JP6173143B2 - Radiation imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to a radiographic image capturing apparatus that captures a radiographic image and a control method thereof.

  In recent years, a flat panel detector (hereinafter referred to as “FPD”) in which imaging elements made of single crystal silicon or amorphous silicon are two-dimensionally arranged has been widely put into practical use. Such an image capturing apparatus having an FPD is also used when capturing a radiographic image in medical diagnostic equipment.

  In FPD, radiation such as X-rays that have passed through a subject is captured by an image sensor directly or indirectly through a phosphor sensitive to radiation and converted into electric charge. In a radiographic image capturing apparatus having an FPD, thin film transistors (TFTs) connected to the image sensor are driven in a matrix to sequentially read out electrical signals based on the charges accumulated in the image sensor. Furthermore, in the radiographic imaging device having the FPD, radiographic image data reflecting subject information is generated based on the read electrical signal.

  At this time, two types of methods are mainly known as methods for starting shooting by FPD. The first method is a method in which the FPD receives an exposure signal that informs the irradiation of radiation from the radiation generation apparatus, and synchronizes the imaging drive in the FPD based on the exposure signal (hereinafter, “synchronous imaging method”). Called). In the second method, for example, as described in Patent Document 1 below, the FPD does not receive an exposure signal from the radiation generation device, and detects radiation irradiation by the FPD itself, and performs imaging driving. (Hereinafter referred to as “asynchronous imaging method”).

  In this asynchronous imaging method, since there is no mechanism for informing the FPD of the irradiation timing of the radiation from the radiation generating device in advance, the FPD can always detect the radiation so that it can be detected whenever the radiation is irradiated. Must be waiting in a state. At this time, several methods for detecting radiation have been proposed. For example, in a method of detecting using an existing image sensor (especially, an imaging element dedicated to radiation detection is not provided), the sensitivity of radiation detection (hereinafter referred to as “radiation detection capability”) during dark detection standby is dark. Due to the current, it decreases over time.

JP 2012-32182 A

  If the radiation detection capability of the FPD is reduced and the radiation detection fails, the FPD cannot move to the imaging drive and cannot accumulate the radiation signal. Increase opportunities. In this case, since re-photographing is required, the photographing efficiency is also hindered. For these reasons, there is a need for a mechanism that suppresses the decrease in radiation detection capability in imaging using the asynchronous imaging method. Conventionally, the improvement over time of the radiation detection capability that occurs during radiation detection standby in imaging using the asynchronous imaging method is required. There was no idea.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a mechanism for suppressing a decrease in radiation detection capability when performing imaging by an asynchronous imaging method.

The radiographic image capturing apparatus of the present invention is a radiographic image capturing apparatus including an image capturing unit that detects radiation transmitted through a subject using a plurality of image sensors and captures a radiographic image based on the radiation. Storage means for storing a threshold value of radiation detection capability in the standby state for detection of radiation and time characteristic data of the radiation detection capability, and an elapsed time from the time when the imaging unit started standby for detection of radiation Measurement means, acquisition means for acquiring parameters relating to imaging processing by the imaging means, time characteristic data of the radiation detection capability, parameters acquired by the acquisition means, and elapsed time measured by the measurement means Based on the estimation means for estimating the amount of change in the radiation detection capability, the amount of change in the radiation detection capability estimated by the estimation means, and the radiation detection Based on the threshold value of the ability, and a determination means for determining whether or not to reset the standby state of the detection of said radiation by said imaging means.
The present invention also includes a method for controlling the radiographic imaging apparatus described above.

  ADVANTAGE OF THE INVENTION According to this invention, when performing imaging | photography by an asynchronous imaging | photography method, the fall of a radiation detection capability can be suppressed. As a result, it is possible to reliably detect the radiation that has passed through the subject within the range of the existing image sensor and without performing invalid exposure.

