JP2021108910A - Radiation imaging apparatus and control method thereof - Google Patents

Abstract

To provide a mechanism to execute radiation irradiation stop control appropriately.SOLUTION: A radiation imaging apparatus including a detection element D for detecting incident radiation as an electric signal, and a reading unit 114 for reading the electric signal output to a signal line Sig connected to the detection element D predicts radiation irradiation stop time on the basis of the electric signal read by the reading unit 114, and determines whether the cumulative dose of the radiation has reached a target dose on the basis of the electric signal read by the reading unit 114 when the predicted irradiation stop time is reached.SELECTED DRAWING: Figure 2

Description

The present invention relates to a radiation imaging device that performs imaging using radiation and a control method thereof.

As a radiation imaging device used for medical image diagnosis and non-destructive inspection by radiation such as X-rays, pixels in which a switch element such as a TFT (thin film) and a conversion element such as a photoelectric conversion element are combined are arranged in two dimensions. A radiation imaging device having an array has been put into practical use. At this time, the switch element is arranged between the conversion element and the column signal line, and by making the switch element conductive, an electric signal is read from the conversion element via the column signal line.

In recent years, multi-functionalization of such a radiation imaging device has been studied. As one of them, the incorporation of an automatic exposure control (AEC) function is being studied. This is used as a means for the radiation imaging device to grasp the irradiation information while the radiation generator is irradiating the radiation. For example, it can be used to grasp the stop timing at which radiation irradiation is stopped, and to grasp the radiation irradiation dose and the cumulative irradiation dose (cumulative dose). In addition, this AEC function can monitor the cumulative dose of radiation, and when the cumulative dose reaches the target dose, which is an appropriate amount, the radiation imaging device can control the radiation generator and end the irradiation of radiation.

At the site where radiography (radiation imaging) is performed, radiation of various irradiation intensities is used depending on the imaging site, and the irradiation time also varies depending on the irradiation intensity. In practice, a wide range of radiation irradiation times are used, from a short time of about 1 ms to a long time of about 500 ms.

Patent Document 1 discloses a technique for notifying a radiation generator in advance of a stop timing by calculating a dose per unit time from a cumulative dose of radiation based on AEC data and predicting an optimum irradiation stop time. Has been done. As a result, it is possible to reduce the irradiation of an excess dose of radiation generated due to a delay in the timing of stopping the irradiation of radiation.

Japanese Unexamined Patent Publication No. 2013-138829

Patent Document 1 describes that when AEC is performed, the later the time of prediction of the irradiation stop time is from the start of irradiation, the more accurate the prediction of the irradiation stop time is. However, in the field of radiography (radiation imaging), for example, radiation with a very short irradiation time may be used, so it is not always good if the time of prediction is late. Further, for example, when radiation having a weak irradiation intensity and a long irradiation time is used, it is affected by various noise factors when monitoring the irradiation dose of the radiation with AEC. In particular, when AEC is performed using a conversion element in a radiation imaging device, it is easily affected by quantum noise and disturbance noise generated during radiation irradiation. Therefore, a cumulative error of the irradiation dose of radiation may occur, and under such a situation, the accuracy of the prediction of the irradiation stop time deteriorates even if the time of prediction of the irradiation stop time is later than the start of radiation irradiation. In some cases. Then, in this case, there may be a problem that the radiation stop control cannot be properly performed.

The present invention has been made in view of such problems, and an object of the present invention is to provide a mechanism capable of appropriately controlling irradiation stop of radiation.

The radiation imaging apparatus of the present invention has a detection element that detects incident radiation as an electric signal, a reading unit that reads out the electric signal output to a signal line connected to the detection element, and a reading unit. Based on the predictive means for predicting the irradiation stop time of the radiation based on the generated electric signal, and the electric signal read by the reading unit when the irradiation stop time predicted by the predictive means is reached, the said It has a determination means for determining whether the cumulative dose of radiation has reached the target dose.
The present invention also includes the method for controlling the radiation imaging apparatus described above.

According to the present invention, radiation stop control can be appropriately performed.

It is a figure which shows an example of the schematic structure of the radiation imaging system including the radiation imaging apparatus which concerns on embodiment of this invention. It is an equivalent circuit diagram which shows an example of the internal structure of the image pickup part shown in FIG. It is a flowchart which shows an example of the processing procedure in the control method of the radiation imaging apparatus which concerns on embodiment of this invention. It is a timing chart which shows a comparative example and shows an example of the processing procedure in the control method of a radiation imaging apparatus. It is a timing chart which shows the 1st example of the processing procedure in the control method of the radiation imaging apparatus which concerns on embodiment of this invention. It is a timing chart which shows the 2nd example of the processing procedure in the control method of the radiation imaging apparatus which concerns on embodiment of this invention. It is a timing chart which shows the 3rd example of the processing procedure in the control method of the radiation imaging apparatus which concerns on embodiment of this invention.

Hereinafter, embodiments (embodiments) for carrying out the present invention will be described with reference to the drawings. However, the embodiments of the present invention described below do not limit the invention according to the claims. Further, although a plurality of features are described in the embodiments of the present invention described below, not all of the plurality of features are essential to the present invention, and the plurality of features are described. It may be combined arbitrarily. Further, in the present specification, the radiation according to the present invention is not limited to X-rays, but α-rays, β-rays, and γ-rays, which are beams produced by particles (including photons) emitted by radiation decay. In addition to the above, particle rays and cosmic rays are also included.

FIG. 1 is a diagram showing an example of a schematic configuration of a radiation imaging system 10 including a radiation imaging device 100 according to an embodiment of the present invention. In the present embodiment, as shown in FIG. 1, the radiation imaging system 10 includes a radiation imaging device 100, a control computer 200, a radiation control device 300, a radiation generator 400, and an exposure switch 500. ing.

The radiation imaging device 100 is a device that images a subject H using radiation R. As shown in FIG. 1, the radiation imaging device 100 includes an imaging unit 110, a dose monitor unit 120, and a drive control unit 130.

