Radiation imaging apparatus, radiation imaging system, and control method of radiation imaging apparatus

Abstract

To perform afterimage correction with high precision while achieving improvement in a frame rate and reduction of noise in a radiation image.SOLUTION: A radiation imaging apparatus generates a radiation afterimage generated by subtracting a first offset image based on a first signal from a radiation image, and generates an offset afterimage by subtracting a second offset image based on a second signal from an offset image during imaging. The radiation imaging apparatus generates an adjusted afterimage in which a pixel value of the offset afterimage is corrected using a correction coefficient adjusted according to an afterimage quantity determined on the basis of statistical information acquired by statistical processing of the pixel value in the offset afterimage acquired for each frame in which the radiation image is captured, and generates a radiation image corrected by subtracting the adjusted afterimage from the radiation afterimage.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The disclosed technology relates to a radiation imaging apparatus, a radiation imaging system, and a method for controlling a radiation imaging apparatus. [Background technology]

[0002] Radiation imaging devices have been put to practical use as imaging devices used in medical image diagnosis and non-destructive testing. Radiation images generated by radiation imaging devices contain noise due to dark current flowing through photodiodes, residual images due to previous radiation exposure, and the like. In order to reduce such noise, radiation images are corrected using offset images acquired when radiation is not being irradiated by the radiation imaging device. One method of correction involves reading out an offset image without irradiating radiation before radiation exposure and subtracting it from the image obtained at the time of radiation exposure. In this method, the frame rate is high because the offset image is acquired in advance, but residual images cannot be corrected.

[0003] There is also a method in which the acquisition of a radiographic image by irradiating radiation and the acquisition of an offset image without irradiating radiation are alternately performed, and the offset image is subtracted from the radiographic image. In this method, an offset image is acquired after radiation irradiation and then subtracted, so it is possible to correct for residual images, but it is necessary to acquire two images, a radiographic image and an offset image, to acquire one frame of image, and the frame rate cannot be increased.

[0004] Patent Document 1 describes a technique for correcting a radiographic image using primary offset data and reference secondary offset data acquired before the start of imaging, and immediately preceding secondary offset data acquired after the start of imaging, in order to achieve high frame rate and low residual image. The immediately preceding secondary offset data is acquired with a shorter exposure time than the radiographic image. The primary offset data is acquired with the same exposure time as the radiographic image. The reference secondary offset data is acquired with the same exposure time as the immediately preceding secondary offset data. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-168602 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology described in Patent Document 1, the exposure time length of long accumulation data (primary offset data and radiography) is different from the exposure time length of short accumulation data (reference secondary offset data and immediately preceding secondary offset data). Therefore, it is difficult to accurately reduce noise in a radiography image.

[0007] Therefore, by multiplying the residual image components to be removed by the ratio of the exposure time length of the long accumulation data to the exposure time length of the short accumulation data as a coefficient, noise in the radiation image can be reduced with high accuracy. However, if the coefficient is large, while the effect of reducing the residual image is improved, random noise may increase.

[0008] Therefore, an object of the disclosed technology is to provide a technology that enables highly accurate afterimage correction while improving the frame rate (higher frame rate) and reducing noise in radiation images (low noise). [Means for solving the problem]

[0009] A radiation imaging apparatus according to one aspect of the disclosed technique includes a radiation detection panel having a plurality of pixels arranged to form a plurality of rows and a plurality of columns; a control circuit that controls an operation of the radiation detection panel to control reading of signals based on the charges accumulated in the plurality of pixels; an image generating circuit that generates an image based on the signal; The control circuit includes: In the absence of radiation exposure, a first read control for reading out a first signal based on the charge accumulated in a first period; and executing a second read control for reading out a second signal based on the charge accumulated during a second period shorter than the first period; a third readout control for reading out, as a third signal, a radiation signal based on charges accumulated during a third period having the same time length as the first period while the radiation is being applied; a fourth read control is executed to read out a fourth signal based on charges accumulated during a fourth period having the same time length as the second period in a state in which the radiation is not irradiated after the third signal is read out; The image generating circuit includes: generating a radiation residual image by subtracting a first offset image based on the first signal from a radiation image based on the third signal; generating an offset residual image by subtracting a second offset image based on the second signal from an offset image at the time of imaging based on the fourth signal; generating an adjusted residual image by correcting pixel values ​​of the offset residual image acquired for each frame of the radiographic image using a correction coefficient adjusted according to an amount of residual image determined based on statistical information acquired by statistical processing of pixel values; A corrected radiation image is generated by subtracting the adjusted radiation residual image from the radiation residual image. Effect of the Invention

[0010] According to the disclosed technology, it is possible to improve the frame rate and reduce noise in radiological images while performing highly accurate afterimage correction. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram illustrating an example of the arrangement of a radiation imaging system according to some embodiments. [Diagram 2] FIG. 2 is an equivalent circuit diagram illustrating an example of the configuration of a radiation detection panel according to some embodiments. [Diagram 3]5A to 5C are diagrams for explaining an example of the operation of the radiation imaging system according to some embodiments. [Figure 4] 5A to 5C are diagrams for explaining a process of generating an offset image by the radiation imaging system according to some embodiments. [Diagram 5] 4A to 4C are diagrams for explaining an operation example 1 of the radiation imaging system according to some embodiments. [Figure 6] 10A to 10C are diagrams for explaining an operation example 2 of the radiation imaging system according to some embodiments. [Figure 7] FIG. 13 is a graph illustrating the attenuation characteristics of the amount of residual image. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0013] (Overview of Radiation Imaging System) 1 shows an example of the configuration of a radiation imaging system 100 according to some embodiments. The radiation imaging system 100 is configured to generate an electrical radiation image by electrically capturing an optical image formed by radiation. The radiation is typically X-rays, but may be α rays, β rays, γ rays, etc. The radiation imaging system 100 includes, for example, a radiation imaging device 110, a computer 120, a display 170, an exposure control device 130, and a radiation generation device 140.

[0014] The radiation generating device 140 starts emitting radiation 160 in accordance with an exposure command (radiation command) from the exposure control device 130. The radiation 160 irradiated from the radiation generating device 140 passes through the subject 150 and enters the radiation imaging device 110. In addition, the radiation generating device 140 stops emitting the radiation 160 in accordance with a stop command from the exposure control device 130.

[0015] The radiation imaging device 110 includes a radiation detection panel 111, a control circuit 112, an image generation circuit 113, and a storage device 114. The radiation detection panel 111 generates a radiation image according to radiation 160 incident on the radiation imaging device 110, and transmits the image to the computer 120. The control circuit 112 controls the operation of the radiation detection panel 111. For example, the control circuit 112 generates a stop signal for stopping the irradiation of radiation 160 from the radiation generation device 140 based on an image signal obtained from the radiation detection panel 111. The stop signal is supplied to the exposure control device 130. In response to the stop signal, the exposure control device 130 sends a stop command to the radiation generation device 140.

[0016] The control circuit 112 may be formed of a dedicated circuit, for example, a PLD (Programmable Logic Device) such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Alternatively, the control circuit 112 may be formed of a combination of a general-purpose processing circuit such as a processor and a storage circuit such as a memory. In this case, the function of the control circuit 112 may be realized by the general-purpose processing circuit executing a program stored in the storage circuit. The control circuit 112 controls the accumulation of charges in the imaging element of the radiation detection panel 111 and the readout timing of a signal based on the charges accumulated in the imaging element.

[0017] The image generating circuit 113 stores in the storage device 114 the radiation image and offset image generated based on the signal supplied from the radiation detection panel 111. In addition, the image generating circuit 113 performs image correction processing including offset correction, which will be described later, using various correction data stored in the storage device 114.

