Information processing device, and control method of the same, radiography system and program

Abstract

To reduce an impact of grid stripes in correcting defective rows occurring in a radiation image captured upon automatically detecting radiation irradiation.SOLUTION: An information processing device is configured to acquire radiation images captured by a radiation imaging device detecting a radiation irradiation start and performing radiography, on the basis of a signal to be read by simultaneously driving and resetting a plurality of pixels arranged in a matrix, and a continuous n-th row every the n-th row; synthesize the continuous n-th row of the radiation image to a single row, using a weighting factor suppressing an impact of an anti-scatter grid to thereby generate a binning image; acquire a correction coefficient for correcting a pixel value of the row of a correction object in the binning image on the basis of a pixel value of the row adjacent to the row of the correction object in the binning image; and correct the n-th row of the radiation image corresponding to the row of the correction object on the basis of the correction coefficient.SELECTED DRAWING: Figure 1A

Description

[Technical field]

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

[0002] In recent years, flat panel detectors (hereinafter, FPDs) that accumulate radiation such as X-rays as charge signals and convert them into digital signals to provide diagnostic images have been put to practical use. There is also a strong market demand to replace the imaging units of existing modalities, such as films and imaging plates, with FPDs. However, because synchronization between the FPD and the radiation generator is required, when attempting to replace the imaging units of existing modalities with FPDs, it can be difficult to build an interface between the radiation generator and the FPD. In order to eliminate the need to build such an interface, FPDs have been proposed that detect radiation irradiation and automatically start accumulation operations (Patent Document 1, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-249891 A [Patent Document 2] JP 2015-19157 A [Patent Document 3] JP 2014-150844 A (referred to in the embodiments) Summary of the Invention [Problem to be solved by the invention]

[0004] Radiation exposure is detected by monitoring the accumulated charge by sequentially reading and resetting the accumulated charge in units of scanning rows. A certain amount of radiation exposure is required from when radiation is actually applied until the radiation is detected and the accumulation operation begins, and a time lag occurs between the start of actual radiation exposure and when the FPD begins the accumulation operation. The charge discharged by the reset operation during this time lag cannot contribute to the output value. For this reason, even if the incident dose is the same, there will be a difference in output value between a pixel from which charge has been discharged during the time lag (hereinafter, this pixel will be called a defective pixel) and a pixel from which charge has not been discharged (hereinafter, this pixel will be called a normal pixel).

[0005] In Patent Document 1, the reset operation during radiation detection is performed row by row, and the even and odd rows are alternated for each frame to perform the reset operation. Therefore, the charge is discharged from every other row between the time of radiation irradiation and the start of the accumulation operation. As a result, rows of defective pixels from which the charge has been discharged (hereinafter, these rows will be referred to as defective rows) and rows of normal pixels from which the charge has not been discharged (hereinafter, these rows will be referred to as normal rows) occur alternately, and the difference in output value between the rows appears as stripes on the image. Since the output values ​​differ between the defective rows and normal rows even with the same incident radiation, correction is necessary. Patent Documents 1 and 2 propose correcting the output value of such defective rows.

[0006] On the other hand, radiation generates scattered rays inside the subject, and the scattered rays are imaged together with the direct rays that have passed through the subject. For this reason, imaging may be performed by placing an instrument called a grid, which removes such scattered rays, between the subject and the image receiving surface of the radiation. The grid is made by alternately arranging radiation shielding materials such as lead and radiation-transmitting materials such as aluminum and carbon at a predetermined width to remove scattered rays, but also removes some of the direct rays that pass through the radiation shielding materials. For this reason, periodic signals (grid stripes) are generated on the image. When radiation imaging is performed by automatically detecting radiation using a grid, the above-mentioned missing rows and grid stripes are mixed. Patent Document 1 and Patent Document 2 do not take such grid stripes into consideration, and appropriate correction cannot be performed in radiation imaging using a grid.