The imaging unit 110 is a component unit for acquiring a radiographic image of the subject H. In the present embodiment, the imaging unit 110 includes a pixel array in which a plurality of pixels for generating a radiation image are arranged, and the pixel array includes the radiation R incident on the dose monitor unit 120. A plurality of detection elements for monitoring the irradiation dose and the cumulative irradiation dose (cumulative dose) of the above are configured. Further, the imaging unit 110 outputs the information of the generated radiation image to, for example, a control computer.

The dose monitor unit 120 acquires an electric signal detected based on the radiation R incident on the detection element configured in the image pickup unit 110 from the detection element of the image pickup unit 110. Then, the dose monitor unit 120 was incident based on the electric signal acquired from the detection element of the imaging unit 110 in order to perform automatic exposure control (more specifically, in the present embodiment, radiation stop irradiation control). Monitor the irradiation dose of radiation R and the cumulative irradiation dose (cumulative dose). Specifically, the dose monitor unit 120 calculates the electric signal output from the detection element of the imaging unit 110 during the irradiation of the radiation R, and the irradiation dose, the cumulative irradiation dose (cumulative dose), and the radiation of the incident radiation R. Outputs information including time variation of intensity. A digital signal processing circuit such as FPGA may be used for the dose monitor unit 120, or an analog circuit such as a sample hold circuit or an operational amplifier may be used. Further, in FIG. 1, the dose monitor unit 120 has a configuration provided inside the radiation imaging device 100, but a part or all of the functions of the dose monitor unit 120 are included in the control computer 200. You may. In this case, the functions of the radiation imaging device 100 and the dose monitor unit 120 of the control computer 200 can be said to be the "radiation imaging device" of the present invention.

The drive control unit 130 is a component that controls the drive of the imaging unit 110 and the dose monitor unit 120.

The control computer 200 controls the entire radiation imaging system 10 to control the irradiation of radiation R and acquire a radiation image. Further, the control computer 200 can function as a user interface when the user uses the radiation imaging system 10.

The radiation control device 300 operates the radiation generator 400 according to a signal related to irradiation control of the radiation R received from the control computer 200.

The radiation generator 400 irradiates the subject H and the radiation imaging device 100 with the radiation R according to the control of the radiation control device 300.

The exposure switch 500 is a physical switch that inputs an on / off signal of radiation R irradiation to the radiation control device 300.

FIG. 2 is an equivalent circuit diagram showing an example of the internal configuration of the imaging unit 110 shown in FIG.
As shown in FIG. 2, the image pickup unit 110 includes a pixel array 111, a drive unit (drive circuit) 112, a bias power supply 113, a read unit (read circuit) 114, and an A / D conversion unit 115. ..

In FIG. 2, for the sake of simplicity of explanation, the pixels 210 having 5 rows × 5 columns are shown inside the pixel array 111, but in reality, more pixels 210 are arranged. For example, a radiation imaging apparatus 100 including a 17-inch imaging unit 110 (pixel array 111) may have pixels 210 of about 2800 rows × about 2800 columns.

The pixel array 111 is configured to have a plurality of pixels 210 arranged in a matrix. One pixel 210 includes a conversion element 211 (for example, S11 in FIG. 2) that converts the incident radiation R into an electric charge, and a switch element for outputting an electric signal corresponding to the electric charge to the signal lines Sigma1 to Sigma5. It is configured to include 212 (for example, T11 in FIG. 2). The conversion element 211 of the present embodiment includes, for example, a wavelength converter (for example, a scintillator) that converts radiation R into light that can be detected by the photoelectric conversion element, and a photoelectric that converts light converted by the wavelength converter into electric charges. A conversion element and is used. At this time, the photoelectric conversion element is used, for example, a MIS-type photodiode which is arranged on an insulating substrate such as a glass substrate and whose main material is amorphous silicon, or a PIN-type photodiode which is arranged on a semiconductor substrate such as silicon. May be done. Further, the conversion element 211 is not limited to the indirect type conversion element provided with the above-mentioned wavelength converter, and a direct type conversion element that directly converts the incident radiation R into an electric charge may be used. .. Amorphous selenium or the like may be used as the main material of this direct type conversion element. Further, the switch element 212 may use a transistor having a control terminal and two main terminals. As the switch element 212 of the present embodiment, for example, a thin film transistor (TFT) is used.

One electrode of the conversion element 211 is electrically connected to one of the two main terminals of the switch element 212, and the other electrode of the conversion element 211 is electrically connected to the bias power supply 113 via a common bias wiring. Will be done. The control terminals of the switch elements T11 to T15 of the switch elements 212 arranged in the row direction (horizontal direction in FIG. 2) are electrically connected to the drive wiring Vg1 in common. A drive signal for controlling the conduction state of the switch elements T11 to T15 is given to the switch elements T11 to T15 from the drive unit 112 in line units via the drive wiring Vg1. Of the switch elements 212 arranged in the row direction (vertical direction in FIG. 2), the switch elements T11 to T51 have the other main terminal electrically connected to the signal line Sigma1. While the switch elements T11 to T51 are in a conductive state, an electric signal corresponding to the electric charge accumulated in the conversion elements S11 to S51 is output to the reading unit 114 via the signal line Sigma1. The signal lines Sigma1 to Sigma5 arranged in the column direction (vertical direction in FIG. 2) of the pixel array 111 parallel the electric signals output from the pixels 210 (for example, pixels P11 to P15) connected to the same drive wiring Vg1. Is transmitted to the reading unit 114.

In the present embodiment, the period during which the drive signal for controlling the conduction state of the switch elements T21 to T25 connected to the drive wiring Vg2 controls the exposure, that is, the irradiation dose of the radiation R incident during the irradiation of the radiation R is determined. To detect. That is, in the present embodiment, the pixel 210 connected to the drive wiring Vg2 operates as a “detection element”. Here, in FIG. 2, in the pixel array 111, the pixels that function as the detection element that detects the incident radiation R as an electric signal are referred to as detection elements D (for example, detection elements D21 to D25). Further, in the pixel array 111, pixels other than the detection element D are described as pixels P for acquiring a radiation image, if necessary.

