JP6417368B2 - Radiation imaging apparatus and radiation imaging system - Google Patents

Description

  The present invention relates to a radiation imaging apparatus and a radiation imaging system.

  At present, radiation imaging apparatuses using a flat panel detector (hereinafter abbreviated as FPD) made of a semiconductor material are widely used as radiation imaging apparatuses used for medical image diagnosis and nondestructive inspection using X-rays. . For example, in medical image diagnosis, a radiation imaging apparatus is used as a digital imaging apparatus for still image shooting such as general shooting and moving image shooting such as fluoroscopic shooting. The FPD has a detection unit in which a plurality of photoelectric conversion elements that convert radiation into an electrical signal are arranged in a matrix, and a readout circuit for reading out an electrical signal from the detection unit.

  An image acquired by the FPD includes an offset component (noise component) due to capacitance variation in the detection unit and offset variation in the readout circuit. Therefore, after reading the image without exposing the radiation and obtaining the offset image, the radiation image is read after exposing the radiation to obtain the radiation image, and the offset image is subtracted from the radiation image. There is a method of performing image correction to remove components. Such image correction is called offset correction.

  There are two methods for capturing an offset image: a method in which an offset image is read in advance before capturing a radiographic image and the information is stored, and a method in which the information is acquired immediately before or after acquisition of the radiographic image. When performing moving image shooting using FPD, the method of acquiring an offset image immediately before or immediately after acquisition of a radiographic image doubles the imaging interval and has a noise of √2 compared to a method of acquiring the image in advance. It will be doubled. In recent years, moving image shooting using an FPD has been required to reduce noise and frame rate, and a method of acquiring an offset image in advance is advantageous. In such a system, an offset image is prepared for each shooting mode, and the offset image is switched according to the shooting mode.

  However, it is known that the offset component changes transiently immediately after the shooting mode is switched. In addition, since the transitional change is not highly reproducible, it is difficult to correct correctly even if the radiographic image immediately after switching the imaging mode is corrected using the offset image acquired in advance. As a result, artifacts are superimposed on the image.

  In Patent Document 1, transient offset image data for correcting a component that changes transiently is acquired in advance, and, for example, several radiation images immediately after switching of an imaging mode are corrected using transient offset image data as well. Is disclosed.

JP 2014-108284 A

  However, in the technique disclosed in Patent Document 1, it is necessary to acquire the transient offset image data in advance with all shooting mode switching patterns before shooting, and it takes time to acquire the data. In addition, the transient offset image data becomes enormous.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an advantageous technique for suppressing deterioration in image quality immediately after mode switching.

One aspect of the present invention provides a pixel array in which a plurality of pixels are arranged to form a plurality of rows and a plurality of columns, and the plurality of rows of the pixel array according to a mode selected from a plurality of modes. A radiation imaging apparatus comprising: a scanning circuit that scans; and a readout circuit that reads out signals of pixels in a row selected by scanning by the scanning circuit, wherein the radiation imaging apparatus has a plurality of modes at a first frame rate. a first mode for capturing a plurality of frames in, and a second mode in which the imaging of a plurality of frames at a lower second frame rate than the first frame rate, and the first mode and the second mode the difference in the number of scans per unit time by the scanning circuit during such decrease, the double by the scanning circuit in one frame period of the first mode Row there are more number of said plurality of rows are scanned by the scanning circuit in one frame period of said second mode than the number of times to be scanned.

  According to the present invention, an advantageous technique is provided in order to suppress deterioration in image quality immediately after mode switching.

The figure which shows the structure of the radiation imaging system of one embodiment of this invention. The figure which illustrates the equivalent circuit of the imaging part in the radiation imaging device of the radiation imaging system of FIG. The figure which illustrates the operating method of the radiation imaging system of FIG. 1, and a radiation imaging device. The figure which illustrates the transitional change of the offset component accompanying the change of a mode. The figure which illustrates operation | movement of a 1st mode. The figure which illustrates operation | movement of a 2nd mode. The figure which illustrates operation | movement of a 3rd mode.