[0007] An object of the present invention is to reduce the influence of grid stripes in correcting missing lines that occur in a radiographic image captured by automatically detecting irradiation with radiation. [Means for solving the problem]

[0008] A radiation imaging system according to an aspect of the present invention includes the following arrangement: a holding means for holding a radiation image captured by a radiation imaging apparatus that performs radiation imaging by simultaneously driving and resetting consecutive n rows of a plurality of pixels arranged in a matrix, every n rows being equal to each other, and detecting the start of irradiation of radiation based on signals read out from the pixels; a generating means for generating a binned image by combining the n consecutive rows of the radiation image into one row using a weighting factor that suppresses the influence of an anti-scatter grid; an acquisition means for acquiring a correction coefficient for correcting pixel values ​​of a row to be corrected in the binning image based on pixel values ​​of rows adjacent to the row to be corrected in the binning image; and a correction unit that corrects n rows of the radiation image corresponding to the row to be corrected based on the correction coefficient. Effect of the Invention

[0009] According to the present invention, it is possible to correct missing lines that occur in a radiographic image captured by automatically detecting radiation exposure while reducing the influence of grid stripes, thereby improving the image quality of the radiographic image. [Brief description of the drawings]

[0010] [Figure 1A] FIG. 1 is a diagram showing an example of the arrangement of a radiation imaging system according to an embodiment. [Figure 1B] FIG. 2 is a diagram showing an example of the hardware configuration of an imaging control device. [Diagram 2] 4 is a flowchart showing a process according to an embodiment. [Diagram 3] FIG. 2 is a diagram for explaining the circuit configuration of an FPD. [Figure 4] FIG. 2 is a diagram for explaining the driving of an FPD. [Diagram 5] FIG. 13 is a diagram for explaining the decrease in output value at an X-ray defect line. [Figure 6] 11A and 11B are diagrams for explaining an example in which correction accuracy deteriorates. [Figure 7] A diagram explaining the effect of the grid. [Figure 8] 4 is a diagram for explaining the operation of a correction coefficient calculation unit 109. [Figure 9] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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.

[0012] 1A is a diagram showing an example of the configuration of a radiation imaging system 100 according to an embodiment. The radiation imaging system 100 has a function for automatically detecting radiation irradiation and correcting defective pixels that occur when acquiring a radiation image. The radiation imaging system 100 includes a radiation generating device 104, a radiation generating unit 101, a flat panel detector (FPD) 102, and an imaging control device 120. The imaging control device 120 includes an FPD control unit 105, an image storage unit 108, a correction coefficient calculation unit 109, a correction unit 110, and a post-processing unit 111 as functional units.

[0013] In the radiography system 100, the radiation generating unit 101 irradiates the subject 103 with radiation. The radiation generating device 104 applies a high voltage pulse to the radiation generating unit 101 in response to pressing of an irradiation switch (not shown) to generate radiation. Under the control of the FPD control unit 105, the FPD 102 converts the radiation transmitted through the subject 103 into visible light using a phosphor, converts the visible light into an electrical signal using a photodiode, converts the electrical signal into a digital signal by AD conversion, and transmits the digital signal to the FPD control unit 105. The FPD control unit 105 is connected to a correction coefficient calculation unit 109, a correction unit 110, a post-processing unit 111, and an image storage unit 108. The correction coefficient calculation unit 109 calculates a coefficient for correcting defective pixels. The correction unit 110 corrects defective pixels using the correction coefficient calculated by the correction coefficient calculation unit 109. The post-processing unit 111 performs various processes, such as gradation processing and emphasis processing, on the image in which the defective pixels have been corrected by the correction unit 110, to generate an image suitable for diagnosis. The FPD control unit 105 displays the diagnostic image corrected by the post-processing unit 111 on the monitor 106. The operation unit 107 accepts instructions for the post-processing unit 111 and user instructions for the FPD 102, and provides the user instructions to the FPD control unit 105. The image storage unit 108 stores the digital signal output from the FPD control unit 105 and the image data processed by the post-processing unit 111.

[0014] 1A shows a configuration in which all of the functional units, namely, the FPD control unit 105, the correction coefficient calculation unit 109, the correction unit 110, the post-processing unit 111, and the image storage unit 108, are included in one imaging control device 120, but the present invention is not limited to this. That is, the above-mentioned functional units of the imaging control device 120 may be realized by one computer device (information processing device) or by multiple computer devices.