As shown in FIG. 2, the reading unit 114 includes a reference power supply 220, an amplifier circuit 230, a multiplexer 240, and a buffer amplifier 250.

The amplifier circuit 230 is provided for each of the signal lines Sigma 1 to Sigma 5, and amplifies the electric signal output in parallel from the pixels 210 arranged in the pixel array 111. The amplifier circuit 230 includes an integrator amplifier 231, a variable amplifier 232, and a sample hold circuit 233. The integrator amplifier 231 amplifies the electric signal output from the pixel P and the detection element D. More specifically, the integrating amplifier 231 includes an operational amplifier that amplifies and outputs an electric signal read from the pixel P and the detection element D, an integrating capacitance, and a reset switch. The integrator amplifier 231 can change the amplification factor by changing the value of the integrator capacitance. An electric signal output from the pixel P or the detection element D is input to the inverting input terminal of the operational amplifier included in the integrating amplifier 231, and a reference voltage Vref is input from the reference power supply 220 to the forward rotation input terminal. .. Further, the amplified electric signal is output from the output terminal of the operational amplifier included in the integrating amplifier 231. Further, the integrated capacitance included in the integrating amplifier 231 is arranged between the inverting input terminal and the output terminal of the operational amplifier. The variable amplifier 232 amplifies the electric signal output from the integrating amplifier 231. The sample hold circuit 233 samples and holds the electric signal amplified by the integrating amplifier 231 and the variable amplifier 232. The sample hold circuit 233 includes a sampling switch and a sampling capacitance.

The multiplexer 240 sequentially outputs the electric signals read in parallel from the amplifier circuit 230 and outputs them as a series electric signal. The buffer amplifier 250 converts the electrical signal output from the multiplexer 240 into impedance and outputs the signal.

The A / D conversion unit 115 converts the analog electric signal output from the buffer amplifier 250 into a digital electric signal (data). During the irradiation of the radiation R, the digital data output from the detection element D via the A / D conversion unit 115 is supplied to the dose monitor unit 120 described above. Further, after the irradiation of the radiation R, the electric signal converted into digital data output from each pixel P via the A / D conversion unit 115 is supplied to the control computer 200 as radiation image information. The control computer 200 functions as a signal processing unit that processes an electric signal supplied from the pixel P of the radiation imaging device 100 and displays it as a radiation image on a display unit of the control computer 200 or an external display (not shown). You may.

Further, the image pickup unit 110 includes a reference power supply 220 of the amplifier circuit and a bias power supply 113 as power supply units for supplying various power supplies. The reference power supply 220 supplies a reference voltage Vref to the forward rotation input terminal of the operational amplifier of the integrating amplifier 231. The bias power supply 113 supplies a common bias voltage Vs to the conversion element 211 of each pixel 210 via the bias wiring.

The drive unit 112 is a drive signal including a conduction voltage that causes the switch element 212 to be in a conductive state and a non-conducting voltage that causes the switch element 212 to be in a non-conducting state in accordance with the control signals D-CLK, OE, and DIO supplied from the drive control unit 130. Is output to each drive wiring Vg. As a result, the drive unit 112 controls the conduction state and the non-conduction state of the switch element 212, and drives the pixel array 111. Specifically, the control signal D-CLK is a shift clock signal of the shift register used as the drive unit 112. The control signal DIO is a pulse signal transferred by the shift register. The control signal OE is a signal that controls the output end of the shift register. With the above, the required driving time and the scanning direction are set.

Further, the drive control unit 130 controls the operation of each component of the reading unit 114 by supplying the control signals RC, SH, and CLK to the reading unit 114. Specifically, the control signal RC is a signal for controlling the operation of the reset switch of the integrating amplifier 231. The control signal SH is a signal for controlling the operation of the sample hold circuit 233. The control signal CLK is a signal for controlling the operation of the multiplexer 240.

In the present embodiment, as shown in FIG. 2, a specific pixel P for acquiring a radiation image is specified without forming a detection element D independent of the pixel P for acquiring a radiation image. All the pixels in the row may also function as the detection element D. In this case, since the pixel P connected to the drive wiring Vg in the specific row in the region of interest is used as the detection element, for example, the pixel 210 connected to the drive wiring Vg2 also functions as the detection element.

FIG. 3 is a flowchart showing an example of a processing procedure in the control method of the radiation imaging apparatus 100 according to the embodiment of the present invention. In FIG. 3, FIG. 3A shows a flowchart showing the entire processing procedure in the control method of the radiation imaging apparatus 100. Further, FIG. 3B shows a flowchart showing a detailed processing procedure of step S310 of FIG. 3A, and FIG. 3C shows a detailed processing procedure of step S320 of FIG. 3A. The flowchart, FIG. 3 (d) shows a flowchart showing the detailed processing procedure of step S330 of FIG. 3 (a), and FIG. 3 (e) shows the detailed processing procedure of step S340 of FIG. 3 (a). The flowcharts are described respectively.

First, in step S310 of FIG. 3A, for example, the drive control unit 130 sets imaging conditions for acquiring a radiation image using the radiation imaging device 100. The detailed processing procedure of step S310 will be described with reference to FIG. 3 (b).

In step S310 of FIG. 3A, first, in step S311 of FIG. 3B, for example, the drive control unit 130 has a tube current C (mA) and a tube voltage V, which are irradiation conditions of radiation R, as imaging conditions. (KV) setting and irradiation conditions such as frame rate are set.

Subsequently, in step S312 of FIG. 3B, for example, the drive control unit 130 sets the position of the region of interest (ROI) for performing automatic exposure control (Automatic Exposure Control: AEC) as a shooting condition.

