Radiation imaging system, imaging control device, method of controlling radiation imaging system, method of controlling imaging control device, and program

Abstract

To reduce a deviation between a set dose target value which is set as a threshold value of radiation exposure and a dose index value at the time of actual imaging, and perform proper dose management.SOLUTION: A radiation imaging system comprises: a radiation imaging device including a dose detection pixel for detecting a dose of radiation radiated from a radiation source; and an imaging control device for controlling the radiation imaging device. The imaging control device identifies a position of the dose detection pixel in a region of interest for calculating a dose index value for a radiation image before radiation imaging, determines a threshold value dependent on the position of the dose detection pixel, and sends the position and the threshold value of the dose detection pixel to the radiation imaging device. The radiation imaging device sets the position and the threshold value of the dose detection pixel in the region of interest sent from the imaging control device, and performs imaging on the basis of the settings.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a radiation imaging system, an imaging control device, a radiation imaging device, a radiation imaging method, and a program. [Background technology]

[0002] 2. Description of the Related Art A radiation imaging device used for medical image diagnosis and non-destructive testing using radiation such as X-rays has a matrix substrate having a pixel array in which switches such as TFTs (thin film transistors) and conversion elements such as photoelectric conversion elements are combined.

[0003] This radiation imaging device has an extremely wide dynamic range for radiation dose, and has the advantage of being able to obtain stable density output even in cases of insufficient or excessive dose due to automatic density correction by image processing, compared to conventional analog radiation imaging. On the other hand, there is a problem that even if a radiographer takes an image with an inappropriate dose, it is difficult for the radiographer to notice this, and especially in the case of an excessive dose, the amount of radiation exposure to the patient increases.

[0004] To solve this problem, it is common to display a value (hereinafter referred to as a dose index value) that is a guideline for the imaging dose of a digital radiographic image together with the image. Various methods have also been proposed for calculating the dose index value. In recent years, the International Electrotechnical Commission (IEC) has issued the international standard IEC62494-1, which defines EI (Exposure Index) as a standardized dose index value. This international standard also defines EIt (Target Exposure Index) as the target dose value (hereinafter referred to as the dose target value), and provides a method of dose management using the deviation DI (Deviation Index) that indicates the amount of deviation between the dose index value EI and the dose target value EIt.

[0005] Patent Document 1 describes an apparatus that has an AEC function that stops X-ray irradiation at a target dose, automatically sets a detection field, which is the area of ​​detection pixels that detects the dose, during X-ray irradiation based on the pixel values ​​of the detection pixels, and calculates a dose index value EI based on a representative value V extracted from the pixel values ​​of the detection field.

[0006] Patent Document 2 describes a method of dividing a radiological image into a plurality of anatomical regions, extracting at least one of the plurality of anatomical regions, and calculating a radiation imaging dose index value EI for the extracted region based on pixel values ​​in the extracted region. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2014-158580 A [Patent Document 2] JP 2020-25730 A Summary of the Invention [Problem to be solved by the invention]

[0008] In radiation imaging, it is required that the deviation between the dose index value EI and the dose target value EIt be small.

[0009] Therefore, an object of the present invention is to provide a radiation imaging technology that can reduce the deviation between a dose target value set as a threshold for radiation exposure and a dose index value when actually photographed, thereby enabling appropriate dose management. [Means for solving the problem]

[0010] A radiation imaging system according to one aspect of the present invention includes a radiation imaging device including dose detection pixels for detecting a dose of radiation irradiated from a radiation source, and an imaging control device for controlling the radiation imaging device, The imaging control device, before radiation imaging, identifying positions of the dose detection pixels in a region of interest for calculating a dose index value of a radiographic image, determining a threshold value according to the positions of the dose detection pixels, and transmitting the positions of the dose detection pixels and the threshold value to the radiographic imaging apparatus; The radiation imaging apparatus includes: The position of the radiation amount detection pixel in the region of interest and the threshold value transmitted from the imaging control device are set, and imaging is performed based on the settings. Effect of the Invention

[0011] According to the present invention, it is possible to reduce the deviation between a dose target value set as a threshold value for radiation exposure and a dose index value during actual imaging, thereby enabling appropriate dose management. [Brief description of the drawings]

[0012] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Figure 1] 1 is a diagram showing an example of the configuration of a radiation imaging system including a radiation imaging apparatus. [Diagram 2] FIG. 2 is a diagram showing an example of data communication in the radiation imaging system. [Diagram 3] FIG. 1 is a diagram illustrating an example of the external configuration of a radiation imaging apparatus. [Figure 4] FIG. 2 is a block diagram for explaining the functional configuration of a radiation imaging system according to an embodiment. [Diagram 5] FIG. 1 is a diagram showing an example of the operation of a radiation imaging system based on a digital signal. [Figure 6A] 1 is a diagram illustrating an internal configuration of a radiation imaging apparatus according to an embodiment; [Figure 6B] 1 is a diagram illustrating an internal configuration of a radiation imaging apparatus according to an embodiment; [Figure 6C] 1 is a diagram illustrating an internal configuration of a radiation imaging apparatus according to an embodiment; [Figure 7] 3 is a timing chart showing an internal operation of the radiation imaging apparatus according to the embodiment. [Figure 8] FIG. 4 is a diagram for explaining the flow of a process for calculating a dose index value. [Figure 9] FIG. 13 is a diagram for explaining pre-irradiation adjustment of a dose index value calculation method. [Figure 10] 13A and 13B are diagrams for explaining adjustment during irradiation of a calculation method of a dose index value. [Figure 11] 13 is a diagram for explaining processing when a predetermined radiation collection field is misaligned with an area of ​​radiation that is actually irradiated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the present invention according to the claims, and not all of the combinations of features described in the present embodiments are necessarily essential to the solution of the present invention. In the following embodiments and claims, radiation includes X-rays, α-rays, β-rays, γ-rays, and various particle beams.

[0014] <Configuration of Radiation Imaging System> The configuration and processing of a radiation imaging system 1000 of this embodiment will be described below with reference to Fig. 1. Fig. 1 is a block diagram showing an example of the configuration of a radiation imaging system including a radiation imaging apparatus of this embodiment. The radiation imaging system 1000 is used, for example, when capturing a radiation image in a hospital, and includes, as its system configuration, a radiation imaging apparatus 1001, an imaging control device 1002, a radiation source 1003, a high-voltage generator 1004, a LAN 1005 (hospital LAN), and a display unit 1006.

[0015] The radiation imaging device 1001 detects radiation transmitted through a subject (not shown) and forms an image in response to an operator operating the operation switch 46. The imaging control device 1002 performs, for example, settings of imaging conditions and operation control settings for the radiation imaging device 1001, and the radiation imaging device 1001 performs communication with the imaging control device 1002, for example, image transfer, transmission of reaching radiation dose, and automatic exposure control signals for controlling irradiation of the radiation source 1003.

[0016] The imaging control device 1002 has, for example, a mouse and a keyboard as input devices for enabling input of information such as imaging condition settings, operation settings, and image information, and has a display or the like as an output device for enabling output. The imaging control device 1002 also controls irradiation of radiation to the high-voltage generator 1004. The imaging control device 1002 has, as its functional configuration, a communication control unit 1021 that performs and mediates communication, and a control unit 1022 that performs operation settings, dose information notification, and the like, and monitors the states of the radiation imaging device 1001 and the high-voltage generator 1004 and controls irradiation of radiation and imaging. It is also possible to dispose the communication control unit 1021 as a separate unit of the imaging control device 1002, and have the communication control unit 1021 operate as a circuit for mediating communication with the imaging control device 1002.

[0017] The radiation source 1003 holds, for example, an X-ray tube and a rotor that accelerates electrons with high voltage to generate radiation and causes them to collide with an anode. The radiation emitted from the radiation source 1003 is irradiated onto a subject, and the radiation imaging device 1001 detects the radiation that has passed through the subject and forms an image. For convenience, FIG. 1 shows a state in which the imaging control device 1002 and the high voltage generator 1004 are arranged in separate locations, but the imaging control device 1002 and the high voltage generator 1004 may be arranged in the same unit. Furthermore, each function other than the imaging function may be arranged anywhere other than in the radiation imaging device 1001.

[0018] Fig. 2 is a diagram showing an example of data communication in a radiation imaging system. Fig. 2 shows an example of data communication between an imaging control device 1002, a radiation imaging device 1001, and a high-voltage generator 1004. In the communication between the imaging control device 1002 and the radiation imaging device 1001, information such as imaging condition settings, operation control settings, image transfer, AEC threshold, achieved dose, automatic exposure control signal, and automatic exposure time information is transmitted and received. The radiation imaging device 1001 has two communication units, a wireless communication unit and a wired communication unit, and can be connected to a communication control unit 1021 of the imaging control device 1002 using the two communication units.

[0019] Furthermore, information such as dose information, irradiation control signals, and optical image information by visible light or infrared light related to the area to be irradiated with radiation is transmitted and received in the communication between the imaging control device 1002 and the high-voltage generator 1004. This optical image information is information that enables the imaging control device 1002 and the high-voltage generator 1004 to share information on the focus and aperture optically the same as that of radiation.

[0020] In addition, the imaging control device 1002 does not necessarily have to act as an intermediary in the transmission path when communicating information. Data may be sent and received directly through communication between the radiation imaging device 1001 and the high-voltage generator 1004, or information may be shared between the imaging control device 1002, the radiation imaging device 1001, and the high-voltage generator 1004 through communication based on a data transfer standard such as CAN (Controller Area Network).

[0021] The “dose information” refers to the exposure dose of radiation emitted from the radiation source 1003 , and the “reaching dose” refers to the amount of radiation emitted from the radiation source 1003 that reaches the radiation imaging device 1001 .

[0022] The "AEC threshold" is set as a dose target value, and is threshold information that serves as a reference for comparison with the reached dose. This "AEC threshold" corresponds to dose information per unit area. The "AEC threshold" is set to reflect a preset dose target value EIt. The imaging control device 1002 compares the "AEC threshold" with the reached dose calculated within the radiation imaging device 1001, and notifies the high-voltage generator 1004 when the reached dose exceeds the AEC threshold. The imaging control device 1002 appropriately converts the information into dose information per unit area and performs a comparison process between the AEC threshold and the reached dose.