[0015] 1B is a block diagram showing an example of a hardware configuration of a computer device that can be used as the imaging control device 120. The computer device includes, for example, a main control unit 151 such as a CPU, a storage unit such as a ROM (Read Only Memory) 152, and a RAM (Random Access Memory) 153. The computer device may also include a graphics control unit 154 such as a GPU (Graphics Processing Unit), a communication unit 155 such as a network card, and an input / output unit 156 (corresponding to the monitor 106 and the operation unit 107) such as a keyboard, a display, or a touch panel. These components are connected by a bus 157 or the like, and the above-mentioned functional units are realized by the main control unit 151 executing a program stored in the storage unit.

[0016] The operation of the radiation imaging system 100 of this embodiment having the above-mentioned configuration will be specifically described with reference to the flowchart shown in FIG.

[0017] First, in S201, the FPD control unit 105 acquires a radiographic image. In acquiring a radiographic image, the radiation generating device 104 first applies a high voltage pulse to the radiation generating unit 101, causing the subject 103 to be irradiated with radiation. When radiation irradiation starts, the FPD 102 automatically detects this radiation irradiation and starts an accumulation operation to capture a radiographic image. The FPD 102 transmits the captured radiographic image to the FPD control unit 105, which receives it.

[0018] Here, the configuration and driving of the FPD 102 for automatically detecting radiation irradiation will be specifically described with reference to FIGS.

[0019] FIG. 3 shows the circuit configuration of the FPD 102. The FPD 102 has a glass substrate 301, on which several thousand pixels are arranged in a matrix. Each pixel has a TFT 302 and a photodiode 303. For the sake of explanation, FIG. 3 shows an FPD consisting of four pixels in both the vertical and horizontal directions. A scanning line control circuit 306 sequentially applies an ON signal to the scanning lines G1 to G4 to turn on the switches of the TFTs 302 that constitute the pixels connected to the scanning lines. When an ON signal is applied to a scanning line, the TFTs 302 connected to the scanning line to which the ON signal is applied are switched on. This causes the output charges of all the photodiodes 303 connected to the scanning line to be read. The charges read from the photodiodes 303 are transmitted through the signal lines S1 to S4 and read by the signal detection circuit 305. The signal detection circuit 305 performs processes such as holding, amplifying, and AD conversion of the read signal, outputs a digital signal, and resets the pixel from which the signal was read. The digital signal output from the signal detection circuit 305 is transmitted as a radiation image to the FPD control unit 105. The power supply 304 supplies driving voltages for the scanning line control circuit 306 and the signal detection circuit 305, operating voltages for each photodiode 303, and the like.

[0020] FIG. 4 is a timing chart for explaining the driving of the FPD 102 in this embodiment. The FPD 102 waits while performing radiation detection driving for detecting the start of radiation irradiation until radiation imaging is started. In the radiation detection driving, n consecutive rows of a plurality of pixels arranged in a matrix are simultaneously driven and reset for every n rows, and the start of radiation irradiation is detected based on the signals read out. Here, n is an integer of 3 or more. The case of n=3 will be described below. As shown in FIG. 4, during the radiation detection driving, the scanning line control circuit 306 simultaneously drives three consecutive scanning lines, and executes this simultaneous driving sequentially for every three consecutive scanning lines. That is, in the first frame (hereinafter also referred to as an odd-numbered frame), the scanning line control circuit 306 simultaneously drives three scanning lines [G1, G2, G3], and the signal detection circuit 305 reads out the accumulated charges of the pixels connected to the three driven scanning lines. The pixels connected to the three simultaneously driven scanning lines are simultaneously reset. At this time, the accumulated charges of three pixels lined up in the Y direction in Figure 3 (three pixels connected to the same signal line) are output simultaneously, and the sum of the accumulated charges of these three pixels is read. This improves the radiation detection sensitivity, enabling radiation exposure to be detected more quickly.