[0018] The computer 120 has a control unit that controls the radiation imaging device 110 and the exposure control device 130, a receiving unit (not shown) that receives a radiation image from the radiation imaging device 110, and a signal processing unit (not shown) that processes the radiation image obtained by the radiation imaging device 110. The control unit, the receiving unit, and the signal processing unit may each be configured by a dedicated circuit, as with the control circuit 112, or may be configured by a combination of a general-purpose processing circuit and a storage circuit. In one example, the exposure control device 130 has an exposure switch (not shown), and when the exposure switch is turned on by a user, the exposure control device 130 sends an exposure command to the radiation generation device 140 and sends a start notification indicating the start of radiation irradiation to the computer 120. In response to the start notification, the computer 120 notifies the control circuit 112 of the radiation imaging device 110 of the start of radiation irradiation. When the exposure control device 130 and the computer 120 are not synchronously connected, the radiation detection panel 111 may detect the start of irradiation of radiation 160 based on pixel signals.

[0019] FIG. 2 shows a configuration example of the radiation detection panel 111. The radiation detection panel 111 includes, for example, a pixel array 200, a drive circuit 210, a readout circuit 220, a buffer circuit 230, and an analog-digital (AD) converter 240. The drive circuit 210 and the readout circuit 220 function as peripheral circuits of the pixel array 200. The pixel array 200 includes, for example, a plurality of pixels P, a plurality of drive lines Vg1 to Vgm, a plurality of signal lines Sig1 to Sign, and a bias line Bs. The drive lines Vg1 to Vgm and the signal lines Sig1 to Sign are collectively referred to as the drive line Vg and the signal line Sig, respectively. The plurality of pixels P are arranged to form a plurality of pixel rows and a plurality of pixel columns. The pixel row refers to a set of a plurality of pixels arranged in the horizontal direction in FIG. 2. The pixel column refers to a set of a plurality of pixels arranged in the vertical direction in FIG. 2. In one example, the radiation detection panel 111 has a dimension of 17 inches and the pixel array 200 has approximately 3000 pixel rows and approximately 3000 pixel columns.

[0020] The pixel rows of the pixel array 200 are referred to as the 1st row to the mth row (m is an integer equal to or greater than 1) from the top of the drawing, and the pixel columns of the pixel array 200 are referred to as the 1st column to the nth column (n is an integer equal to or greater than 1) from the left of the drawing. Each pixel P is composed of a combination of one conversion element C and one switch element S. The pixel P located in the i-th row and j-th column of the pixel array 200 is represented as pixel P(i,j). The conversion element C and switch element S included in pixel P(i,j) are represented as conversion element C(i,j) and switch element S(i,j), respectively. For example, pixel P(1,2) represents pixel P located in the first row and second column.

[0021] The conversion element C generates an electric charge in response to radiation incident on the pixel P and accumulates this electric charge. The conversion element C can accumulate not only an electric charge in response to radiation, but also an electric charge generated by dark current. The generation and accumulation of an electric charge by the conversion element C of the pixel P is expressed as the pixel P generating and accumulating an electric charge.

[0022] The switch element S is connected between the conversion element C and the signal line Sig corresponding to this conversion element C. For example, the switch elements S(1,1) to S(m,1) are respectively connected between the multiple conversion elements C(1,1) to C(m,1) and the signal line Sig1. When the switch element S is turned on, the conversion element C and the signal line Sig are brought into a conductive state, and the charge obtained by the conversion element C (for example, the charge accumulated in the conversion element C) is transferred to the signal line Sig.

[0023] The conversion element C may be, for example, an MIS type photodiode arranged on an insulating substrate such as a glass substrate and made mainly of amorphous silicon. Alternatively, the conversion element C may be a PIN type photodiode. The conversion element C may be configured as a direct type that directly converts radiation into electric charges, or as an indirect type that converts radiation into light and then detects the light. In the indirect type, the scintillator may be shared by multiple pixels P.

[0024] The switch element S is composed of a transistor such as a thin film transistor (TFT) having a control terminal (gate) and two main terminals (source, drain). The conversion element C has two main electrodes. One main electrode of the conversion element C is connected to one of the two main terminals of the switch element S, and the other main electrode of the conversion element is connected to a bias power supply Vs via a common bias line Bs. The bias power supply Vs generates a bias voltage.

[0025] The control terminal of the switch element S of the pixel P in the first row is connected to the drive line Vg1. The control terminal of the switch element S of the pixel P in the second row is connected to the drive line Vg2. The same is true for the third to mth rows.

[0026] The drive circuit 210 supplies a drive signal to a control terminal of the switch element S of each pixel P through a drive line Vg in accordance with the drive signal supplied from the control circuit 112. The drive signal includes an ON signal (high-level voltage in the following description) for turning on the switch element S, and an OFF signal (low-level voltage in the following description) for turning off the switch element S. The drive circuit 210 includes, for example, a shift register, and this shift register performs a shift operation in accordance with a control signal (for example, a clock signal) supplied from the control circuit 112.

[0027] Supplying an on signal (i.e., a high-level drive signal) to a pixel P is referred to as selecting a pixel P. That is, the drive signal is a signal for selecting one of the multiple pixels P. The same drive signal is supplied to multiple pixels included in the same pixel row. Selection of multiple pixels included in one pixel row is referred to as selecting that pixel row.

[0028] The readout circuit 220 amplifies and reads out the signal that appears on the signal line Sig by selecting the pixel P. This signal is based on the charge accumulated in the conversion element C. Reading out a signal based on the charge accumulated in the conversion element C of the pixel P is expressed as reading out a signal based on the charge accumulated in the pixel P.

[0029] The readout circuit 220 includes one amplifier circuit 221 for each signal line Sig. In the example of FIG. 2, since the pixel array 200 has n signal lines Sig, the readout circuit 220 includes n amplifier circuits 221. The amplifier circuit 221 includes, for example, an integral amplifier 222, a variable amplifier 223, a switch element 224, a capacitance 225, and a buffer circuit 226. The switch element 224 and the capacitance 225 configure a sample-and-hold circuit. The integral amplifier 222 includes, for example, an operational amplifier, an integral capacitance connected in parallel between an inverting input terminal and an output terminal of the operational amplifier, and a reset switch. A reference voltage is supplied from a reference power supply Vref to a non-inverting input terminal of the operational amplifier. When the reset switch is turned on in response to a control signal RC (reset pulse) supplied from the control circuit 112, the integral capacitance is reset and the potential of the signal line Sig is reset to a reference potential. The variable amplifier 223 amplifies the signal from the integral amplifier 222 at a set amplification factor. The sample and hold circuit samples and holds the signal from variable amplifier 223. The on / off of switch element 224 constituting the sample and hold circuit is controlled by a control signal SH supplied from control circuit 112. Buffer circuit 226 buffers (impedance converts) the signal from the sample and hold circuit and outputs it.

[0030] The read circuit 220 also includes a multiplexer 227 that selects and outputs signals from the multiple amplifier circuits 221 in a predetermined order. The multiplexer 227 includes, for example, a shift register, and this shift register performs a shift operation according to a control signal (for example, a clock signal) supplied from the control circuit 112. By this shift operation, one signal from the multiple amplifier circuits 221 is selected.

[0031] The buffer circuit 230 buffers (impedance converts) the signal output from the multiplexer 227. The AD converter 240 converts into a digital signal the analog signal output from the buffer circuit 230. The output of the AD converter 240, i.e., the pixel signal, is transmitted to the computer 120.

[0032] (Offset image generation process) FIG. 3 is a diagram for explaining an operation example of the radiation imaging system 100 of the embodiment, and FIG. 4 is a diagram for explaining a generation process of an offset image by the radiation imaging system 100 of the embodiment.

[0033] The offset image generation process will be described below with reference to a timing chart 310 in Fig. 3, a correction process flow 320, and the flowchart in Fig. 4. The upper part of Fig. 3 shows the timing chart 310, and the lower part of Fig. 3 shows the correction process flow 320.

[0034] 3 indicates whether radiation 160 is being irradiated from the radiation generating device 140 to the radiation imaging device 110. A low level indicates a state in which the radiation 160 is not being irradiated, and a high level indicates a state in which the radiation 160 is being irradiated.