  Hereinafter, the present invention will be described through exemplary embodiments thereof with reference to the drawings. The category of radiation may include α rays, β rays, γ rays, etc. in addition to X-rays.

  FIG. 1 shows the configuration of a radiation imaging system RIS according to one embodiment of the present invention. The radiation imaging system RIS obtains a radiation image of a subject by irradiating the subject with radiation such as X-rays and detecting the X-ray transmitted through the subject. The radiation imaging system RIS can include, for example, a radiation source 112, an exposure control device 113, a control device 111, and a radiation imaging device 100. The exposure control device 113 causes the radiation source 112 to generate radiation in response to an exposure command from the operator. The control device 111 controls the radiation imaging apparatus 100 and acquires a radiation image from the radiation imaging apparatus 100. Further, the control device 111 controls the exposure control device 113.

  The radiation imaging apparatus 100 includes an imaging unit 104 that captures a radiation image, a communication unit 107 that communicates with the control device 111, a control unit 106 that controls the imaging unit 104, and a power supply unit 108 that supplies power to the imaging unit 104. sell. Further, the radiation imaging apparatus 100 can include an analysis unit 109 that analyzes an image output from the imaging unit 104 and a processing unit 105 that performs image calculation processing. Some of the components of the radiation imaging apparatus 100 may be incorporated in the control device 111, or the radiation imaging apparatus 100 and the control device 111 may be integrated. For example, in the example illustrated in FIG. 1, the analysis unit 109 and the processing unit 105 are incorporated in the radiation imaging apparatus 100, but the analysis unit 109 and the processing unit 105 may be incorporated in the control device 111.

  The imaging unit 104 can include, for example, a pixel array 101, a scanning circuit 102, and a readout circuit 103. The pixel array 101 is configured by arranging a plurality of pixels so as to form a plurality of rows and a plurality of columns. The scanning circuit 102 scans a plurality of rows of the pixel array 101 according to a mode selected from a plurality of modes (imaging modes). The readout circuit 103 reads out a signal from the pixel array 101. More specifically, the readout circuit 103 reads out signals of pixels in a row selected in scanning by the scanning circuit 102 among a plurality of rows of the pixel array 101. Reading a signal from the pixel array 101 means processing a signal output from the pixel array 101 and outputting a signal corresponding to the signal.

  FIG. 2 exemplarily shows an equivalent circuit of the imaging unit 104. The pixel PIX can include, for example, a conversion element 201 that converts radiation or light into electric charge, and a switch element 202 that outputs an electric signal corresponding to the electric charge. In one example, the conversion element 201 is a photoelectric conversion element that converts light applied to the conversion element 201 into an electric charge, and is a PIN photodiode that is disposed on an insulating substrate such as a glass substrate and has amorphous silicon as a main material. This is a MIS type photodiode. In addition, as the conversion element 201, there is an indirect type conversion element having a wavelength converter that converts radiation into light in a wavelength band that can be detected by the photoelectric conversion element, or a direct type conversion element that directly converts radiation into electric charges. It can be adopted.

  As the switch element 202, a transistor having a control terminal and two main terminals, for example, a thin film transistor (TFT) may be employed. One electrode of the conversion element 201 is electrically connected to one of the two main terminals of the switch element 202, and the other electrode is electrically connected to the power supply unit 108 via a common bias line Vs. In FIG. 2, in order to distinguish the conversion elements 201 from each other, the conversion elements 201 are denoted by Sij (i is a row number and j is a column number). Further, in order to distinguish the switch elements 202 from each other, the switch elements 202 are denoted by the symbols Tij (i is a row number and j is a column number).

  The control terminals of the switch elements 202 of the plurality of pixels PIX constituting one row are connected to the drive line Gi (i is the row number) of the row. For example, the control terminals of the switch elements T11 to T1n of the plurality of pixels PIX configuring the first row are electrically connected to the drive line G1 of the first row. Therefore, the minimum unit for driving the plurality of pixels PIX of the pixel array 101 by the scanning circuit 102 is the pixels PIX constituting one row.