Subsequently, in step S313 of FIG. 3B, for example, the drive control unit 130 has a target dose to be compared with the cumulative irradiation dose (cumulative dose) of the radiation R when performing the irradiation stop control of the radiation R as an imaging condition. Make settings. The target dose is set by the maximum or average value of the radiation dose of one or more regions of interest (ROI), the difference or ratio between the maximum and minimum values of the radiation dose, and is set by, for example, the control computer 200. It is converted into a quantity threshold, and the converted threshold is supplied as a target dose to the dose monitoring unit 120 via the drive control unit 130 of the radiation imaging apparatus 100. Here, the conversion of the radiation dose to the threshold value may be performed by, for example, the dose monitor unit 120. In the present embodiment, the dose monitor unit 120 uses the target dose, which is the threshold value of the radiation dose, to determine whether or not the cumulative dose of the radiation R detected by the detection element D of the radiation imaging apparatus 100 has reached the target dose. Will be judged.

When the process of step S313 of FIG. 3 (b) is completed, the process of step S310 of FIG. 3 (a) is completed, and the process proceeds to step S320 of FIG. 3 (a).

Subsequently, in step S320 of FIG. 3A, the drive control unit 130 starts radiography. The detailed processing procedure of this step S320 will be described with reference to FIG. 3 (c).

In step S320 of FIG. 3A, first, in step S321 of FIG. 3C, the drive control unit 130 refers to the pixel array 111 of the imaging unit 110 until the irradiation of radiation R is started. Reset drive (blank reading drive) is performed. In this reset drive, a voltage (conduction voltage) at which the switch element 212 conducts is sequentially applied from the drive unit 112 to each drive wiring Vg, and a dark charge or the like generated by the conversion element 211 of each pixel 210 is reset. Is. Here, in the reset drive, the electric signal acquired from each pixel 210 may be used for offset correction when generating a radiation image. Further, in this reset drive, when the conduction voltage is sequentially applied from the drive unit 112 to each drive wiring Vg, the detection element D also resets at the same time.

Subsequently, in step S322 of FIG. 3C, the drive control unit 130 determines whether or not the radiation R exposure switch 500 is pressed and turned on by the user. As a result of this determination, if the exposure switch 500 is not turned on (S322 / NO), the process returns to step S321 of FIG. 3C, and the process of step S321 is performed again.

On the other hand, if the exposure switch 500 is turned on as a result of the determination in step S322 of FIG. 3 (c) (S322 / YES), the process proceeds to step S323 of FIG. 3 (c).
Proceeding to step S323 of FIG. 3C, the drive control unit 130 stops the reset drive (blank reading drive) of the image pickup unit 110 with respect to the pixel array 111.

Subsequently, in step S324 of FIG. 3C, the drive control unit 130 radiates radiation from the radiation generator 400 toward the subject H and the radiation imaging device 100 via the control computer 200 and the radiation control device 300. Irradiation of R is started.

When the process of step S324 of FIG. 3 (c) is completed, the process of step S320 of FIG. 3 (a) is completed, and the process proceeds to step S330 of FIG. 3 (a).

Subsequently, in step S330 of FIG. 3A, the dose monitor unit 120 automatically controls the exposure from the detection element D during the irradiation of the radiation R (more specifically, in the present embodiment, the irradiation stop control of the radiation R). ) Is acquired and the target dose is predicted. The detailed processing procedure of step S330 will be described with reference to FIG. 3 (d).

In step S330 of FIG. 3A, first, in step S331 of FIG. 3D, the dose monitor unit 120 sequentially conducts the switch element 212 of the detection element D while the drive control unit 130 irradiates the radiation R. By controlling the above, the electric signal read from the detection element D via the reading unit 114 is acquired.

Subsequently, in step S332 of FIG. 3D, the dose monitor unit 120 uses an electric signal (charge) acquired from the detection element D arranged in the same region of interest (ROI) at a predetermined sampling cycle. A monitor index value based on the integrated charge related to the cumulative dose of radiation R is calculated. For example, as the monitor index value, the value of the slope when the value of the integrated charge obtained at that time is approximated by a straight line for each predetermined sampling cycle (for example, in FIG. 5 described later, the drive wiring is performed during irradiation with radiation. The value of the slope when the value of the integrated charge (d) obtained at that time is approximated by a straight line can be applied to each of the first four sampling cycles in which Vg2 is turned ON. The dose monitor unit 120 that performs the process of step S332 for calculating the monitor index value is a component unit corresponding to an example of the calculation means of the present invention.

Subsequently, in step S333 of FIG. 3 (d), the dose monitor unit 120 determines whether the monitor index value calculated in step S332 of FIG. 3 (d) is within the range of the determination reference value arbitrarily determined in advance. Judge whether or not. Here, the determination reference value is a reference value for determining whether or not the variation in the irradiation of the radiation R is suppressed. Therefore, when setting the judgment reference value, the variation in the irradiation amount per unit time of the radiation R at a predetermined predetermined tube current C (mA) and tube voltage V (kV) set in advance is measured, and the variation thereof is measured. It is desirable to set the judgment reference value based on the result. As a result of the determination in step S333 of FIG. 3 (d), if the monitor index value calculated in step S332 of FIG. 3 (d) is not within the determination reference value (S333 / NO), FIG. 3 (d). The process returns to step S331 of the above step S331, and the processes after step S331 are performed again.

On the other hand, if the result of the determination in step S333 of FIG. 3 (d) shows that the monitor index value calculated in step S332 of FIG. 3 (d) is within the range of the determination reference value (S333 / YES), FIG. d) Proceed to step S334.
Proceeding to step S334 of FIG. 3D, the dose monitoring unit 120 acquired an electric signal (acquired from the detection element D from the detection element D at a predetermined sampling cycle during irradiation of radiation R) of an electric signal read from the detection element D by the reading unit 114. The irradiation stop time of the radiation R is predicted and output based on the electric signal). The dose monitor unit 120 that performs the process of step S334 for predicting the irradiation stop time of the radiation R is a component unit corresponding to an example of the prediction means of the present invention.