[0035] A "period" in the timing chart 310 in FIG. 3 indicates a period (length of time) during which a specific operation is performed. Imaging by the radiation imaging device 110 includes an accumulation period ("A" in FIG. 3) during which an accumulation operation is performed, and a readout period ("R" in FIG. 3) during which a readout operation is performed. The control circuit 112 does not select any of the multiple pixels P included in the pixel array 200 during the accumulation period. Specifically, the drive circuit 210 maintains a state in which an off signal is supplied to each of the drive lines Vg1 to Vgm. As a result, the charge generated in each conversion element C is accumulated in the conversion element C, and at the same time, a charge according to the dark current flowing through each conversion element C is also accumulated.

[0036] During the readout period, the control circuit 112 selects each of the multiple pixels P included in the pixel array 200 and reads out a signal from the selected pixel P. Specifically, the drive circuit 210 supplies an ON signal to the drive lines Vg1 to Vgm one by one in sequence. First, the drive circuit 210 supplies an ON signal only to the drive line Vg1. As a result, the switch element S(1,j) (j=1,...,n) is turned on, and the conversion element C(1,j) and the signal line Sigj are brought into a conductive state, so that the charge accumulated in the conversion element C(1,j) is read out to the signal line Sigj. Next, the drive circuit 210 supplies an ON signal only to the drive line Vg2. As a result, the switch element S(2,j) is turned on, and the conversion element C(2,j) and the signal line Sigj are brought into a conductive state, so that the charge accumulated in the conversion element C(2,j) is read out to the signal line Sigj. The driving circuit 210 repeats such an operation up to the driving line Vgm, whereby the charge based on the charge accumulated in the conversion element C is read out by the readout circuit 220 through the signal line Sigj. In the following description, executing a readout operation on a plurality of pixels P means executing a readout operation on each of the plurality of pixels P. The offset image generation process described in the following example is performed during preparation for imaging, and is performed during the periods 301 to 308 in FIG.

[0037] During preparation for imaging, the control circuit 112 alternately executes an accumulation operation and a readout operation in a state where radiation is not being irradiated. As shown in Fig. 3, an accumulation operation is executed during an accumulation period 301, and signals based on charges accumulated in a plurality of pixels P included in the pixel array 200 are read out during a subsequent readout period 302. Similarly, for accumulation periods 303 to readout periods 308, ..., the control circuit 112 reads out signals based on charges accumulated during accumulation periods 303, 305, 307 in the subsequent readout periods 304, 306, 308. During preparation for imaging, signals read out from a plurality of pixels P included in the pixel array 200 are used to generate an offset image.

[0038] 3, accumulation period 303 is shorter than accumulation period 301. Similarly, accumulation period 307 is shorter than accumulation period 305. Hereinafter, accumulation period 301 and accumulation period 305 are also referred to as first periods, and accumulation period 303 and accumulation period 307 are also referred to as second periods that are shorter than the first periods.

[0039] The signal read out during the readout periods 302 and 306 is referred to as a long-term offset signal (hereinafter also referred to as a first signal or a first offset signal), and the signal read out during the readout periods 304 and 308 is referred to as a short-term offset signal (hereinafter also referred to as a second signal or a second offset signal). In a state where no radiation is irradiated, the control circuit 112 alternately executes a first readout control for reading out a first signal based on charges accumulated over the accumulation periods 301 and 305 (first period) and a second readout control for reading out a second signal based on charges accumulated over accumulation periods 303 and 307 (second period) shorter than the first period.

[0040] An offset image generated based on a long-term offset signal (first signal) is referred to as a long-term offset image (hereinafter also referred to as a first offset image), and an offset image generated based on a short-term offset signal (second signal) is referred to as a short-term offset image (hereinafter also referred to as a second offset image).

[0041] In the following description, the long-term offset image acquired when the frame counter is set to N will be represented as "SN" and the short-term offset image will be represented as "TN." For example, the long-term offset image acquired when the frame counter is set to N=1 will be "S.1" and the short-term offset image will be "T.1."

[0042] In step S401, the control circuit 112 sets the frame counter N to 0. After that, in step S402, the control circuit 112 adds 1 to the frame counter N, thereby counting up the frame counter N.

[0043] In step S403, a long-term offset image S.1 is acquired. The operation of acquiring this long-term offset image S.1 includes an accumulation operation performed in the accumulation period 301 of Fig. 3 and a readout operation of a signal (long-term offset signal) performed in the readout period 302. The image generating circuit 113 generates the long-term offset image S.1 based on the signal (long-term offset signal) obtained from the radiation detection panel 111.

[0044] As a specific operation, during the accumulation period 301, as indicated by "radiation" in the timing chart 310 of Fig. 3, the radiation imaging device 110 performs an accumulation operation of charges in all pixels P (all imaging elements) included in the pixel array 200 of the radiation detection panel 111 in a state in which radiation 160 is not being irradiated. Thereafter, in a readout operation executed during a readout period 302, the control circuit 112 controls the radiation detection panel 111 to output a signal (electrical signal) based on the charges accumulated during the accumulation period 301 from the radiation detection panel 111, and the image generation circuit 113 generates image data based on the signal (electrical signal) obtained from the radiation detection panel 111. The image generation circuit 113 stores the generated image data in the storage device 114 as a long-term offset image S.1.

[0045] In step S404, a short-term offset image T.1 is acquired. The operation of acquiring the short-term offset image T.1 includes an accumulation operation performed in the accumulation period 303 in Fig. 3 and a readout operation of a signal (short-term offset signal) performed in the readout period 304. The image generating circuit 113 generates the short-term offset image T.1 based on the signal (short-term offset signal) obtained from the radiation detection panel 111.

[0046] During an accumulation period 303 that is shorter than the accumulation period 301, the radiation imaging device 110 performs an accumulation operation of charges in all pixels P (all imaging elements) included in the pixel array 200 of the radiation detection panel 111 in a state in which radiation 160 is not being irradiated. Thereafter, in a readout operation that is performed during a readout period 304, the control circuit 112 controls the radiation detection panel 111 to output a signal (electrical signal) based on the charges accumulated during the accumulation period 303 from the radiation detection panel 111, and the image generation circuit 113 generates image data based on the signal (electrical signal) obtained from the radiation detection panel 111. The image generation circuit 113 stores the generated image data in the storage device 114 as a short-term offset image T.1.

[0047] Thereafter, in step S405, the control circuit 112 determines whether the frame counter N has reached a prescribed number. Here, as an example, the prescribed number is described as 2. If it is determined in step S405 that the frame counter N has not reached the prescribed number (S405-NO), the process returns to S402. That is, if the frame counter is N=1, the prescribed number has not yet been reached, so the control circuit 112 returns the process to step S402.

[0048] After that, in step S402, the control circuit 112 counts up the frame counter N by adding 1 to the frame counter N, and the process proceeds to step S403.

[0049] In step S403, a long-term offset image S.2 is acquired. The operation of acquiring this long-term offset image S.2 includes an accumulation operation performed during the accumulation period 305 in Fig. 3 and a signal (long-term offset signal) readout operation performed during the readout period 306. The image generating circuit 113 generates the long-term offset image S.2 based on the signal obtained from the radiation detection panel 111.

[0050] The accumulation operation performed in the accumulation period 305 and the readout operation performed in the readout period 306 are the same as the accumulation operation of charges in the accumulation period 301 when generating the long-term offset image S.1, and the readout operation of a signal based on the charges in the readout period 302, respectively. The control circuit 112 controls the radiation detection panel 111 to output a signal (electrical signal) based on the charges accumulated during the accumulation period 305 from the radiation detection panel 111, and the image generation circuit 113 generates image data based on the signal (electrical signal) obtained from the radiation detection panel 111. The image generation circuit 113 stores the generated image data in the storage device 114 as the long-term offset image S.2. As a result, the long-term offset image S.1 and the long-term offset image S.2 are stored in the storage device 114.