[0023] The "automatic exposure control signal" is, for example, a signal that includes a stop signal (irradiation stop signal) for stopping irradiation of radiation and an irradiation start signal (non-irradiation stop signal) for starting irradiation of radiation.

[0024] "Automatic exposure information (ROI / calculation method)" refers to instruction information regarding the region of interest ROI (illumination field) and calculation method for automatic exposure control, which is transmitted from the imaging control device 1002 to the radiation imaging device 1001.Instead, the radiation imaging device 1001 transmits to the imaging control device 1002 information regarding the ROI (illumination field 1012) and the calculation method when automatic exposure is actually performed.

[0025] In addition, the imaging control device 1002 controls the display of the display unit 1006 to display "dose information (dose index value EI / deviation DI)" during imaging, display the setting input of "dose target value EIt", or perform display control to display information set in radiation imaging.

[0026] The wired communication unit that the radiation imaging apparatus 1001 has as a communication medium is a path for transmitting information, and enables transmission and reception of information by a cable connection using a communication standard with a predetermined agreement or a standard such as RS232C, USB, or Ethernet (registered trademark). The wireless communication unit that the radiation imaging apparatus 1001 has as a communication medium is also a path for transmitting information, and includes, for example, a circuit board equipped with a communication IC. The wireless communication unit is electrically connected to an antenna (not shown) and transmits and receives radio waves. The circuit board equipped with a communication IC and the like can perform communication processing of a protocol based on a wireless LAN via the antenna. Note that there are no particular limitations on the frequency band, standard, or method of wireless communication in the wireless communication, and methods such as near field radio communication (NFC) and Bluetooth (registered trademark) or ultra wideband (UWB) may be used. The wireless communication unit has a plurality of wireless communication methods, and may appropriately select one to perform communication.

[0027] The radiation imaging device 1001 can be configured as, for example, a portable cassette-type flat panel detector (FPD (Flat Panel Detector)). Fig. 3 is a diagram showing an example of the external configuration of the portable radiation imaging device 1001. The radiation imaging device 1001 has a power button 1007 for turning the power on or off, a battery unit 1008 for supplying power, and a connector connection unit 1009. The battery unit 1008 is configured to be removable, and the battery main body of the battery unit 1008 is configured to be rechargeable by a battery charger.

[0028] The radiation imaging device 1001 can be connected to the imaging control device 1002 using a sensor cable 1010, and the radiation imaging device 1001 connects the sensor cable 1010 via a connector connection section 1009. When the radiation imaging device 1001 and the imaging control device 1002 are connected via the sensor cable 1010, the connection between them is switched to communication using a wired communication section, and information communication between the radiation imaging device 1001 and the imaging control device 1002 shown in Fig. 2 is executed by wired communication. Furthermore, regardless of the connection form, the imaging control device 1002 may be able to switch the communication section by a user's operation.

[0029] The functional configuration of the radiation imaging system 1000 of this embodiment will be described with reference to Fig. 4. A signal from the radiation source 1003 and a signal from an operation signal generation unit 1041 are input to a radiation generation control unit 1042 of the high voltage generator 1004. A signal indicating a stable state of anode rotation and a signal indicating a temperature state are input from the radiation source 1003 to the radiation generation control unit 1042. An operation switch 46 is connected to the operation signal generation unit 1041, and an input signal of a switch operation by an operator is input to the radiation generation control unit 1042.

[0030] Moreover, various signals are input to the radiation generation control unit 1042 from the radiation imaging apparatus 1001 and the imaging control device 1002 via the signal selection unit 1043, the signal integration determination unit 1044, or the signal processing unit 1045. A signal indicating an imaging preparation state is input from the radiation imaging apparatus 1001 to the radiation generation control unit 1042. A signal related to exposure control, which will be described later, is input to the radiation generation control unit 1042 via the signal selection unit 1043. A stop signal for the radiation 1103 on the analog signal path from the signal integration determination unit 1044 and a stop signal for the radiation 1103 on the digital communication path from the signal processing unit 1045 are input to the signal selection unit 1043, and whichever signal is input first is transmitted to the radiation generation control unit 1042.

[0031] The radiation imaging device 1001 of this embodiment has a digital processing unit 401 that outputs a stop signal when dose information acquired based on a first processing (digital signal processing) of the detection result of the dose detection pixel (detection unit) exceeds a threshold, and an analog processing unit 402 (conversion processing unit) that outputs a signal obtained by performing a second processing (analog conversion processing) on ​​the signal that has been subjected to the first processing (digital signal processing) by the digital processing unit 401.

[0032] The digital processing unit 401 (first processing unit) generates a signal by performing digital signal processing on the detection result of the dose detection pixel as a first process. The digital processing unit 401 (first processing unit) can output the generated signal as a synchronization control signal with the radiation source 1003. The digital processing unit 401 (first processing unit) is configured to detect, for example, irradiation of the radiation imaging device 1001 and calculate the radiation exposure dose and accumulated exposure dose (accumulated dose) based on the generated signal. The digital processing unit 401 (first processing unit) outputs a stop signal (first stop signal) when dose information acquired based on the first process (digital signal processing) on ​​the detection result by the dose detection pixel 121 (detection unit) exceeds a threshold value.

[0033] The analog processing unit 402 (conversion processing unit) and the signal integration determination unit 1044 (integration determination unit) configure a second processing unit in the radiation imaging system 1000 of this embodiment. The second processing unit outputs a stop signal (second stop signal) when dose information acquired based on second processing (analog conversion processing) of a signal that has been subjected to first processing (digital signal processing) by the digital processing unit 401 (first processing unit) exceeds a threshold value.

[0034] Here, the analog processing unit 402 (conversion processing unit) outputs a signal obtained by performing a second processing (analog conversion processing) on ​​a signal that has been subjected to a first processing (digital signal processing) by the digital processing unit 401 (first processing unit), and the signal integration determination unit 1044 determines whether or not dose information obtained by integrating the signal output from the analog processing unit 402 (conversion processing unit) exceeds a threshold value. The second processing unit outputs a stop signal (second stop signal) when the signal integration determination unit 1044 (integration determination unit) determines that the dose information exceeds the threshold value.

[0035] The radiation generation control unit 1042 controls the radiation source 1003 based on a first stop signal output from the digital processing unit 401 (first processing unit) or a second stop signal output from the analog processing unit 402 and the signal integration determination unit 1044 (second processing unit). In other words, the radiation generation control unit 1042 controls the radiation source 1003 to stop emitting radiation based on the first stop signal or the second stop signal.

[0036] The signal selection unit 1043 (selection unit) receives a stop signal (second stop signal) of the radiation 1103 input from the signal integration determination unit 1044 (integration determination unit) via an analog signal path (second signal path) and a stop signal (first stop signal) of the radiation 1103 input from the signal processing unit 1045 via a digital signal path (first signal path). The stop signal input first is selected by the signal selection unit 1043 (selection unit), and the selected stop signal is transmitted to the radiation generation control unit 1042. That is, the signal selection unit 1043 (selection unit) selects the input first stop signal or second stop signal. At this time, the signal selection unit 1043 (selection unit) selects the signal input first from the first stop signal and the second stop signal.

[0037] The radiation generation control unit 1042 controls the generation of radiation while checking the state of each input. The radiation generation control unit 1042 controls the emission of radiation emitted from the radiation source 1003 based on the input signal related to the exposure state. That is, the radiation generation control unit 1042 controls the radiation source 1003 to stop emitting radiation based on the signal selected by a signal selection unit 1043 (selection unit).

[0038] The radiation imaging device 1001 can communicate with a signal processing unit 1045 of the high voltage generator 1004 via a repeater 1023 and a signal generating unit 1024 of the imaging control device 1002. A signal indicating an imaging preparation state is input from the radiation imaging device 1001 to the signal processing unit 1045 via the repeater 1023 and the signal generating unit 1024 of the imaging control device 1002. The signal processing unit 1045 inputs the input signal indicating the imaging preparation state to the radiation generation control unit 1042. Here, when the communication between the radiation imaging device 1001 and the imaging control device 1002 is wireless communication, the repeater 1023 functions as an access point, and when the communication is wired communication, the repeater 1023 functions as a switching hub. A communication control unit 1021 is further connected to the repeater 1023, and the function of the communication control unit 1021 is realized by application software that runs on a platform such as a PC (information processing device).

[0039] In this embodiment, there are two types of signal paths for dose control using analog signals and digital signals. One signal path is a signal path (second signal path) for an analog signal for dose control, which is connected from the communication unit 227 of the radiation imaging device 1001 to the signal integration determination unit 1044 in the high voltage generator 1004. This analog signal is an output signal simulating the output of the dose control sensor 1011 (analog output signal for dose control). This connection form can use the processing circuit of the high voltage generator 1004 for processing the analog output signal of the dose control sensor 1011, so it is a connection form that does not require any change to the processing circuit of the high voltage generator 1004. The dose control sensor 1011 is a dose control sensor of an ion chamber type, a type in which a phosphor is applied to an optical fiber and detected by an image intensifier, a type in which a thin film semiconductor sensor is used, or the like. As described later, this signal path is configured such that the high voltage generator 1004 has a circuit configuration for dose control. Incidentally, it is also possible to configure the dose control redundantly by using the dose control sensor 1011 in place of the radiation imaging device 1001 and also using the output as an analog signal.