[0021] After that, the scanning line control circuit 306 simultaneously drives three consecutive scanning lines every three consecutive scanning lines, such as scanning lines [G7, G8, G9] and scanning lines [G13, G14, G15], and the signal detection circuit 305 reads the accumulated charges. In the next second frame (hereinafter also referred to as an even frame), the scanning line control circuit 306 simultaneously and sequentially drives three consecutive scanning lines that were not driven in the first frame. That is, the scanning line control circuit 306 simultaneously drives the scanning lines [G4, G5, G6] and the scanning lines [G10, G11, G12], and so on, sequentially executing the simultaneous driving of three consecutive scanning lines every three consecutive scanning lines. The signal detection circuit 305 reads and resets the accumulated charges of the pixels connected to the three scanning lines that were simultaneously driven. In the radiation detection drive, the above operations of the first frame and the second frame are alternately repeated to prepare for radiation exposure.

[0022] Here, the signal detection circuit 305 monitors the read-out charge (the reset charge) in order to detect the irradiation of radiation. When radiation is irradiated, charge is generated by the photodiode 303, and the output of the signal line increases. When this output exceeds a predetermined threshold, it is considered that radiation has been irradiated, the above-mentioned radiation detection drive is stopped, and the accumulation operation is started. In this way, the start of irradiation of radiation is automatically detected, and radiography begins. The smaller the threshold is, the faster the irradiation of radiation can be detected, but it is necessary to set the threshold to a relatively large value in consideration of malfunctions due to noise, etc. Therefore, there is a considerable time lag between the actual start of irradiation of radiation and the detection of irradiation by the signal detection circuit 305. In the pixel that is reset during this time lag, the charge due to the radiation irradiated from the start of irradiation to the reset cannot contribute to the output value, and the value becomes smaller than the original output value.

[0023] FIG. 5 is a schematic diagram showing the decrease in output value due to a time lag until X-ray detection when uniform X-rays are irradiated. In image 5a, one rectangle represents one pixel. Bar graph 5b represents the sum of the output values ​​of the pixels of each row of image 5a. When uniform radiation is irradiated, if there is no time lag between the start of actual radiation irradiation and the FPD 102 detecting the radiation irradiation, the sum of the output values ​​of each row will be approximately the same. FIG. 5 shows a case where radiation irradiation is started at the timing when the scanning lines [G4, G5, G6] of the even frames are driven, and radiation irradiation is detected by the signal detection circuit 305 at the scanning lines [G16, G17, G18]. In this case, as shown in bar graph 5b, the values ​​are smaller than the original output values ​​at "G4, G5, G6", "G10, G11, G12", and "G16, G17, G18" where the reset operation was performed during radiation irradiation.

[0024] The decrease in the output value depends on the time difference between the start of radiation irradiation and the start of the reset operation, and the larger this time difference, the greater the decrease in the output value. In the operation of this example, the reset operation is performed sequentially for three scanning lines at a time, starting from [G4, G5, G6]. Therefore, as shown in bar graph 5b, the decrease in the output value increases from [G4, G5, G6], where radiation irradiation is started, to [G10, G11, G12] and [G16, G17, G18]. The decrease in the output value due to the time lag until radiation detection also depends on the shooting conditions. For example, the greater the amount of radiation irradiated, the shorter the time lag before radiation detection. Therefore, the contribution of the charge discharged to detect radiation irradiation to the output value decreases, and depending on the shooting conditions, the decrease may be at a level that is visually negligible (no need to correct defective pixels). However, since the amount of radiation tends to be suppressed in consideration of the effect on the subject, the decrease in the output value due to the time lag until radiation detection should not be ignored.

[0025] The radiation image data obtained by the above-described imaging operation is sent from the FPD 102 to the imaging control device 120 and is stored at least temporarily in, for example, the image storage unit 108. Thereafter, the radiation image data is transferred to the correction coefficient calculation unit 109 and the correction unit 110, where pixels with reduced output values ​​(defective pixels) are corrected. Note that, with regard to the radiation data, scanning line information indicating the scanning line that was driven and reset when the signal detection circuit 305 of the FPD 102 detected radiation irradiation is also notified from the FPD 102 to the FPD control unit 105. Therefore, the scanning line at the time of radiation irradiation detection is known to the FPD control unit 105. Therefore, pixels that may become defective pixels can be identified by tracing back the scanning line that was driven at the time of radiation irradiation detection. The correction described below is performed only on pixels that may become defective pixels.