[0051] Thereafter, in step S404, short-term offset image T.2 is acquired. The operation of acquiring short-term offset image T.2 includes an accumulation operation executed in accumulation period 307 in Fig. 3 and a readout operation of a signal (short-term offset signal) executed in readout period 308. The image generating circuit 113 generates short-term offset image T.2 based on the signal (short-term offset signal) obtained from the radiation detection panel 111.

[0052] The accumulation operation performed in the accumulation period 307 and the readout operation performed in the readout period 308 are the same as the accumulation operation of charges in the accumulation period 303 when generating short-term offset image T.1, and the readout operation of a signal based on the charges in the readout period 304, respectively. The control circuit 112 controls the radiation detection panel 111 to output a signal (electrical signal) based on the charges accumulated during the accumulation period 307 from the radiation detection panel 111, and the image generation circuit 113 generates image data based on the signal (electrical signal) obtained from the radiation detection panel 111. The image generation circuit 113 stores the generated image data in the storage device 114 as short-term offset image T.2. As a result, the short-term offset image T.1 and the short-term offset image T.2 are stored in the storage device 114.

[0053] Then, in step S405, the control circuit 112 again determines whether the frame counter N has reached the specified number. Since the specified number is described as 2 here, the control circuit 112 determines that the specified number has been reached (S405-YES) and proceeds to step S406.

[0054] In step S406, the image generation circuit 113 performs a process of generating a long-term offset image S. The image generation circuit 113 generates a long-term offset image S by performing an averaging process on images from long-term offset image S.1 to long-term offset image SN (here, N=2) stored in the storage device 114. The image generation circuit 113 saves the generated long-term offset image S in the storage device 114.

[0055] Next, in step S407, the image generation circuit 113 performs processing to generate a short-term offset image T. The image generation circuit 113 generates a short-term offset image T by averaging images from short-term offset image T.1 to short-term offset image TN (here, N=2) stored in the storage device 114. The image generation circuit 113 saves the generated short-term offset image T in the storage device 114.

[0056] This completes the process of generating offset images used in image processing of radiation images. As described above, the control circuit 112 alternately generates long-term offset images S and short-term offset images T during preparation for imaging. This generates a plurality of long-term offset images S and a plurality of short-term offset images T. During preparation for imaging, the image generating circuit 113 averages (arithmetic average processing) a plurality of long-term offset images Si (i=1 to N) to generate one long-term offset image S, and stores the image in the storage device 114 for subsequent processing. Similarly, during preparation for imaging, the image generating circuit 113 averages (arithmetic average processing) a plurality of short-term offset images Ti (i=1 to N) to generate one short-term offset image T, and stores the image in the storage device 114 for subsequent processing. By averaging a plurality of offset images in this manner, noise contained in the offset image can be reduced.

[0057] In the example described in FIG. 3 and FIG. 4, the specified number is 2, but the specified number is not limited to this example, and may be any number equal to or greater than 1. The user can set any number via the input device 115 connected to the computer 120. In step S405, when the control circuit 112 determines that the specified number has not been reached (S405-NO), the process returns to S402, and the frame counter N is counted up by adding 1 to the frame counter N. The operation of acquiring the long-term offset image SN and the operation of acquiring the short-term offset image TN are repeated for the specified number (frame counter N) until the value of the frame counter N reaches the specified number. The larger the specified number is, the more noise contained in the long-term offset image S and the short-term offset image T generated by the averaging process can be reduced, and the correction accuracy of the correction process described below can be improved. The specified number, i.e., the number of offset images used for averaging, may be set in advance.

[0058] (Example 1) Fig. 5 is a diagram for explaining a first operation example of the radiation imaging system 100 according to the embodiment, and a process for generating a corrected radiation image X' by correcting a radiation image X will be explained with reference to the timing chart 310 in Fig. 3, the flow chart 320 of the correction process, and the flowchart in Fig. 5. Note that, in the image processing during radiation imaging, the long-term offset image S and the short-term offset image T generated in the offset image generation process are used, so it is assumed that the offset image generation process has been performed in advance. Therefore, the image processing during radiation imaging is performed after preparation for imaging is completed.

[0059] 5, the control circuit 112 checks whether there is a request to start imaging from the computer 120. In one example, the exposure control device 130 has an exposure switch (not shown), and when the exposure switch is turned on by a user, the exposure control device 130 sends an exposure command to the radiation generation device 140 and also sends a start notification indicating the start of radiation irradiation to the computer 120. In response to the start notification, the computer 120 notifies the control circuit 112 of the radiation imaging device 110 of the start of radiation irradiation. The control circuit 112 checks whether there is a notification from the computer 120, and if there is a notification (S501-YES), proceeds to step S502, and if there is no notification from the computer 120 (S501-NO), returns to step S501 again to check whether there is a notification from the computer 120.

[0060] In step S502, the control circuit 112 and the image generating circuit 113 perform a process of generating a radiographic image X. The process of generating a radiographic image X includes an accumulation operation performed during the accumulation period 309 in FIG.

[0061] The accumulation operation during accumulation period 309 is performed in a state where radiation 160 is being irradiated, as indicated by "radiation" in timing chart 310 in Fig. 3. The time length (accumulation time) indicating the length of time of accumulation period 309 when radiological image X is acquired is the same as the time length (accumulation time) of accumulation periods 301 and 305 during which accumulation operations were performed to acquire long-term offset image S during preparation for imaging. Hereinafter, accumulation period 309 is also referred to as a third period, and accumulation period 309 (third period) has the same time length as accumulation periods 301 and 305 (first period).

[0062] During the readout period 310, the control circuit 112 performs a third readout control to read out, as a third signal, a radiation signal based on charges accumulated over an accumulation period 309 (third period) having the same time length as the accumulation periods 301, 305 (first period) while radiation is being irradiated. In the readout operation performed during the readout period 310, the control circuit 112 controls the radiation detection panel 111 to output a signal (electrical signal) based on charges accumulated during the accumulation period 309 from the radiation detection panel 111. The image generating circuit 113 generates a radiation image X based on the signal (electrical signal) output from the radiation detection panel 111, and stores it in the storage device 114. Note that the readout operation performed by the control circuit 112 during the readout period 310 is the same operation as the readout operation performed during the readout periods 302, 306 to acquire a long-term offset image S during preparation for imaging.

[0063] In step S503, the control circuit 112 and the image generation circuit 113 perform a process of generating an offset image U during imaging. The process of generating an offset image U during imaging includes a storage operation performed in the storage period 311 of FIG. 3 and a signal readout operation performed in the readout period 312.

[0064] The accumulation operation of accumulation period 311 is performed in a state where radiation 160 is not being irradiated, as indicated by "radiation" in timing chart 310 in Fig. 3. Note that the time length (accumulation time) indicating the length of time of accumulation period 311 when offset image U is acquired during imaging is the same as the time length (accumulation time) of accumulation periods 303, 307 during which accumulation operation was performed to acquire short-term offset image T during preparation for imaging. Hereinafter, accumulation period 311 is also referred to as a fourth period, and accumulation period 311 (fourth period) has the same time length as accumulation periods 303, 307 (second period).

[0065] In the readout period 312, the control circuit 112 performs a fourth readout control in which, after reading out the radiation signal (third signal) in the readout period 310, a signal based on the charge accumulated over the accumulation period 311 (fourth period) in a state in which radiation is not being irradiated is read as an offset signal during imaging (hereinafter also referred to as the fourth signal). In the readout operation executed in the readout period 312, the control circuit 112 controls the radiation detection panel 111 to output a signal (electrical signal) based on the charge accumulated during the accumulation period 311 from the radiation detection panel 111.

[0066] The image generating circuit 113 generates an offset image U at the time of imaging based on a signal (electrical signal) output from the radiation detection panel 111, and stores the image in the storage device 114. Note that the readout operation performed by the control circuit 112 during the readout period 312 is the same as the readout operation performed during the readout periods 304 and 308 to acquire a short-term offset image T during preparation for imaging.