It is a block diagram which shows an example of a function structure of the radiographic imaging apparatus which concerns on the 1st Embodiment of this invention. It is a block diagram which shows an example of the hardware constitutions of the radiographic imaging apparatus which concerns on the 1st Embodiment of this invention. It is a flowchart which shows an example of the process sequence of the control method of the radiographic imaging apparatus which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the 1st Embodiment of this invention and shows an example of the time characteristic data of a radiation detection ability. It is a schematic diagram which shows the 1st Embodiment of this invention and shows an example of the internal temperature dependence of the sensor in the time characteristic data of radiation detection ability. FIG. 3 shows a first embodiment of the present invention, and shows threshold values TL _Th1 and TL _Th2 (TL _Th1 > TL _Th2 ) of radiation detectability with respect to body thicknesses Th ₁ and Th ₂ (Th ₁ > Th ₂ ) of two types of subjects; FIG. 3 is a schematic diagram showing times t ₁ and t ₂ (t ₁ <t ₂ ) until reset. The 2nd Embodiment of this invention is shown, and an example of the relationship between irradiation time and the imaging | photography part surface arrival dose (detection limit pixel value) requested | required for a radiation detection is shown as an example of the imaging condition dependence of a radiation detection ability. It is a schematic diagram. It is a schematic diagram which shows the 2nd Embodiment of this invention and shows an example of the image artifact which generate | occur | produces at the time of radiation detection.

  Hereinafter, embodiments (embodiments) for carrying out the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram illustrating an example of a functional configuration of the radiographic image capturing apparatus according to the first embodiment of the present invention.
As shown in FIG. 1, the radiographic image capturing apparatus 100 includes an imaging unit 101, a storage unit 102, an elapsed time acquisition unit 103, an imaging unit parameter acquisition unit 104, a detection capability change amount estimation unit 105, and a reset determination unit 106. Each functional configuration is configured. The radiographic image capturing apparatus 100 performs radiography of a subject.

  The imaging unit 101 detects radiation that has passed through the subject, and generates and acquires radiation image data based on the radiation (radiation signal). Further, the imaging unit 101 generates and acquires dark image data under a condition in which no radiation is irradiated in order to correct an offset component of an image such as a dark current component. Furthermore, radiation is uniformly irradiated on the entire effective pixel area of the sensor in the imaging unit 101 without a subject in advance, and the imaging unit 101 detects the radiation and generates and acquires calibration image data.

  The storage unit 102 stores information such as the threshold value of the radiation detection capability and the time characteristic data of the radiation detection capability acquired in advance when the imaging unit 101 is in a radiation detection standby state (radiation detection standby state). And output this information.

  The elapsed time acquisition unit 103 acquires the elapsed time from the time when the imaging unit 101 starts the radiation detection standby, and outputs the acquired elapsed time information as necessary.

  The imaging unit parameter acquisition unit 104 includes an internal temperature of a sensor provided in the imaging unit 101 (for example, an internal temperature of the sensor at the time of imaging) and gain setting information of the imaging unit 101 (for example, gain setting of the imaging unit 101 at the time of imaging). Information) and the like. Then, the imaging unit parameter acquisition unit 104 outputs the acquired imaging unit parameter information as necessary.

  The detection capability change amount estimation unit 105 receives the radiation detection capability time characteristic data from the storage unit 102, the elapsed time from the elapsed time acquisition unit 103, and the imaging parameters from the imaging unit parameter acquisition unit 104 as inputs. The amount of performance change is estimated, and this estimation result is output.

  The reset determination unit 106 receives the radiation detection capability change amount estimated by the detection capability change amount estimation unit 105 and the radiation detection capability threshold value from the storage unit 102, and determines whether or not to reset the radiation detection standby state. judge.

  FIG. 2 is a block diagram illustrating an example of a hardware configuration of the radiographic image capturing apparatus according to the first embodiment of the present invention. Here, FIG. 2 shows a radiographic imaging system including the radiographic imaging device 100 according to the present exemplary embodiment, a radiation generation device 210, and an image display device 220.

The radiation generator 210 irradiates the subject with radiation. At this time, the radiation generation apparatus 210 does not have a means for notifying the radiation image capturing apparatus 100 of the radiation irradiation timing. After the radiation generator 210 irradiates radiation, the radiation image capturing apparatus 100 detects radiation (radiation signal) that has passed through the subject, starts imaging (imaging by an asynchronous imaging method), converts it into a digital signal, The radiographic image data of the subject is acquired.
The image display device 220 displays a radiographic image based on the radiographic image data output from the radiographic image capturing device 100.

  As illustrated in FIG. 2, the radiographic image capturing apparatus 100 is configured to include hardware configurations of an imaging unit 2010, a storage unit 2020, a control unit 2030, a reset determination unit 2040, and an image processing unit 2050. .