[0026] Before describing the correction in detail, the basic concept of the correction according to this embodiment will be described. First, the normal output value V of each pixel (hereinafter, the output value of a pixel may be referred to as a pixel value) is determined by the sum of a gain component proportional to the amount of radiation X incident on the pixel and an offset component D due to dark current or the like. If the proportionality constant is A, the relationship between the pixel value V and the amount of radiation X is expressed by the following formula (1).

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[0027] In contrast, the pixel value of the defective pixel V d In this case, a part of the radiation dose X incident on the pixel is lost due to the reset operation, and the radiation dose contributing to the pixel value is reduced by 1 / G. Therefore, the pixel value V of the defective pixel d The relationship between and radiation dose X is as follows:

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[0028] The pixel value of the defective pixel V is calculated by using equations (1) and (2). d The relationship between the pixel value V and the original pixel value V is given by the following equation (3). Therefore, if G and D in equation (3) can be estimated as correction coefficients, the pixel value V of the defective pixel can be calculated by the following equation (3). d can be corrected to the original pixel value V.

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[0029] Here, G and D can be estimated, for example, by the least squares method. However, in that case, the independent variable V d We need the dependent variable V corresponding to V, i.e., the original pixel value V. Therefore, we assume that "neighboring pixels have similar pixel values," and calculate G and D by using the values ​​of the defective pixel and the adjacent normal pixels as approximations of V.

[0030] The above method assumes that "neighboring pixels have similar pixel values." Therefore, if this assumption does not hold, that is, if "neighboring pixels do not have similar pixel values," the estimation error of G and D becomes large, and accurate correction cannot be performed. Figure 6 shows an example in which correction accuracy differs. For ease of explanation, in this example, as shown in Figure 6(a), a drive is used in which a reset operation is performed every other row. Figures 6(b) and 6(c) show line graphs in the row direction in this case. In the line graph, the black dotted line indicates the original pixel value, and the gray solid line indicates the pixel value whose output value has been reduced by the reset operation. Also, points 601 and 604 indicate pixels that have detected irradiation, and a reduction in output value has occurred in every other row in the previous rows.

[0031] Here, Fig. 6(b) shows a case where the pixel value variation is small, and for example, the original pixel value of point 601 is pixel value 602, which is not significantly different from pixel value 603 in the adjacent row. Therefore, accurate correction can be performed by using pixel value 603 as an approximate value. On the other hand, Fig. 6(c) shows a case where pixel value variation is large, and there is a large difference between original pixel value 605 of point 604 and pixel value 606 in the adjacent row. In this way, when the assumption that "nearby adjacent pixels have similar pixel values" does not hold, accurate correction cannot be performed even if pixel value 606 is simply used as an approximate value.

[0032] A typical example in which the above assumption that "neighboring pixels have similar pixel values" does not hold is when a scatter reduction grid (hereinafter, grid) is attached. FIG. 7 shows the change in pixel value when a grid is attached. FIG. 7(a) shows the case where grid stripes 701 are horizontal, and FIG. 7(b) is a line graph in the row direction in that case. In this case, lead, which has a high radiation absorption rate, and aluminum, which has a low radiation absorption rate, are arranged alternately, so the pixel value varies greatly from row to row. Therefore, the above assumption does not hold, and the correction accuracy of defective pixels (defective rows) deteriorates. On the other hand, when the row direction is parallel to the grid stripes 702 as in FIG. 7(c), no large pixel value variation occurs as in the line graph in FIG. 7(d). Therefore, in this arrangement, the grid stripes have little effect on correction.

[0033] The basic concept of the defective pixel (defective row) correction according to this embodiment has been described above. A specific correction method will now be described.