Subsequently, in step S335 of FIG. 3D, the dose monitor unit 120 determines whether or not the result of the determination repeatedly performed in a predetermined cycle is within the range of the predetermined definite standard. do. Here, the definite criterion may be the number of times that the monitor index value calculated in step S332 falls within the range of the determination reference value, such as being within the range of the determination reference value at least twice in succession. .. Further, at this time, as a definite criterion, for example, a differential value of the monitor index value may be used in order to grasp the tendency of whether or not the variation in the irradiation of the radiation R is suppressed. That is, the definite standard may be a standard that can recognize that the variation in the irradiation of the radiation R is suppressed.

Subsequently, in step S336 of FIG. 3D, the dose monitor unit 120 outputs a prediction of the determined irradiation stop time of the radiation R when it is within the range of the determination standard in step S335. The irradiation stop time at this time is preferably calculated from the cumulative irradiation dose (cumulative dose) of the radiation R from the start of the irradiation of the radiation R to the time of determination. Further, as the irradiation stop time of radiation R, the time from the cumulative irradiation dose (cumulative dose) at the time of confirmation to the time required to reach an appropriate amount of radiation R may be calculated, or the irradiation dose per unit time until confirmation may be calculated. The remaining time may be calculated from the average value.

When the process of step S336 of FIG. 3 (d) is completed, the process of step S330 of FIG. 3 (a) is completed, and the process proceeds to step S340 of FIG. 3 (a).

Subsequently, in step S340 of FIG. 3A, the drive control unit 130 reads out an electric signal from the detection element D by the reading unit 114 until the irradiation stop time predicted in step S330 of FIG. 3A is reached. Control to stop (predicted time standby control). The detailed processing procedure of step S340 will be described with reference to FIG. 3 (e).

In step S340 of FIG. 3A, first, in step S341 of FIG. 3E, the drive control unit 130 is operated by the reading unit 114 until the irradiation stop time predicted in step S330 of FIG. 3A is reached. Control is performed to stop reading the electric signal from the detection element D.

Subsequently, in step S342 of FIG. 3 (e), the drive control unit 130 continues to accumulate the electric signal (charge) by the detection element D until the irradiation stop time predicted in step S330 of FIG. 3 (a) is reached. Take control.

Subsequently, in step S343 of FIG. 3 (e), the drive control unit 130 determines whether or not the irradiation stop time predicted in step S330 of FIG. 3 (a) has been reached. As a result of this determination, if the irradiation stop time predicted in step S330 of FIG. 3A has not been reached (S343 / NO), the process returns to step S341 of FIG. Do it again.

On the other hand, as a result of the determination in step S343 of FIG. 3 (e), when the irradiation stop time predicted in step S330 of FIG. 3 (a) is reached (S343 / YES), step S344 of FIG. 3 (e) is performed. move on.
Proceeding to step S344 of FIG. 3E, the drive control unit 130 controls to restart reading of the electric signal from the detection element D by the reading unit 114 that was stopped in step S341. That is, the drive control unit 130 controls to restart the reading of the electric signal from the detection element D by the reading unit 114 when the irradiation stop time predicted in step S330 of FIG. 3A is reached. Here, for example, the dose monitor unit 120 performs a process of correcting the electric signal read from the detection element D by the reading unit 114, if necessary. The dose monitor unit 120, which performs a process of correcting the electric signal read from the detection element D by the reading unit 114, is a component corresponding to an example of the correction means of the present invention. In this case, the dose monitor unit 120 performs the correction (offset correction) performed after the above-mentioned restart before the above-mentioned restart according to the time during the accumulation period waiting until the predicted irradiation stop time is reached. A correction value (offset correction value) different from the correction performed in (for example, the correction for the electric signal read from the detection element D by the reading unit 114 in step S331) may be used.

Subsequently, in step S345 of FIG. 3 (e), the drive control unit 130 (or the dose monitor unit 120) is connected to the detection element D by the time the irradiation stop time predicted in step S330 of FIG. 3 (a) is reached. It is determined whether or not the cumulative irradiation dose (cumulative dose) of the radiation based on the acquired integrated charge has reached the target dose set in step S313 of FIG. 3 (b). That is, in step S345 of FIG. 3 (e), the drive control unit 130 (or the dose monitor unit 120) reaches the cumulative dose of radiation R when the irradiation stop time predicted in step S330 of FIG. 3 (a) is reached. Determines if the target dose has been reached. The drive control unit 130 (or dose monitor unit 120) that performs the process of step S345 for determining whether the cumulative dose of radiation R has reached the target dose is a component corresponding to an example of the determination means of the present invention.

As a result of the determination in step S345 of FIG. 3 (e), if the cumulative irradiation dose (cumulative dose) of radiation has not reached the target dose (S345 / NO), the process returns to step S344 of FIG. 3 (e). The process of step S344 is performed again. When the process of step S344 is performed again, the drive control unit 130 controls to restart the reading of the electric signal from the detection element D by the reading unit 114, and then the cumulative dose of radiation reaches the target dose in step S345. The reading unit 114 controls to continue reading the electric signal from the detection element D until it is determined that the signal has been read.

On the other hand, as a result of the determination in step S345 of FIG. 3 (e), when the cumulative irradiation dose (cumulative dose) of radiation has reached the target dose (S345 / YES), step S340 of FIG. 3 (a). The process is completed, and the process proceeds to step S350 in FIG. 3A.

Proceeding to step S350 of FIG. 3A, the drive control unit 130 (or the dose monitor unit 120) transmits a signal for stopping the irradiation of the radiation R to the control computer 200. The drive control unit 130 (or the dose monitor unit 120) that transmits a signal for stopping the irradiation of the radiation R is a component corresponding to an example of the irradiation stopping means of the present invention.