  The other main terminal of the switch element 202 of the plurality of pixels PIX constituting one column is connected to the signal line Sigj (j is a column number) of the column. For example, the main terminals of the switch elements T11 to Tm1 of the plurality of pixels PIX configuring the first column are electrically connected to the signal line Sig1 of the first column. While the switch element 202 is in a conductive state, an electrical signal corresponding to the charge of the conversion element 201 is output to the readout circuit 103 via the signal line Sigj. The plurality of signal lines Sig <b> 1 to Sign are electrically connected to the read circuit 103.

  The readout circuit 103 includes a plurality of amplifier circuits 200 that amplify a plurality of electrical signals output in parallel from the pixel array 101 via the plurality of signal lines Sig1 to Sign. Each amplifier circuit 200 can include, for example, an integrating amplifier 203, a variable amplifier 204, a sample and hold circuit 205, and a buffer amplifier 206. The integrating amplifier 203 amplifies the electric signal output via the signal line Sigj. The variable amplifier 204 amplifies the electric signal from the integrating amplifier 203. The sample hold circuit 205 samples and holds the electric signal from the variable amplifier 204. The buffer amplifier 206 buffers the electric signal from the sample hold circuit 205.

  The integrating amplifier 203 can include, for example, an operational amplifier 211, an integrating capacitor 212, and a reset switch 213. The operational amplifier 211 has an inverting input terminal that receives an electrical signal provided via the signal line Sigj, a non-inverting input terminal that receives the reference voltage Vref from the reference power supply 110, and an output terminal. The integration capacitor 212 and the reset switch 213 are arranged in parallel between the inverting input terminal and the output terminal. The integration capacitor 212 can have a variable capacitance value Cf. The sample hold circuit 205 can be constituted by, for example, a sampling switch 221 and a sampling capacitor 222.

  The read circuit 103 can further include a multiplexer 207, a buffer amplifier 208, and an A / D converter 209. The multiplexer 207 sequentially selects and outputs the electrical signals output in parallel from the plurality of amplifier circuits 200 and outputs them as image signals. The buffer amplifier 208 converts the impedance of the image signal output from the multiplexer 207 and outputs an analog electric signal as the image signal Vout. The A / D converter 209 converts the image signal Vout output from the buffer amplifier 208 into digital image data, and provides the digital image data to the processing unit 105 and the analysis unit 109.

  The scanning circuit 102 generates a drive signal Gi in response to control signals (D-CLK, OE, DIO) supplied from the control unit 106 and outputs the drive signal Gi to the drive line Gi. In the present specification, the same reference numerals are assigned to signal lines and signals output to the signal lines. The drive signal Gi has a conduction voltage Vcom that makes the switch element 202 of the pixel PIX conductive, or a non-conduction voltage Vss that makes the switch element 202 non-conductive.

  In one example, the scanning circuit 102 can include a shift register. The control signal D-CLK is a shift clock that causes the shift register to perform a shift operation, the control signal DIO is a pulse transferred by the shift register, and OE is a signal that controls the output terminal of the shift register. Further, the control unit 106 controls the readout circuit 103 by supplying the readout circuit 103 with a control signal RC, a control signal SH, and a control signal CLK. Here, the control signal RC controls the reset switch 213 of the integrating amplifier 203, the control signal SH controls the sampling switch 221 of the sample hold circuit 205, and the control signal CLK controls the multiplexer 207.