[0040] As shown in FIG. 4, five light-measurement fields 1012 are set in the dose control sensor 1011. The setting of the light-measurement fields 1012 is illustrative, and the gist of the embodiment is not limited to this example. In the example shown in FIG. 4, the light-measurement fields 1012 corresponding to the five areas correspond to the plurality of dose detection pixels 121 of the radiation imaging device 1001, respectively. The operator can select the light-measurement fields 1012 from a determined irradiation area pattern on a user interface (setting unit) (not shown) on the high-voltage generator 1004. Based on the operation input by the operator, the user interface (setting unit) sets the irradiation area of ​​the radiation source. When the irradiation area of ​​the radiation source is set, the control circuit 225 (FIGS. 6A to 6C) of the radiation imaging device 1001 can identify the dose detection pixel 121 (detection unit) arranged at a position corresponding to the set irradiation area from among the plurality of dose detection pixels 121 (detection units) arranged in the imaging region 100. Furthermore, the control unit 1022 (acquisition unit) of the imaging control device 1002 can acquire information on the imaging site of the subject from information of an imaging order system such as a Hospital Information System (HIS) / Radiology Information System (RIS) via the LAN 1005. When the control unit 1022 (acquisition unit) acquires information on the imaging site of the subject, the control circuit 225 (identification unit) of the radiation imaging device 1001 can identify the dose detection pixel 121 (detection unit) arranged at a position corresponding to the imaging site of the subject from among a plurality of dose detection pixels 121 (detection units) arranged in the imaging region 100.

[0041] The digital processing unit 401 (first processing unit) of the radiation imaging device 1001 acquires dose information based on the detection result of the specified dose detection pixel 121 (detection unit). In addition, the analog processing unit 402 (conversion processing unit) of the radiation imaging device 1001 generates and outputs an analog output signal (analog output signal for dose control (signal corresponding to the received dose)) simulating the output of the dose control sensor at a position corresponding to each radiation collection field.

[0042] Next, a digital signal path (first signal path) for dose control will be described. This signal transmission path uses a dedicated digital communication path for transmitting a handshake signal for preparing for imaging between the high voltage generator 1004 and the radiation imaging device 1001, or a path equivalent thereto.

[0043] The handshaking operation during radiation imaging will be described with reference to Figures 4 and 5. In the case of a sequence in which the irradiation time is determined on the high voltage generator 1004 side as shown in Figure 5(a), the operator operates the operation switch 46, and the radiation generation control unit 1042 prepares for radiation generation. When the anode rotation speed of the radiation source 1003 has stabilized and other internal circuit preparations have been completed, the signal processing unit 1045 of the high voltage generator 1004 outputs a request signal 501 for imaging preparation as a signal of a request level based on a signal input from the radiation generation control unit 1042 (Figure 5(a)).

[0044] The imaging preparation request signal 501 (request level) output from the signal processing unit 1045 of the high voltage generator 1004 is transmitted to the radiation imaging device 1001 via the signal generating unit 1024 of the imaging control device 1002. Thereafter, when the imaging preparation is completed, the radiation imaging device 1001 outputs a signal indicating the completion of imaging preparation, and based on the signal input from the radiation imaging device 1001, the signal generating unit 1024 of the imaging control device 1002 outputs a signal with the imaging preparation completion signal 502 set to the preparation completion level (FIG. 5(a)). The imaging preparation completion signal 502 (preparation completion level) is input to the radiation generation control unit 1042 via the signal processing unit 1045 of the high voltage generator 1004. Here, the signal indicating the imaging preparation completion output from the radiation imaging device 1001 corresponds to an irradiation start signal for starting irradiation of radiation. The radiation generation control unit 1042 monitors other signal states, and irradiates radiation 1103 after confirming that the preparation state is complete. Here, the radiation generation control unit 1042 can control the radiation irradiation to be stopped based on the radiation irradiation time set by the operator. The radiation 1103 changes from an irradiation state to a non-irradiation state based on the control (irradiation stop control) of the radiation generation control unit 1042 ((a) of FIG. 5).

[0045] Then, based on a signal input from the radiation generation control unit 1042, the signal processing unit 1045 of the high voltage generator 1004 changes the imaging preparation request signal 501 to a non-request level and outputs it (non-request output). That is, based on a signal input from the radiation generation control unit 1042, the signal processing unit 1045 outputs a signal in which the imaging preparation request signal 501 is set to a non-request level (imaging preparation request signal 501 (non-request level)). The imaging preparation request signal 501 (non-request level) output from the signal processing unit 1045 of the high voltage generator 1004 is transmitted to the radiation imaging device 1001 via the signal generating unit 1024 of the imaging control device 1002. In response to the imaging preparation request signal 501 (non-request level), the radiation imaging device 1001 transitions the state of the radiation imaging device 1001 from an imaging preparation complete state to a preparation not complete state.

[0046] Next, an operation sequence when a sufficient reaching dose is detected before the set radiation irradiation time has elapsed will be described with reference to (b) of FIG. 5. The operation sequence is the same as that of (a) of FIG. 5 until radiation 1103 is actually irradiated. After that, when a sufficient reaching dose is detected inside the radiation imaging device 1001 by a method to be described later, the signal generating unit 1024 outputs a signal that transitions the imaging preparation completion signal 502 from a preparation completion level to a preparation non-completion level (non-completion level) based on a signal output from the radiation imaging device 1001 even if the imaging preparation request signal 501 is in a request level state. Here, when a sufficient reaching dose is detected inside the radiation imaging device 1001, the signal output from the radiation imaging device 1001 corresponds to a stop signal (first stop signal) output from the digital processing unit 401 (first processing unit) when the dose information acquired based on the first processing (digital signal processing) exceeds a threshold value. 5B, when a sufficient radiation dose is detected inside the radiation imaging device 1001, the state transitions from the preparation complete level to the preparation non-completion level (non-completion state) before the set radiation irradiation time has elapsed. A completion signal 502 (non-completion level) of imaging preparation is input from the signal generating unit 1024 to the signal processing unit 1045 of the high voltage generating device 1004. When the request signal 501 for imaging preparation is in the request level state and the completion signal 502 for imaging preparation is in the non-completion level state, the signal processing unit 1045 outputs the completion signal 502 for imaging preparation (non-completion state) input from the signal generating unit 1024 to the signal selecting unit 1043 as a stop signal of radiation 1103 in the digital signal path. That is, the stop signal (first stop signal) output from the digital processing unit 401 (first processing unit) is input to the signal selection unit 1043 via the repeater 1023 and signal generating unit 1024 of the imaging control device 1002 and the signal processing unit 1045 of the high voltage generating device 1004.

[0047] 5(b), for example, when a stop signal (first stop signal) output from the digital processing unit 401 (first processing unit) is input to the signal selection unit 1043 prior to a stop signal (second stop signal) via an analog signal path (second signal path), the radiation generation control unit 1042 detects that the imaging preparation completion signal 502 has transitioned from a preparation complete state to a preparation not complete state, based on the stop signal (first stop signal) input earlier to the signal selection unit 1043. In other words, the radiation generation control unit 1042 detects that the dose information (accumulated dose) has reached a predetermined dose, and controls the radiation source 1003 to stop irradiating radiation 1103.

[0048] 5, the signals are expressed in a circuit signal format, but the communication between the high voltage generator 1004 and the radiation imaging device 1001 for the image capture preparation request signal 501 and the image capture preparation completion signal 502 can also be realized by command communication. In this embodiment, the signal path is configured to be capable of transmitting a signal for controlling the radiation irradiation stop in, for example, 1 ms or less in order to be used for the handshaking operation during irradiation and for controlling the radiation dose. From this perspective, the device used for the signal generating unit 1024 can be, for example, a photocoupler, a photoMOS relay, or the like. In addition, for command communication, a communication method that can guarantee communication time and delay time, such as wired 100BaseTX / 1000BaseT, can be used. It is also possible to configure a signal path using wireless communication by ensuring reliability and responsiveness.

[0049] On the other hand, if the intention is simply to suppress the dose of excessive radiation exposure that does not contribute to improving image quality, and the specifications stipulate that a stop function should be activated when exposure lasts for a long period of time, for example, around 1 s, the purpose can be achieved even with a delay of around 100 ms, so it is possible to realize the function using an interface that performs normal imaging handshakes that are not intended to suppress the dose.

[0050] Next, an operation relating to radiation dose detection for the automatic exposure function or dose suppression function will be described. Figures 6A to 6C are diagrams illustrating an example of the internal configuration of a radiation imaging apparatus according to an embodiment.

[0051] The radiation imaging device 1001 has a plurality of pixels arranged in an imaging region 100 to form a plurality of rows and a plurality of columns. In this embodiment, an example in which each pixel is made of amorphous silicon or polycrystalline silicon will be described. The plurality of pixels include a plurality of imaging pixels 101 for detecting radiation and acquiring a radiation image based on the detected radiation, and a dose detection pixel 121 (detection unit) for detecting the dose of radiation irradiated from a radiation source.

[0052] In order to accurately control the dose for forming an image by automatic exposure control, it is extremely important that the input / output relationship for radiation between the imaging pixels 101 and the dose detection pixels 121 is clearly understood. It is impossible to accurately grasp the spectrum of the radiation quality that changes for each location on the human body after passing through a subject. Therefore, if the imaging pixels 101 for forming an image and the dose detection pixels 121 for automatic exposure control have different outputs for the same radiation due to the radiation quality, the difference in output between the imaging pixels 101 and the dose detection pixels 121 cannot be corrected. This makes it impossible to perform accurate automatic exposure control.

[0053] For this reason, in order to perform accurate automatic exposure control, it is necessary to clearly understand the input / output relationship with respect to radiation, and the easiest way to achieve this is to make the imaging pixels 101 and the dose detection pixels 121 exactly the same. In the case of an imaging element that can perform non-destructive readout, such as an imaging element configured with CMOS, it is possible to make the imaging pixels 101 and the dose detection pixels 121 exactly the same. That is, the functions of imaging and dose detection can be performed by one imaging element. In the case of amorphous silicon or polycrystalline silicon of this embodiment, since the pixel structure is for destructive readout, non-destructive readout cannot be performed. As a second best solution, the imaging pixels 101 and the dose detection pixels 121 are different pixels, but their structures are made the same. This makes it possible to make the output characteristics, such as radiation quality dependency, the same, with only a slight difference in spatial location between the imaging pixels 101 and the dose detection pixels 121.

