Here, the term radiation includes electromagnetic radiation such as X-rays and gamma rays, as well as particle radiation such as alpha rays, beta rays, particle beams, proton beams, heavy ion beams, and meson beams.

[0014] First Embodiment Hereinafter, a radiation imaging apparatus, a radiation imaging system, and a method for controlling a radiation imaging apparatus according to a first embodiment of the present disclosure will be described with reference to Fig. 1A to Fig. 5. Fig. 1A shows an example of a schematic configuration of a radiation imaging apparatus 100 according to this embodiment. The radiation imaging apparatus 100 is provided with a sensor unit 221 having a sensor function and a communication unit 223 for communicating with the outside. The sensor unit 221 is provided with a power supply circuit 140 for supplying voltage, a drive circuit 150 for driving pixels, a readout circuit 160 for reading out signals from the pixels, a signal processing unit 170 for processing the readout signals, and a control unit 180 for controlling each component.

[0015] The sensor unit 221 is provided with a plurality of pixels arranged in the imaging region IR to form a plurality of rows and a plurality of columns, a plurality of drive lines 110, and a plurality of signal lines 120. The plurality of drive lines 110 are arranged corresponding to the plurality of rows of pixels, and each drive line 110 corresponds to one of the pixel rows. The plurality of signal lines 120 are arranged corresponding to the plurality of columns of pixels, and each signal line 120 corresponds to one of the pixel columns.

[0016] The multiple pixels include multiple imaging pixels 101 used to acquire a radiation image, one or more detection pixels 104 used to monitor the amount of radiation exposure, and one or more correction pixels 107 used to correct the amount of radiation exposure. The sensitivity of the correction pixels 107 to radiation is lower than the sensitivity of the detection pixels 104 to radiation. The correction pixels 107 are used to correct, for example, temperature fluctuation components and offset components of the radiation exposure dose.

[0017] The imaging pixel 101 is provided with a conversion element 102 that converts radiation into an electric signal, and a switch element 103 that connects the corresponding signal line 120 and the conversion element 102 to each other. The detection pixel 104 is provided with a conversion element 105 that converts radiation into an electric signal, and a switch element 106 that connects the corresponding signal line 120 and the conversion element 105 to each other. The detection pixel 104 is arranged so as to be included in a row and column formed by a plurality of imaging pixels 101. The correction pixel 107 is provided with a conversion element 108 that converts radiation into an electric signal, and a switch element 109 that connects the corresponding signal line 120 and the conversion element 108 to each other. The correction pixel 107 is arranged so as to be included in a row and column formed by a plurality of imaging pixels 101. In FIG. 1A, the imaging pixel 101, the detection pixel 104, and the correction pixel 107 are distinguished from each other by applying different hatching to the conversion element 102, the conversion element 105, and the conversion element 108.

[0018] The conversion element 102, the conversion element 105, and the conversion element 108 may be composed of a scintillator that converts radiation into light and a photoelectric conversion element that converts light into an electrical signal. The scintillator is generally formed in a sheet shape so as to cover the imaging region IR, and is shared by a plurality of pixels. Alternatively, the conversion element 102, the conversion element 105, and the conversion element 108 may be composed of a conversion element that directly converts radiation into an electrical signal.

[0019] The switch element 103, the switch element 106, and the switch element 109 may each include a thin film transistor (TFT) whose active region is made of a semiconductor such as amorphous silicon or polycrystalline silicon.

[0020] A first electrode of the conversion element 102 is connected to a first main electrode of the switch element 103, and a second electrode of the conversion element 102 is connected to a bias line 130. One bias line 130 extends in the column direction and is commonly connected to second electrodes of a plurality of conversion elements 102 arranged in the column direction. The bias line 130 receives a bias voltage VS from a power supply circuit 140. Second main electrodes of the switch elements 103 of one or more imaging pixels 101 included in one column are connected to one signal line 120. Control electrodes of the switch elements 103 of one or more imaging pixels 101 included in one row are connected to one drive line 110.

[0021] The detection pixel 104 and the correction pixel 107 also have the same pixel configuration as the imaging pixel 101, and are connected to a corresponding bias line 130, a corresponding drive line 110, and a corresponding signal line 120. The detection pixel 104 and the correction pixel 107 are exclusively connected to the signal line 120. That is, the correction pixel 107 is not connected to the signal line 120 to which the detection pixel 104 is connected. Furthermore, the detection pixel 104 is not connected to the signal line 120 to which the correction pixel 107 is connected. The imaging pixel 101 may be connected to the same signal line 120 as the detection pixel 104 or the correction pixel 107.

[0022] The driving circuit 150 is configured to supply driving signals to the pixels to be driven through the multiple driving lines 110 in accordance with control signals from the control unit 180. In this embodiment, the driving signals are signals for turning on switch elements included in the pixels to be driven. The switch elements of each pixel are turned on by a high-level signal and turned off by a low-level signal. Therefore, this high-level signal is called a driving signal. By supplying the driving signal to the pixel, the signal accumulated in the conversion element of this pixel becomes readable by the readout circuit 160. When the driving line 110 is connected to at least one of the detection pixel 104 and the correction pixel 107, the driving line 110 is called a detection driving line 111.

[0023] The readout circuit 160 is configured to read out signals from a plurality of pixels through a plurality of signal lines 120. The readout circuit 160 is provided with a plurality of amplifiers 161, a multiplexer 162, and an analog-to-digital converter (hereinafter, AD converter) 163. Each of the plurality of signal lines 120 is connected to a corresponding one of the plurality of amplifiers 161 in the readout circuit 160. One signal line 120 corresponds to one amplifier 161. The multiplexer 162 selects the plurality of amplifiers 161 in a predetermined order, and supplies a signal from the selected amplifier 161 to the AD converter 163. The AD converter 163 converts the supplied signal into a digital signal and outputs it.

[0024] The signals read out from the imaging pixels 101 by the readout circuit 160 are supplied to a signal processing unit 170, which performs processing such as calculation and storage. The signal processing unit 170 is provided with a calculation unit 171 and a storage unit 172. The calculation unit 171 generates a radiographic image based on the signals read out from the imaging pixels 101, and supplies the generated radiographic image to the control unit 180. The storage unit 172 can store the read out signals and the generated radiographic image.

[0025] The signals read out from the detection pixel 104 and the correction pixel 107 by the readout circuit 160 are supplied to the signal processing unit 170, and the signal processing unit 170 performs processing such as calculation and storage. Specifically, the signal processing unit 170 outputs information indicating irradiation of radiation to the radiation imaging apparatus 100 based on the signals read out from the detection pixel 104 and the correction pixel 107. For example, the signal processing unit 170 detects irradiation of radiation to the radiation imaging apparatus 100, and determines the irradiation amount and / or dose (accumulated achieved dose) D of radiation. In addition, the signal processing unit 170 can use the signal read out from the detection pixel 104 together with the signal read out from the imaging pixel 101 to generate a radiation image. Furthermore, the signal processing unit 170 may use the signal read out from the correction pixel 107 together with these signals to generate a radiation image. The storage unit 172 can also store the signals read out from these pixels.

[0026] The control unit 180 controls the drive circuit 150 and the readout circuit 160 based on information from the signal processing unit 170. The control unit 180 controls, for example, the start and end of exposure (accumulation of charges corresponding to irradiated radiation by the imaging pixels 101) based on information from the signal processing unit 170.

[0027] To determine the radiation exposure dose, the control unit 180 controls the drive circuit 150 to scan only the detection drive lines 111 and to make it possible to read out only signals from the detection pixels 104 and the correction pixels 107. Next, the control unit 180 controls the readout circuit 160 to read out signals from columns corresponding to the detection pixels 104 and the correction pixels 107 and output them as information indicating the radiation exposure dose. Through such an operation, the radiation imaging apparatus 100 can obtain exposure information at the detection pixels 104 during radiation exposure.

[0028] FIG. 1B shows an example of a detailed circuit configuration of the amplifier unit 161. The amplifier unit 161 is provided with a differential amplifier circuit AMP and a sample-and-hold circuit SH. The differential amplifier circuit AMP amplifies and outputs a signal appearing on the signal line 120. The control unit 180 can reset the potential of the signal line 120 by supplying a control signal φR to the switch element of the differential amplifier circuit AMP. The output from the differential amplifier circuit AMP can be held by the sample-and-hold circuit SH. The control unit 180 causes the sample-and-hold circuit SH to hold a signal by supplying a control signal φSH to the switch element of the sample-and-hold circuit SH. The signal held in the sample-and-hold circuit SH is read out by the multiplexer 162.

[0029] Next, the configuration of the radiation imaging system according to this embodiment will be described with reference to Fig. 2. Fig. 2 shows an example of a schematic configuration of a radiation imaging system 200 according to this embodiment. In this embodiment, the radiation imaging system 200 can be used particularly for medical purposes. However, the radiation imaging system 200 may also be used for other purposes, such as non-destructive testing. The radiation imaging system 200 includes a radiation generating device 210 that generates radiation, a radiation imaging device 100 that detects radiation and generates a radiation image, and a control device 230 that controls the operations of the radiation generating device 210 and the radiation imaging device 100.