  The imaging unit 2010 includes an imaging unit parameter acquisition circuit 2011, a drive circuit 2012, a sensor 2013, and a readout circuit 2014. The imaging unit 2010 performs radiography of a subject, converts a radiation signal of the subject into an electrical signal, and generates and acquires radiation image data. At this time, the imaging unit 2010 detects radiation by the imaging unit 2010 itself without receiving a signal informing the irradiation of radiation from the radiation generator 210 from outside, and performs imaging asynchronously (imaging by an asynchronous imaging method). Start. Further, the imaging unit 2010 generates and acquires dark image data under a condition in which no radiation is irradiated in order to correct an image offset component such as a dark current component. Further, the radiation is uniformly irradiated on the entire effective pixel area of the sensor 2013 in advance without a subject, and the imaging unit 101 detects the radiation and generates and acquires calibration image data.

  The imaging unit parameter acquisition circuit 2011 acquires imaging unit parameters that are imaging information, and outputs the acquired imaging unit parameters as necessary. Here, the imaging unit parameter is imaging information indicating the internal temperature of the sensor 2013 (for example, the internal temperature of the sensor at the time of imaging), gain setting information (for example, gain setting information of the imaging unit 101 at the time of imaging), or the like.

  The drive circuit 2012 is controlled by the control unit 2030 to perform each drive during photographing.

The sensor 2013 includes, for example, each pixel including an imaging device arranged in a lattice (two-dimensional matrix) on a two-dimensional plane made of amorphous silicon, and a phosphor that converts a radiation signal of a subject into a visible light signal. Configured. In other words, the sensor 2013 has a plurality of image sensors arranged in a two-dimensional matrix. As the phosphor, for example, CsI: Tl and Gd ₂ O ₂ S: Tb, or the like can be used. When radiation transmitted through the subject enters the sensor 2013, first, the radiation signal is converted into a visible light signal in the phosphor, and then the visible light signal is converted into a charge signal, which is an electrical signal, in the imaging device.

  The readout circuit 2014 reads out a digital signal based on the charge signal accumulated in each image sensor of the sensor 2013. Specifically, the readout circuit 2014 reads out radiation image data (radiation image signal), dark image data (dark image signal), calibration image data (calibration image signal), and the like.

The storage unit 2020 stores information such as the threshold value 2021 of the radiation detection capability when the imaging unit 101 is in the radiation detection standby state and the time characteristic data 2022 of the radiation detection capability measured in advance, and resets the information as necessary. The data is output to the determination unit 2040.
Here, when the imaging unit parameter acquisition circuit 2011 acquires the internal temperature of the sensor 2013 as an imaging unit parameter, the storage unit 2020 stores at least the radiation detection capability time characteristic data 2022 for each internal temperature. In addition, when acquiring gain setting information in imaging processing by the imaging unit 2010 as an imaging unit parameter in the imaging unit parameter acquisition circuit 2011, the storage unit 2020 includes at least radiation detection time characteristic data 2022 for each gain setting information. Remember.

  The control unit 2030 controls the drive timing of the drive circuit 2012. In addition, when receiving a reset determination from the reset determination unit 2040, the control unit 2030 causes the drive circuit 2012 to transition to reset driving.

  The reset determination unit 2040 includes an elapsed time measurement circuit 2041, a detectability change amount estimation circuit 2042, and a reset determination circuit 2043.

  The elapsed time measuring circuit 2041 measures and acquires the elapsed time from the time when the imaging unit 101 starts the radiation detection standby.

  Based on the time characteristic data 2022 of the radiation detection capability from the storage unit 102, the elapsed time from the elapsed time acquisition unit 103, and the imaging parameter from the imaging unit parameter acquisition unit 104, the detection capability variation estimation circuit 2042 Estimate the amount of change in detectability.

  Whether or not the reset determination circuit 2043 resets the radiation detection standby state based on the radiation detection capability change amount estimated by the detection capability change amount estimation unit 105 and the radiation detection capability threshold value 2021 from the storage unit 102. Determine. Then, the reset determination circuit 2043 outputs the determination result to the control unit 2030.

  The image processing unit 2050 includes an offset correction processing circuit 2051, a sensitivity correction processing circuit 2052, a frequency processing circuit 2053, a gradation processing circuit 2054, a defect correction processing circuit 2055, a CPU 2056, a RAM 2057, and a ROM 2058.