[0067] In step S504, the image generating circuit 113 performs a process of generating a radiation afterimage image. The image generating circuit 113 reads out the radiation image X and the long-term offset image S (first offset image) stored in the storage device 114, and generates a radiation afterimage image ("XS" in FIG. 3) by subtracting the long-term offset image S (first offset image) from the radiation image X.

[0068] Next, in step S505, the image generating circuit 113 performs a process of generating an offset residual image. The image generating circuit 113 reads out the offset image U at the time of capturing and the short-term offset image T (second offset image) stored in the storage device 114, and generates an offset residual image ("UT" in FIG. 3) by subtracting the short-term offset image T (second offset image) from the offset image U at the time of capturing.

[0069] The amount of residual image contained in each of the radiation residual image (XS) and the offset residual image (UT) is proportional to the time length during which charge is accumulated in the pixel P. In step S506, the image generating circuit 113 determines the amount of residual image in the offset residual image (UT) based on statistical information acquired by statistical processing of pixel values. Here, the statistical information includes, for example, at least one of the maximum pixel value, minimum pixel value, standard deviation of pixel values, and average pixel value (in-plane average pixel value) in the offset residual image (UT).

[0070] Next, the image generating circuit 113 adjusts the correction coefficient k according to the amount of residual image determined based on statistical information obtained by statistical processing of pixel values ​​in the offset residual image (UT). Here, the amount of residual image is information indicating the amount of residual image components contained in the offset residual image (UT).

[0071] The comparison of the amount of residual image with the threshold is illustrative, but for example, when the statistical information is equal to or greater than the threshold th1 (first threshold), the image generating circuit 113 determines that the amount of residual image contained in the offset residual image image (UT) is large (the amount of residual image is large), and sets the correction coefficient k based on the charge accumulation time. For example, the image generating circuit 113 may calculate the correction coefficient k based on the ratio (time length of the third period / time length of the fourth period) of the charge accumulation time in a state where radiation is irradiated (time length of the third period) to the charge accumulation time in a state where radiation is not irradiated (time length of the fourth period).

[0072] As the charge accumulation time, for example, when using the charge accumulation period based on radiation (e.g., period 309 (the third period) in FIG. 3) and the charge accumulation period of the charge accumulated in a state where no radiation is irradiated (e.g., period 311 (the fourth period) in FIG. 3), the ratio of period 309 to period 311 (that is, the value obtained by dividing the time length of period 309 by the time length of period 311) may be used as the correction coefficient k. Since the time length of period 309 is longer than that of period 311, the value obtained by dividing period 309 by period 311 is greater than "1".

[0073] Also, when the statistical information is less than the threshold value th1 (the first threshold value) and is greater than or equal to the threshold value th2 (the second threshold value) which is smaller than the threshold value th1 (th1 > afterimage amount ≧ th2), the image generation circuit 113 sets "1" as the correction coefficient k. In this case, the image generation circuit 113 determines that the afterimage amount included in the offset afterimage image (U-T) is small (the afterimage amount is small), and the image generation circuit 113 sets "1" as the correction coefficient k.

[0074] Also, when the statistical information is less than the threshold value th2 (the second threshold value) (afterimage amount < th2), the image generation circuit 113 determines that no afterimage has occurred and sets the correction coefficient k to zero (0). In this case, the image generation circuit 113 determines that no afterimage component is included in the offset afterimage image (U-T) (afterimage amount: none), and the image generation circuit 113 sets zero (0) as the correction coefficient k.

[0075] The above is an example. However, the image generation circuit 113 determines the afterimage amount by a determination process of comparing the statistical information obtained by statistical processing of the pixel values in the offset afterimage image (U-T) with the threshold value, and adjusts the correction coefficient k step by step according to the afterimage amount. In this example, a configuration using the first threshold value and the second threshold value is illustrated, but it is not limited to this example. The number of threshold values used for determining the afterimage amount, the set values of each threshold value, etc. can be arbitrarily set by the user via the input device 115. For example, the set values of each threshold value may be changed according to the intensity of the irradiated radiation, the irradiation time, the imaging site, the imaging conditions, etc.

[0076] In step S507, the image generating circuit 113 generates an adjusted residual image (k(UT) in FIG. 3) by correcting the pixel values ​​of the offset residual image (UT) using the correction coefficient k calculated in step S506. That is, the image generating circuit 113 generates the adjusted residual image (k(UT) in FIG. 3) by multiplying the pixel values ​​of the offset residual image (UT) by the correction coefficient k.

[0077] In step S508, the image generating circuit 113 subtracts the adjusted residual image (k(UT)) from the radiation residual image (XS) generated in step S504 to generate a radiographic image X' (X'=(XS)-k(UT) in FIG. 3) obtained by correcting the radiographic image X. The corrected radiographic image X' has reduced residual images from the radiographic image X.

[0078] The radiographic image X' obtained by correcting the radiographic image X is an image obtained by correcting the radiographic image X using the long-time offset image S (first offset image), the short-time offset image T (second offset image), the offset image U at the time of imaging (third offset image), and the correction coefficient k. The image generating circuit 113 transmits the corrected radiographic image X' to the computer 120.

[0079] The above-mentioned calculation order for generating the radiographic image X' is an example, and calculation may be performed in another order. The radiographic image X', i.e., XSk(UT), is transformed into X-kU+(kT-S). Therefore, the image generating circuit 113 may calculate kT-S using the long-time offset image S, the short-time offset image T, and the correction coefficient k during preparation for imaging, and store this value as a correction value in the memory of the image generating circuit 113. The correction coefficient k may be determined based on a pre-setting of the timing at which the driving circuit 210 supplies an ON signal to the pixel array 200. During imaging of a moving image, the image generating circuit 113 may correct the radiographic image X using the offset image U at the time of imaging, the correction value stored in the storage device 114, and the correction coefficient k. In this way, by storing the correction value instead of storing the long-time offset image S and the short-time offset image T, the memory consumption of the image generating circuit 113 can be reduced.

[0080] After that, in step S509, the control circuit 112 judges whether to continue imaging. In one example, the exposure control device 130 has an exposure switch (not shown), and when the exposure switch is switched off by the user, the exposure control device 130 sends an exposure stop command to the radiation generation device 140 and a stop notification indicating the stop of radiation irradiation to the computer 120. In response to the stop notification, the computer 120 notifies the control circuit 112 of the radiation imaging device 110 of the stop of radiation irradiation. The control circuit 112 checks whether there is a request to end imaging from the computer 120, and if imaging is not to be continued (S509-NO), ends the generation process of the radiation image. On the other hand, if there is no request to end imaging yet in order to perform imaging of multiple frames such as video imaging, it judges that imaging is to be continued (S509-YES), and the control circuit 112 returns the process to step S502 again and repeats the same process. When continuing imaging, the control circuit 112 and the image generating circuit 113 perform the same operations during the accumulation period 313 (third period), the readout period 314, the accumulation period 315 (fourth period), and the readout period 316.

[0081] Thereafter, the process from step S502 to step S508 is repeated again. By generating a corrected radiographic image X' by correcting the radiographic image X for each imaging frame through the process described above, it is possible to improve the frame rate and reduce noise in the radiographic image while achieving highly accurate afterimage correction.

[0082] (Example 2) Next, a second operation example of the radiation imaging apparatus 110, which is different from the first operation example of the radiation imaging apparatus 110 described in Fig. 5, will be described with reference to the flowchart of Fig. 6. Fig. 6 is a diagram for explaining the second operation example of the radiation imaging system 100 according to the embodiment, and a process for generating a corrected radiation image X' by correcting the radiation image X will be described with reference to the timing chart 310 of Fig. 3, the flow 320 of the correction process, and the flowchart of Fig. 6.

[0083] As a different operation example 2, the calculation process of the correction coefficient k may be made more efficient as shown in the flowchart of Fig. 6. After irradiation with high-intensity radiation, the amount of residual image components contained in the offset residual image image (UT) attenuates nonlinearly over time, and the attenuation amount of the residual image components has the characteristic of converging to zero (0).