[0030] The radiation generating device 210 irradiates radiation toward a subject (not shown) based on the control of the control device 230 (more specifically, the imaging control unit 231). The radiation generating device 210 includes, for example, a radiation tube which is an example of a radiation generating unit that generates radiation, and a collimator that defines the beam spread angle of the radiation generated by the radiation tube.

[0031] The radiation imaging apparatus 100 may include, for example, an FPD. The radiation imaging apparatus 100 includes a sensor unit 221, a threshold determination unit 222, a communication unit 223, a threshold change control unit 224, and a timer unit 225.

[0032] As described above, the sensor unit 221 is provided with the imaging pixels 101, the detection pixels 104, and the correction pixels 107, which are two-dimensionally distributed. The sensor unit 221 detects radiation irradiated from the radiation generation device 210 and incident thereon. The radiation imaging device 100 can detect information (dose information) of a two-dimensional distribution of the amount of radiation that has reached an imaging element (conversion element) in the sensor unit 221, and generate radiation image data. Thereafter, the radiation imaging device 100 transmits the generated radiation image data to the control device 230 via the communication unit 223. The control device 230 can acquire and process the radiation image data captured by the radiation imaging device 100.

[0033] The threshold determination unit 222 determines whether the radiation dose has reached a threshold value, using the dose information detected by the sensor unit 221. The threshold determination unit 222 calculates the radiation dose (accumulated reached dose) detected by the sensor unit 221, and when it is determined that the radiation dose has reached the threshold value, causes the control unit 180 to stop reading out signals indicating the dose from the detection pixels 104.

[0034] Furthermore, when the threshold determination unit 222 determines that the radiation dose has reached the threshold, or when the radiation dose has reached the threshold and the standby time has elapsed, the threshold determination unit 222 transmits (outputs) an irradiation stop signal 226 to the control device 230 via the communication unit 223. When the control device 230 receives the irradiation stop signal 226 (irradiation stop notification) from the radiation imaging apparatus 100 via the communication unit 233, the imaging control unit 231 of the control device 230 performs irradiation stop control to stop the radiation irradiation from the radiation generation device 210. Specifically, the imaging control unit 231 transmits an irradiation stop signal 236 to the radiation generation device 210 and performs irradiation stop control. At the same time, the imaging control unit 231 returns a response to the reception of the irradiation stop signal 226 to the radiation imaging apparatus 100 via the communication unit 233. Note that, if no response is received for a certain period of time after transmitting the irradiation stop signal 226, the radiation imaging apparatus 100 can transmit the irradiation stop signal 226 to the control device 230 again.

[0035] The threshold determination unit 222 can hold an irradiation start threshold for detecting the start of irradiation, in addition to the threshold for transmitting the irradiation stop signal 226. When the dose detected by the sensor unit 221 reaches the irradiation start detection threshold, the threshold determination unit 222 notifies the threshold change control unit 224 of that effect.

[0036] The threshold change control unit 224 controls the change of the threshold for transmitting an irradiation stop signal. When the threshold determination unit 222 notifies the threshold change control unit 224 that the dose has reached the irradiation start threshold, the threshold change control unit 224 determines the time point as a threshold change reference point. The threshold change control unit 224 changes the threshold for transmitting an irradiation stop signal based on the elapsed time from the threshold change reference point while referring to the counter of the timer unit 225.

[0037] The communication unit 223 may be configured using any communication interface, and is capable of wired and wireless communication with the control device 230. Prior to imaging, the radiation imaging device 100 communicates with the communication unit 233 of the control device 230 via the communication unit 223, and can count the communication response time between the two devices with the timer unit 225. The threshold change control unit 224 calculates a communication delay time based on the counted communication response time, and holds the communication delay time TDc. The threshold change control unit 224 reflects the calculated communication delay time TDc in the threshold setting.

[0038] The threshold determination unit 222, the threshold change control unit 224, and the timer unit 225 may be included in the control unit 180. The calculation unit 171, the control unit 180, the threshold determination unit 222, the threshold change control unit 224, and the timer unit 225 may be configured using one or more arbitrary processors and a program read from a storage unit (not shown). The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processor may also be a GPU (Graphical Processing Unit) or an FPGA (Field-Programmable Gate Array). These components may also be configured by a circuit or the like that performs a specific function, such as an ASIC. The storage unit (not shown) that stores the storage unit 172 and the program may be configured by using any memory, optical disk, SSD (Solid State Drive), or other arbitrary storage medium.

[0039] Next, the control device 230 will be described. The control device 230 includes an imaging control unit 231, an imaging condition setting unit 232, a communication unit 233, an image processing unit 234, and a display unit 235. The imaging control unit 231 controls radiation imaging using the radiation generation device 210 and the radiation imaging device 100. The control device 230 can communicate with the radiation imaging device 100 via the communication unit 233. The control device 230 is connected to the radiation generation device 210, and the imaging control unit 231 can transmit an irradiation stop signal 236 to the radiation generation device 210 to stop radiation irradiation from the radiation generation device 210, thereby performing irradiation stop control.

[0040] The imaging condition setting unit 232 sets imaging condition data including imaging condition information input by, for example, an operator. The imaging conditions may include, for example, the imaging part of the subject, the tube voltage and tube current in the radiation generating device 210, a target value Dref of the dose (accumulated reached dose) of radiation that passes through the subject and reaches the radiation imaging device 100, and the like. Here, the dose generally means the accumulated reached dose during radiation irradiation, and therefore, hereinafter, the accumulated reached dose is used as the dose. However, a dose value similar to the accumulated reached dose or a dose value linked to the accumulated reached dose may be used as the dose value.

[0041] The communication unit 233 may be configured using any communication interface, and is capable of communicating with the radiation imaging apparatus 100 in a wired and wireless manner.

[0042] The image processing unit 234 can perform image processing such as gradation processing and noise reduction processing on the radiation image data transmitted from the radiation imaging apparatus 100. The image processing unit 234 can transmit the radiation image data after the image processing to the display unit 235.

[0043] The display unit 235 may include any monitor or the like, and may display on the monitor a radiological image or the like based on the radiological image data transmitted from the image processing unit 234. The display unit 235 may include a monitor or the like connected to the control device 230, or may include a monitor or the like integrated into the control device 230.

[0044] The control device 230 can be configured by a computer provided with a processor and a memory. The control device 230 may be configured by a general computer, or may be configured by a computer dedicated to the radiation imaging system.

[0045] Each component of the control device 230 other than the display unit 235 can be configured using, for example, one or more processors such as CPUs and a program read from a storage unit (not shown). The processor may be, for example, an MPU, a GPU, or an FPGA. Each component of the control device 230 other than the display unit 235 may be configured using an integrated circuit that performs a specific function such as an ASIC. The internal configuration of the control device 230 may include a graphics control unit such as a GPU, an input / output control unit such as a keyboard, a display, or a touch panel, and the like. The storage unit (not shown) may be configured using any memory or any storage medium such as an optical disk or SSD.

[0046] The timing of transmitting the irradiation stop signal 226 from the radiation imaging apparatus 100 according to this embodiment to the control device 230 can be set to a timing that takes into consideration the delay time until irradiation of radiation stops, in addition to the above-mentioned communication delay time. Here, the communication delay time is a delay time related to communication when transmitting the irradiation stop signal 226 from the radiation imaging apparatus 100 to the control device 230. Moreover, the delay time until irradiation of radiation stops is a delay time from when the control device 230 transmits an irradiation stop signal 236 for stopping irradiation of radiation to when irradiation of radiation stops in the radiation generation device 210.

[0047] The time when radiation irradiation is stopped in the radiation generating device 210 is the time when the tube voltage in the radiation tube of the radiation generating device 210 starts to drop or the time when the tube voltage has dropped completely. Here, when setting the delay time based on the time when the tube voltage has dropped completely, the delay time can be set by taking into consideration the time of the unsteady period from when the tube voltage in the radiation tube starts to drop until it has dropped completely, multiplied by a coefficient considering the change in dose and radiation quality. More specifically, the delay time TD includes a steady period Ta from when the signal is transmitted until the tube voltage starts to drop, and an unsteady period Tb from when the tube voltage starts to drop until it has dropped completely. At this time, the unsteady period Tb is multiplied by a coefficient k (here, the coefficient k is 1 or less) and added to the steady period Ta, since the tube voltage in the radiation tube drops. That is, the delay time TD when the unsteady period Tb is taken into consideration can be determined based on the following formula. TD = Ta + kTb

[0048] In this embodiment, the delay time TD can be acquired for each radiation generation device before irradiation with radiation for radiography of the subject (before imaging). A value actually measured when the radiography device 100 is installed can be used as the delay time TD. Furthermore, the imaging environment and the radiation generation device 210 to be used may be registered in a database in advance, and the delay time TD may be calculated by referring to the database. The threshold change control unit 224 can acquire the delay time TD in advance and set a threshold taking the delay time TD into consideration.

[0049] 3A is a flowchart showing an example of a processing procedure in a series of control methods from the start to the end of imaging of a subject in the radiation imaging system 200 according to this embodiment. In the imaging process according to this embodiment, a dose (accumulated reaching dose) threshold Dth, a time change of the threshold Dth, and a dose threshold Dthcor required for correcting a radiographic image are set, and radiation imaging of the subject is performed. Specifically, the threshold change control unit 224 sets the threshold Dth, the time change of the threshold Dth, and the dose threshold Dthcor based on a delay time TD stored in advance, a communication delay time TDc acquired in advance, and a target dose value Dref.