  The offset correction processing circuit 2051 receives the radiation image data and dark image data acquired by the imaging unit 2010, and performs an offset correction process of the radiation image data based on the dark image data.

  The sensitivity correction processing circuit 2052 performs the radiation image data sensitivity correction processing based on the calibration image data and the sensitivity variation correction data from the imaging unit 2010. Here, the sensitivity variation correction data is data indicating individual variations in sensitivity for each photographing unit, and is represented, for example, by the ratio of the sensitivity of each photographing unit to the sensitivity target value set for each model. This sensitivity variation correction data is measured for each photographing unit at the time of factory shipment, for example, and stored in a dedicated storage area.

  The frequency processing circuit 2053 performs frequency processing such as frequency enhancement processing and noise suppression processing on the radiation image data.

  The gradation processing circuit 2054 performs gradation processing on the radiation image data based on dose information at the time of imaging, part information on the subject, and the like.

  The defect correction processing circuit 2055 performs defect correction on the radiation image data based on the defect data acquired in advance. At this time, the defect data is measured for each photographing at the time of factory shipment, for example, and stored in a dedicated storage area.

  For example, the CPU 2056 comprehensively controls the operation of the image processing unit 2050 using programs, data, and information stored in the ROM 2058.

  The RAM 2057 includes an area for temporarily storing programs, data, and information loaded from the ROM 2058 and a work area necessary for the CPU 2056 to perform various processes.

  The ROM 2058 stores programs that do not need to be changed, various data, various information, and the like.

  Note that the image processing unit 2050 may be configured such that, for example, the configurations of 2051 to 2055 are realized by the CPU 2056 executing software (for example, a program stored in the ROM 2058), or configured by a GPU or a dedicated processing board. Form may be sufficient.

Here, an example of a correspondence relationship between the configuration illustrated in FIG. 1 and the configuration illustrated in FIG. 2 will be described.
The imaging unit 101 in FIG. 1 has a configuration corresponding to the imaging unit 2010 in FIG.
The storage unit 102 in FIG. 1 has a configuration corresponding to the storage unit 2020 in FIG.
The elapsed time acquisition unit 103 in FIG. 1 has a configuration corresponding to the elapsed time measurement circuit 2041 in FIG.
The imaging unit parameter acquisition unit 104 in FIG. 1 has a configuration corresponding to the imaging unit parameter acquisition circuit 2011 in FIG.
The detectability change amount estimation unit 105 in FIG. 1 has a configuration corresponding to the detectability change amount estimation circuit 2042 in FIG.
The reset determination unit 106 in FIG. 1 has a configuration corresponding to the reset determination circuit 2043 in FIG.

Next, a control method of the radiation image capturing apparatus 100 according to the present embodiment will be described.
FIG. 3 is a flowchart illustrating an example of a processing procedure of the control method of the radiographic imaging apparatus according to the first embodiment of the present invention. In the description of the flowchart shown in FIG. 3, description will be made using the configuration shown in FIG.

  When the imaging unit 2010 is turned on, in step S300, the imaging unit 2010 starts a standby state (radiation detection standby state) for detecting radiation from the radiation generator 210. At this time, the sensor 2013 is similarly turned on. In this case, after the power is turned on, the sensor 2013 may wait for a certain time until the characteristics of the sensor are stabilized.

  Subsequently, in step S301, the control unit 2030 causes the drive circuit 2012 to start radiation detection standby drive. Here, the radiation detection standby drive is a drive in which the radiation signal can be detected when a reverse bias voltage is applied to each image sensor in the sensor 2013 and a radiation signal is incident. Refers to that. When this radiation detection standby drive is continued, electric charges due to dark current accumulate in the capacitance existing in the sensor 2013, and the net bias voltage applied to each image sensor in the sensor 2013 decreases. . Thereby, the radiation detection ability decreases with time.

  In step S <b> 302, first, the elapsed time measurement circuit 2041 measures and acquires the elapsed time from the time when the imaging unit 101 starts standby for radiation detection, and outputs this to the detection capability change amount estimation circuit 2042. The imaging unit parameter acquisition circuit 2011 acquires the imaging unit parameter and outputs it to the detection capability change amount estimation circuit 2042. Next, the detection capability variation estimation circuit 2042 selects appropriate data from the radiation detection capability time characteristic data 2022 stored in the storage unit 2020 based on the imaging unit parameters received from the imaging unit parameter acquisition circuit 2011. .