  FIG. 3 exemplarily shows an operation method of the radiation imaging system RIS and the radiation imaging apparatus 100. When the power of the radiation imaging apparatus 100 is turned on, the radiation imaging apparatus 100 performs a startup operation for stabilizing the operation of the radiation imaging apparatus 100 in step S301. This operation can be controlled by the control unit 106. In the start-up operation, a reset operation for removing charges accumulated due to dark current can be performed. The reset operation is an operation of resetting the electric charge accumulated in the conversion element 201 by making the switch element 202 conductive. The reset operation can be performed by the scanning circuit 102 scanning a plurality of rows constituting the pixel array 101 in units of at least one row. In one example, in the reset operation, the reset switch 213 is turned on, and the operational amplifier 211 is set in the voltage follower state, whereby the signal line Sigj is fixed to the reference voltage Vref. In this state, the switch element 202 is turned on, whereby the charge accumulated in the conversion element 201 is removed, and the voltage of the conversion element 201 is reset.

  In step S302, an operation for acquiring an offset image is performed. This operation can be controlled by the control unit 106. The offset image is acquired by performing an imaging operation in a state where no radiation is applied to the radiation imaging apparatus 100. An offset image is obtained by performing imaging (for example, addition averaging) of images obtained by performing imaging a plurality of times (for example, 30 times). In the imaging operation, after charges are accumulated in a plurality of pixels PIX of the pixel array 101, a plurality of rows of the pixel array 101 are sequentially selected (scanned) by the scanning circuit 102, and signals of the pixels PIX in the selected rows are read out. An operation of reading by the circuit 103 is included.

  The radiation imaging apparatus 100 has a plurality of modes (imaging modes). Information specifying the mode can be notified to the control unit 106 via the control device 111 operated by the operator. In the plurality of modes, for example, at least one of the frame rate (the number of frames acquired per unit time (number of imaging)), the signal amplification factor (gain) of the readout circuit 103, the number of added pixels (binning), and the imaging range is different. . The plurality of modes can include, for example, a first mode in which a radiographic image is captured at a first frame rate and a second mode in which a radiographic image is captured at a second frame rate that is slower than the first frame rate. In other words, the first mode is a mode for capturing a radiation image for one frame in the first period, and the second mode is a mode for capturing a radiation image for one frame in a second period longer than the first period. is there. The plurality of modes may include one or more other modes in addition to the first mode and the second mode.

  An offset image is acquired for each of the plurality of modes. For example, the control unit 106 performs control such that the offset image is acquired in the state set in the first mode, and the offset image is acquired in the state set in the second mode.

  After acquiring the offset image in step S302, in step S303, the control unit 106 performs fluoroscopic imaging (moving image capturing) in a mode set by the operator. Specifically, the control unit 106 repeats the imaging operation according to the frame rate, signal amplification factor (gain), pixel addition number (binning), and imaging range defined by the mode set by the operator. In fluoroscopic imaging, radiation is intermittently emitted from the radiation source 112, and the radiation imaging apparatus 100 repeats an imaging operation in synchronization with radiation irradiation.

  Here, when fluoroscopic imaging is performed for a long time, an offset component included in an image captured by the radiation imaging apparatus 100 changes due to a change in environmental temperature or the like, and correct offset correction cannot be performed, and artifacts may occur in the image. . Therefore, in step S305, the control unit 106 determines whether to update the offset image. The update of the offset image may be determined by the control unit 106 according to the fluoroscopic imaging time, temperature, or the like, or may be determined according to an instruction from the operator. If it is determined to update the offset image, the process returns to step S302, and the offset image is reacquired. When the offset image is reacquired, the intermittent irradiation of radiation by the radiation source 112 is stopped. After the re-acquisition of the offset image is completed, the process returns to fluoroscopic imaging in step S303.