[0050] First, in step S301, the imaging condition setting unit 232 receives an instruction to start imaging input by the operator via an input unit (not shown), and sets imaging condition information (irradiation condition information) according to the instruction from the operator, for example. Here, the imaging condition setting unit 232 sets the tube voltage and tube current of the radiation tube, the target value Dref of the dose, the delay time TD, and the threshold value Dthcor, etc., as the imaging condition information. Thereafter, the imaging condition setting unit 232 transmits the acquired instruction to start imaging and the set imaging condition information to the radiation imaging apparatus 100. Note that the value of the delay time TD and / or the threshold value Dthcor may be stored in any of the devices constituting the radiation imaging system 200, and the imaging condition setting unit 232 may refer to the stored value. In addition, the threshold value Dthcor of the dose required for correcting the radiation image may be determined, for example, as a ratio to the target value Dref (for example, 60% of the target value Dref), or may be determined as an absolute value based on the dose information required for correcting the radiation image.

[0051] Next, in step S302, the threshold change control unit 224 sets the dose threshold Dth, its time change, and the threshold Dthcor based on the dose target value Dref, delay time TD, and communication delay time TDc set in step S301. The setting of the dose threshold Dth, its time change, and the threshold Dthcor will be described later with reference to FIG.

[0052] Next, in step S303, the imaging control unit 231 transmits an irradiation execution signal for irradiating radiation to the radiation generating device 210 together with the imaging condition information received from the imaging condition setting unit 232 in step S301. In response to this, the radiation generating device 210 irradiates radiation to the subject under irradiation conditions based on the imaging condition information received from the imaging condition setting unit 232.

[0053] Next, in step S304, the threshold change control unit 224 changes the threshold to be compared with the dose according to the elapsed time from the threshold change reference point. More specifically, when the threshold Dth that changes with time is greater than the threshold Dthcor in the elapsed time, the threshold change control unit 224 changes the threshold to be compared with the dose from the threshold Dth to the threshold Dthcor. In step S304, when the threshold Dth that changes with time is equal to or less than the threshold Dthcor in the elapsed time, the threshold change control unit 224 determines not to change the threshold to be compared with the dose from the threshold Dth, and the process proceeds to step S305. On the other hand, when the threshold Dth that changes with time is greater than the threshold Dthcor in the elapsed time, the threshold change control unit 224 determines to change the threshold to be compared with the dose from the threshold Dth to the threshold Dthcor, and the process proceeds to step S306.

[0054] In step S305, first, the threshold determination unit 222 calculates a value representative of the radiation dose detected by the sensor unit 221, and calculates a cumulative value of the values ​​representative of the radiation dose. Note that the value representative of the radiation dose here may be a maximum value, an average value, a median value, or the like of the dose. In the following description, the cumulative value of the values ​​representative of the radiation dose is described as a cumulative reached dose D. However, in the following, the dose value compared with the dose threshold Dth and the dose threshold Dthcor is not limited to the cumulative reached dose D, and may be a dose similar to the cumulative reached dose or a value linked to the cumulative reached dose, etc.

[0055] The threshold determination unit 222 compares the calculated cumulative reach dose D with the threshold Dth set in step S302, and determines whether the cumulative reach dose D is smaller than the threshold Dth. If the result of this determination is that the cumulative reach dose D is smaller than the threshold Dth (step S305 / YES), the process proceeds to step S304. On the other hand, if the result of the determination in step S305 is that the cumulative reach dose D is not smaller than the threshold Dth (the cumulative reach dose D is equal to or greater than the threshold Dth) (step S305 / NO), the process proceeds to step S307.

[0056] In step S306, first, the threshold determination unit 222 calculates a value representative of the radiation dose detected by the sensor unit 221, and calculates a cumulative value of the value representative of the radiation dose. The calculation method of the cumulative value representative of the radiation dose may be the same as the method in step S305. The threshold determination unit 222 compares the calculated cumulative reach dose D with the threshold Dthcor set in step S302, and determines whether the cumulative reach dose D is smaller than the threshold Dthcor. If the result of this determination is that the cumulative reach dose D is smaller than the threshold Dthcor (YES in step S306), the process repeats step S306. On the other hand, if the result of the determination in step S306 is that the cumulative reach dose D is not smaller than the threshold Dthcor (the cumulative reach dose D is equal to or greater than the threshold Dthcor) (NO in step S306), the process proceeds to step S307'.

[0057] In step S307, since the cumulative reached dose D has exceeded (reached) the threshold Dth, the threshold determination unit 222 issues a stop instruction to the control unit 180 to stop the readout operation. Having received the stop instruction, the control unit 180 causes the drive circuit 150 to stop outputting a drive signal to the pixel to be driven. This turns off the switch element of the pixel to be driven, and the operation of accumulating dose information is started. When the output of the drive signal is stopped, the process proceeds to step S309.

[0058] On the other hand, in step S307', since the cumulative reached dose D exceeds (reaches) the threshold value Dthcor, the threshold value determination unit 222 issues a stop instruction to the control unit 180 to stop the readout operation. The control unit 180, which has received the stop instruction, causes the drive circuit 150 to stop outputting a drive signal to the pixel to be driven. This turns off the switch element of the pixel to be driven, and the operation of accumulating dose information is started. When the output of the drive signal is stopped, the process proceeds to step S308.

[0059] In step S308, since the pixel to be driven is performing an accumulation operation, the detected radiation dose is not read out, and the cumulative reached dose D calculated based on the read dose does not increase. However, in reality, radiation continues to be irradiated, so the actual cumulative reached dose D increases over time. Therefore, in step S308, the threshold determination unit 222 predicts the timing at which the cumulative reached dose D that has actually reached the sensor unit 221 reaches the threshold Dth based on the calculated cumulative reached dose D and the elapsed time from the threshold change reference point. In other words, the threshold determination unit 222 predicts the timing at which the irradiation stop signal 226 for stopping the irradiation of radiation from the radiation generation device 210 is output. The details of the prediction method will be described later with reference to FIG. 4. When the predicted timing is reached, the process proceeds to step S309.

[0060] In step S309, since the cumulative achieved dose D has exceeded (reached) the threshold value Dth or is predicted to exceed it, the radiation imaging apparatus 100 transmits an irradiation stop signal 226 to the control device 230 via the communication unit 223. When the control device 230 receives the irradiation stop signal, the imaging control unit 231 transmits an irradiation stop signal 236 to the radiation generation device 210 and performs irradiation stop control.

[0061] At this time, a communication delay time TDc is required for transmitting the irradiation stop signal 226 from the radiation imaging apparatus 100 to the control device 230. Furthermore, a delay time TD is required from when the imaging control unit 231 transmits the irradiation stop signal 236 to the radiation generation apparatus 210 until the radiation irradiation is actually stopped in the radiation generation apparatus 210. Therefore, radiation continues to be irradiated during the communication delay time TDc and the delay time TD. In contrast, the threshold value Dth is a threshold value set in consideration of the communication delay time TDc and the delay time TD. Therefore, by transmitting the irradiation stop signal in step S309, the radiation irradiated during the communication delay time TDc and the delay time TD can bring the actually irradiated cumulative reached dose D closer to the target value Dref of the cumulative reached dose D.

[0062] Next, in step S310, the drive circuit 150 controls the imaging element in the sensor unit 221 to stop conversion to dose information. The calculation unit 171 of the signal processing unit 170 generates radiation image data using the signal read out by the readout circuit 160. The control unit 180 transmits the generated radiation image data to the control device 230 via the communication unit 223.

[0063] In step S311, the image processing unit 234 of the control device 230 performs image processing such as gradation processing and noise reduction processing on the radiation image data received from the radiation imaging apparatus 100. Thereafter, the image processing unit 234 transmits the radiation image data after the image processing to the display unit 235.

[0064] In step S312, the display unit 235 outputs and displays a radiographic image based on the radiographic image data received from the image processing unit 234 on a monitor or the like, and presents the radiographic image to the operator. When the process of step S312 ends, the process of the flowchart related to radiography of the subject shown in Fig. 3A ends.

[0065] Next, the process of setting the cumulative reach dose threshold Dth, the time change of the threshold Dth, and the threshold Dthcor in step S302 in Fig. 3A will be described with reference to Fig. 4. When setting the time change of the cumulative reach dose threshold Dth, if a positive determination is made in step S305 (step S305 / YES), the threshold change control unit 224 performs the same process as the setting of the threshold Dth in step S302.

[0066] Fig. 4 is a diagram showing an example of the threshold value Dth according to the present embodiment, the change in the threshold value Dth over time, and the relationship between the threshold value Dthcor and the cumulative reached dose D. Fig. 4 shows the relationship between the dose D (cumulative reached dose D) shown on the vertical axis and the time (elapsed time) shown on the horizontal axis.

[0067] First, the threshold Dth and its change over time will be described. As shown in Fig. 4, the threshold change control unit 224 performs control to change the threshold Dth according to the time elapsed from the start of radiation irradiation. As an example, as shown in Fig. 4, the threshold change control unit 224 performs control to increase the threshold Dth according to the elapsed time. Here, the starting point for measuring the elapsed time is the threshold change reference point O shown in Fig. 4.