FIG. 4 is a schematic diagram illustrating an example of time characteristic data of radiation detection ability according to the first embodiment of this invention.
The time characteristic data 2022 of the radiation detection capability is a look-up table (LUT) composed of an elapsed time from the start of radiation detection standby and the radiation detection capability, which is expressed by a curve as shown in FIG. The time characteristic data 2022 of the radiation detection capability is obtained by measuring the radiation detection capability by changing the elapsed time from the start of the radiation detection standby and the imaging unit parameters such as the internal temperature of the sensor 2013 and gain setting information in advance. It is obtained. Specifically, FIG. 4 shows time characteristic data 2022 of the radiation detection capability when the internal temperature T of the sensor 2013 is T ₁ ° C., and the radiation detection capability at the elapsed time t from the start of the radiation detection standby. Is shown to be S _T1 .

  The time characteristic data 2022 of the radiation detection capability varies depending on the imaging unit parameters. For example, the time characteristic data 2022 of the radiation detection capability varies depending on the internal temperature of the sensor 2013.

FIG. 5 is a schematic diagram illustrating an example of the internal temperature dependence of the sensor in the time characteristic data of the radiation detection capability according to the first embodiment of this invention.
For example, when the internal temperature of the sensor 2013 is high, the dark current component increases, so that the accumulation in the capacitance in the sensor 2013 is accelerated, and as a result, the radiation detection capability is also deteriorated. At this time, the time characteristic data 2022 of the radiation detection capability is a curve as shown by T = T ₂ in FIG.
On the other hand, for example, when the internal temperature of the sensor 2013 is low, the dark current component decreases, so the decrease in radiation detection capability becomes gradual, resulting in a curve as shown by T = T ₀ in FIG.
The amount of change in the radiation detection capability is expressed as a ratio when the radiation detection capability at the start of radiation detection standby is 1. Note that the data between the measurement points may be supplemented by using a straight line interpolation or the like, or may be supplemented by an approximate curve when approximation is possible with high accuracy.

  Next, the detection capability change amount estimation circuit 2042 uses the selected radiation detection capability time characteristic data 2022 and the elapsed time from the start of the radiation detection standby received from the elapsed time measurement circuit 2041. Is estimated. Then, the detectability change amount estimating circuit 2042 outputs the estimation result to the reset determining circuit 2043.

  Subsequently, in step S <b> 303, first, the reset determination circuit 2043 acquires the radiation detection capability threshold value 2021 from the storage unit 2020. The radiation detection capability threshold 2021 is set for each imaging protocol related to the body thickness of the subject. The threshold value 2021 of the radiation detection capability for each body thickness of the subject will be described with reference to FIG.

FIG. 6 shows a first embodiment of the present invention, and thresholds TL _Th1 and TL _Th2 (TL _Th1 > TL) of radiation detection ability with respect to body thicknesses Th ₁ and Th ₂ (Th ₁ > Th ₂ ) of two types of subjects. _Th2), and is a schematic diagram showing the time to reset t ₁ and _{t 2 (t 1 <t 2} ).
The radiation detection signal is proportional to the amount of charge accumulated in the sensor 2013 immediately after radiation irradiation. For this reason, even if the radiation output from the radiation generator 210 is the same, if the subject's body thickness is large, sufficient radiation does not pass through the subject at the time of radiation detection, and the radiation dose to the sensor 2013 is reduced. . In FIG. 6, when images are taken with the same dose, the body thickness Th ₁ of the subject is larger than the body thickness Th _{2 of the} subject, so that the radiation reaching the sensor 2013 is reduced. For this reason, for reliable radiation detection, it is necessary to select a larger threshold value TL _Th1 for radiation detection capability and to shorten the time to reset (t ₁ ).

  Next, the reset determination circuit 2043 receives the radiation detection capability change amount estimated in step S302 from the detection capability change amount estimation circuit 2042, and compares it with the radiation detection capability threshold value 2021 acquired in this step. Specifically, the reset determination circuit 2043 determines whether or not the amount of change in radiation detection capability estimated in step S302 is greater than or equal to a threshold value for radiation detection capability.

  If the result of determination in step S303 is that the amount of change in radiation detection capability estimated in step S302 is not greater than or equal to the threshold value for radiation detection capability (that is, less than the threshold value) (S303 / NO), the process proceeds to step S304.