[0054] The imaging pixel 101 includes a first conversion element 102 that converts radiation into an electrical signal, and a first switch 103 arranged between a column signal line 105 and the first conversion element 102. The dose detection pixel 121 includes a second conversion element 122 that converts radiation into an electrical signal, and a second switch 123 arranged between a detection signal line 125 and the second conversion element 122.

[0055] The first conversion element 102 and the second conversion element 122 are 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 100, and can be shared by multiple pixels. Alternatively, the first conversion element 102 and the second conversion element 122 can be composed of a conversion element that directly converts radiation into light.

[0056] The first switch 103 and the second switch 123 may include, for example, a thin film transistor (TFT) having an active region made of a semiconductor such as amorphous silicon or polycrystalline silicon (preferably polycrystalline silicon).

[0057] The radiation imaging device 1001 has a plurality of column signal lines 105 and a plurality of drive lines 104. Each column signal line 105 corresponds to one of a plurality of columns in the imaging region 100. Each drive line 104 corresponds to one of a plurality of rows in the imaging region 100. Each drive line 104 is driven by a drive circuit 221 (row selection unit).

[0058] A first electrode of the first conversion element 102 is connected to a first main electrode of the first switch 103, and a second electrode of the first conversion element 102 is connected to a bias line 108. Here, one bias line 108 extends in the column direction and is commonly connected to the second electrodes of the multiple first conversion elements 102 arranged in the column direction. The bias line 108 receives a bias voltage Vs from a power supply circuit 226. Second main electrodes of the first switches 103 of multiple imaging pixels 101 constituting one column are connected to one column signal line 105. Control electrodes of the first switches 103 of multiple imaging pixels 101 constituting one row are connected to one drive line 104.

[0059] The column signal lines 105 are connected to a readout circuit 222. The readout circuit 222 may include a plurality of detection units 132, a multiplexer 134, and an analog-to-digital converter (hereinafter, AD converter) 136. Each of the column signal lines 105 is connected to a corresponding one of the detection units 132 of the readout circuit 222. Each column signal line 105 corresponds to one detection unit 132. The detection unit 132 includes, for example, a differential amplifier. The multiplexer 134 selects the detection units 132 in a predetermined order, and supplies a signal from the selected detection unit 132 to the AD converter 136. The AD converter 136 converts the supplied signal into a digital signal and outputs it.

[0060] A first electrode of the second conversion element 122 is connected to a first main electrode of the second switch 123, and a second electrode of the second conversion element 122 is connected to the bias line 108. A second main electrode of the second switch 123 is electrically connected to a detection signal line 125. A control electrode of the second switch 123 is electrically connected to a drive line 124. The radiation imaging device 1001 may have a plurality of detection signal lines 125. One or a plurality of radiation amount detection pixels 121 may be connected to one detection signal line 125. The drive line 124 is driven by a drive circuit 241. One or a plurality of radiation amount detection pixels 121 may be connected to one drive line 124.

[0061] The detection signal lines 125 are connected to a readout circuit 242 (AEC sensor readout circuit). Here, the readout circuit 242 may include a plurality of detection units 142, a multiplexer 144, and an AD converter 146. Each of the plurality of detection signal lines 125 may be connected to a corresponding one of the plurality of detection units 142 of the readout circuit 242. Here, one detection signal line 125 corresponds to one detection unit 142. The detection unit 142 includes, for example, a differential amplifier. The multiplexer 144 selects the plurality of detection units 142 in a predetermined order, and supplies a signal from the selected detection unit 142 to the AD converter 146. The AD converter 146 converts the supplied signal into a digital signal and outputs it.

[0062] The output of the AD converter 146 of the readout circuit 242 is supplied to the signal processing unit 224 and processed by the signal processing unit 224. The signal processing unit 224 outputs information indicating irradiation of radiation to the radiation imaging device 1001 based on the output of the AD converter 146 of the readout circuit 242.

[0063] The signal processing unit 224 of the radiation imaging device 1001 of this embodiment has a digital processing unit 401 that outputs a stop signal when dose information acquired based on a first processing (digital signal processing) on ​​the result of detection by the dose detection pixel 121 (detection unit) exceeds a threshold, and an analog processing unit 402 (conversion processing unit) that outputs a signal obtained by performing a second processing (analog conversion processing) on ​​the signal that has been subjected to the first processing (digital signal processing) by the digital processing unit 401.

[0064] Specifically, the digital processing unit 401 detects irradiation of radiation to the radiation imaging device 1001, and calculates the amount of irradiation and / or the accumulated amount of irradiation, for example. For this purpose, the second conversion elements 122 are configured to have a pixel number ratio of 1% or less of the first conversion elements 102, which are the original imaging elements. This is to suppress the amount of radiation that does not contribute to image formation to less than the amount absorbed by existing AEC sensors. In addition, in order for the second conversion elements 122 to be compatible with various measurements, it is useful to distribute the second conversion elements 122 uniformly or in the center where the region of interest is concentrated, or to increase the density of the peripheral areas for use in irradiation area detection, etc.

[0065] The analog processing unit 402 converts the irradiation dose that has been digitally processed by the digital processing unit 401 into an analog signal, and generates an analog output signal that simulates the output of a dose control sensor (such as an ion chamber / photo timer). The control circuit 225 controls the drive circuits 221, 241 and the readout circuits 222, 242 based on information from the signal processing unit 224. The control circuit 225 generates a signal that can indicate, for example, the start and end of exposure (accumulation of electric charges by the imaging pixels 101 corresponding to the irradiated radiation) based on information from the signal processing unit 224. The radiation imaging device 1001 also has a communication unit 227 that is responsible for communication with the imaging control device 1002. The communication unit 227 has two communication units, a wired communication unit and a wireless communication unit, for outputting a signal via a signal path for a digital signal (first signal path), and an analog output unit that outputs an analog output signal (analog output signal for dose control) that simulates the output of the dose control sensor via a signal path for an analog signal (second signal path). That is, the communication unit 227 outputs the signal output from the digital processing unit 401 (first processing unit) via a digital signal path (first signal path), and outputs the signal output from the analog processing unit 402 (conversion processing unit) via an analog signal path (second signal path).

[0066] Fig. 6A shows an example in which the dose detection pixels 121 are arranged in 1 x 1 pixel units, while Fig. 6B and Fig. 6C show an example in which the dose detection pixels 121 are arranged in row units of m x 1, etc. When the dose detection pixels 121 are arranged in row units of m x 1, etc., it becomes possible to generate a line profile in real time, and it becomes possible to use the detection information of the dose detection pixels 121 in real time exposure dose determination by more advanced image processing and in the processing for that determination.

[0067] In addition, Figures 6A and 6B show an example in which the imaging pixels 101 and the dose detection pixels 121 are read out using independent and different circuit configurations (readout circuit 222, readout circuit 242), while Figure 6C shows a configuration in which the imaging pixels 101 and the dose detection pixels 121 are read out using a common circuit configuration.

[0068] In FIG. 6C, a readout circuit that serves both as the readout circuit 222 and the readout circuit 242 is denoted as "222C", and a drive circuit that serves both as the drive circuit 221 and the drive circuit 241 is denoted as "221C".

[0069] Also, in FIG. 6C, the detection unit that serves as both detection unit 132 and detection unit 142 is indicated as "132C," the multiplexer that serves as both multiplexer 134 and multiplexer 144 is indicated as "134C," and the AD converter that serves as both AD converter 136 and AD converter 146 is indicated as "136C."

[0070] In the circuit configuration of FIG. 6C , the control in the shared drive circuit 221C and readout circuit 222C becomes slightly more complicated; however, the drive circuit 241 and readout circuit 242 of the dose detection pixel 121 are shared with the drive circuit 221 and readout circuit 222 of the imaging pixel 101, resulting in a simpler circuit configuration and a reduced number of components, which is advantageous in terms of quality and cost.

[0071] Furthermore, in the case of imaging in which the dose detection pixel 121 is not used in the circuit configuration of Fig. 6C, the dose detection pixel 121 can also be used as the imaging pixel 101. Fig. 6C also includes a correction pixel 151 shown with hatching. The correction pixel 151 is made up of one or more pixels used to correct the amount of radiation applied, and the sensitivity of the correction pixel 151 to radiation is set lower than the sensitivity of the imaging pixel 101 to radiation. The correction pixel 151 basically has the same structure as the dose detection pixel 121 and the imaging pixel 101, but differs in structure from the dose detection pixel 121 and the imaging pixel 101 in that the second conversion element 122 is covered with a film that blocks visible light from the outside. The correction pixel 151 is blocked by covering the second conversion element 122 with a metal layer such as aluminum.

[0072] The radiation imaging system 1001 of this embodiment includes a radiation imaging device 1001 including dose detection pixels 121 that detect a dose of radiation irradiated from a radiation source 1003, and an imaging control device 1002 that controls the radiation imaging device 1001. Prior to radiation imaging, the imaging control device 1002 identifies the positions of the dose detection pixels in a region of interest (radiation measurement field 1012) for calculating a dose index value of a radiation image, determines a threshold value according to the positions of the dose detection pixels, and transmits the positions of the dose detection pixels and the threshold value to the radiation imaging device 1001. A control circuit 225 of the radiation imaging device 1001 sets the positions of the dose detection pixels in the region of interest (radiation measurement field 1012) and the threshold value transmitted from the imaging control device 1002, and performs imaging based on the settings.

[0073] An example of the operation of the radiation amount detection pixel 121 in Fig. 6C will now be described with reference to the timing chart in Fig. 7. This operation is performed by cooperation between the control circuit 225, which controls the drive circuit 221C and the readout circuit 222C, and the signal processing unit 224. Therefore, the combination of the signal processing unit 224 and the control circuit 225 may be called an exposure determination unit.

[0074] 7, "radiation" indicates whether radiation is being irradiated to the radiation imaging device 1001. When it is low (signal is OFF), radiation is not being irradiated, and when it is high (signal is ON), radiation is being irradiated.