[0068] As for the threshold change reference point O, as described above, when the threshold determination unit 222 determines that the accumulated reached dose D detected by the sensor unit 221 has reached the irradiation start threshold, the threshold determination unit 222 notifies the threshold change control unit 224 of that point as the threshold change reference point O. Note that in this embodiment, it is assumed that the accumulated reached dose D detected by the sensor unit 221 is used to determine whether the accumulated reached dose D has reached the irradiation start threshold when determining the threshold change reference point O. On the other hand, when the S / N ratio (signal-to-noise ratio) of the dose detected by the sensor unit 221 is sufficiently high, the threshold determination unit 222 may use the dose per sample instead of the reached dose to perform the irradiation start threshold reach determination.

[0069] The threshold change control unit 224 uses the timer unit 225 to count the elapsed time from the threshold change reference point O, and controls to change (increase) the threshold Dth according to the elapsed time. In this embodiment, as shown in Fig. 4, the change in the threshold Dth over time is continuously changed with respect to the elapsed time, but the threshold Dth may be expressed as a step function that changes stepwise with respect to the elapsed time, for example, taking into account memory capacity. In this case, the length of the time segment of the step function related to the threshold Dth may be different for each time segment.

[0070] In this embodiment, the threshold value Dth for the elapsed time T can be set to satisfy the following formula (1) using the elapsed time T, the delay time TD, the communication delay time TDc, and the target value Dref of the cumulative arrival dose. Dth(T)=T / (T+(TD+TDc))×Dref ···(1) That is, as shown in formula (1), the threshold change control unit 224 can change the threshold Dth according to the elapsed time T, and set the time change of the threshold Dth based on the target value Dref, the delay time TD, and the communication delay time TDc. When a step function is used as the threshold Dth, a function can be set such that each step of the step intersects with formula (1).

[0071] Next, the process of setting the threshold Dthcor will be described. As shown in Fig. 4, the threshold change control unit 224 according to this embodiment sets the threshold Dthcor as a certain constant value. As described above, the threshold Dthcor may be determined based on a predetermined ratio of the target value Dref, and in the example shown in Fig. 4, the threshold Dthcor intersects with the threshold Dth at the position of point P.

[0072] Here, the threshold value Dthcor can be determined so that dose information required for correcting the radiographic image remains in the detection pixel 104. For example, the threshold value Dthcor may be determined from a correction limit such that the S / N ratio of the generated radiographic image is acceptable in terms of image quality, based on the S / N ratio. More specifically, the threshold value Dthcor can be determined proportionally to the target value Dref from an acceptable S / N ratio, based on the amount of noise N and the target value Dref.

[0073] Also, the threshold value Dthcor may change with time, like the threshold value Dth. In such a case, for example, the threshold value Dthcor may be set to decrease with time as a linear expression of time. Also, the threshold value Dthcor may be set to decrease with time as a linear expression of time taking into account the S / N ratio. In these cases, the longer the irradiation time, the more dose information can be left in the detection pixel 104, and for example, deterioration of the S / N ratio due to the influence of temperature drift or the like can be suppressed. Also, the threshold value Dthcor may be set to be constant until or after a predetermined time, or may be set to change with time.

[0074] Next, a specific threshold determination method (stop notification determination method) using the thresholds Dth and Dthcor will be described. First, in Fig. 4, the point P is defined as the boundary, and the region from the threshold change reference point O to point P based on the time axis is defined as region 1, and the region after point P is defined as region 2. In this case, in region 1, threshold Dth≦threshold Dthcor, and in region 2, threshold Dth>threshold Dthcor.

[0075] First, the operation of the radiation imaging apparatus 100 according to the threshold determination method in the region 1 will be described. In the region 1, since the threshold Dth≦threshold Dthcor, the threshold determination unit 222 determines whether the cumulative reached dose D detected by the sensor unit 221 is equal to or greater than the threshold Dth that changes with the elapsed time shown in FIG. 4. When the cumulative reached dose D is equal to or greater than the threshold Dth (step S305 / NO), in step S307 in FIG. 2, the threshold determination unit 222 issues a stop instruction to the control unit 180 to stop the readout operation. Specifically, the control unit 180 that has received the stop instruction causes the drive circuit 150 to stop outputting a drive signal to the pixel to be driven. As a result, the switch element of the pixel to be driven is turned off, and the accumulation operation of dose information is started.

[0076] Thereafter, the radiation imaging apparatus 100 transmits an irradiation stop signal 226 to the control device 230. Upon receiving the irradiation stop signal 226, the imaging control unit 231 transmits an irradiation stop signal 236 to the radiation generating apparatus 210 to stop the irradiation of radiation from the radiation generating apparatus 210, thereby performing irradiation stop control. At this time, radiation continues to be irradiated for the communication delay time TDc and the delay time TD.

[0077] In the example shown in FIG. 4, when radiation with a high dose rate is incident on the radiation imaging apparatus 100, the cumulative radiation dose 401 is high As a result, the irradiation time T high At this point, the radiation imaging apparatus 100 transmits an irradiation stop signal 226 to the control device 230, and thereafter, the irradiation of radiation by the radiation generation device 210 is stopped at the timing when the cumulative achieved dose 401 reaches the target value Dref.

[0078] The threshold value Dth is a threshold value that takes into consideration the communication delay time TDc and the delay time TD, so when the irradiation from the radiation generating device 210 actually stops, radiation of the target value Dref reaches the radiation imaging device 100. Therefore, in region 1, the threshold value Dth is used to stop outputting the irradiation stop notification signal and the drive signal to the pixel to be driven.

[0079] Furthermore, dose information according to the radiation output irradiated from when the switch element 106 of the detection pixel 104 is turned off until irradiation is stopped can be accumulated in the detection pixel 104. When the cumulative reached dose D in the region 1 reaches the threshold value Dth, the radiation irradiated to the radiation imaging apparatus 100 is radiation with a relatively high dose rate. Therefore, the irradiation time T at which the cumulative reached dose D becomes equal to or greater than the threshold value Dth is high Even if an irradiation stop signal 226 is sent in the terminating state, the amount of dose information accumulated in the detection pixels 104 until the irradiation of radiation stops will be sufficient for use in correcting the radiographic image. Therefore, the calculation unit 171 of the radiography apparatus 100 can correct the pixel output with higher accuracy than when information is lost by correcting the pixel using the dose information accumulated in the detection pixels 104.

[0080] Next, the operation of the radiography apparatus 100 according to the threshold determination method in the region 2 will be described. In the region 2, since the threshold Dth>the threshold Dthcor, the cumulative reached dose D reaches the threshold Dthcor before the threshold Dth. Therefore, in the region 2, the threshold determination unit 222 determines whether the cumulative reached dose D detected by the sensor unit 221 is equal to or greater than a certain threshold Dthcor shown in FIG. 4. When the cumulative reached dose D is equal to or greater than the threshold Dthcor (step S306 / NO), in step S307' in FIG. 2, the threshold determination unit 222 issues a stop instruction to the control unit 180 to stop the readout operation. Specifically, the control unit 180 that has received the stop instruction causes the drive circuit 150 to stop outputting a drive signal to the pixel to be driven. As a result, the switch element of the pixel to be driven is turned off, and the accumulation operation of the dose information is started.

[0081] Thereafter, the threshold determination unit 222 predicts the timing to output a radiation stop notification signal. The threshold determination unit 222 can calculate the gradient (first-order approximation) of the cumulative reached dose that changes over time, for example, by using the cumulative reached dose D at the time when the cumulative reached dose D reaches the threshold Dthcor and time information (elapsed time) from the threshold change reference point O. Thereafter, the threshold determination unit 222 can calculate the remaining time (standby time) until the intersection of the first-order approximation of the cumulative reached dose and the threshold Dth, by using the calculated gradient information.

[0082] Putting this into a formula, the waiting time Twait is expressed as the following formula (2) using the elapsed time T, the target value Dref, the delay time TD, and the communication delay time TDc. Twait=(Dref-D(T)) / (D(T) / T)-(TD+TDc) ···(2)

[0083] After the cumulative achieved dose D reaches the threshold value Dthcor, the radiation imaging apparatus 100 waits for a waiting time Twait and transmits an irradiation stop signal 226 to the control device 230. Upon receiving the irradiation stop signal 226, the imaging control unit 231 transmits an irradiation stop signal 236 to the radiation generation apparatus 210 to stop the irradiation of radiation from the radiation generation apparatus 210, thereby performing irradiation stop control. At this time, radiation continues to be irradiated for the communication delay time TDc and the delay time TD.

[0084] In the example shown in FIG. 4, when radiation with a low dose rate is incident on the radiation imaging apparatus 100, the cumulative radiation dose 402 is low The accumulated dose 402 reaches the threshold Dth at 100 s. However, when the accumulated dose 402 reaches the threshold Dthcor, the detection pixel 104 starts accumulating, so the detected accumulated dose 402 does not change with time. Therefore, the threshold determination unit 222 predicts the timing at which the accumulated dose that actually reaches the sensor unit 221 will reach the threshold Dth, and calculates the waiting time Twait until that timing. The accumulated dose that actually reaches the sensor unit 221 after the waiting time Twait has elapsed is equal to or greater than the threshold Dth, so that the irradiation time T low At this point, the radiation imaging apparatus 100 transmits an irradiation stop signal 226 to the control device 230. Thereafter, the imaging control unit 231 performs irradiation stop control, and the radiation generation device 210 stops irradiating radiation.