  In step S304, the control unit 2030 receives a reset determination (determination to reset the radiation detection standby state) from the reset determination circuit 2043, and causes the drive circuit 2012 to perform reset driving. Here, the reset drive is a drive in which the bias voltage applied to the sensor 2013 is changed and the dark current component accumulated in the electrostatic capacity in the sensor 2013 is discharged. Thereby, the time-dependent sensitivity fall resulting from dark current is eliminated, and the radiation detection ability is restored. Specifically, for example, the control unit 2030 sets the bias voltage applied to the image sensor of the sensor 2013 to 0 V, discharges the charge of the dark current component accumulated in the capacitance inside the sensor 2013, and detects radiation. Control to reset the standby state. After completing the reset driving, the process proceeds to step S301, and the radiation detection standby driving is resumed.

  On the other hand, if the result of determination in step S303 is that the amount of change in radiation detection capability estimated in step S302 is greater than or equal to the radiation detection capability threshold (S303 / YES), the drive circuit 2012 continues the radiation detection standby drive, The process proceeds to step S305.

  In step S305, for example, the imaging unit 2010 determines whether or not radiation (radiation signal) is detected by the sensor 2013 when radiation is emitted from the radiation generation apparatus 210.

  As a result of the determination in step S305, if no radiation (radiation signal) is detected by the sensor 2013 (S305 / NO), the process proceeds to step S302, and the drive circuit 2012 is in a radiation detection standby drive state, and step S302 is performed. The subsequent processing is performed again.

  On the other hand, as a result of the determination in step S305, when radiation (radiation signal) is detected by the sensor 2013 (S305 / YES), the process proceeds to step S306.

In step S306, first, the imaging unit 2010 performs imaging processing to generate and acquire radiation image data.
At this time, specifically, the drive circuit 2012 switches from the radiation detection standby drive to the imaging drive for storing radiation signals. In addition, the drive circuit 2012 sequentially performs drive for reading out the charge signal accumulated in the sensor 2013, and reads out the charge signal based on the radiation signal by the readout circuit 2014, thereby acquiring the radiation image data.
Next, after acquiring the radiographic image data, the imaging unit 2010 acquires the dark image data without irradiating the radiation with the same accumulation time as the radiographic image data in order to offset-correct the dark current component existing in the radiographic image data. To do.
Then, the imaging unit 2010 outputs the acquired radiation image data, dark image data, and the like to the image processing unit 2050.

Subsequently, in step S307, the image processing unit 2050 performs various types of image processing on the radiation image data output from the imaging unit 2010.
Specifically, the offset correction processing circuit 2051 acquires the radiation image data and dark image data received from the imaging unit 2010, and performs offset correction processing by subtracting the dark image data from the radiation image data.
Subsequently, sensitivity correction processing by the sensitivity correction processing circuit 2052, frequency processing by the frequency processing circuit 2053, gradation processing by the gradation processing circuit 2054, and defect correction processing by the defect correction processing circuit 2055 are performed on the radiation image data. Do.
Thereafter, the image processing unit 2050 outputs the radiation image data subjected to the image processing to the image display device 220.

  Subsequently, in step S308, the image display device 220 performs a process of displaying a radiographic image based on the radiographic image data after image processing received from the image processing unit 2050, and ends the process of the flowchart illustrated in FIG.

In the embodiment of the present invention, the amount of change in radiation detection capability is estimated (S302 in FIG. 3), and the radiation detection standby state of the imaging unit is based on the estimated amount of change in radiation detection capability and the threshold value of radiation detection capability. It is determined whether or not to reset (S303).
According to such a configuration, when performing imaging using the asynchronous imaging method, it is possible to estimate a decrease in radiation detection capability over time due to dark current generated while the imaging unit is waiting for radiation detection. It is possible to perform a recovery process as appropriate. That is, when performing imaging by the asynchronous imaging method, it is possible to suppress a decrease in radiation detection capability. As a result, it is possible to reliably detect the radiation that has passed through the subject within the range of the existing image sensor and without performing invalid exposure.

[Modification]
For example, in the reset determination circuit 2043 or the like, when the imaging unit 2010 is in the radiation detection standby state, the time until reset (remaining time until reset) t ₁ and t ₂ shown in FIG. 6 may be calculated. In this case, the reset determination circuit 2043 and the like that calculate the time until reset (remaining time until reset) constitute a calculation unit.
In this case, for example, the control unit 2030 or the like performs a process of displaying the time until reset (remaining time until reset) calculated by the calculation unit on the display unit such as the image display device 220. It may be. In this case, the control unit 2030 or the like that performs processing for displaying the time until reset (remaining time until reset) calculated by the calculation unit constitutes a display processing unit.