Subsequently, when the process proceeds to step S360 of FIG. 3A, the control computer 200 irradiates the radiation R from the radiation generator 400 via the radiation control device 300 in response to the signal transmitted in step S350. Stop it.

In the present embodiment, the drive control unit 130 (or the dose monitor unit 120) directly transmits a signal for stopping the irradiation of the radiation R to the radiation control device 300, and the radiation control device accordingly. The 300 may stop the radiation generator 400 from irradiating the radiation R. As described above, the radiation imaging apparatus 100 determines whether or not the cumulative dose of the incident radiation R has reached the target dose, and stops the irradiation of the radiation R when the cumulative dose reaches the target dose. Thereby, it is possible to have an AEC function.

Subsequently, when the process proceeds to step S370 of FIG. 3A, the drive control unit 130 causes the reading unit 114 to read the electrical signal for generating the radiation image stored in each pixel P. Drive. That is, in the process of step S370, the reading unit 114 is for generating a radiation image accumulated in each pixel P after the irradiation of radiation R is stopped by the process of step S360 of FIG. 3 (a). The main reading drive to read the electric signal is performed. This main reading drive is an operation in which a conduction voltage is sequentially applied from the drive unit 112 to the drive wiring Vg, and the electric charge accumulated in the conversion element 211 connected to each drive wiring Vg is read out by the reading unit 114 as an electric signal. .. The electric signal read by the reading unit 114 is converted into a digital signal by the A / D conversion unit 115 and transferred to the control computer 200 as radiographic image information. In the information of the radiation image, the pixel value at the position where the detection element D is arranged is close to zero because it is read out during the irradiation of the radiation R, and is missing as the pixel value of the radiation image. .. Therefore, the pixel value of the pixel P arranged around the detection element D may be used to complement the pixel value at the position where the detection element D is arranged. Further, the cumulative value of the electric signal read from the detection element D during the irradiation of the radiation R can be the same amount as the electric signal (charge) accumulated in the detection element D during the irradiation of the radiation R. For this reason, the cumulative value of the electric signal read from the detection element D may be used as the pixel value at the position where the detection element D is arranged.

When the process of step S370 of FIG. 3 (a) is completed, the process of the flowchart of FIG. 3 (a) is completed.

From the explanation of the flowchart of FIG. 3, the drive control unit 130 is at least one of the irradiation stop time predicted in step S330 of FIG. 3A and the result of the determination in step S345 of FIG. 3E. Based on one, at least one of the reading of the electric signal from the detection element D by the reading unit 114 and the accumulation of the electric signal by the detection element D is controlled. The drive control unit 130 that performs this control is a component corresponding to an example of the control means of the present invention.

Next, the timing chart in the control method of the radiation imaging apparatus 100 will be described.

FIG. 4 is a timing chart showing a comparative example and showing an example of a processing procedure in the control method of the radiation imaging apparatus. In the comparative example shown in FIG. 4, the reading of the electric signal from the detection element D during the irradiation of the radiation R is performed in the same sampling cycle.

In the comparative example shown in FIG. 4, an example of the processing procedure after the start of photographing in step S320 of FIG. 3A is shown. Specifically, the blank reading drive is performed until the exposure switch 500 is pressed and turned ON, and when the exposure switch 500 is pressed and turned ON, the blank reading drive is stopped. Then, when the permission instruction information permitting the irradiation of the radiation R is transmitted to the radiation control device 300, the radiation control device 300 starts the irradiation of the radiation R from the radiation generator 400. At the start of irradiation of radiation R from the radiation generator 400, electric charges are accumulated in the detection elements D21 to D25 of the imaging unit 110. Then, the dose monitor unit 120 performs sampling drive for reading an electric signal at regular time intervals from, for example, a dose detection line composed of one line of Vg2 or a plurality of lines. At this time, since the electric charge disappears every time the electric signal is read from the dose detection line, the dose monitor unit 120 integrates the electric signal (charge) of the read out dose detection line to calculate the integrated value. Hereinafter, the integrated value calculated by integrating the electric signals (charges) of the dose detection line will be referred to as "integrated charge value".

When the sampling drive of a predetermined period is performed, the signal value of the electric signal (charge) read out at one time becomes smaller with respect to the weak and long radiation R. When the signal value of the electric signal is small, the number of samplings until the integrated charge value of the sampled electric signal (charge) reaches the dose arrival value set as the target dose increases. Random noise of the reading unit 114, an error between the offset signal acquired in advance before irradiation of the radiation R and the offset amount during the period of exposure control, and the like are integrated as the number of samplings increases. Therefore, errors may be accumulated and a large error may occur with respect to the target dose.

Next, the timing chart in the control method of the radiation imaging apparatus 100 according to the present embodiment will be described.

FIG. 5 is a timing chart showing a first example of a processing procedure in the control method of the radiation imaging apparatus 100 according to the embodiment of the present invention. As shown in FIG. 5, when the pixel 210 connected to the drive wiring Vg2 is driven as the detection element D, the radiation imaging device 100 applies an ON voltage to the drive wiring Vg2 when the exposure switch 500 is pressed. , Acquires an electric signal from the detection element D during irradiation with radiation R. Then, the dose monitor unit 120 calculates a monitor index value based on the integrated charge related to the cumulative dose of radiation R from the detection element D using the electric signal (charge) acquired in a predetermined sampling cycle (FIG. 3 (FIG. 3). d) S332). Then, the dose monitor unit 120 determines whether or not the calculated monitor index value is within the range of the determination reference value arbitrarily determined in advance (S333 in FIG. 3D), and the predicted irradiation stop time. (S336 in FIG. 3D) is determined to be feasible. Then, the drive control unit 130 (or the dose monitor unit 120) sets the cumulative dose of radiation R calculated from the electric signal of the detection element D when the predicted irradiation stop time indicated by the predicted time in FIG. 5 is reached. It is determined whether the integrated charge value has reached the dose reached value related to the predetermined target dose (S345 in FIG. 3 (e)), and the integrated charge value has not reached the dose reached value as shown in FIG. For example, the electric signal is acquired from the detection element D again during the irradiation of the radiation R (S344 in FIG. 3E).