  The fluoroscopy can be finished at any time. In addition, the mode can be changed during fluoroscopic imaging. When ending fluoroscopic imaging, the intermittent irradiation of the radiation from the radiation source 112 is stopped, and the radiation imaging apparatus 100 stops the imaging operation. When the operator instructs the control device 111 to change the mode, a command for requesting the mode change may be sent from the control device 111 to the control unit 106 of the radiation imaging apparatus 100. In step S307, the control unit 106 changes the mode according to a command from the control device 111. When the operator instructs the control device 111 to change the mode, the control device 111 sends an instruction to the exposure control device 113 to temporarily stop the generation of radiation from the radiation source 112, and the radiation Temporarily stops the occurrence of When the mode is changed in the radiation imaging apparatus 100 and the fluoroscopic imaging can be resumed, the control device 111 sends a command for starting radiation irradiation by the radiation source 112 to the exposure control device 113. Thereby, in step S303, fluoroscopic imaging in a new mode is started. When the control unit 106 of the radiation imaging apparatus 100 receives a mode change command while reading an image of a certain frame by the reading circuit 103, the control unit 106 changes the mode after the reading of the image of the frame is completed.

  As described above, it is known that the offset component changes transiently immediately after the mode is changed. In addition, since the transitional change time is relatively long, even if an offset image is prepared for offset correction in the transient state, it is difficult to perform correct offset correction, and artifacts are superimposed on the output image. End up.

  The inventor has confirmed that the offset component that changes transiently has a correlation with the difference (change amount) in the frame rate before and after the mode switching. Specifically, when the difference between the frame rates before and after the mode switching is large, the offset component that changes transiently is large, and the time required for the transitional change to end becomes long. On the other hand, when the difference between the frame rates before and after the mode switching is small, the offset component that changes transiently is small, and the time required for the transitional change to end is shortened.

  FIG. 4 illustrates a transitional change of the offset component accompanying the mode change. Modes A and C are high frame rate modes and have the same frame rate. Mode B is a low frame rate mode and has a lower frame rate than modes A and C. Immediately after the change from mode A to mode B and immediately after the change from mode B to mode A, the transitional change of the offset component is large, and it takes a long time to complete the change. On the other hand, in the change from mode A to mode C, which is a mode change not accompanied by a change in the frame rate, the transitional change of the offset component is small and the time required for the change to end is short. For example, the mode A and the mode C are modes in which the signal amplification factor (gain) or the pixel addition number (binning) of the readout circuit 103 is different and the frame rates are equal to each other.

  From the above results, the magnitude of the transient change of the offset component due to the mode change is the number of toggles of each switch element 202 per unit time, in other words, the scanning of the pixel array 101 by the scanning circuit 102 per unit time. It is considered that there is a strong correlation with the number of times. The toggle of the switch element 202 means an operation for turning the switch element 202 on and off. The scanning of the pixel array 101 by the scanning circuit 102 sequentially selects a plurality of rows of the pixel array 101, and switches the switch elements 202 of the pixels PIX in the selected row from an off state (non-conducting state) to an on state (conducting state). It means to do.

  That is, it is possible to suppress the change in the offset component due to the mode change by not changing the number of scans of the pixel array 101 by the scanning circuit 102 per unit time by the mode change. The scanning of the pixel array 101 by the scanning circuit 102 is performed both in the reset operation of the pixel PIX (conversion element 201) and in the reading of a signal from the pixel PIX. Therefore, if the number of reset operations per frame in the mode with a low frame rate is increased, even if the mode is changed with a change in the frame rate, the change in the offset component can be reduced.

  FIG. 5 and FIG. 6 illustrate operations in two modes based on the above concept. Here, a first mode in which a radiographic image is captured at a first frame rate and a second mode in which a radiographic image is captured at a second frame rate lower than the first frame rate are considered. FIG. 5 illustrates the operation in the first mode, and FIG. 6 illustrates the operation in the second mode. First, the operation in the first mode will be described. One frame period of the first mode includes an accumulation period in which a plurality of pixels PIX accumulate signals corresponding to the irradiated radiation, and one frame from the pixel array 101 by the readout circuit 103 while scanning a plurality of rows by the scanning circuit 102. A readout period for reading out the minute signal. The operation during the accumulation period is called accumulation operation, and the operation during the readout period is called read operation. During the accumulation period, the non-conductive voltage Vss is applied to the switch elements 202 of all the pixels PIX, and the switch elements 202 of all the pixels PIX are in the non-conductive state. When the accumulation period ends, the reading period starts. In the readout period, signals are read from the plurality of pixels PIX of the pixel array 101 by the readout circuit 103 while scanning the plurality of rows of the pixel array 101 by the scanning circuit 102. Scanning by the scanning circuit 102 is an operation of sequentially selecting the driving lines G1 of the first row to the driving lines Gm of the m-th row. That is, in the readout period, the conduction voltage Vcom is sequentially supplied from the drive line G1 of the first row to the drive line Gm of the m-th row by the scanning circuit 102 (that is, the first to m-th rows are selected in order). ), The signal of the pixel PIX in the selected row is read out by the readout circuit 103. As described above, in the first mode, a plurality of rows of the pixel array 101 are scanned only once in one frame period.