  In the above-described embodiment of the present invention, as shown in FIG. 2, the imaging unit parameter acquisition circuit 2011 is configured inside the imaging unit 2010. However, for example, outside the imaging unit 2010, It may be configured.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.
The functional configuration of the radiographic image capturing apparatus according to the second embodiment of the present invention is substantially the same as the functional configuration of the radiographic image capturing apparatus according to the first embodiment shown in FIG. In addition to the information shown in the first embodiment, it has irradiation time characteristic data of radiation detection ability.

  Here, as an example of the irradiation condition characteristic data of the radiation detection ability, the irradiation time characteristic data of the radiation detection ability is shown in FIG. The data example shown in FIG. 7 shows a case where the radiographic imaging device has a characteristic that the pixel value (imaging unit surface dose) required for radiation detection is larger and the radiation detection capability is lower as the irradiation time is shorter. Yes. These characteristics arise from the following process.

  When the signal lines for radiation detection and image signals are independent from each other, the radiation signal irradiated to the imaging unit 101 before the radiation is detected passes through the signal line for radiation detection to detect the radiation. used. As a result, the image signal accumulated after the radiation detection is reduced by the amount of the radiation signal used for the radiation detection. This appears in the image as an image artifact as shown in FIG. Since this image artifact causes a decrease in image quality, it is necessary to set an allowable value to prevent occurrence of an image artifact of a certain amount or more. In other words, radiation must be detected within a range where the image artifact does not exceed the allowable value. The amount of image artifact is the ratio of the total radiation dose irradiated to the imaging unit and the radiation dose used for radiation detection. When the irradiation time is short, the total radiation dose is irradiated in a short time. Therefore, unless the radiation detection is completed in a short time, the dose ratio is increased and the image artifact is increased. Therefore, when the irradiation time is short, higher radiation detection capability is required. As described above, depending on the radiation detection method, in addition to the temporal deterioration of the radiation detection capability considered in the first embodiment, the difference in detection capability depending on the imaging conditions must be taken into consideration.

  The imaging unit parameter acquisition unit 104 acquires the irradiation conditions (tube voltage, tube current, and irradiation time) in addition to the imaging parameters shown in the first embodiment. This is acquired at the timing when the user selects the shooting protocol.

  The hardware configuration of the radiographic imaging apparatus according to the second embodiment of the present invention is substantially the same as the hardware configuration of the radiographic imaging apparatus according to the first embodiment shown in FIG. The partial parameter acquisition circuit 2011 acquires irradiation conditions in addition to the imaging parameters shown in the first embodiment. In addition to the information shown in the first embodiment, the storage unit 2020 stores irradiation condition characteristic data of radiation detectability.

Next, a control method of the radiographic image capturing apparatus 100 according to the second embodiment of the present invention will be described.
Since the processing procedure of the control method of the radiographic imaging apparatus according to the second embodiment of the present invention is almost the same as that of the first embodiment, only the difference will be described with reference to FIG. In the description of the flowchart shown in FIG. 3, the description will be made using the configuration shown in FIG.

The processing up to step S302 is the same as in the first embodiment.
In step S303, when the user selects an imaging protocol, first, the imaging unit parameter acquisition circuit 2011 acquires irradiation conditions. Next, the detection capability change amount estimation circuit 2042 calculates a reduction coefficient of the radiation detection capability based on the irradiation condition and irradiation time characteristic data of the radiation detection capability stored in the storage unit 2020. For example, the reduction coefficient may be calculated by setting the imaging condition having the highest detection capability within the imaging conditions permitted by the radiographic imaging apparatus as the coefficient 1.
Next, the reset determination circuit 2043 acquires the radiation detection capability threshold value 2021 from the storage unit 2020, and further calculates the radiation detection capability threshold value by taking into account the change in the radiation detection capability depending on the imaging conditions by dividing by the reduction coefficient. To do. The subsequent processing is the same as in the first embodiment.

(Other embodiments)
The present invention can also be realized by executing the following processing.
That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.
This program and a computer-readable recording medium storing the program are included in the present invention.