[0075] "Vg1" to "Vgn" indicate drive signals supplied from the drive circuit 221C to the multiple drive lines 104. "Vgk" indicates a drive signal supplied to the drive line 104 in the kth row (k=1,..., number of drive lines n). Some of the multiple drive lines supplied from the drive circuit 221C function as drive lines 124 that supply drive signals for driving the radiation amount detection pixels 121 or the correction pixels 151. "Vgk / Vdj" corresponds to the drive line 124 in the kth row, the jth detection drive line (k=1,..., number of drive lines n, j=1,..., number of detection drive lines). For example, "Vg2 / Vd1" indicates a drive signal supplied to the drive line 124 in the second row, the first detection drive line.

[0076] The "dose detection pixel signal" indicates the value of a signal read out from the dose detection pixel 121. The "correction pixel signal" indicates the value of a signal read out from the correction pixel 151. The "accumulated exposure dose" indicates the accumulated value of radiation irradiated to the radiation imaging device 1001. A method for determining this accumulated value will be described later.

[0077] The period from time t0 to t4 is defined as a "reset operation period." At time t0, the control circuit 225 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, it is an operation of turning on the switch element (first switch 103, second switch 123) of each pixel by supplying a drive signal to the drive lines 104 and 124 from the drive circuit 221C. The control circuit 225 resets each pixel connected to the drive line 104 of the first row by controlling the drive circuit 221C. Then, the control circuit 225 resets each pixel connected to the drive line 124 of the second row. The control circuit 225 repeats this operation up to the drive line 104 of the last row. At time t1, the control circuit 225 ends the reset operation of the drive line 104 of the last row, and then repeats the reset operation again from the drive line 104 of the first row.

[0078] At time t3, the imaging control device 1002 transmits an irradiation start request signal to the control circuit 225, thereby activating the "irradiation start request signal." At this point, the imaging condition settings are finalized by the information transmitted from the imaging control device 1002. In addition, the imaging control device 1002 transmits the maximum radiation irradiation time and, in some cases, irradiation area information, direct radiation dose information, an automatic exposure control signal, automatic exposure time information (ROI / calculation method), and the like to the control circuit 225 of the radiation imaging device 1001. The control circuit 225 can use the information transmitted from the imaging control device 1002 as correction information for the AEC operation.

[0079] In response to receiving the irradiation start request signal, the control circuit 225 performs the reset operation up to the last row and ends the reset operation. The control circuit 225 may end the reset operation before performing the reset operation up to the last row and proceed to the next process. For example, when the control circuit 225 receives the irradiation start request signal during the reset operation of the kth row drive line 104 (124), it is also possible to control so as to proceed to the next process without performing the reset operation of the k+1th row and subsequent drive lines 104 (124). In this case, a step-like image artifact may occur near the k+1th row, but the step-like image artifact can be reduced by adjusting the drive when acquiring a correction image for correcting the radiation image, such as by similarly ending the drive at the k+1th row, and by image processing of the radiation image.

[0080] The period from time t4 to t8 is referred to as a "readout operation period." At time t4, the control circuit 225 starts a measurement operation for measuring the amount of radiation being irradiated to the radiation imaging device 1001. In the measurement operation, the control circuit 225 repeatedly executes a readout operation to read out data from the dose detection pixels 121 and the correction pixels 151. Of the multiple readout operations, one or more readout operations in the first half are performed to determine a correction value, and the readout operations repeated in the second half are performed to continuously measure the amount of radiation at each time.

[0081] At time t5, the control circuit 225 activates the “irradiation and read enable signal”. The read operation during the active period of the “irradiation and read enable signal” is performed only for the drive line 124 (AEC drive line), and is not performed for the other drive lines 104. Specifically, the control circuit 225 supplies a drive signal to the drive line 124 (AEC drive line) that is connected to at least one of the dose detection pixels 121 and the correction pixel 151, among the multiple drive lines 104, 124. The control circuit 225 does not supply a drive signal to the drive line 104 that is not connected to either the dose detection pixel 121 or the correction pixel 151, among the multiple drive lines 104, 124.

[0082] Furthermore, the control circuit 225 may drive the drive lines 124, 124, which are connected to at least one of the dose detection pixels 121 and the correction pixel 151, to simultaneously supply drive signals. This allows signals from multiple pixels connected to the same drive line to be simultaneously read out to the readout circuit 222C. The imaging pixels 101 (including the dose detection pixels 121 and the correction pixel 151) are connected to the column signal lines 105C (105, 125) but are selectively read out by the control circuit 225, so that the readout circuit 222C can read out signals for AEC detection separately from signals for image detection.

[0083] The control circuit 225 performs a read operation a predetermined number of times, which is equal to or greater than one, to determine the correction value. The signal processing unit 224 determines a correction value Od based on signals read from the radiation amount detection pixels 121 by the predetermined number of read operations, and a correction value Oc based on signals read from the correction pixels 151 by the predetermined number of read operations.

[0084] Next, the determination of the correction values ​​Od and Oc will be described. The parameters for determining the correction values ​​are actually composed of outputs from a plurality of pixels, and how each pixel is used will be described later.

[0085] If the predetermined number of times in the readout operation is one, one signal is read out from the radiation amount detection pixel 121 per pixel, and the signal processing unit 224 sets the value of that signal as the correction value Od. If the predetermined number of times is multiple, the signal processing unit 224 sets the average value of the multiple readout signals as the correction value Od. Other statistical values ​​can be used instead of the average value, and the value of the correction value (offset signal) is represented as Od. Similarly, the correction value Oc can be determined as the value of the correction value (offset signal) based on the signal read out from the correction pixel 151. The signal processing unit 224 stores the correction values ​​Od and Oc determined in this manner in the storage unit 172, and makes them available for subsequent processing.

[0086] Since the value of the offset signal changes depending on the temperature environment of the sensor, etc., by acquiring the offset signal immediately before radiation detection, as in this embodiment, the difference between the offset component at the time the offset signal is acquired and the offset component at the time radiation is detected can be reduced, and the offset component at the time radiation is detected can be accurately corrected.

[0087] Conversely, there may be cases where the error due to random noise components becomes larger than the fluctuation components due to temperature changes during the "read operation period" (times t4 to t8) because the number of samples required to generate the correction values ​​Od and Oc is small. In such cases, it is also possible to generate the correction values ​​Od and Oc at a timing where there is ample time, such as a reset operation period, and where the number of samples is sufficient to suppress errors due to random noise components such as thermal noise.

[0088] The time from when the imaging control device 1002 transmits an "irradiation start request signal" to the control circuit 225 until the control circuit 225 transmits an "irradiation and readout enable signal" to the high-voltage generator 1004 via the imaging control device 1002 is called an "exposure delay." In this case, since data acquisition is not required during the period from t4 to t5 (the "exposure delay" period), the period corresponding to the exposure delay can be shortened.

[0089] After completing one or more readout operations of the correction values ​​Od and Oc, the control circuit 225 transmits an "irradiation and readout enable signal" to the high-voltage generator 1004 via the imaging control device 1002 at time t5. After actively transmitting the irradiation and readout enable signal, the control circuit 225 repeatedly executes the above-mentioned readout operation. The signal processing unit 224 measures an "accumulated DOSE" as an integrated value of the radiation exposure amount described below for each readout operation, and determines whether or not the integrated value exceeds a preset "AEC threshold value." After the control circuit 225 transmits the "irradiation and readout enable signal" to the high-voltage generator 1004 at time t5, irradiation of radiation begins at time t6.

[0090] A method for determining the radiation dose DOSE will be described below. The signal value read from the dose detection pixel 121 by the most recent read operation is represented as Sd. The signal value read from the correction pixel 151 by the most recent read operation is represented as Sc. The signal processing unit 224 calculates the radiation dose DOSE by applying Sd, Sc, Od, and Oc to the following formulas (1) and (2). Since the "AEC threshold" corresponds to the dose per unit area, formula (2) showing the accumulated dose DOSE is also normalized to the dose per unit area for comparison. The control circuit 225 of the radiation imaging device 1001 corrects the signals read from the dose detection pixels 121 in the region of interest (illumination field 1012) specified by the imaging control device 1002 based on the signals read from the correction pixels 151 in which visible light is blocked, and calculates the accumulated dose of radiation based on the corrected signals.

[0091] DOSE per unit sample = (Sd-Od)-(Sc-Oc) (1) Accumulated DOSE = Σ{(Sd-Od)-(Sc-Oc)} (2) The DOSE for each unit sample shown in Fig. 7 shows an example of the calculation result of the above formula (1). In reality, it is a discrete value that is updated each time a drive signal is supplied to each drive line 124 (AEC drive line) to operate the dose detection pixel 121 and read out the irradiated radiation, but is shown continuously in Fig. 7. The accumulated DOSE shown in Fig. 7 shows an example of the calculation result of the integrated DOSE using the above formula (2). As shown in Fig. 7, the integrated DOSE shows a tendency to be updated and increase each time it is read out.

[0092] The signal processing unit 224 acquires a difference (Sd-Od) between the value Sd of the signal read from the dose detection pixel 121 after the control circuit 225 transmits the irradiation and readable signal, and a correction value Od determined based on the signal read from the dose detection pixel 121 before transmitting the irradiation and readable signal. The signal processing unit 224 also acquires a difference (Sc-Oc) between the value Sc of the signal read from the correction pixel 151, and a correction value Oc determined based on the signal read from the correction pixel 151 before transmitting the irradiation and readable signal. Then, the signal processing unit 224 calculates the radiation exposure dose DOSE (DOSE per unit sample) and the accumulated DOSE based on the acquired difference (Sd-Od) and difference (Sc-Oc).

[0093] 7, the "dose detection pixel 121 signal (Sd-Od)" which is a signal read from the dose detection pixel 121 that is not shaded changes significantly immediately after the end of the reset operation (immediately after time t4) and stabilizes over time, for example, in about 100 ms. Therefore, even if the radiation exposure dose DOSE is calculated using only the signal value Sd and the correction value Od obtained from the dose detection pixel 121, the offset amount cannot be sufficiently removed. If the start of the read operation for acquiring the correction value Od is delayed until the signal read from the dose detection pixel 121 stabilizes, the time from the transmission of the irradiation start request signal to the actual start of radiation irradiation (the time from time t3 to t5, exposure delay) becomes longer.