[0085] As described above, the threshold value Dth is a threshold value that takes into consideration the communication delay time TDc and the delay time TD. Therefore, by transmitting the irradiation stop signal 226 at the timing when the predicted cumulative arrival dose reaches the threshold value Dth, when the irradiation from the radiation generating device 210 actually stops, radiation of the target value Dref reaches the radiation imaging device 100.

[0086] 4, the dose information stored in the detection pixel 104 increases or decreases based on the relationship between the radiation dose rate and time related to the cumulative reached dose 401 and the cumulative reached dose 402. In FIG. 4, for example, if the threshold value is set to only the threshold value Dth, the actual cumulative reached dose D changes depending on the difference in the dose rate, and in the case of a low dose rate, the amount of dose information that can be stored in the detection pixel 104 decreases (for example, the target value Dref and the irradiation time T low (This is the difference in dose between the two points.) For this reason, it is possible that sufficient dose information for use in correcting a radiation image cannot be accumulated in the detection pixel 104, and the detection pixel 104 can only output dose information similar to that of a pixel with missing information.

[0087] In contrast, in this embodiment, as shown in FIG. 4, the threshold change control unit 224 changes the threshold used in the threshold determination process between region 1 where the threshold Dth≦threshold Dthcor and region 2 where the threshold Dth>threshold Dthcor. More specifically, in region 1, the threshold change control unit 224 sets the threshold used in the threshold determination process to the threshold Dth. In this case, when the threshold determination unit 222 determines that the cumulative reached dose D is equal to or greater than the threshold Dth, the radiation imaging apparatus 100 simultaneously stops the drive signal of the switch element 106 of the detection pixel 104 and outputs an irradiation stop signal. On the other hand, in region 2, the threshold change control unit 224 sets the threshold used in the threshold determination process to the threshold Dthcor. In this case, when the threshold determination unit 222 determines that the cumulative reached dose D is equal to or greater than the threshold Dthcor, the radiation imaging apparatus 100 stops the switch element 106 of the detection pixel 104 at the threshold Dthcor. Thereafter, the threshold determination unit 222 predicts the timing at which the cumulative reaching dose D reaches the threshold Dth, and the radiation imaging apparatus 100 outputs an irradiation stop notification signal at that timing.

[0088] By this processing, in both the case of a high dose rate and a low dose rate, the cumulative reached dose D that actually reaches the sensor unit 221 can be made to approach the target value Dref with high accuracy, and sufficient dose information can be left in the detection pixel 104. As a result, regardless of the magnitude of the dose rate, control to stop irradiation of radiation can be performed with high accuracy, and the dose information left in the detection pixel 104 can be used to correct the pixel value, thereby reducing degradation in image quality.

[0089] Next, an example of the operation of the radiation imaging apparatus 100 according to this embodiment will be described with reference to Fig. 5. This operation is performed by cooperation between the control unit 180, which controls the drive circuit 150 and the readout circuit 160, and the signal processing unit 170. Therefore, the combination of the signal processing unit 170 and the control unit 180 may be called an exposure determination unit.

[0090] "Radiation" in FIG. 5 indicates whether radiation is irradiated to the radiographic imaging apparatus 100. Low indicates that radiation is not irradiated, and high indicates that radiation is irradiated. "Vg1" to "Vgn" indicate drive signals supplied from the drive circuit 150 to each of the multiple drive lines 110 (1 to n). "Vgk" corresponds to the drive line 110 in the kth row (k=1,...,n (total number of drive lines)). As described above, some of the multiple drive lines 110 are also called detection drive lines 111. The jth detection drive line 111 is represented as "Vdj" (j=1,...,m (total number of detection drive lines)). "φSH" indicates the level of a control signal supplied to the sample hold circuit SH of the amplifier 161. "φR" indicates the level of a control signal supplied to the differential amplifier circuit AMP of the amplifier 161.

[0091] Furthermore, in FIG. 5, "detection pixel signal" indicates the value of the signal read out from the detection pixel 104. "correction pixel signal" indicates the value of the signal read out from the correction pixel 107. "Cumulative reached dose" indicates the integrated value of the radiation irradiated to the radiation imaging apparatus 100. This integrated value is determined by calculation of the detection pixel signal and the correction pixel signal, but a detailed description will be omitted in this embodiment. Furthermore, "threshold Dthcor" and "threshold Dth at t8" indicate the above-mentioned threshold Dthcor and threshold Dth at time t8. The horizontal axis in FIG. 5 indicates time.

[0092] At time t0, the control unit 180 starts a reset operation of a plurality of pixels. The reset operation is an operation of removing the electric charge accumulated in the conversion element of each pixel, and specifically, a switching element of each pixel is turned on by supplying a driving signal to the driving line 110. The control unit 180 controls the driving circuit 150 to supply a driving signal Vg1 to the driving line 110 of the first row, thereby resetting each pixel connected to the driving line 110 of the first row. Next, the control unit 180 controls the driving circuit 150 to supply a driving signal Vg2 to the driving line 110 of the second row, thereby resetting each pixel connected to the driving line 110 of the second row. The control unit 180 repeats this operation up to the driving line 110 of the last row. At time t1, the control unit 180 finishes the reset operation of the driving line 110 of the last row, and then repeats the reset operation again from the driving line 110 of the first row.

[0093] At time t2, the control unit 180 receives a start request signal from the imaging control unit 231. In response to receiving the start request signal, the control unit 180 performs the reset operation up to the last row and then ends the reset operation. The control unit 180 may end the reset operation before performing the reset operation up to the last row and move on to the next process. For example, when the control unit 180 receives the start request signal during the reset operation of the kth row of the drive line 110, the control unit 180 may move on to the next process without performing the reset operation of the drive line 110 of the k+1th row and onward. In this case, the control unit 180 may adjust the drive for acquiring the radiographic image, or the signal processing unit 170 may perform image processing on the radiographic image, thereby reducing steps that may occur in the radiographic image.

[0094] At time t3, the control unit 180 starts a determination operation for determining the amount of radiation being irradiated to the radiation imaging apparatus 100. A signal read operation related to the determination operation is performed for the detection drive line 111, and is not performed for the other drive lines 110. Specifically, the drive circuit 150 supplies a drive signal to the detection drive line 111, which is the drive line 110 connected to at least one of the detection pixel 104 and the correction pixel 107 among the multiple drive lines 110. On the other hand, the drive circuit 150 does not supply a drive signal to the drive line 110 that is not connected to either the detection pixel 104 or the correction pixel 107 among the multiple drive lines 110. In addition, the drive circuit 150 simultaneously supplies a drive signal to the drive line 110 that is connected to at least one of the detection pixel 104 and the correction pixel 107 among the multiple drive lines 110. As a result, signals from multiple pixels connected to the same signal line 120 are combined and read out to the readout circuit 160. Since the detection pixel 104 and the correction pixel 107 are exclusively connected to the signal line 120, the readout circuit 160 can separately read out signals of pixels with different sensitivities.

[0095] In one readout operation, the control unit 180 performs an operation from time t3 to time t4. Specifically, the control unit 180 temporarily supplies a drive signal to one or more detection drive lines 111. Thereafter, the control unit 180 temporarily sets the control signal φSH to a high level, thereby holding the signal read out from the pixel to the readout circuit 160 through the signal line 120 in the sample-and-hold circuit SH. Thereafter, the control unit 180 temporarily sets the control signal φR to a high level, thereby resetting the readout circuit 160 (specifically, the differential amplifier circuit AMP of the amplifier unit 161). When a region of interest is set within the imaging region IR, it is not necessary to read out signals from the detection pixels 104 that are not included in this region of interest.

[0096] After completing one or more readout operations, at time t5, the control unit 180 transmits a start possible signal to the radiation generation device 210. From time t6 after time t5, the radiation generation device 210 starts irradiating radiation.

[0097] After transmitting the start possible signal, the control unit 180 repeatedly executes the above-mentioned read operation. The threshold determination unit 222 measures the dose for each read operation and determines whether the cumulative reached dose D has exceeded the threshold. When the cumulative reached dose D is equal to or greater than the irradiation start threshold, the threshold determination unit 222 determines that irradiation of radiation has started. Furthermore, when the cumulative reached dose D is equal to or greater than the threshold Dth or the threshold Dthcor, the threshold determination unit 222 determines that a stop instruction should be issued to the control unit 180.

[0098] Time t7 is the timing at which the threshold determination unit 222 issues a stop instruction to the control unit 180 to stop the readout operation in step S307'. In the example shown in Fig. 5, the cumulative reached dose reaches the threshold Dthcor at time t7, so the threshold determination unit 222 issues a stop instruction to the control unit 180. The control unit 180, which has received the stop instruction, causes the drive circuit 150 to stop outputting a drive signal to the pixel to be driven. This turns off the switch element of the pixel to be driven, and the operation of accumulating dose information is started. Therefore, there is no change over time in the detection pixel signal, the correction pixel signal, and the cumulative reached dose.