  Note that the above-described embodiments of the present invention are merely examples of implementation in practicing the present invention, and the technical scope of the present invention should not be construed as being limited thereto. It is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 100 Radiographic imaging apparatus, 210 Radiation generation apparatus, 220 Image display apparatus, 2010 Imaging part, 2011 Imaging part parameter acquisition circuit, 2012 Drive circuit, 2013 Sensor, 2014 Reading circuit, 2020 Storage part, 2021 Radiation detection capability threshold, 2022 Time characteristics data of radiation detectability, 2030 control unit, 2040 reset determination unit, 2041 elapsed time measurement circuit, 2042 detectability change estimation circuit, 2043 reset determination circuit, 2050 image processing unit, 2051 offset correction processing circuit, 2052 sensitivity correction Processing circuit, 2053 frequency processing circuit, 2054 gradation processing circuit, 2055 defect correction processing circuit, 2056 CPU, 2057 RAM, 2058 ROM

Claims (10)

A radiographic imaging device including imaging means for detecting radiation transmitted through a subject using a plurality of imaging elements and imaging a radiation image based on the radiation,
Storage means for storing a threshold value of radiation detection capability and time characteristic data of the radiation detection capability when the imaging unit is in a standby state of detection of the radiation;
Measuring means for measuring an elapsed time from the time when the imaging means started waiting for detection of the radiation;
Obtaining means for obtaining parameters relating to photographing processing by the photographing means;
Estimating means for estimating the amount of change in the radiation detectability based on the time characteristic data of the radiation detectability, the parameter acquired by the acquiring means, and the elapsed time measured by the measuring means;
A determination unit that determines whether to reset the standby state of the detection of the radiation by the imaging unit based on a change amount of the radiation detection capability estimated by the estimation unit and a threshold value of the radiation detection capability; A radiographic imaging device comprising: The determination unit determines to reset the standby state of the radiation detection by the imaging unit when the amount of change in the radiation detection capability estimated by the estimation unit is equal to or greater than a threshold value of the radiation detection capability. ,
2. The radiation according to claim 1, further comprising a control unit configured to perform control for resetting a standby state of detection of the radiation by the imaging unit when the determination unit determines that the reset is performed. Image shooting device. The acquisition means acquires the internal temperature of the photographing means as the parameter,
The radiographic imaging apparatus according to claim 1, wherein the storage unit stores time characteristic data of the radiation detection capability for each internal temperature. The acquisition unit acquires, as the parameter, gain setting information in shooting processing by the shooting unit,
The radiographic image capturing apparatus according to claim 1, wherein the storage unit stores time characteristic data of the radiation detection capability for each gain setting information.   The radiographic image capturing apparatus according to claim 1, wherein the radiation detection capability threshold is set for each imaging protocol.   The radiographic imaging apparatus according to claim 5, wherein the storage unit stores a plurality of radiation detection capability threshold values that differ for each imaging condition.   The radiographic image capturing apparatus according to claim 5, wherein the imaging protocol is selected according to a body thickness of the subject. A calculation means for calculating a (remaining) time until the reset when the imaging means is in a standby state for detection of the radiation;
The radiographic imaging apparatus according to claim 1, further comprising: a display processing unit that performs a process of displaying a time until the reset calculated by the calculating unit.   The control means performs a control for resetting by setting a bias voltage applied to the image pickup device to 0 V, discharging a charge of a dark current component accumulated in a capacitance inside the photographing means, and the resetting. The radiographic imaging device according to claim 2. An imaging unit that detects radiation transmitted through a subject using a plurality of imaging elements and captures a radiation image based on the radiation, a threshold of radiation detection capability when the imaging unit is in a standby state of detection of the radiation, and the radiation detection And a radiographic imaging device control method including storage means for storing time characteristic data of
A measuring step of measuring an elapsed time from a time when the imaging unit starts waiting for detection of the radiation;
An acquisition step of acquiring a parameter relating to a photographing process by the photographing unit;
An estimation step for estimating the amount of change in the radiation detection capability based on the time characteristic data of the radiation detection capability, the parameter acquired in the acquisition step, and the elapsed time measured in the measurement step;
A determination step of determining whether or not to reset the standby state of the radiation detection by the imaging means based on the amount of change in the radiation detection capability estimated in the estimation step and the threshold value of the radiation detection capability; A method for controlling a radiographic imaging apparatus, comprising:

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