[0034] The correction coefficient calculation unit 109 executes each step of S202 to S204 in FIG. 2 to calculate the correction coefficient. In this embodiment, before calculating the correction coefficient, a weighted sum is applied to every three rows that are simultaneously reset, and a binned image in which the influence of grid stripes is eliminated is generated. FIG. 8 is a diagram showing how the influence of grid stripes is eliminated by generating a binned image. FIG. 8(b) shows a line graph in the row direction of the image 8a shown in FIG. 8(a). In a portion 801 of the line graph, there are three rows of defective pixels with reduced pixel values, every third row, but they are buried in the pixel value fluctuation of the grid stripes, making it difficult to estimate them. Therefore, as shown in FIG. 8(a), every three rows of the image 8a are binned into one row while performing weighted summation to eliminate the grid stripes, and a binned image 8b is generated. FIG. 8(c) is a diagram showing a line graph in the row direction of the binned image 8b. As shown in Fig. 8(c), in the binned image 8b, the grid stripes are removed, and only the state 802 of the missing rows with reduced pixel values ​​remains, making it possible to estimate the correction coefficients with high accuracy. In this example, in the binned image, three rows of the radiographic image are binned into one row, so that missing rows occur every other row. Therefore, in the binned image, the rows adjacent to the missing rows are used as normal rows, so that the correction coefficients for each missing row can be obtained. Then, the correction coefficients obtained from each missing row of the binned image are used to correct the three missing rows in the radiographic image before binning.

[0035] Here, in order to achieve the above object, it is first necessary to determine a weighting coefficient for removing grid stripes as a weighting coefficient used for binning three rows of a radiographic image into one row. Therefore, in S202, the correction coefficient calculation unit 109 calculates a weighting coefficient for suppressing the influence of the grid. The amplitude spectrum perpendicular to the grid stripes has a property of consolidating into a single frequency as shown in 901 of FIG. 9(a). Therefore, the influence of the grid can be suppressed by calculating the weighting coefficients (filter coefficients) of the three rows so as to remove this frequency component. For example, the weighting coefficient applied to the pixels of the center row of the three rows is a, and the weighting coefficient applied to the other two rows is b, and the weighting coefficients a and b are calculated by the following formula (4). In formula (4), g represents the grid density (lines / cm), and S represents the sampling pitch of the pixels (mm).

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[0036] Here, the amplitude response of the weighting coefficients (b, a, b) according to equation (4) is approximately 0 at frequency 902, which is the same as the frequency of the grid stripes, as shown in FIG. 9(b). Therefore, the influence of the grid stripes can be removed by performing weighted addition (filtering) using this weighting coefficient. FIG. 9(c) is a diagram showing the output value when weighted addition is performed for every three rows. In the output after binning shown on the right of FIG. 9(c), the fluctuation of the output value due to the grid stripes has been effectively removed.

[0037] In addition, although the weighting coefficient is calculated from the grid density and the sampling pitch in the formula (4), this is not limiting. For example, the weighting coefficient may be calculated from the grid frequency fg (rad / sample) on the image using the following formula (5).

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[0038] Here, the grid frequency fg can be calculated in advance from an image in which only the grid is photographed. The method of calculating the grid frequency fg is not particularly limited, but for example, the method of Patent Document 3 already applied for by the present applicant can be used. This method detects the presence, orientation, and frequency of a grid by comparing the power spectrum of a determined measurement area, but the details are publicly known from Patent Document 3, so a description thereof will be omitted here.

[0039] Next, in S203, the correction coefficient calculation unit 109 uses the calculated weighting coefficient to synthesize three consecutive rows into one row to generate a binned image. i , 3 i+1 , 3 i+2 (i=0,1,...,n), and the pixel values ​​of each jth column are denoted by V 3i,j , V 3i+1,j , V 3i+2,j Then, the pixel value after binning is B i,j is calculated using the following formula (6).

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[0040] Next, in S204, the correction coefficient calculation unit 109 calculates the correction coefficients G and D of the formula (3) from the binned image generated in S203 by regression analysis. Note that the drop in output value is the same for pixel values ​​in each row of the binned image, but is different for other rows. Therefore, the correction coefficients G and D are calculated for each row. Specifically, i,j For |j=1,2,...,n}, the normal rows B on both sides i-1,j , B i+1,j The average value of {A i,j If |j=1,2,...,n} is an estimate of the actual value, the relationship between the two is expressed by the following equation (7).

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[0041] As shown in the above formula (7), A i,j and Bi,j The relationship between these two is expressed by a linear equation with a slope G and an intercept D (1-G), and G and D can be calculated by linear regression. For example, when least squares regression is used as the linear regression method, the slope α and intercept β that minimize the error E expressed by the following equation (8) are found.

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[0042] From the slope α and intercept β obtained by equation (8), the correction coefficients G and D can be calculated by the following equation (9).