[0099] The threshold determination unit 222 predicts time t8 at which the cumulative reached dose will reach the threshold Dth, based on the elapsed time from time 6 to time t7, the cumulative reached dose during this period, and the threshold Dth. When the control unit 180 determines that the cumulative reached dose D has reached the threshold Dth at time t8 based on the prediction, the radiation imaging apparatus 100 transmits an irradiation stop signal 226 to the control device 230 via the communication unit 223. The control device 230, having received the irradiation stop signal 226, transmits an irradiation stop signal 236 to the radiation generation device 210 to stop irradiation of radiation.

[0100] At time t9 after the delay time TD and the communication delay time TDc have elapsed from time t8 when the radiation imaging apparatus 100 transmits the irradiation stop signal 226, the irradiation of radiation from the radiation generation apparatus 210 stops. As a result, dose information is accumulated in the detection pixel 104 between time t7 and time t9. The calculation unit 171 can reduce degradation of the image quality of the radiation image caused by the detection pixel 104 by using the dose information in the correction process of the radiation image.

[0101] As described above, the radiation imaging system 200 according to the present embodiment includes the radiation generating device 210 that generates radiation, the control device 230 that controls the radiation generating device 210, and the radiation imaging device 100 that detects radiation and generates a radiation image. The radiation imaging device 100 includes a sensor unit 221, a control unit 180, a threshold determination unit 222, and a calculation unit 171. The sensor unit 221 functions as an example of an imaging unit in which a plurality of pixels that detect radiation are arranged. Here, the plurality of pixels may include an imaging pixel 101 that generates a signal used to generate a radiation image, and a detection pixel 104 that generates a signal indicating the dose of irradiated radiation. The control unit 180 is a control unit that controls the plurality of pixels, and functions as an example of a control unit that stops reading out a signal indicating the dose from the detection pixel 104 when a detected dose based on a signal indicating the dose of radiation is equal to or greater than either a threshold Dth (first threshold) that changes with time or a threshold Dthcor (second threshold) different from the threshold Dth. The threshold determination unit 222 functions as an example of an output unit that outputs a stop signal to stop irradiation of radiation when the detected radiation amount is equal to or greater than the first threshold, or when the detected radiation amount is equal to or greater than the second threshold and the waiting time Twait has elapsed. The calculation unit 171 functions as an example of a generation unit that generates a radiographic image using signals accumulated in the imaging pixels 101 and the detection pixels 104.

[0102] With this configuration, the radiation imaging apparatus 100 according to this embodiment can stop reading out the dose by the detection pixel 104 in accordance with the smaller of the threshold value Dth and the threshold value Dthcor. Furthermore, the radiation imaging apparatus 100 can transmit a radiation stop signal to stop irradiation of radiation when the detected dose exceeds the threshold value Dth, or when the detected dose exceeds the threshold value Dthcor and the standby time has elapsed. Therefore, the radiation imaging apparatus 100 can control the stop of irradiation of radiation from the radiation generation apparatus 210 with high accuracy, and can reduce degradation of image quality caused by the detection pixel 104.

[0103] Here, the threshold value Dth can increase with time. Furthermore, the relationship between the threshold value Dth and the threshold value Dthcor can change from a relationship in which the threshold value Dth is equal to or less than the threshold value Dthcor (equal to or less than the second threshold) to a relationship in which the threshold value Dth is greater than the threshold value Dthcor with time. In this case, a smaller threshold value can be used as the threshold value for stopping the reading of the dose by the detection pixel 104 with time elapsed, and more dose information can be stored in the detection pixel 104. Therefore, degradation of image quality due to the detection pixel 104 can be further reduced.

[0104] Furthermore, the threshold value Dth can be determined based on a delay time from outputting a radiation stop signal to stopping irradiation of radiation. Here, the delay time can include a communication delay time of the radiation stop signal and a delay time required for control to stop irradiation of radiation. More specifically, the threshold value Dth can include a communication delay time when the radiation imaging apparatus 100 transmits a radiation stop signal to the control device 230 and a delay time when the control device 230 controls the radiation generating apparatus 210 to stop irradiation of radiation. In this case, the radiation imaging apparatus 100 can transmit a radiation stop signal when the detected dose exceeds the threshold value Dth or a threshold value smaller than the threshold value Dth. Therefore, the radiation imaging apparatus 100 can perform radiation irradiation stop control with high accuracy by taking into account the delay time from outputting a radiation stop signal to stopping irradiation of radiation.

[0105] The threshold value Dth can increase over time with the start time of radiation irradiation as a reference. The start time of radiation irradiation can be the time when the detected dose becomes equal to or greater than an irradiation start threshold value (third threshold value) different from the threshold value Dth and the threshold value Dthcor. In this case, the radiation imaging apparatus 100 can specify the reference time when the threshold value Dth increases over time as the start time of radiation irradiation based on the detected dose.

[0106] Furthermore, the threshold determination unit 222 can calculate a waiting time Twait until the dose of the irradiated radiation exceeds the threshold Dth, using the detected dose and the elapsed time from when reading out of the signal indicating the dose from the detection pixel 104 was stopped. More specifically, the threshold determination unit 222 can calculate the waiting time Twait further using a target value Dref, which is the target dose, and a delay time from when the radiation stop signal is output until when the irradiation of radiation is stopped.

[0107] Moreover, the radiation imaging apparatus 100 may further include a threshold change control unit 224. The threshold change control unit 224 may function as an example of a change unit that changes the threshold to be compared with the detected dose from the time-varying threshold Dth to the threshold Dthcor based on the elapsed time from the start of radiation irradiation. More specifically, the threshold change control unit 224 may change the threshold to be compared with the detected dose from the threshold Dth to the threshold Dthcor when the threshold Dth is greater than the threshold Dthcor at the elapsed time. With this configuration, it is possible to reduce the number of times the detected dose is compared with the threshold, thereby reducing the processing load and speeding up the processing.

[0108] The threshold value Dthcor may be a threshold value for accumulating signals used to generate a radiographic image in the detection pixels. The threshold value Dthcor may be determined, for example, by a predetermined ratio to a target dose. The threshold value Dthcor may be determined by an absolute amount of dose required to generate a radiographic image. In this case, when the detected dose exceeds the threshold value Dthcor or a threshold value smaller than the threshold value Dthcor, the detection pixels 104 stop reading out signals indicating the dose, so that the dose required to generate a radiographic image can be more reliably accumulated in the detection pixels 104. The threshold value Dthcor may decrease over time based on the start time of radiation irradiation. In this case, the longer the irradiation time, the more dose information can be left in the detection pixels 104, and deterioration of the S / N ratio of the radiographic image can be suppressed.

[0109] Each of the multiple pixels provided in the sensor unit 221 can include a detection element that detects radiation and a switch element that switches the output of a signal from the detection element. Here, the conversion elements 102 and 105 function as an example of a detection element, and the switch elements 103 and 106 can function as an example of the switch element. In this case, the control unit 180 can stop reading out a signal indicating the radiation dose from the detection pixel 104 by controlling the drive circuit to turn off the switch element 106 of the detection pixel 104.

[0110] In this embodiment, the threshold change control unit 224 changes the threshold from the threshold Dth to the threshold Dthcor according to the elapsed time. In contrast, the threshold change control unit 224 may not change the threshold, and the threshold determination unit 222 may determine whether the cumulative reached dose D exceeds the threshold Dthcor when the cumulative reached dose D is smaller than the threshold Dth. Such processing will be described with reference to FIG. 3B. FIG. 3B is a flowchart showing another example of a series of control methods for photographing a subject according to this embodiment. In FIG. 3B, the same processes as those in FIG. 3A are denoted by the same reference symbols, and description thereof will be omitted.

[0111] 3B, when radiation is irradiated toward the subject in step S303, the process proceeds to step S305'. In step S305', first, the threshold determination unit 222 calculates a value representative of the radiation dose detected by the sensor unit 221, and calculates a cumulative value of the values ​​representative of the dose. This process may be similar to the process of calculating the cumulative value of the values ​​representative of the dose in step S305.

[0112] The threshold determination unit 222 compares the calculated cumulative reach dose D with the threshold Dth set in step S302, and determines whether the cumulative reach dose D is smaller than the threshold Dth. If the result of this determination is that the cumulative reach dose D is smaller than the threshold Dth (step S305' / YES), the process proceeds to step S306'. On the other hand, if the result of the determination in step S305' is that the cumulative reach dose D is not smaller than the threshold Dth (the cumulative reach dose D is equal to or greater than the threshold Dth) (step S305' / NO), the process proceeds to step S307.

[0113] In step S306', the threshold determination unit 222 compares the cumulative reach dose D calculated in step S305' with the threshold Dthcor set in step S302, and determines whether the cumulative reach dose D is smaller than the threshold Dthcor. If the cumulative reach dose D is smaller than the threshold Dthcor as a result of this determination (step S306' / YES), the process proceeds to step S305'. On the other hand, if the cumulative reach dose D is not smaller than the threshold Dthcor (the cumulative reach dose D is equal to or larger than the threshold Dthcor) as a result of the determination in step S306' (step S306' / NO), the process proceeds to step S307'. Note that, if a positive determination is made in step S306' (step S306' / YES), the threshold change control unit 224 performs the same process as the setting of the threshold Dth in step S302. The process after step S307 and step S307' is the same as the process in FIG. 3A, and therefore the description will be omitted.