[0094] In the circuit configuration shown in Fig. 6C, the radiation dose DOSE is measured further using the signal value Sc and correction value Oc read from the correction pixel 151. Since the correction pixel 151 has a lower sensitivity to radiation than the dose detection pixel 121 and the imaging pixel 101, the signal value Sc read from the correction pixel 151 after the start of radiation irradiation can be considered to represent an offset component of the signal value Sd read from the dose detection pixel 121. Furthermore, in this embodiment, the radiation dose DOSE is determined using the correction values ​​Od and Oc based on the signals read from the dose detection pixel 121 and the correction pixel 151 before the start of radiation irradiation. This makes it possible to correct characteristic differences inherent to each pixel (for example, differences in the channels of the detection circuit, differences in the parasitic resistance and parasitic capacitance of each pixel, etc.).

[0095] At time t7 in FIG. 7, the accumulated DOSE reaches the AEC threshold preset by the control circuit 225. In response to this, the control circuit 225 transmits information indicating that the AEC threshold has been reached by transmitting a "threshold reaching signal" to the high voltage generator 1004 via the imaging control device 1002, or by deactivating the "irradiation and readout enable signal". The imaging control device 1002 controls the irradiation of the radiation source so that the dose target value set as the threshold is equal to the dose index value in the radiation image. Instead of transmitting the threshold reaching signal to the imaging control device 1002 at the timing when the accumulated DOSE reaches the AEC threshold, the control circuit 225 may estimate the time when the accumulated exposure reaches the threshold and transmit the threshold reaching signal at this estimated time. The high voltage generator 1004, which receives the threshold reaching signal notifying that the AEC threshold has been reached via the imaging control device 1002, ends the irradiation of radiation at time t8.

[0096] In order to accurately accumulate the radiation dose and stop the radiation irradiation at an appropriate response time, the readout period of the drive line 124 (AEC drive line) Vgk / Vdj may be set to a sufficiently short period, for example, at most 1 / 10 of the actual irradiation time. Normally, when an amorphous silicon sensor is used, it takes 10 μs to 50 μs to read out one row of signals. For this reason, in order to read out a wide area, it is necessary to set the operation of the entire dose detection pixel 121 to fall within the optimal time, for example, by simultaneously enabling a plurality of drive lines 124 (AEC drive lines) Vgk / Vdj and reading out the output. Similarly, when the actual irradiation time is particularly several ms or less, the delay time from the detection of accumulated radiation irradiation to the AEC threshold value, the comparison of the reached threshold value, and the output of the "threshold reached signal" can be set to, for example, 1 ms or less. In addition, it is also possible to control by setting the AEC threshold value smaller by the delay time in advance, taking into account the delay time, according to the slope of the accumulated dose.

[0097] At this time, the control circuit 225 also transmits to the imaging control device 1002 the actually adopted “automatic exposure time information (ROI / calculation method)”, the arrival dose information, and the like.

[0098] From time t9 to t10, a predetermined time after the expected delay time from time t7 until the radiation stops, the drive circuit 221C again supplies drive signals Vg1 to Vgn to the multiple drive lines 104, the readout circuit 222C reads out signals from the multiple imaging pixels 101, and the signals processed by the readout circuit 222C are transmitted from the communication unit 227 to the imaging control device 1002 via the signal processing unit 224. The imaging control device generates a radiographic image based on the signal transmitted from the communication unit 227 of the radiation imaging device 1001, and performs image processing on the generated radiographic image. The radiographic image generated by the imaging control device 1002 and subjected to image processing is transmitted to the display unit 1006 via the imaging control device 1002 and displayed.

[0099] In the above example, the control circuit 225 starts a predetermined number of read operations for determining the correction values ​​Od and Oc immediately after the end of the reset operation. Alternatively, the control circuit 225 may start a predetermined number of read operations after a predetermined time (e.g., several ms to several tens of ms) has elapsed after the end of the reset operation. This makes it possible to suppress signal readout during a period in which time fluctuations are particularly large.

[0100] Regarding the calculation of a general dose index value EI, there are two typical examples: one where the calculation area of ​​the dose index value EI is not changed depending on the difference in the image according to the protocol, the shooting posture of the subject, the part of the subject being imaged, etc., and one where the calculation area of ​​the dose index value EI is changed. When the calculation area of ​​the dose index value EI is not changed, the dose index value EI is calculated in a fixed ROI, and the fixed ROI is calculated in a predetermined area (fixed ROI) of the imaging device. This has the advantage that the operator can clearly determine which area of ​​the image is being calculated. On the other hand, a fixed ROI has the disadvantage that it is difficult to set the dose target value EIt and manage the deviation DI because there is a large variation due to the difference in the protocol and the difference in the subject.

[0101] On the other hand, when changing the calculation area of ​​the dose index value EI, the control circuit 225 first identifies an EI value calculation area for calculating the dose index value EI for each imaging, sets the identified EI value calculation area as an ROI for EI value calculation, and calculates the dose index value EI by obtaining a representative value in the set ROI.

[0102] During imaging, it is difficult for the operator to know in which area the dose index value EI is calculated, but by sharing the calculation algorithm with the operator in advance and, if necessary, displaying the ROI used after calculation, the operator can check the set ROI. Furthermore, since the dose index value EI is calculated after identifying the irradiation area, the variation due to differences in protocols and subject images is smaller than with a fixed ROI, and medical facilities can accurately manage the dose during imaging by setting the dose target value EIt and managing the deviation DI.

[0103] From the viewpoint of appropriate exposure dose management, which is the purpose of introducing the dose index value EI, it is better to calculate the dose index value EI by changing the area (ROI setting) while considering the effective area of ​​the actual image, rather than calculating the dose index value EI in a fixed ROI that does not change the area of ​​the imaging device regardless of the subject's conditions (e.g., the subject's shooting posture, imaging part, etc.).

[0104] Fig. 8 is a flowchart for explaining the flow of a process for calculating a dose index value EI. Fig. 8 illustrates an example of a procedure for calculating a dose index value EI from an image after imaging. First, in step S801 (removal of outside irradiation area), an area from the imaging image that is not irradiated with radiation and that is obviously outside the region of interest of the diagnostic image is excluded from the calculation area of ​​the dose index value EI. As a processing method, a method of calculation based on collimator information, tube-FPD distance (FDD) information, etc., a method of extracting irradiation areas from an image using information on each imaging part in advance, etc., or a method of AI judgment by machine learning can be used.

[0105] Next, in step S802 (removal of direct ray equivalent regions), direct ray regions including regions of only grids are identified and regions outside the region of interest are excluded from the calculation area of ​​the dose index value EI. As a processing method, an empirical fixed threshold method, a mode method, a differential histogram method, a p-tile method, a discriminant analysis method, and the like can be used.

[0106] Furthermore, in step S803 (removal of unnecessary regions such as metal), low-dose regions that are within the region of interest but should not be used as a dose index for the region of interest in a normal diagnostic image are excluded from the calculation area of ​​the dose index value EI. As a processing method, a region growing method, a snake method, etc. can be used. By the processing up to this point (S801 to S803), the calculation area of ​​the dose index value EI in the captured image can be determined as the extraction area.

[0107] Next, in step S804 (calculation of extraction area representative value), a representative value such as the average value or median value of pixel values ​​in the calculation area (extraction area: region of interest) of the dose index value EI is calculated. Finally, in step S805 (conversion of representative value to EI value), the representative value calculated in step S804 is converted to, for example, 100=1 μGy to calculate the dose index value EI. In addition, a deviation DI between the calculated dose index value EI and the dose target value EIt is calculated. Based on the calculated deviation DI, the operator can confirm whether the radiographic image capture was performed with the expected radiation dose. Currently, even if the deviation DI can be confirmed, it is often the case that the hospital facility, including the operator, must determine how to correct and reduce the deviation DI through trial and error.

[0108] Fig. 9 is a diagram for explaining pre-exposure adjustment of the dose index value calculation method, and Fig. 10 is a diagram for explaining during-exposure adjustment of the dose index value calculation method. Specific processing of the adjustment processing in Fig. 9 and Fig. 10 and the processing flow of this embodiment in Fig. 8 will be described. Note that, although the dose index value EI is used as the dose index in this embodiment, the same technology can be applied to dose indices in general.

[0109] Before radiation imaging, the imaging control device 1002 is capable of identifying a region of interest using at least one of a radiation projection area calculated based on position measurement information of the radiation source 1003 and the radiation imaging device 1001, an optical image of the subject in the radiation projection area acquired by a camera, and a radiation image of the subject previously captured.

[0110] 9 and 10, an example will be described in which an operator acquires radiation images of both knees of a subject. The operator positions the subject on a table (not shown) disposed between the radiation source 1003 and the radiation imaging device 1001. As shown in FIG. 9(a), an image 5310 (optical image) is displayed on the display unit 1006 as a real-time video camera image of visible light or infrared light, corresponding to an area (radiation projection area) captured in a radiation image of the subject. A two-dimensional outer shape 5301 of the radiation imaging device 1001, a radiation projection area 5302, and a direct ray area 5303 are displayed on this image 5310.

[0111] The simplest method for realizing this display may be to simply display in real time with an indicator lamp indicating the radiation irradiation area lit, which is a general function of a collimator (not shown) in the radiation source 1003. In this case, the outer shape 5301 indicates the two-dimensional outer shape of the tabletop radiation imaging device 1001, or the two-dimensional outer shape of the radiation imaging device 1001 under a table top made of a material that transmits visible light, such as acrylic.