[0084] FIG. 7 is a diagram illustrating the attenuation characteristic of the amount of residual image, where the horizontal axis indicates time and the vertical axis indicates the amount of residual image (amount of residual image component). When radiation 701 is irradiated, the amount of residual image component attenuates according to a nonlinear attenuation characteristic 703 over time. In FIG. 7, the amount of residual image 710 is n The offset residual image P when the radiation image X is captured n (P n =U n -T n ) and the residual image amount 711 is the amount of residual image in the n+1th frame F n+1 The offset residual image P when the radiation image X is captured n+1 (P n+1 =U n+1 -T n+1 ) The residual image amount 712 is the (n+2)th frame F n+2 The offset residual image P when the radiation image X is captured n+2 (Pn+2 =U n+2 -T n+2 ).

[0085] A range 700 in FIG. 7 illustrates a range of a plurality of offset residual images used to obtain an average offset residual image generated in step S613 in FIG. 6. In the example shown in FIG. 7, an average offset residual image is generated using three offset residual images included in the range 700. The image generating circuit 113 generates an average offset residual image using a plurality of offset residual images previously acquired by continuing imaging (for example, P in FIG. 7). n , P n+1 , P n+2 ) to generate an average offset residual image. The correction coefficient calculated in the average offset residual image is K AVE Let us assume that.

[0086] In FIG. 7, the residual image amount 713 is the (n+3)th frame F n+3 The offset residual image P when the radiation image X is captured n+3 (P n+3 =U n+3 -T n+3 ) and the residual image amount 713 is calculated based on the attenuation characteristic 703 of the previous frame F n+2 It becomes attenuated from.

[0087] The residual image amounts 714a and 714b indicate the amount of residual image after the radiation 702 is irradiated. The residual image amount 714a is the amount of residual image after the (n+4)th frame F n+4 The offset residual image P when the radiation image X is captured n+4a (P n+4a =U n+4a -T n+4a ) The residual image amount 714b is the (n+4)th frame F n+4 The offset residual image P when the radiation image X is captured n+4b (P n+4b =U n+4b -T n+4b ).

[0088] Even after the radiation 702 is irradiated, the residual image amount 714a is attenuated according to the attenuation characteristic 703 from the previous frame F n+3 On the other hand, the amount of residual image 714b is an amount of residual image that deviates from the attenuation characteristic 703.

[0089] The offset residual image (P n+3 , P n+4a ), the amount of residual image changes according to the attenuation characteristic 703, and each offset residual image (P n+3 , P n+4a ), the correction coefficient k is calculated in the average offset residual image, AVE In this case, as described in steps S620-YES, S621, and S622 of FIG. 6 below, the offset residual image (P n+3 , P n+4a If the difference between the average pixel value in the average offset residual image and the average pixel value in the average offset residual image is within a specified range (S620-YES), the correction coefficient K AVE Using the adjusted residual image (K AVE (U n+3 -T n+3 ), K AVE (U n+4a -T n+4a )).

[0090] On the other hand, the offset residual image (P n+4b If the difference between the average pixel value in the average offset residual image and the average pixel value in the average offset residual image exceeds a prescribed range (S620-NO), the newly acquired offset residual image (P n+4b ), the adjusted residual image (K(U n+4b -T n+4b ) are generated (S625, S626). A specific process flow will be described below with reference to the flowchart in FIG.

[0091] The flowchart in Fig. 6 shows a process flow for improving the efficiency of the calculation process of the correction coefficient k, taking into account the attenuation characteristics of the residual image component contained in the offset residual image (UT). Note that the process in Fig. 6 includes processes common to those in the flowchart in Fig. 5, and to avoid duplication, the details of the processes will be described for the different parts.

[0092] In step S601, the control circuit 112 checks whether or not there is a request to start imaging from the computer 120. This process is similar to the process in step S501 in FIG.

[0093] In step S602, the control circuit 112 resets an internal shooting counter n to 0. The control circuit 112 has an internal memory (not shown) and is capable of storing the setting of the shooting counter n. In this step, the control circuit 112 resets the setting of the shooting counter n stored in the memory (not shown).

[0094] In step S603, the control circuit 112 increments the shooting counter n.

[0095] The processes of steps S604 to S611 are similar to the processes of S502 to S509 in Fig. 5. That is, the processes of S604 to S611 are similar to the processes of S502 (generation of radiographic image X), S503 (generation of offset image U at the time of imaging), S504 (generation of radiographic afterimage image (XS)), S505 (generation of offset afterimage image (UT)), S506 (calculation of correction coefficient k), S507 (generation of adjusted afterimage image k(UT)), S508 (generation of corrected radiographic image X'), and S509 (determination of continuation of imaging) in Fig. 5.

[0096] In step S612, the control circuit 112 judges whether the photographing counter n has reached a prescribed number, and if it is judged that the photographing counter n has not exceeded the prescribed number (S612-NO), the control circuit 112 returns the process to S603 and repeats the processes from step S603 onwards. On the other hand, if it is judged in the judgment process of step S612 that the photographing counter n has reached the prescribed number (S612-YES), the control circuit 112 advances the process to step S613.

[0097] In step S613, the image generating circuit 113 reads the offset residual image (UT) of the last few times stored in the storage device 114 in S607, for example, P n , P n+1 , P n+2 , and the pixel information (pixel value information) of the most recent several read offset residual images (UT) is averaged to generate an average offset residual image, which is an average image of the offset residual images (UT).

[0098] In step S614, the image generating circuit 113 calculates a correction coefficient k for the amount of residual image of the average offset residual image generated in step S613 in the same manner as in step S506 in FIG. 5, and stores the calculated correction coefficient k in the storage device 114. The correction coefficient k calculated in this step is the correction coefficient K AVE is equivalent to:

[0099] The processing in steps S615 to S618 is the same as the processing in steps S502 to S505 in FIG. 5, i.e., steps S502 (generation processing of radiation image X), S503 (generation processing of offset image U at the time of imaging), S504 (generation processing of radiation afterimage image (XS)), and S505 (generation processing of offset afterimage image (UT)) in FIG. 5.

[0100] In step S619, the image generating circuit 113 calculates the difference (absolute value of the difference) between the average pixel value of the offset residual image (UT) at the time of capture generated in step S616 and the average pixel value of the average offset residual image generated in step S613.

[0101] The image generation circuit 113 adjusts the correction coefficient used in the process of generating the adjusted afterimage image by determining (S620) whether the difference between the average pixel value in the offset afterimage image newly acquired by continuing imaging and the average pixel value in the average offset afterimage image is within a specified range.

[0102] In step S620, the image generating circuit 113 determines whether the difference (absolute value of the difference) calculated in step S619 is within a specified range. If the difference (absolute value of the difference) exceeds the specified range (S620-NO), the image generating circuit 113 advances the process to step S625.

[0103] On the other hand, if the difference (absolute value of the difference) is within the specified range in the determination process of step S620 (S620-YES), the image generating circuit 113 proceeds to step S621. Here, if the absolute value of the difference between the average pixel value of the offset afterimage image (UT) calculated in step S619 and the average pixel value of the average offset afterimage image does not exceed the specified range in the determination of S620, no significant change is observed in the characteristics of the afterimage.

[0104] In step S621, the image generating circuit 113 calculates the correction coefficient k of the average offset residual image calculated in step S614 (the correction coefficient K AVE ) as the correction coefficient k for generating the adjusted afterimage image. If the difference (absolute value of the difference) does not exceed a specified range, the image generating circuit 113 determines the correction coefficient k calculated in the average offset afterimage image (S614, the correction coefficient K AVE ) to generate an adjusted residual image, and by continuing imaging, the adjusted residual image (k(UT)) is subtracted from a newly acquired radiation residual image X to generate a corrected radiation image X'.