[0114] In this configuration, the threshold determination unit 222 can compare the detected dose with the threshold without changing the threshold by the threshold change control unit 224. Even with this configuration, the radiation imaging apparatus 100 can control the stop of irradiation of radiation from the radiation generation device 210 with high accuracy and reduce degradation of image quality caused by the detection pixel 104.

[0115] Second Embodiment Next, a radiation imaging apparatus, a radiation imaging system, and a method for controlling a radiation imaging apparatus according to a second embodiment of the present disclosure will be described with reference to Figs. 4 and 6. The configurations of the radiation imaging apparatus and the radiation imaging system according to this embodiment may be similar to those of the first embodiment, and therefore the same reference numerals will be used and the description will be omitted. The radiation imaging apparatus according to this embodiment will be described below, focusing on the differences from the radiation imaging apparatus according to the first embodiment. In the radiation imaging apparatus 100 according to this embodiment, the prediction operation is different from that of the radiation imaging apparatus 100 according to the first embodiment. Note that other points may be similar to those of the first embodiment, and therefore duplicated descriptions will be omitted.

[0116] Fig. 6 is a flow chart showing an example of a series of control methods for photographing a subject according to the embodiment. In Fig. 6, the processes with the same numbers mean the same processes as those in Fig. 3A, and therefore the explanations are omitted. In step S306 in Fig. 6, if the cumulative reached dose D is not smaller than the threshold value Dthcor (the cumulative reached dose D is equal to or greater than the threshold value) (step S306 / NO), the process proceeds to step S307'.

[0117] When the process proceeds to step S307', since the cumulative achieved dose D has exceeded (reached) the threshold value Dthcor, the output of the drive signal is stopped, the switch element of the pixel to be driven is turned off, and the accumulation operation of the dose information is started, as in the first embodiment. When the output of the drive signal is stopped, the process proceeds to step S601.

[0118] In step S601, since the detection pixel 104 is performing an accumulation operation, the read-out cumulative reached dose D does not increase. Therefore, the threshold determination unit 222 starts predicting the timing for outputting an irradiation stop notification. First, the threshold determination unit 222 calculates (predicts) the reached dose Dsmp per sampling. Here, the reached dose Dsmp per sampling can be expressed as in the following formula (3) using the number of samplings Stotal, the cumulative reached dose D, and the elapsed time T from the threshold change reference point O in FIG. 4 to the time when the cumulative reached dose reaches the threshold Dthcor. Dsmp = D(T) / Stotal (3)

[0119] Note that formula (3) means gradient information of the dose of irradiated radiation. In this embodiment, the reached dose Dsmp (gradient information) per sampling is calculated as a linear approximation, but the reached dose Dsmp per sampling is not limited to this and may be calculated as a quadratic approximation or an exponential function. The reached dose Dsmp per sampling may be calculated in advance from the irradiation conditions obtained in step S301. When the calculation of the reached dose Dsmp per sampling is completed, the process proceeds to step S602.

[0120] In step S602, when one sampling time has elapsed, the accumulated reached dose D calculated in step S601 is predicted when one sampling time has elapsed. Specifically, the threshold determination unit 222 adds the reached dose Dsmp per sampling to the accumulated reached dose D up to the elapsed time T. This makes it possible to calculate the accumulated reached dose D when one sampling time has elapsed for the accumulated reached dose D that has stopped increasing by turning off the switch element 106 of the detection pixel 104 in step S307'. The accumulated reached dose D(T+1) when one sampling time has elapsed can be expressed as in the following formula (4) using the accumulated reached dose D, the elapsed time T, and the reached dose Dsmp per sampling. D(T+1)=D(T)+Dsmp (4) The process proceeds to step S603 when the addition of the reached dose Dsmp per sampling is completed to the accumulated reached dose D. When setting the time change of the threshold Dth of the accumulated reached dose, in step S602, the threshold change control unit 224 performs the same process as the setting of the threshold Dth in step S302.

[0121] In step S603, first, the threshold determination unit 222 compares the cumulative reaching dose D calculated in step S602 with a threshold Dth to determine whether the cumulative reaching dose D is smaller than the threshold Dth. If the result of this determination is that the cumulative reaching dose D is smaller than the threshold Dth (step S603 / YES), the process proceeds to step S602. On the other hand, if the result of the determination in step S603 is that the cumulative reaching dose D is not smaller than the threshold Dth (the cumulative reaching dose D is equal to or larger than the threshold Dth) (step S603 / NO), the process proceeds to step S309. The process from step S309 onwards is similar to the process in the first embodiment, and therefore will not be described.

[0122] In this embodiment, the processes of steps S602 and S603 are repeated each time one sampling period has elapsed until the cumulative radiation dose D calculated in step S602 exceeds the threshold Dth. In addition, when the cumulative radiation dose D calculated in step S602 becomes equal to or greater than the threshold Dth, it is determined that the waiting time Twait has elapsed. Therefore, in this embodiment as well, after the cumulative radiation dose D exceeds the threshold Dthcor, the accumulation operation of the detection pixel 104 is continued until the predicted cumulative radiation dose D becomes equal to or greater than the threshold Dth, thereby obtaining dose information used to correct a radiological image. In addition, since the threshold Dth is a threshold that takes into account the communication delay time TDc and the delay time TD, radiation irradiation can be stopped with high accuracy.

[0123] As described above, the threshold determination unit 222 according to the present embodiment can determine whether the waiting time has elapsed by further using the detected dose, the elapsed time when the readout of the signal indicating the dose from the detection pixel 104 was stopped, and the threshold Dth. More specifically, the threshold determination unit 222 can obtain the dose per sampling time of the detection of the dose by using the detected dose and the elapsed time when the readout of the signal indicating the dose from the detection pixel 104 was stopped. In addition, the threshold determination unit 222 can add the dose per sampling time to the detected dose for each sampling time. Furthermore, the threshold determination unit 222 can determine that the waiting time has elapsed when the cumulative value of the dose to which the dose per sampling time is added is equal to or greater than the threshold Dth. Even with this configuration, it is possible to output a radiation stop signal based on the threshold Dth, and it is possible to control the radiation irradiation stop control with high accuracy.

[0124] In this embodiment, similarly to the modified example of the first embodiment, the threshold change control unit 224 may not change the threshold, and the threshold determination unit 222 may compare the detected radiation dose with the threshold. In this case, steps S601 to S603 may be performed instead of step S308 in Fig. 3B. Even with this configuration, the radiation imaging apparatus 100 can control the stop of irradiation of radiation from the radiation generation device 210 with high accuracy, and can reduce degradation of image quality caused by the detection pixel 104.

[0125] (Other embodiments) The present disclosure can also be realized by a process in which a program for implementing one or more functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) for implementing one or more functions. A computer may have one or more processors or circuits, and may include separate computers or a network of separate processors or circuits for reading and executing computer-executable instructions.

[0126] The processor or circuitry may include a central processing unit (CPU), a microprocessing unit (MPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), or a field programmable gateway (FPGA), and the processor or circuitry may include a digital signal processor (DSP), a data flow processor (DFP), or a neural processing unit (NPU).