On the other hand, if the integrated charge value reaches the dose arrival value, the control computer 200 stops the irradiation of the radiation R from the radiation generator 400 via the radiation control device 300 (S360 in FIG. 3A). ).

Next, when the irradiation of the radiation R is stopped, the drive control unit 130 drives the main reading of the pixels 210 connected to the drive wirings Vg1 to Vg5 (S370 in FIG. 3A). In the main reading drive, the ON voltage of the switch element 212 is sequentially applied from the drive unit 112 to the drive wirings Vg1 to Vg5, and the electric signal based on the electric charge accumulated in the conversion element 211 of each pixel 210 is read out by the reading unit 114. Then, it is converted into a digital signal by the A / D conversion unit 115 and transferred to the control computer 200 as radiation image information.

Since the pixel value of the detection element D in the information of the radiation image is read out during the irradiation of the radiation R, the pixel value becomes zero, and the detection element D becomes a defective pixel. However, the integrated charge value of the electric signal (charge) read from the detection element D during the irradiation of the radiation R is accumulated in the detection element D when the ON voltage is not applied to the switch element 212 during the irradiation of the radiation R. It becomes an electric signal (charge) to be generated. That is, by converting the integrated charge value of the electric signal (charge) read from the detection element D into the pixel value for the radiographic image, the detection element D can also be used as the information of the radiographic image in the same manner as the pixel P for the image.

FIG. 6 is a timing chart showing a second example of the processing procedure in the control method of the radiation imaging apparatus 100 according to the embodiment of the present invention. FIG. 6 shows a timing chart of the operation of the radiation imaging apparatus 100 when the predicted irradiation stop time is calculated as a time later than the target dose arrival time.

As shown in FIG. 6, when the pixel 210 connected to the drive wiring Vg2 is driven as the detection element D, the radiation imaging device 100 applies an ON voltage to the drive wiring Vg2 when the exposure switch 500 is pressed. , Acquires an electric signal from the detection element D during irradiation with radiation R. Then, the dose monitor unit 120 calculates a monitor index value based on the integrated charge related to the cumulative dose of radiation R from the detection element D using the electric signal (charge) acquired in a predetermined sampling cycle (FIG. 3 (FIG. 3). d) S332). Then, the dose monitor unit 120 determines whether or not the calculated monitor index value is within the range of the determination reference value arbitrarily determined in advance (S333 in FIG. 3D), and the predicted irradiation stop time. (S336 in FIG. 3D) is determined to be feasible. Then, the drive control unit 130 (or the dose monitor unit 120) sets the cumulative dose of radiation R calculated from the electric signal of the detection element D when the predicted irradiation stop time indicated by the predicted time in FIG. 6 is reached. It is determined whether the integrated charge value has reached the dose reaching value related to the predetermined target dose (S345 in FIG. 3 (e)), and if the integrated charge value has not reached the dose reaching value, the radiation R is irradiated again. An electric signal is acquired from the detection element D inside (S344 in FIG. 3 (e)).

The dose monitor unit 120 counts (measures) the number of drives (number of reads) or the time from when the drive of the detection element D is restarted until the target dose is reached, and reflects the counted value in the next imaging. Therefore, it has a function of adjusting the predicted irradiation stop time. The dose monitor unit 120 having a function of adjusting the predicted irradiation stop time is a component unit corresponding to an example of the adjusting means of the present invention.

For example, as shown in FIG. 6, 0 ms after the drive of the detection element D is restarted, that is, the integrated charge value related to the cumulative dose of radiation R has already reached the dose reaching value related to the predetermined target dose. If so, from the integrated charge value Ds of the detection element D, the dose arrival value Th which is a predetermined threshold value, the average dose value Davg per sampling, and the sampling interval St [us], the following (1) ), The adjustment value Dadj of the next irradiation stop time is calculated.
Dadj = ((Ds-Th) / Davg) x St ... (1)

In the example shown in FIG. 6, in the next radiography (radiation imaging), −Dadj [us] = -3 sampling is performed from the time when the irradiation stop time is fixed, and the irradiation stop time is adjusted. As a result, the accuracy of the AEC of the radiation imaging apparatus 100 is expected to be improved, and it is possible to provide a technique advantageous for improving the accuracy of the AEC.

FIG. 7 is a timing chart showing a third example of the processing procedure in the control method of the radiation imaging apparatus 100 according to the embodiment of the present invention. FIG. 7 shows a timing chart of the operation of the radiation imaging apparatus 100 when the predicted irradiation stop time is calculated as a time earlier than the target dose arrival time.

As shown in FIG. 7, when the pixel 210 connected to the drive wiring Vg2 is driven as the detection element D, the radiation imaging device 100 applies an ON voltage to the drive wiring Vg2 when the exposure switch 500 is pressed. , Acquires an electric signal from the detection element D during irradiation with radiation R. Then, the dose monitor unit 120 calculates a monitor index value based on the integrated charge related to the cumulative dose of radiation R from the detection element D using the electric signal (charge) acquired in a predetermined sampling cycle (FIG. 3 (FIG. 3). d) S332). Then, the dose monitor unit 120 determines whether or not the calculated monitor index value is within the range of the determination reference value arbitrarily determined in advance (S333 in FIG. 3D), and the predicted irradiation stop time. (S336 in FIG. 3D) is determined to be feasible. Then, the drive control unit 130 (or the dose monitor unit 120) sets the cumulative dose of radiation R calculated from the electric signal of the detection element D when the predicted irradiation stop time indicated by the predicted time in FIG. 7 is reached. It is determined whether or not the integrated charge value has reached the dose reached value related to the predetermined target dose (S345 in FIG. 3 (e)), and as shown in FIG. 7, the integrated charge value has reached the dose reached value. If not, an electric signal is acquired from the detection element D again during irradiation with radiation R (S344 in FIG. 3E).