[0105] The process for acquiring various new images by continuing imaging (the process of steps S622 to S624) is the same as the process of steps S507 to S509 in Fig. 5. That is, it is the same process as step S507 (generation of adjusted residual image k(UT)), S508 (generation of corrected radiographic image X'), and S509 (determination of continuation of imaging) in Fig. 5.

[0106] In step S622, the image generating circuit 113 calculates the correction coefficient k determined in step S621 (the correction coefficient K AVE ) to generate an adjusted residual image (k(UT)).

[0107] In step S623, the image generating circuit 113 subtracts the adjusted residual image (k(UT)) generated in step S622 from the radiation residual image (XS) generated in step S617 to generate a corrected radiation image (X'=(XS)-k(UT)) in which the residual image is reduced from the radiation image X. The image generating circuit 113 transmits the generated corrected radiation image X' to the computer 120.

[0108] Then, in step S624, the control circuit 112 performs the same determination process as in step S611 to determine whether to continue imaging, and if it is determined that imaging should be continued (S624-YES), the process returns to step S615 and repeats the same process. Note that the process from step S613 may be repeated in order to update the correction coefficient k used in step S621 every time imaging is performed.

[0109] If it is determined that imaging should not be continued (S624-NO), the radiographic image generation process is terminated. In this manner, if no significant change is observed in the characteristics of the afterimage, the afterimage can be reduced even using the correction coefficient k calculated in step S614, and therefore, the calculation process can be made more efficient by omitting the calculation of the correction coefficient k.

[0110] On the other hand, if the difference (absolute value of the difference) calculated in step S619 exceeds the specified range (S620-NO), a large change that exceeds the specified range has occurred in the characteristics of the afterimage during imaging (for example, amount of afterimage 714b in FIG. 7). In this case, it is considered that strong radiation (for example, radiation 702 in FIG. 7) has been irradiated again, and the image generating circuit 113 advances the process to step S625. In the subsequent processes, if the difference (absolute value of the difference) exceeds the specified value, the image generating circuit 113 determines that a new offset afterimage image (UT: for example, P in FIG. 7) obtained by continuing imaging is generated. n+4b ), an adjusted residual image (k(UT)) is generated using the recalculated correction coefficient k, and a corrected radiation image X' is generated by subtracting the adjusted residual image (k(UT)) from a radiation residual image (XS) newly acquired by continuing imaging.

[0111] In step S625, the image generating circuit 113 recalculates the correction coefficient k. When recalculating, the image generating circuit 113 recalculates the offset residual image (UT: for example, P in FIG. 7) generated in step S618. n+4b ) is used to calculate the correction coefficient k in the same calculation process as in step S608 (S506). In this way, by switching the calculation method of the correction coefficient k depending on the amount of change in the afterimage over time, the calculation of the correction coefficient k can be made more efficient.

[0112] The processes in steps S626 and S627 are similar to those in steps S507 and S508 in Fig. 5. That is, they are similar to those in steps S507 (generation of adjusted residual image k(UT)) and S508 (generation of corrected radiographic image X') in Fig. 5.

[0113] In step S626, the image generating circuit 113 performs a process of generating an adjusted residual image (k(UT)) using the correction coefficient k calculated in step S625. Then, the image generating circuit 113 subtracts the adjusted residual image (k(UT)) from the radiation residual image (XS) generated in step S617 to generate a corrected radiographic image X' (X'=(XS)-k(UT)) in which the residual image has been reduced from the radiographic image X. The image generating circuit 113 transmits the generated corrected radiographic image X' to the computer 120. Thereafter, the process returns to step S602, and the same process is performed. According to the process described in FIG. 6, when a significant change occurs in the characteristics of the residual image during imaging, the adjusted residual image (k(UT)) is generated using the recalculated correction coefficient k to generate a corrected radiographic image X' by correcting the radiographic image X, thereby making it possible to more accurately reduce the influence of the residual image.

[0114] In the above-described embodiment, the pixel array 200 includes only pixels P used for generating radiographic images. Alternatively, the pixel array 200 may include pixels used for purposes other than generating radiographic images, such as pixels used for automatic exposure control.

[0115] According to the techniques disclosed in the above embodiments, it is possible to improve the frame rate and reduce noise in radiographic images while performing highly accurate afterimage correction.

[0116] The technology disclosed in this specification includes the following radiation imaging apparatus, radiation imaging system, and method for controlling the radiation imaging apparatus. [Item 1] A radiation imaging device, a radiation detection panel in which a plurality of pixels are arranged to form a plurality of rows and a plurality of columns; a control circuit that controls an operation of the radiation detection panel to control reading of signals based on the charges accumulated in the plurality of pixels; an image generating circuit that generates an image based on the signal; The control circuit includes: In the absence of radiation exposure, a first read control for reading out a first signal based on the charge accumulated in a first period; and executing a second read control for reading out a second signal based on the charge accumulated during a second period shorter than the first period; a third readout control for reading out, as a third signal, a radiation signal based on charges accumulated during a third period having the same time length as the first period while the radiation is being applied; a fourth read control is executed to read out a fourth signal based on charges accumulated during a fourth period having the same time length as the second period in a state in which the radiation is not irradiated after the third signal is read out; The image generating circuit includes: generating a radiation residual image by subtracting a first offset image based on the first signal from a radiation image based on the third signal; generating an offset residual image by subtracting a second offset image based on the second signal from an offset image at the time of imaging based on the fourth signal; generating an adjusted residual image by correcting pixel values ​​of the offset residual image acquired for each frame of the radiographic image using a correction coefficient adjusted according to an amount of residual image determined based on statistical information acquired by statistical processing of pixel values; A radiation imaging apparatus that generates a corrected radiation image by subtracting the adjusted residual image from the radiation residual image. [Item 2] The radiation imaging device according to item 1, wherein the image generating circuit generates the adjusted residual image by multiplying pixel values ​​of the offset residual image acquired for each frame by the correction coefficient. [Item 3] A radiation imaging device as described in item 1 or 2, wherein the image generation circuit determines the amount of residual image contained in the offset residual image acquired for each frame by comparing the statistical information with a threshold value, and sets a different correction coefficient depending on the amount of residual image. [Item 4] The radiation imaging device described in Item 3, wherein the image generating circuit sets the ratio of the length of the third period to the length of the fourth period as the correction coefficient when the statistical information is equal to or greater than a first threshold value as the threshold value. [Item 5] The radiation imaging device according to Item 4, wherein the image generating circuit sets the correction coefficient to 1 when the statistical information is less than the first threshold and greater than or equal to a second threshold that is smaller than the first threshold. [Item 6] In the radiation imaging apparatus according to Item 5, the image generating circuit sets the correction coefficient to zero when the statistical information is less than the second threshold value. [Item 7] The image generating circuit is generating an average offset residual image by averaging pixel values ​​of the plurality of offset residual images previously acquired by continuing to capture images; A radiation imaging device described in any one of items 1 to 6, which adjusts the correction coefficient used in the generation process of the adjusted residual image by determining whether the difference between the average pixel value in the offset residual image newly acquired by continuing the imaging and the average pixel value in the average offset residual image is within a specified range. [Item 8] When the difference is within the specified range, the image generating circuit generates the adjusted residual image using the correction coefficient calculated in the average offset residual image, 8. The radiation imaging apparatus according to item 7, wherein a corrected radiation image is generated by subtracting the adjusted residual image from the radiation residual image newly acquired by continuing the imaging. [Item 9] When the difference exceeds the specified range, the image generating circuit generates the adjusted residual image using a recalculated correction coefficient in the offset residual image newly acquired by continuing the imaging, 8. The radiation imaging apparatus according to item 7, wherein a corrected radiation image is generated by subtracting the adjusted residual image from the radiation residual image newly acquired by continuing the imaging. [Item 10] A radiation imaging device described in any one of items 1 to 9, wherein the image generating circuit generates the first offset image by averaging offset images based on multiple first signals acquired in a state where the radiation is not irradiated. [Item 11] A radiation imaging device described in any one of items 1 to 10, wherein the image generating circuit generates the second offset image by averaging offset images based on multiple second signals acquired in a state where the radiation is not irradiated. [Item 12] A radiation imaging device described in any one of items 1 to 11, wherein the statistical information includes at least one of the maximum pixel value, minimum pixel value, standard deviation of pixel values, and average pixel value in the offset residual image. [Item 13] A radiation imaging device according to any one of items 1 to 12, a processing means for processing a radiation image obtained by the radiation imaging device; A radiation imaging system comprising: [Item 14] A method for controlling a radiation imaging apparatus having a radiation detection panel in which a plurality of pixels are arranged to form a plurality of rows and a plurality of columns, a control circuit that controls an operation of the radiation detection panel and controls reading of signals based on charges accumulated in the plurality of pixels, and an image generation circuit that generates an image based on the signals, comprising: In the absence of radiation exposure, Executing a first read control for reading out a first signal based on charges accumulated in a first period, and a second read control for reading out a second signal based on charges accumulated in a second period shorter than the first period; In a state where the radiation is being irradiated, executing a third readout control for reading out, as a third signal, a radiation signal based on charges accumulated during a third period having the same time length as the first period; After the third signal is read out, in a state where the radiation is not being irradiated, executing a fourth read control for reading out a fourth signal based on charges accumulated during a fourth period having the same time length as the second period; generating a radiation residual image by subtracting a first offset image based on the first signal from a radiation image based on the third signal; generating an offset residual image by subtracting a second offset image based on the second signal from an offset image at the time of imaging based on the fourth signal; generating an adjusted residual image by correcting pixel values ​​of the offset residual image acquired for each frame of the radiographic image using a correction coefficient adjusted according to an amount of residual image determined based on statistical information acquired by statistical processing of pixel values; generating a corrected radiation image by subtracting the adjusted radiation residual image from the radiation residual image; A method for controlling a radiation imaging apparatus comprising the steps of:

[0117] [Other embodiments] The disclosed technology can also be realized by a process in which a program for realizing one or more functions of the above-mentioned embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) for realizing one or more functions.

[0118] The disclosed technology is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to disclose the scope of the invention. [Explanation of symbols]

[0119] 100: Radiation imaging system, 110: Radiation imaging device, 111: Radiation detection panel, 112: Control circuit, 113: Image generating circuit, 114: Storage device, 120: Computer, 130: Exposure control device, 140: Radiation generating device, 150: Subject, 160: Radiation, 170: Display (display device)

Claims

1. A radiation imaging apparatus comprising: a radiation detection panel in which a plurality of pixels are arranged to form a plurality of rows and a plurality of columns; a control circuit that controls an operation of the radiation detection panel to control reading of signals based on the charges accumulated in the plurality of pixels; an image generating circuit that generates an image based on the signal; The control circuit includes: In the absence of radiation exposure, a first read control for reading out a first signal based on the charge accumulated in a first period; and executing a second read control for reading out a second signal based on the charges accumulated during a second period shorter than the first period; a third read control for reading, as a third signal, a radiation signal based on charges accumulated during a third period having the same time length as the first period while the radiation is being applied; a fourth read control is executed to read out a fourth signal based on charges accumulated during a fourth period having the same time length as the second period in a state in which the radiation is not irradiated after the third signal is read out; The image generating circuit includes: generating a radiation residual image by subtracting a first offset image based on the first signal from a radiation image based on the third signal; generating an offset residual image by subtracting a second offset image based on the second signal from an offset image at the time of imaging based on the fourth signal; generating an adjusted residual image by correcting pixel values ​​of the offset residual image acquired for each frame of the radiographic image using a correction coefficient adjusted according to an amount of residual image determined based on statistical information acquired by statistical processing of pixel values; A radiation imaging apparatus that generates a corrected radiation image by subtracting the adjusted residual image from the radiation residual image.

2. The radiation imaging apparatus according to claim 1 , wherein the image generating circuit generates the adjusted residual image by multiplying pixel values ​​of the offset residual image acquired for each frame by the correction coefficient.

3. The radiation imaging device according to claim 1 , wherein the image generating circuit determines an amount of residual image contained in the offset residual image acquired for each frame by comparing the statistical information with a threshold value, and sets a different correction coefficient depending on the amount of residual image.

4. 4. The radiation imaging apparatus according to claim 3, wherein the image generating circuit sets the correction coefficient to a ratio of a duration of the third period to a duration of the fourth period when the statistical information is equal to or greater than a first threshold value.

5. 5. The radiation imaging apparatus according to claim 4, wherein the image generating circuit sets the correction coefficient to 1 when the statistical information is less than the first threshold and is equal to or greater than a second threshold that is smaller than the first threshold.

6. The radiation imaging apparatus according to claim 5 , wherein the image generating circuit sets the correction coefficient to zero when the statistical information is less than the second threshold value.

7. The image generating circuit includes: generating an average offset residual image by averaging pixel values ​​of the plurality of offset residual images previously acquired by continuing to capture images; The radiation imaging device of claim 1, wherein the correction coefficient used in the process of generating the adjusted residual image is adjusted by determining whether the difference between the average pixel value in the offset residual image newly acquired by continuing the imaging and the average pixel value in the average offset residual image is within a specified range.

8. The image generating circuit generates the adjusted residual image using the correction coefficient calculated in the average offset residual image when the difference is within the specified range; The radiation imaging apparatus according to claim 7 , wherein a corrected radiation image is generated by subtracting the adjusted residual image from the radiation residual image newly acquired by continuing the imaging.

9. When the difference exceeds the specified range, the image generating circuit generates the adjusted residual image using a recalculated correction coefficient in the offset residual image newly acquired by continuing the imaging, The radiation imaging apparatus according to claim 7 , wherein a corrected radiation image is generated by subtracting the adjusted residual image from the radiation residual image newly acquired by continuing the imaging.

10. 2. The radiation imaging device according to claim 1, wherein the image generating circuit generates the first offset image by averaging offset images based on a plurality of the first signals acquired in a state in which the radiation is not irradiated.

11. 2. The radiation imaging device according to claim 1, wherein the image generating circuit generates the second offset image by averaging offset images based on a plurality of the second signals acquired in a state in which the radiation is not irradiated.

12. The radiation imaging apparatus according to claim 1 , wherein the statistical information includes at least one of a maximum pixel value, a minimum pixel value, a standard deviation of pixel values, and an average value of pixel values ​​in the offset residual image.

13. A radiation imaging apparatus according to any one of claims 1 to 12, a processing means for processing a radiation image obtained by the radiation imaging device; A radiation imaging system comprising:

14. A method for controlling a radiation imaging apparatus having a radiation detection panel in which a plurality of pixels are arranged to form a plurality of rows and a plurality of columns, a control circuit that controls an operation of the radiation detection panel and controls reading of signals based on charges accumulated in the plurality of pixels, and an image generation circuit that generates an image based on the signals, comprising: In the absence of radiation exposure, Executing a first read control for reading out a first signal based on charges accumulated in a first period, and a second read control for reading out a second signal based on charges accumulated in a second period shorter than the first period; In a state where the radiation is being irradiated, executing a third readout control for reading out, as a third signal, a radiation signal based on charges accumulated during a third period having the same time length as the first period; After the third signal is read out, in a state where the radiation is not being irradiated, executing a fourth read control for reading out a fourth signal based on charges accumulated during a fourth period having the same time length as the second period; generating a radiation retention image by subtracting a first offset image based on the first signal from a radiation image based on the third signal; generating an offset residual image by subtracting a second offset image based on the second signal from an offset image at the time of imaging based on the fourth signal; generating an adjusted residual image by correcting pixel values ​​of the offset residual image acquired for each frame of the radiographic image using a correction coefficient adjusted according to an amount of residual image determined based on statistical information acquired by statistical processing of pixel values; generating a corrected radiation image by subtracting the adjusted radiation residual image from the radiation residual image; A method for controlling a radiation imaging apparatus comprising the steps of:

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