  Next, the operation in the second mode will be described. One frame period of the second mode includes an accumulation period in which a plurality of pixels PIX accumulate signals corresponding to irradiated radiation, and one frame from the pixel array 101 by the readout circuit 103 while scanning a plurality of rows by the scanning circuit 102. A readout period for reading out the minute signal. Further, one frame period in the second mode includes one or more reset periods. One reset period is a period during which a plurality of rows of the pixel array 101 are scanned by the scanning circuit 102 so that the plurality of pixels PIX of the pixel array 101 are reset. The operation in the reset period is called a reset operation.

  The accumulation period in the second mode is longer than the accumulation period in the first mode, and therefore the frame rate in the second mode is lower than the frame rate in the first mode. Therefore, the number of times the pixel array 101 is scanned per unit time is smaller than that in the first mode if only one frame period in the second mode includes the accumulation period and the readout period. Therefore, in the second mode, one frame period includes a reset period in addition to the accumulation period and the readout period. Accordingly, the plurality of rows of the pixel array 101 are scanned by the scanning circuit 102 in one frame period of the second mode than the number of times that the scanning circuit 102 scans the plurality of rows of the pixel array 101 in one frame period of the first mode. The number of times that it is done becomes more.

  Since a plurality of frame periods are continuous in moving image capturing, the reset period may be provided after the reading period or may be provided before the accumulation period. The reading operation in the reading period in the second mode is the same as the reading operation in the first mode. In the reset period, the scanning circuit 102 scans from the first row of drive lines G1 to the mth row of drive lines Gm. That is, in the reset period, the scanning circuit 102 sequentially supplies the conduction voltage Vcom to the first row of drive lines G1 to the mth row of drive lines Gm (that is, sequentially selects the first row to the mth row). ), The conversion element 201 of the pixel PIX in the selected row is reset.

  When one frame period in the second mode includes a plurality of reset periods, a scanning time in the last reset period among the plurality of reset periods (a time required for the scanning circuit 102 to scan a plurality of rows of the pixel array 101). ) Is preferably the same as the scanning time (the time required for the scanning circuit 102 to scan a plurality of rows of the pixel array 101) in the reading period of the second mode. More specifically, the number of rows selected at the same time is the same in the scan in the reset period and the scan in the readout period, and the time from the start of selection of one row to the start of selection of the next row (line It is preferable that the time is the same.

  When the scanning time in the last reset period is different from the scanning time in the subsequent readout period, the time from the reset of the i-th row in the last reset period to the readout of the i-th row in the subsequent readout period is between a plurality of rows. Are different from each other. For this reason, artifact components (for example, dark current and afterimage) to be superimposed by time integration are different in each row, and artifacts are superimposed on the image or artifact correction becomes difficult.

  By making the scanning time in the last reset period the same as the scanning time in the subsequent readout period, artifacts can be reduced or correction can be easily performed, and a high-quality image can be provided. .