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[0043] In this embodiment, a method using least squares regression has been described, but the present invention is not limited to this method, and the correction coefficients can be calculated in the same manner using already known methods such as MA regression and RMA regression.

[0044] In this embodiment, the pixel value B i,j The actual value of is the estimated value A i,j However, when there is a steep edge, etc., there are some pixels for which this assumption does not hold. Therefore, as a measure against such outliers, known robust regression such as M estimation, LMeDS estimation, and RANSAC can be used.

[0045] The calculation method of the correction coefficients G and D for one row of defective pixels (one defective row) has been described above, but the same process is performed for all defective rows of the binning image to calculate the correction coefficients G and D for each defective row. Note that the timing at which irradiation is detected is known by notification from the FPD 102, but the timing at which radiation irradiation actually starts is unknown. Therefore, it is unclear which rows are defective, that is, which rows need to be corrected retroactively. In this embodiment, since the adjacent row where irradiation is detected is assumed to be a normal row, the correction coefficient calculation unit 109 calculates the correction coefficients G and D while tracing back rows where a reset operation has been performed in sequence from the row where irradiation is detected to the row just before the adjacent normal row. That is, the rows to be corrected are each set to be rows going back from the first row where the start of radiation irradiation is detected by automatic detection to the second row where resetting has been performed immediately after the row adjacent to the first row in the order in which resetting was performed. For example, when radiation irradiation is detected in [G16, G17, G18] of the m-th frame in FIG. 8(a), correction is performed from GB6 through GB4 and GB2 to GB9 of the m-1-th frame in the binned image shown in FIG. 8(c). As described above, the row GB7 adjacent to the row GB6 where irradiation was detected is assumed to be a normal row, and the rows after GB7 are not corrected. Note that in this example, if rows after GB7 are defective, the rows that should be treated as normal rows become defective rows, and the assumption of correction in this embodiment is lost. Therefore, it is desirable to adjust the detection sensitivity and threshold of radiation detection by the FPD 102 so that the length of the time lag that may occur in detecting the start of radiation irradiation is within a length that does not cause such a defective row under the assumed imaging conditions. Note that the range of rows to be corrected as described above is an example, and is not limited thereto. For example, each row from the row where the start of radiation irradiation was detected to a row going back a predetermined number of rows that is less than the number of rows to be corrected as described above in the order in which resetting was performed may be the row to be corrected. In this case as well, it is desirable to adjust the detection sensitivity and threshold of radiation detection by the FPD 102 so that the time lag from actual irradiation of radiation to detection of the irradiation is within the time required to reset the above-mentioned predetermined number of rows.

[0046] Next, in S205, the correction unit 110 corrects the radiographic image using the correction coefficients G and D calculated by the correction coefficient calculation unit 109. Specifically, the correction coefficient calculated from the i-th row after binning is G i , D i And B i,j The three pixels before binning are V 3i,j , V 3i+1,j , V 3i+2,j Then, each pixel value of the radiation image can be corrected by the following equation (10).

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[0047] In this manner, the missing lines in the radiographic image captured by automatic detection of the start of radiation irradiation are corrected. After that, the post-processing unit 111 performs various processes, such as a correction process for reducing grid stripes caused by the grid, a gradation process, and an emphasis process, on the radiographic image in which the missing lines have been corrected, to generate an image suitable for diagnosis. Note that a well-known correction method can be used for the correction to reduce the grid stripes in the radiographic image.

[0048] In this embodiment, an example has been described in which scanning lines are driven (reset operation is performed) every three rows in radiation detection drive, but the present invention is also applicable to a case in which four or more scanning lines are driven (reset) simultaneously. In that case, the weighting coefficient for binning N rows that are driven simultaneously (reset operation is performed) into one row may be set so that the amplitude response of the grid is approximately 0. For example, when scanning lines are driven every n rows, n being an integer of 4 or more, a method can be used in which three consecutive rows out of the n rows are added using the weighting coefficients a and b shown in equation (4) or equation (5), and then simply averaged. For example, the values ​​of n consecutive pixels in n rows that are reset simultaneously are calculated as V i (i=0, 1, 2, n-1), and binning can be performed according to equation (11).