[0112] In FIG. 9(b), in addition to FIG. 9(a), five default measurement fields 1012 (AEC measurement fields) are overlaid. When photographing a knee, the five default measurement fields 1012 are not appropriate because they do not cover the knee joint to be photographed. For this reason, for example, an operator issues an instruction to change the position of the measurement field 1012 (AEC measurement field) to match the position of the knee joint, as shown in FIG. 9(c). Furthermore, if the operator recognizes in advance that metal is inserted in the knee joint on the left side of FIG. 9, the operator can also issue an instruction to exclude the left knee joint from the measurement field 1012 (AEC measurement field) during photographing.

[0113] Alternatively, as shown in Fig. 9(d), it is possible to display the status of the treatment part previously performed by performing an overlay display in which a past image captured in the past is semi-transparently superimposed on the image of Fig. 9(c) etc., so that it is easy to clearly indicate the status. In Fig. 9(c), it is also possible to display the status of the position of the treatment part such as the metal by display control such as hatching or coloring the treatment part such as the metal inserted in the knee joint, such as the metal area 5304 in Fig. 9(d). As in the case where the operator recognizes it in advance, the operator instructs to exclude the left knee joint from the irradiation field 1012 (AEC irradiation field) at the time of imaging as necessary, and instructs to change the position of the irradiation field 1012 so that it matches the position of the knee joint.

[0114] 9 is an example, and it is possible to set the light-collection field 1012, which is the operating area of ​​the dose detection pixel 121, after performing the processes of "removal of outside irradiation area" (S801), "removal of area equivalent to direct radiation" (S802), and "removal of unnecessary area such as metal" (S803). By calculating the dose index value EI of the captured image using the imaging pixels 101 near the dose detection pixel 121 shown in Fig. 6 and area information of the set light-collection field 1012 as the dose index value EI, it is possible to perform dose management with higher accuracy than before.

[0115] In addition, as for the reference of the past image for follow-up observation, as described above, it is possible to use it to determine the measurement field 1012 (AEC measurement field) more proactively than simply displaying it as a reference image for the operator to determine the measurement field 1012 (AEC measurement field). For example, if the measurement field 1012 (AEC measurement field) of the referenced past image is determined in the same procedure as described in this embodiment, the measurement field 1012 (AEC measurement field) when the target past image was captured may be read from the information at the time of capture recorded in the manufacturer's arbitrary area of ​​the DICOM header, and displayed as the default recommended measurement field of the measurement field 1012 (AEC measurement field) of the current capture. Alternatively, it is possible to perform processing to remove the direct ray area 5303 and the metal area 5304 from the past image in the same manner as the method used this time, and to derive an appropriate measurement field 1012 together with calculating the dose index value EI. In this process, a recommended shape of the measurement field 1012 appropriate for the current capture may be derived. Furthermore, when displaying the recommended measurement field to the operator, the measurement field 1012 that is considered to be in an appropriate position for the image 5310 may be displayed after the image 5310 and the outline are recognized in advance.

[0116] Here, another method of determining the radiation collection field in accordance with the flowchart of Fig. 8 will be described. For example, when the radiation imaging device 1001 is placed in a table, the distance (FDD) between the focal point of the radiation source 1003 and the center of the radiation imaging device 1001 and the positional relationship are automatically measured. In addition, the collimator opening degree is measured by a collimator function (not shown) of the radiation source 1003. These measurements can be performed based on position measurement information of the table and the tube holding mechanism, or the tube which is the radiation source 1003 equipped with an automatic positioning function capable of general imaging and the holding mechanism of the radiation imaging device 1001. The imaging control device 1002 acquires these measured information via the high voltage generator 1004 and the like, and can calculate the outer shape 5301 and the radiation projection area 5302 based on this information.

[0117] Alternatively, the imaging control device 1002 can retain the outer shape 5301 and the radiation projection area 5302 as information by image recognition from a real-time video image. Here, the optical axis, focal point, and image forming point are arranged optically almost identically to the indicator light projection system from the collimator, the actual radiation irradiation system, and the real-time video camera imaging optical system, so that the accurate outer shape 5301 and the radiation projection area 5302 can be obtained.

[0118] Although this is unlikely to be a problem when photographing a knee joint as shown in Fig. 9, the continued projection of visible light may place a heavy burden on the subject when photographing the head, etc. For this reason, it is preferable to provide a near-infrared light real-time imaging system light-projecting system and light-receiving system, as well as an infrared light-receiving system simply as a thermal distribution imaging system, in addition to the visible light optical system.

[0119] Based on this information, the imaging control device 1002 can also control the display so that the outline 5301 and the radiation projection area 5302 are overlaid on the real-time video camera image. This makes it possible to perform the process of removing the outside irradiation area in step S801 in Fig. 8 before imaging.

[0120] Next, a method for deriving the direct ray region 5303 will be described. This can be calculated by image extraction from a real-time video image. In order to improve accuracy, a tabletop (not shown) or the radiation imaging device 1001 may be painted with a color that is easy to distinguish, particularly a paint with high sensitivity to a video camera, or a real-time video camera that uses infrared light may be used to distinguish the subject based on the temperature difference of the tabletop or the radiation imaging device 1001. It is also possible to extract the direct ray region 5303 from the image 5310 (optical image) by using threshold information of a fixed threshold method or a p-tile method for similar areas and region discrimination with a sample image in which direct rays have been previously determined using imaging site information or past image information. It is useful for the imaging control device 1002 to calculate the ratio information of direct rays for the entire dose detection pixel 121 region in FIG. 10 described later and for each detection line, and to send the calculated information to the radiation imaging device 1001 immediately before radiation imaging so that the direct ray region 5303 can be accurately excluded from the integrated value for AEC threshold calculation and comparison.

[0121] The imaging control device 1002 is capable of performing display control to cause an optical image to be displayed on the display unit 1006 in accordance with the radiation projection area in which the radiation image is captured, and the imaging control device 1002 is further capable of performing display control to cause an image in which a radiation image of a subject previously captured is superimposed on an optical image on the display unit 1006.

[0122] Based on these pieces of information, the imaging control device 1002 can also perform display control so as to overlay and display the direct ray region 5303 on the real-time video camera image. This makes it possible to perform the process of removing the direct ray equivalent region in step S802 of FIG. 8 before imaging. This allows the region within the irradiation area and outside the direct ray equivalent region to be automatically derived as the remaining irradiation field 1012 equivalent. Furthermore, it is also possible to specify the irradiation field 1012 as the region of interest based on the irradiation field template based on the imaging part information of the subject. For example, in the case of FIG. 9, since it is determined that the regions are "both knees," it is possible to automatically select a calculation area (extraction area) of the dose index value EI from the inside of the region within the irradiation area and outside the direct ray equivalent region, centered on the part that can be recognized as the knees.

[0123] Here, the process of removing unnecessary regions such as metal before performing radiation imaging of the knee joint as shown in Fig. 9 is mainly a process performed after transmitting information based on the subject information to the radiation imaging device 1001. However, it is possible to remove unnecessary regions such as metal based on a past image of the same subject. The imaging control device 1002 can superimpose the past image on the previous image 5310 (optical image) and notify the radiation imaging device 1001 of the region obtained by excluding the metal region from the region equivalent to the radiation measurement field 1012 extracted from the image 5310 (optical image) as the radiation measurement field 1012 in the calculation area (extraction area) of the dose index value EI.

[0124] 9, changes to the imaging region and changes to the relative position for imaging are completed by time t3 before the operation switch 46 is operated. After the operation switch 46 is operated to instruct radiation irradiation by the operator, the imaging control device 1002 and the high-voltage generator 1004 do not accept changes to the imaging region and changes to the relative position for imaging. After time t3, the measurement field 1012 in the calculation area (extraction area) of the dose index value EI is determined, and the imaging control device 1002 notifies the radiation imaging device 1001 of the determined measurement field 1012.

[0125] In the above description, an embodiment has been shown in which the light measurement field 1012 (AEC light measurement field) is set to a limited area within the irradiation area and the subject area, but as described with reference to Fig. 6 and Fig. 4, it is also possible to set the entire area within the irradiation area and the subject area as the light measurement field 1012 (AEC light measurement field). In this case, the number of rows of the dose detection pixels 121 to be read out within the light measurement field 1012 (AEC light measurement field) increases, so the cycle for determining whether the AEC threshold has been reached becomes longer. For this reason, this is not suitable for cases in which the irradiation time of within a few ms is assumed.

[0126] Next, the operation mainly during the period from time t3 to t7 in Fig. 7 will be described with reference to Fig. 10. Based on information on the radiation measurement field 1012 (AEC measurement field) notified to the radiation imaging device 1001 after time t3, the control circuit 225 determines the dose detection pixels 121 to be used this time for AEC dose calculation, among the dose detection pixels 121 distributed in the imaging region 100.

[0127] As shown in Fig. 10(a), five rows of drive lines 1241-1245 corresponding to the determined light measurement field 1012 are selected. As shown in Fig. 10(b), the light measurement field 1012 (AEC light measurement field) and the five rows of drive lines 1241-1245 selected within the light measurement field 1012 are displayed superimposed on a radiation image to be captured. The other dose detection pixels 121 not selected this time are not driven at all during the radiation irradiation period in order to shorten the AEC response time and to be used as normal pixels in the image.

[0128] By time t5, the driving for the correction of the corresponding five dose detection pixels 121 is completed, and the control circuit 225 outputs an irradiation and readout enable signal at time t5 and simultaneously starts driving for measuring the AEC dose. At this time, the driving signals may be output sequentially to the five rows of driving lines 124 (AEC driving lines) to drive them as five rows, or the five rows of driving lines may be simultaneously selected and driven as one row. When driving as five rows, the time required for reading is five times longer than the time required for reading when driving as one row, but the spatial resolution is increased, so that the judgment for each line area described later can be performed in detail. On the other hand, when driving as one row, the time is 1 / 5 and the signal components can be secured five times, so that it is excellent in short-time response, but the spatial resolution is inferior to that when driving as five rows, so that the accuracy may be reduced when accumulating while performing fine line area processing. The control circuit 225 can control the driving so as to change the number of lines to be driven during imaging, such as driving five rows of driving lines together when radiation irradiation begins, and then driving a few lines at a time after a predetermined time has elapsed.