  Further, it is preferable that the scan time of the reset period before the last reset period among the plurality of reset periods in one frame period is shorter than the scan time of the last reset period. For example, the scan time of the reset period before the last reset period among the plurality of reset periods in the first frame period is preferably 1/5 or less of the scan time of the last reset period. Alternatively, in the reset period before the last reset period among the plurality of reset periods in one frame period, the scanning circuit 102 may scan a plurality of rows of the pixel array 101 in units of at least two rows. Such control is advantageous for shortening the scanning time and increasing the number of scans, and is advantageous for reducing the difference in the number of scans per unit time between modes.

  Ideally, there is no difference in the number of scans per unit time between modes. However, if the reset period is inserted within one frame period in the low frame rate mode, the difference in the number of scans per unit time between the first mode at the high frame rate and the second mode at the low frame rate is reduced. A reasonable effect can be obtained.

  As described above, the offset component at the time of mode change can be obtained by inserting the reset period into the frame period of the mode having a lower frame rate than the other modes so that the difference in the number of scans per unit time between the modes becomes small. It is possible to reduce the transitional change of. As a result, it is possible to reduce the time for acquiring a large amount of offset images for the offset correction of the images at the time of transitional changes and the memory area for holding them.

  In the description so far, by inserting the reset period into one frame period in the low frame rate mode, the difference in the number of scans per unit time between the first mode at the high frame rate and the second mode at the low frame rate is obtained. It is made smaller. However, the same effect can be obtained by inserting a dummy readout period in one frame period. The dummy read period can be similar to the normal read period, but the signal read by the read circuit 103 during the dummy read period will not normally be used. Alternatively, a scanning period for scanning a plurality of rows without resetting the pixels PIX may be inserted in one frame period. Alternatively, at least one of a reset period, a dummy reading period, and a scanning period may be inserted in one frame period. Alternatively, at least one of a dummy reading period and a scanning period may be inserted in one frame period, and then a reset period may be inserted.

  Hereinafter, the operation in the case of having three or more modes will be exemplified.

  First, the case where the radiation imaging apparatus 100 has the first mode, the second mode, and the third mode, and the frame rate of each mode is first mode> third mode> second mode will be described. The first mode and the second mode have the above relationship. FIG. 7 illustrates the operation in the third mode, and the number of reset operations in the third mode is one. In the third mode, it is preferable that the number of reset operations in one frame period is greater than the number of reset operations in one frame period in the second mode and less than the number of reset operations in one frame period in the first mode. The number of reset operations is determined so that the difference in the number of scans per unit time in the first mode, the second mode, and the third mode is small, and preferably the difference is eliminated. In the third mode shown in FIG. 7, since the number of reset operations is one, the scan time in the reset period is preferably the same as the scan time in the readout period. More specifically, the number of rows selected at the same time is the same in the scan in the reset period and the scan in the readout period, and the time from the start of selection of one row to the start of selection of the next row (line It is preferable that the time is the same. As described above, such control is advantageous for reducing artifacts or allowing easy correction and providing a high-quality image.

  Next, a case will be described in which the radiation imaging apparatus 100 has the first mode, the second mode, and the fourth mode, and the frame rate of each mode is first mode≈fourth mode> second mode. The first mode and the second mode have the above relationship. The operation in the fourth mode is basically the same as the operation in the first mode, and the reset operation as performed in the second mode is not necessary. This is because, for example, even when the mode is switched from the first mode to the fourth mode, artifacts due to transiently changing components are reduced if the frame rate difference is small.

Claims (12)