[0127] The above disclosure includes the following configurations, methods, and programs. (Configuration 1) an imaging section in which a plurality of pixels for detecting radiation are arranged, the plurality of pixels including imaging pixels for generating signals used to generate a radiographic image, and detection pixels for generating signals indicative of a dose of the irradiated radiation; a control unit that controls the plurality of pixels, the control unit stopping reading of the signal indicating the dose from the detection pixel when a detected dose based on the signal indicating the dose of radiation is equal to or greater than either a first threshold that changes with time or a second threshold that is different from the first threshold; an output unit that outputs a stop signal to stop the irradiation of the radiation when the detected radiation amount is equal to or greater than the first threshold, or when the detected radiation amount is equal to or greater than the second threshold and a standby time has elapsed; a generating unit that generates a radiographic image using signals accumulated in the imaging pixels and the detection pixels; A radiation imaging apparatus comprising: (Configuration 2) the first threshold increases over time; 2. The radiation imaging apparatus of claim 1, wherein the relationship between the first threshold and the second threshold changes from a relationship in which the first threshold is less than or equal to the second threshold to a relationship in which the first threshold is greater than the second threshold over time. (Configuration 3) 3. The radiation imaging apparatus according to configuration 2, wherein the first threshold value is determined based on a delay time from when the stop signal is output until when the irradiation of the radiation is stopped. (Configuration 4) 4. The radiation imaging apparatus according to configuration 3, wherein the delay time includes a communication delay time of the stop signal and a delay time required for control to stop the irradiation of the radiation. (Configuration 5) 5. The radiation imaging apparatus according to any one of configurations 2 to 4, wherein the first threshold value increases with time, based on a start time of the irradiation of the radiation. (Configuration 6) 6. The radiation imaging apparatus according to configuration 5, wherein the start time of the radiation irradiation is a time when the detected radiation dose becomes equal to or greater than a third threshold value different from the first and second threshold values. (Configuration 7) The radiation imaging device according to any one of configurations 1 to 6, wherein the output unit calculates the waiting time until the dose of the irradiated radiation exceeds the first threshold value using the detected dose and the elapsed time from when reading out of the signal indicating the dose from the detection pixel was stopped. (Configuration 8) 8. The radiation imaging apparatus according to claim 7, wherein the output unit calculates the waiting time by further using a target dose and a delay time from when the stop signal is output until when the irradiation of the radiation is stopped. (Configuration 9) The radiation imaging device according to any one of configurations 1 to 6, wherein the output unit determines whether the waiting time has elapsed by using the detected dose, the elapsed time from when reading of the signal indicating the dose from the detection pixel was stopped, and the first threshold value. (Configuration 10) The output unit is calculating a dose per sampling time of the detection of the dose by using the detected dose and an elapsed time from when the reading of the signal indicating the dose from the detection pixel was stopped; adding a dose per sampling time to the detected dose for each sampling time; 10. The radiation imaging apparatus according to configuration 9, wherein it is determined that the standby time has elapsed when a cumulative value of the dose added per sampling time is equal to or greater than the first threshold value. (Configuration 11) 11. The radiation imaging apparatus according to any one of configurations 1 to 10, further comprising a change unit that changes a threshold value to be compared with the detected dose from the first threshold value to the second threshold value based on the elapsed time from the start of the irradiation of the radiation. (Configuration 12) the first threshold increases over time; a relationship between the first threshold and the second threshold changes over time from a relationship in which the first threshold is equal to or smaller than the second threshold to a relationship in which the first threshold is greater than the second threshold, 12. The radiation imaging apparatus according to claim 11, wherein the change unit changes the threshold to be compared with the detected dose from the first threshold to the second threshold when the first threshold is greater than the second threshold during the elapsed time. (Configuration 13) 13. The radiographic apparatus according to any one of configurations 1 to 12, wherein the second threshold value is a threshold value for accumulating, in the detection pixels, signals used to generate the radiographic image. (Configuration 14) 14. The radiation imaging apparatus according to any one of configurations 1 to 13, wherein the second threshold is determined by a predetermined ratio to a target dose. (Configuration 15) 14. The radiation imaging apparatus according to any one of configurations 1 to 13, wherein the second threshold is determined based on an absolute amount of radiation required to generate the radiation image. (Configuration 16) 14. The radiation imaging apparatus according to any one of configurations 1 to 13, wherein the second threshold value decreases over time with the start time of the irradiation of the radiation as a reference. (Configuration 17) Each of the plurality of pixels includes a detection element that detects radiation and a switch element that switches an output of a signal from the detection element, 17. The radiation imaging apparatus according to any one of configurations 1 to 16, wherein the control unit stops reading out the signal indicating the dose from the detection pixel by turning off a switch element of the detection pixel. (Configuration 18) A radiation generating device that generates radiation; A control device for controlling the radiation generating device; A radiographic imaging apparatus according to any one of configurations 1 to 17, A radiation imaging system comprising: (Method 1) A method for controlling a radiographic imaging apparatus including an imaging section in which a plurality of pixels for detecting radiation are arranged, the plurality of pixels including imaging pixels for generating signals used to generate a radiographic image and detection pixels for generating signals indicative of a dose of the irradiated radiation, the method comprising the steps of: stopping reading of the signal indicating the dose from the detection pixel when a detected dose based on the signal indicating the dose of radiation is equal to or greater than either a first threshold value that changes with time or a second threshold value different from the first threshold value; outputting a stop signal for stopping the irradiation of the radiation when the detected radiation amount is equal to or greater than the first threshold value, or when the detected radiation amount is equal to or greater than the second threshold value and a standby time has elapsed; generating a radiation image using signals accumulated in the imaging pixels and the detection pixels; A method for controlling a radiation imaging apparatus comprising: (Program 1) A program that, when executed by a processor, causes the processor to execute the control method for a radiation imaging apparatus according to method 1.

[0128] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above embodiments. Inventions modified within the scope of the present disclosure and inventions equivalent to the present disclosure are also included in the present disclosure. In addition, the above-mentioned embodiments can be appropriately combined within the scope of the present disclosure. [Explanation of symbols]

[0129] 100: Radiography device, 101: Shooting pixel, 104: Detection pixel, 171: Calculation unit (generation unit), 180: Control unit, 221: Sensor unit (shooting unit), 222: Threshold determination unit (output unit)

Claims

1. an imaging section in which a plurality of pixels for detecting radiation are arranged, the plurality of pixels including imaging pixels for generating signals used to generate a radiographic image, and detection pixels for generating signals indicative of a dose of the irradiated radiation; a control unit that controls the plurality of pixels, the control unit stopping reading of the signal indicating the dose from the detection pixel when a detected dose based on the signal indicating the dose of radiation is equal to or greater than either a first threshold that changes with time or a second threshold that is different from the first threshold; an output unit that outputs a stop signal to stop the irradiation of the radiation when the detected radiation amount is equal to or greater than the first threshold, or when the detected radiation amount is equal to or greater than the second threshold and a standby time has elapsed; a generating unit that generates a radiographic image using signals accumulated in the imaging pixels and the detection pixels; A radiation imaging apparatus comprising:

2. the first threshold increases with time; 2. The radiation imaging apparatus according to claim 1, wherein the relationship between the first threshold and the second threshold changes from a relationship in which the first threshold is less than or equal to the second threshold to a relationship in which the first threshold is greater than the second threshold over time.

3. The radiation imaging apparatus according to claim 2 , wherein the first threshold value is determined based on a delay time from when the stop signal is output until when the irradiation of the radiation is stopped.

4. The radiation imaging apparatus according to claim 3 , wherein the delay time includes a communication delay time of the stop signal and a delay time required for control to stop the irradiation of the radiation.

5. The radiation imaging apparatus according to claim 2 , wherein the first threshold value increases with time based on a start time of the irradiation of the radiation.

6. The radiation imaging apparatus according to claim 5 , wherein the radiation irradiation start time is a time when the detected radiation amount becomes equal to or greater than a third threshold value different from the first and second threshold values.

7. 2. The radiation imaging apparatus according to claim 1, wherein the output unit calculates the waiting time until the dose of the irradiated radiation exceeds the first threshold value, using the detected dose and an elapsed time from when reading out of the signal indicating the dose from the detection pixel was stopped.

8. The radiation imaging apparatus according to claim 7 , wherein the output unit calculates the waiting time by further using a target dose and a delay time from when the stop signal is output until when the irradiation of the radiation is stopped.

9. 2. The radiation imaging apparatus according to claim 1, wherein the output unit determines whether the standby time has elapsed by using the detected radiation amount, the elapsed time from when reading of the signal indicating the radiation amount from the detection pixel was stopped, and the first threshold value.

10. The output unit is calculating a dose per sampling time of the detection of the dose by using the detected dose and an elapsed time from when the reading of the signal indicating the dose from the detection pixel was stopped; adding a dose per sampling time to the detected dose for each sampling time; The radiation imaging apparatus according to claim 9 , wherein the waiting time is determined to have elapsed when a cumulative value of the dose per sampling time added is equal to or greater than the first threshold value.

11. The radiation imaging apparatus according to claim 1 , further comprising a change unit that changes a threshold value to be compared with the detected dose from the first threshold value to the second threshold value based on an elapsed time from a start of the irradiation of the radiation.

12. the first threshold increases over time; a relationship between the first threshold and the second threshold changes over time from a relationship in which the first threshold is equal to or smaller than the second threshold to a relationship in which the first threshold is greater than the second threshold, The radiation imaging apparatus according to claim 11 , wherein the change unit changes the threshold to be compared with the detected radiation dose from the first threshold to the second threshold when the first threshold is greater than the second threshold during the elapsed time.

13. The radiographic imaging apparatus according to claim 1 , wherein the second threshold value is a threshold value for accumulating, in the detection pixels, signals used to generate the radiographic image.

14. The radiation imaging apparatus according to claim 1 , wherein the second threshold is determined by a predetermined ratio to a target dose.

15. The radiation imaging apparatus according to claim 1 , wherein the second threshold is determined based on an absolute amount of radiation required to generate the radiation image.

16. The radiation imaging apparatus according to claim 1 , wherein the second threshold value decreases with time based on a start time of the irradiation of the radiation.

17. Each of the plurality of pixels includes a detection element that detects radiation and a switch element that switches an output of a signal from the detection element, The radiation imaging apparatus according to claim 1 , wherein the control unit stops reading out the signal indicating the radiation amount from the detection pixel by turning off a switch element of the detection pixel.

18. A radiation generating device that generates radiation; A control device for controlling the radiation generating device; A radiation imaging apparatus according to any one of claims 1 to 17, A radiation imaging system comprising:

19. A method for controlling a radiographic imaging apparatus including an imaging section in which a plurality of pixels for detecting radiation are arranged, the plurality of pixels including imaging pixels for generating signals used to generate a radiographic image and detection pixels for generating signals indicative of a dose of the irradiated radiation, the method comprising the steps of: stopping reading of the signal indicating the dose from the detection pixel when a detected dose based on the signal indicating the dose of radiation is equal to or greater than either a first threshold value that changes with time or a second threshold value different from the first threshold value; outputting a stop signal for stopping the irradiation of the radiation when the detected radiation amount is equal to or greater than the first threshold value, or when the detected radiation amount is equal to or greater than the second threshold value and a standby time has elapsed; generating a radiation image using signals accumulated in the imaging pixels and the detection pixels; A method for controlling a radiation imaging apparatus comprising:

20. A program which, when executed by a processor, causes the processor to execute the method for controlling a radiographic apparatus according to claim 19.

Images