The dose monitor unit 120 counts (measures) the number of drives (number of reads) or the time from when the drive of the detection element D is restarted until the target dose is reached, and reflects the counted value in the next imaging. Therefore, it has a function of adjusting the predicted irradiation stop time. The dose monitor unit 120 having a function of adjusting the predicted irradiation stop time is a component unit corresponding to an example of the adjusting means of the present invention.

For example, as shown in FIG. 7, when the integrated charge value related to the cumulative dose of radiation R reaches the dose reaching value related to the predetermined target dose after +3 sampling after the driving of the detection element D is restarted. In the next radiography (radiation imaging), +3 sampling will be performed from the time when the irradiation stop time is fixed, and the irradiation stop time will be adjusted. As a result, the accuracy of the AEC of the radiation imaging apparatus 100 is expected to be improved, and it is possible to provide a technique advantageous for improving the accuracy of the AEC.

As described above, in the radiation imaging apparatus 100 according to the present embodiment, the cumulative dose of radiation R is set to the target dose based on the electric signal read by the reading unit 114 when the predicted irradiation stop time is reached. It is determined whether or not the signal has been reached (S345 in FIG. 3 (e)).
According to such a configuration, the irradiation stop control of the radiation R can be appropriately performed.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.
This program and a computer-readable storage medium that stores the program are included in the present invention.

It should be noted that the above-described embodiments of the present invention merely show examples of embodiment in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. Is. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features.

10: Radiation imaging system, 100: Radiation imaging device, 110: Imaging unit, 111: Pixel array, 112: Drive unit (drive circuit), 113: Bias power supply, 114: Read unit (read circuit), 115: A / D Conversion unit, 120: Dose monitor unit, 130: Drive control unit, 200: Control computer, 210: Pixel, 211: Conversion element, 212: Switch element, 300: Radiation control device, 400: Radiation generator, 500: Exposure Radiation switch, D: detection element, R: radiation, H: subject

Claims (16)

A detection element that detects incident radiation as an electrical signal,
A reading unit that reads out the electric signal output to the signal line connected to the detection element, and
A predictive means for predicting the irradiation stop time of the radiation based on the electric signal read by the reading unit, and
A determination means for determining whether the cumulative dose of the radiation has reached the target dose based on the electric signal read by the reading unit when the irradiation stop time predicted by the prediction means is reached.
A radiation imaging device characterized by having. The radiation imaging device according to claim 1, wherein the reading unit reads out the electric signal output to the signal line during irradiation with the radiation. The radiation imaging apparatus according to claim 1 or 2, wherein the predicting means predicts the irradiation stop time based on the electric signal read out at a predetermined cycle by the reading unit. Further, it has a calculation means for calculating a monitor index value related to the cumulative dose by using the electric signal read out at a predetermined cycle in the reading unit.
The radiation imaging apparatus according to any one of claims 1 to 3, wherein the prediction means predicts the irradiation stop time when the monitor index value is within the range of the determination reference value. Of the reading of the electric signal by the reading unit and the accumulation of the electric signal by the detecting element based on at least one of the irradiation stop time predicted by the predicting means and the result of the determination by the determining means. The radiation imaging device according to any one of claims 1 to 4, further comprising a control means for controlling at least one of the above. The radiation imaging apparatus according to claim 5, wherein the control means controls to stop the reading of the electric signal by the reading unit until the irradiation stop time predicted by the prediction means is reached. The radiation imaging device according to claim 5 or 6, wherein the control means controls the detection element to continue accumulating the electric signal until the irradiation stop time predicted by the prediction means is reached. Any one of claims 5 to 7, wherein the control means controls to restart reading of the electric signal by the reading unit when the irradiation stop time predicted by the predicting means is reached. The radiation imaging apparatus according to. After performing the restart control, the control means controls to continue reading the electric signal by the reading unit until the determination means determines that the cumulative dose has reached the target dose. The radiation imaging apparatus according to claim 8. When the control means determines that the cumulative dose has not reached the target dose when the resuming control is performed, the cumulative dose reaches the target dose by the determination means. The time until it is determined that the signal has been read or the number of times the electric signal is read by the reading unit is counted.
The radiation imaging apparatus according to claim 8 or 9, further comprising an adjusting means for adjusting the irradiation stop time predicted by the predicting means according to the counted value. When the control means performs the restart control, when the determination means determines that the cumulative dose has reached the target dose, the prediction is made according to the cumulative dose and the target dose. The radiation imaging apparatus according to claim 8 or 9, further comprising an adjusting means for adjusting the irradiation stop time predicted by the means. Further having a correction means for correcting the electric signal read by the reading unit,
The correction made by the correction means after the restart is described in any one of claims 8 to 11, wherein a correction value different from the correction made by the correction means is used before the restart. Radiation imaging device. The invention according to any one of claims 1 to 12, further comprising an irradiation stopping means for stopping the irradiation of the radiation when the determination means determines that the cumulative dose has reached the target dose. The radiation imaging apparatus described. The radiation imaging apparatus according to claim 13, wherein the reading unit performs a main reading drive for reading out the electrical signal for generating a radiation image after the irradiation of the radiation is stopped by the irradiation stopping means. .. Any of claims 1 to 14, wherein the detection element includes a conversion element that converts the radiation into the electric signal and a switch element that outputs the electric signal to the signal line. The radiation imaging device according to item 1. A control method for a radiation imaging device including a detection element that detects incident radiation as an electric signal and a reading unit that reads out the electric signal output to a signal line connected to the detection element.
A prediction step for predicting the irradiation stop time of the radiation based on the electric signal read by the reading unit, and
A determination step of determining whether the cumulative dose of the radiation has reached the target dose based on the electric signal read by the reading unit when the irradiation stop time predicted in the prediction step is reached.
A method for controlling a radiation imaging apparatus, which comprises.

Images