A pixel array in which a plurality of pixels are arranged to form a plurality of rows and a plurality of columns; a scanning circuit that scans the plurality of rows of the pixel array according to a mode selected from a plurality of modes; and the scanning A radiation imaging apparatus comprising: a readout circuit that reads out signals of pixels in a row selected in scanning by the circuit,
The plurality of modes include a first mode for capturing a plurality of frames at a first frame rate and a second mode for capturing a plurality of frames at a second frame rate lower than the first frame rate,
The plurality of rows are scanned by the scanning circuit in one frame period of the first mode so that the difference in the number of scans per unit time by the scanning circuit between the first mode and the second mode is small. The number of times that the plurality of rows are scanned by the scanning circuit in one frame period of the second mode is greater than the number of times that is performed.
A radiation imaging apparatus. One frame period of the first mode includes an accumulation period in which the plurality of pixels accumulate signals corresponding to irradiated radiation, and the readout circuit scans the plurality of rows from the pixel array while scanning the plurality of rows. A readout period for reading out signals for one frame,
One frame period of the second mode includes an accumulation period in which the plurality of pixels accumulate signals corresponding to the irradiated radiation, and the readout circuit scans the plurality of rows from the pixel array while scanning the plurality of rows. It further includes a readout period for reading out signals for one frame and a reset period for scanning the plurality of rows by the scanning circuit so that the plurality of pixels are reset.
The radiation imaging apparatus according to claim 1. One frame period of the second mode includes a plurality of reset periods including the reset period.
The radiation imaging apparatus according to claim 2. The time required for the scanning circuit to scan the plurality of rows in the last reset period among the plurality of reset periods in the second mode is the time required for the scanning circuit to scan the plurality of rows in the readout period in the second mode. The same as the time it takes to scan the line,
The radiation imaging apparatus according to claim 3. The scanning circuit scans the plurality of rows in the last reset period among the plurality of reset periods in the second mode, and the scanning circuit performs the plurality of rows in the readout period in the second mode. The scanning circuit and the scanning circuit simultaneously select the same number of rows,
The radiation imaging apparatus according to claim 4. The scanning circuit scans the plurality of rows in the last reset period among the plurality of reset periods in the second mode, and the scanning circuit performs the plurality of rows in the readout period in the second mode. 6. The radiation imaging apparatus according to claim 4, wherein the time from the start of selection of a certain row to the start of selection of the next row is the same as when scanning is performed. The reset period before the last reset period among the plurality of reset periods is shorter in time required for the scanning circuit to scan the plurality of rows than the last reset period.
The radiation imaging apparatus according to claim 3, wherein: In the reset period prior to the last reset period among the plurality of reset periods, the scanning circuit scans the plurality of rows in units of at least two rows.
The radiation imaging apparatus according to claim 4, wherein: A control unit that changes from one of the first mode and the second mode to the other of the first mode and the second mode when capturing a moving image;
The radiation imaging apparatus according to claim 1, wherein: A radiation source that generates radiation; and
The radiation imaging apparatus according to any one of claims 1 to 9,
A radiation imaging system comprising: A pixel array in which a plurality of pixels are arranged to form a plurality of rows and a plurality of columns; a scanning circuit that scans the plurality of rows of the pixel array according to a mode selected from a plurality of modes; and the scanning A readout circuit for reading out signals of pixels in a row selected in scanning by a circuit, and an operation method of a radiation imaging apparatus comprising:
The plurality of modes include a first mode for capturing a plurality of frames at a first frame rate and a second mode for capturing a plurality of frames at a second frame rate lower than the first frame rate,
The plurality of rows are scanned by the scanning circuit in one frame period of the first mode so that the difference in the number of scans per unit time by the scanning circuit between the first mode and the second mode is small. The number of times that the plurality of rows are scanned by the scanning circuit in one frame period of the second mode is greater than the number of times that is performed.
An operation method of the radiation imaging apparatus. One frame period of the first mode includes an accumulation period in which the plurality of pixels accumulate signals corresponding to irradiated radiation, and the readout circuit scans the plurality of rows from the pixel array while scanning the plurality of rows. A readout period for reading out signals for one frame,
One frame period of the second mode includes an accumulation period in which the plurality of pixels accumulate signals corresponding to the irradiated radiation, and the readout circuit scans the plurality of rows from the pixel array while scanning the plurality of rows. It further includes a readout period for reading out signals for one frame and a reset period for scanning the plurality of rows by the scanning circuit so that the plurality of pixels are reset.
The operation method of the radiation imaging apparatus according to claim 11.

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