[0129] When radiation irradiation is started at time t6, an output corresponding to each of the drive lines 124 (AEC drive lines) is output from the readout circuit 222C (AEC readout circuit).

[0130] 10(c) and (e) are diagrams showing a line graph and a histogram of the final image linear to the dose before post-processing of the part corresponding to the driving line 1243 (AEC driving line). Also, FIG. 10(d) and (f) are diagrams showing the output waveform of one amplifying of the driving line 1243 (AEC driving line) and a histogram. Here, in FIG. 10(c) and (e), the reference numeral 5411 indicates the maximum value of the pixel value, the reference numeral 5412 indicates the maximum value of the pixel value PV used when calculating the integrated DOSE, and the reference numeral 5413 indicates the level corresponding to the pixel value corresponding to the minimum value. And, in FIG. 10(d) and (f), the reference numeral 5420 indicates the maximum value of the pixel value of the dose detection pixel 121 in one line, the reference numeral 5421 indicates the pixel value corresponding to the reference numeral 5411 which is the maximum value in the final image, the reference numeral 5422 indicates the maximum value of the pixel value PV used when calculating the integrated DOSE, and the reference numeral 5423 indicates the pixel value level corresponding to the minimum value.

[0131] There are several methods for determining target pixels when calculating the accumulated DOSE in this embodiment. The simplest method is to accumulate all outputs of pixels corresponding to the dose detection pixels 121 within an area determined by the imaging control device 1002 as determined by the contents described above in FIG. 9. For example, this is a method of accumulating all outputs of pixels corresponding to the dose detection pixels 121 after correction between the reference symbols 5401 and 5402 and between the reference symbols 5403 and 5404 in FIG. 10(a). Note that, as described above in FIG. 9, the area between the reference symbols 5401 and 5402 is filled with metal, so it may be excluded from the accumulation target.

[0132] Furthermore, as shown in FIG. 10(c), the maximum value 5412 and the minimum value 5413 of the pixel value PV may be determined in advance by referring to a past image, and the pixel value PV may be excluded from the integration target in the previously specified region for integration processing. In this case, the maximum value 5412 can prevent the radiation exposure amount in the region of interest from reaching the AEC threshold at an underdose when direct rays from the direct ray region 5303 are mixed in unintentionally, unlike the instruction of the imaging control device 1002, due to a positional shift between the subject and the radiation imaging device 1001, etc. Similarly, the minimum value 5413 can suppress the influence of outside the irradiation area or metal areas, and prevent the radiation exposure amount in the region of interest from reaching the AEC threshold at an overdose. The excluded dose detection pixels 121 are treated as being outside the target from the beginning, and normalization is performed using only the dose detection pixels 121 used for integration to calculate the integrated DOSE so as to appropriately correspond to the dose per unit area.

[0133] In reality, it is difficult to perform sampling every time from FIG. 10(c) and determine the pixel value of FIG. 10(d). This is because the amount of radiation irradiated at each sampling is not determined. Therefore, the maximum value 5412 and the minimum value 5413 are determined based on the ratio to the direct ray region. Furthermore, since the amount of radiation that has reached is naturally different between FIG. 10(c) and FIG. 10(d), the pixel value 5420 (maximum pixel value: FIG. 10(d)) of the direct ray region in the output waveform of one amplifying is different from the pixel value 5411 (maximum pixel value: FIG. 10(c)) of the direct ray region of the final image. Therefore, in order to determine the pixel value level 5423 corresponding to the maximum value 5422 and minimum value of the pixel value PV in the output waveform of one amplifying before radiation irradiation, the imaging control device 1002 needs to calculate the pixel value 5420 of the direct ray region from the setting information of the radiation generation device immediately before the start of irradiation and notify it to the radiation imaging device 1001.

[0134] Another method for obtaining the pixel value level 5423 corresponding to the maximum value 5422 and minimum value of the pixel value PV is to prepare a memory for storing the integration result for each pixel of the line graph shown in Fig. 10(d) and perform the integration calculation based on the added or averaged line graph updated after each sampling. In this case, the calculation is performed while calculating the histogram of the line graph (Fig. 10(f)). If the calculation process can be completed in time, the calculation result may be obtained for each sampling period, or the histogram may be calculated every few line periods since the integration result in the form of a line graph is stored.

[0135] Since the imaging control device 1002 knows the ratio of the direct ray area calculated from the camera image or the like in advance, it is possible to calculate the maximum value 5422 from the histogram in FIG. 10(f) using the direct ray area information as the threshold information of the p-tile method. Similarly, the imaging control device 1002 can calculate the minimum value 5423 from the histogram in FIG. 10(f) by obtaining the ratio of the metal part by referring to the non-irradiated area and past images. This makes it possible to determine the range of the pixel values ​​of the dose detection pixels 121 to be converted to compare with the AEC threshold during irradiation. Note that the advantage of using the histogram is that it is not necessary to know the absolute value of the pixel value of the direct ray part, and even if the direct ray part is saturated, it is possible to derive the maximum value 5422 as described above as long as the ratio between the direct ray area and the other parts is known.

[0136] Next, the processing when the position information of the subject before imaging and irradiation, that is, the predetermined light collection field 1012 and the area of ​​the actually irradiated radiation are misaligned, will be described with reference to Fig. 11. The state of Fig. 11(a) and Fig. 11(b) should have been assumed, but in reality, the right foot has shifted to the right as shown in Fig. 11(c) and Fig. 11(d). Possible causes of the position shift include the subject moving, or a misalignment between the optical axis of the camera and the optical axis of the radiation.

[0137] 11(d), if the entire area of ​​the measurement field 1012 is simply integrated, the direct line area 5303 is included in the area of ​​the measurement field 1012, and the AEC threshold is reached while the dose in the area of ​​interest is insufficient. This results in underexposure shooting, which can lead to graininess and reduced image quality, and may require reshooting.

[0138] By using the method described in FIG. 10, it is possible to prevent the AEC threshold from being reached while the exposure is underexposed. In other words, if the maximum value 5422 can be obtained by previously obtaining the area of ​​direct rays using a video camera image or the like, even if the direct rays unexpectedly enter the area of ​​the light-gathering field 1012, it is possible to exclude them from the area to be integrated, and comparison with the AEC threshold is possible with almost no loss of accuracy. Similarly, the equivalent of the minimum value 5423 can be obtained by previously obtaining the ratio with the area outside the irradiation area using a video camera image or collimator information. This makes it possible to prevent information outside the irradiation area from affecting the comparison calculation between the AEC threshold and the integrated value even if the light-gathering field 1012 is not determined in advance. In other words, it is sufficient to obtain the integrated value only from the results of the dose detection pixels 121 between the maximum value 5422 and the minimum value 5423, and compare it with the AEC threshold. This method is particularly effective for imaging conditions in which the ratio between the direct rays and the object does not change significantly even if the position of the object moves slightly, such as when the object is small compared to the irradiation area.

[0139] As described above, the radiation imaging device 1001 outputs a threshold reaching signal to stop radiation irradiation at an appropriate timing. After that, the radiation image is transferred to the imaging control device 1002, and the equivalent of the integrated DOSE value compared with the actual AEC threshold is transferred to the imaging control device 1002. The imaging control device 1002 recalculates the dose index value EI from the acquired radiation image using a calculation algorithm for the dose index value EI, compares the dose target value EIt set as the AEC threshold with the dose index value EI calculated from the image, and the integrated DOSE value when the AEC threshold is exceeded, and calculates the difference between them, particularly the dose target value EIt and the dose index value EI and their deviation DI. In addition, it is also possible to derive a conversion coefficient or the like when setting the AEC threshold from the dose target value EIt so that the deviation DI between the dose target value EIt and the dose index value EI is minimized by machine learning the deviations, and feed it back to the setting of the AEC threshold.

[0140] The imaging control device 1002 can reduce the deviation DI by associating a portion of the radiation image in the radiation measurement field 1012 that corresponds to the dose target value EIt with the dose detection pixels 121. The imaging control device 1002 can also perform display control to cause the display unit 1006 to identifiably display a location in the region of interest that corresponds to the dose target value set as a threshold value. The imaging control device 1002 performs display control such as hatching or coloring to make it possible to distinguish the portion of the radiation measurement field 1012 that corresponds to the dose target value EIt from the location of the dose detection pixels 121, and displays the display unit 1006, thereby improving usability for the operator.

[0141] (Other embodiments) The present invention can also be realized by a process in which a program for implementing one or more of the 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 a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0142] The present invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0143] 1001: radiation imaging device, 1002: imaging control device, 1021: communication control unit, 1022: control unit, 1003: radiation source, 1103: radiation, 1004: high voltage generator, 1042: radiation generation control unit, 1043: signal selection unit, 100: imaging region, 101: imaging pixel, 102: first conversion element, 103: first switch, 104: drive line, 105: signal line (column signal line), 121: dose detection pixel, 12 2: second conversion element, 123: second switch, 124: driving line, 125: detection signal line, 132: detection unit, 142: detection unit, 151: correction pixel, 221, 221C: driving circuit, 222, 222C: readout circuit, 224: signal processing unit, 225: control circuit, 226: power supply circuit, 227: communication unit, 241: driving circuit, 242: readout circuit, 401: digital processing unit, 402: analog processing unit, 1012: light collection field

Claims

[Claim 1] A radiation imaging system including a radiation imaging device including dose detection pixels that detect a dose of radiation irradiated from a radiation source, and an imaging control device that controls the radiation imaging device, The imaging control device, before radiation imaging, identifying positions of the dose detection pixels in a region of interest for calculating a dose index value of a radiographic image, determining a threshold value according to the positions of the dose detection pixels, and transmitting the positions of the dose detection pixels and the threshold value to the radiographic imaging apparatus; The radiation imaging apparatus includes: The positions of the radiation amount detection pixels in the region of interest and the threshold value transmitted from the imaging control device are set, and imaging is performed based on the settings. A radiation imaging system comprising:

Images