[0049]

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[0050] In order to make the amplitude response of the grid zero, at least three consecutive pixels are required, but it is not necessary that three pixels are consecutive in the row direction (Y direction in FIG. 3) as in this embodiment. For example, it is possible to generate a binned image by combining three consecutive pixels in the diagonal direction in the three rows of images to be binned, and obtain the correction coefficient. This is particularly effective when the grid is attached diagonally with respect to the matrix arrangement of the pixels of the FPD 102. However, when binning three consecutive pixels in the diagonal direction, the weighting coefficient is obtained by multiplying the value in cos() of formula (4) by √2. Also, in this case, it is clear that n rows (n≧4) can be binned by using formula (11).

[0051] As described above, in this embodiment, in order to correct missing rows in a radiographic image captured by automatically detecting the start of radiation irradiation while simultaneously driving and resetting consecutive n rows every n rows, a binning image obtained by combining n rows of the radiographic image into one row is used. In this combination, the values ​​of n pixels arranged in the same column of consecutive n rows or the values ​​of n pixels arranged in a diagonal direction (n is an integer of 3 or more) are combined, and a weighting coefficient that suppresses grid stripes is used at this time. As a result, a correction coefficient calculated from the binning image from which the influence of the grid stripes has been removed is used to correct missing rows (missing pixels) in the radiographic image. Therefore, even when a grid is used in radiography by automatically detecting the start of radiation irradiation, it is possible to accurately correct missing pixels.

[0052] <Other embodiments> The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0053] The disclosure of this specification includes the following radiography system, method, and program. (Item 1) a holding means for holding a radiation image captured by a radiation imaging apparatus that performs radiation imaging by simultaneously driving and resetting consecutive n rows of a plurality of pixels arranged in a matrix, every n rows being equal to each other, and detecting the start of irradiation of radiation based on signals read out from the pixels; a generating means for generating a binned image by combining the n consecutive rows of the radiation image into one row using a weighting factor that suppresses the influence of an anti-scatter grid; an acquisition means for acquiring a correction coefficient for correcting pixel values ​​of a row to be corrected in the binning image based on pixel values ​​of rows adjacent to the row to be corrected in the binning image; a correction unit that corrects n rows of the radiation image corresponding to the row to be corrected based on the correction coefficient. (Item 2) 2. The information processing device according to item 1, wherein the correction coefficient is a coefficient that corrects pixel values ​​of each column in the row to be corrected so as to approach an average value of pixel values ​​of corresponding columns in rows on both sides of the row to be corrected. (Item 3) 2. The information processing device according to item 1, wherein the row to be corrected is a row on which the reset has been executed, from the row on which the start of the radiation irradiation was detected to a row going back a predetermined number of rows in the order in which the reset was executed. (Item 4) 2. The information processing device according to item 1, wherein the row to be corrected is a row on which the reset has been performed, going back in order of the resetting from the row on which the start of the radiation irradiation was detected to the row on which the resetting was performed immediately after the row adjacent to the detected row. (Item 5) n is an integer of 3 or more, 5. The information processing device according to any one of items 1 to 4, wherein the generating means obtains a pixel value of the binned image by combining values ​​of n pixels arranged in the same column of the n consecutive rows of the radiological image or values ​​of n pixels arranged in a diagonal direction of the n consecutive rows of the radiological image using the weighting coefficient. (Item 6) 6. The information processing device according to any one of items 1 to 5, wherein the generating means generates the binned image by weighting and adding n pixel values ​​using a weighting coefficient that sets an amplitude response of a grid frequency in a radiation image obtained by radiation imaging using the anti-scatter grid to approximately 0. (Item 7) The weighted sum is calculated by dividing the values ​​of three consecutive pixels by V i+k (k=0,1,2), g is the grid density (lines / cm), and S is the pixel sampling pitch (mm), the pixel value B of the binned image is expressed as follows: 7. The information processing device according to item 6, wherein the information processing device acquires the image data by using TIFF2025065993000013.tif59108. (Item 8) The weighted sum is calculated by dividing the values ​​of three consecutive pixels by V i+k (k=0, 1, 2), and the grid frequency in the radiation image is fg (rad / sample), the pixel value B of the binned image is expressed as 7. The information processing device according to item 6, wherein the information processing device acquires the image data by using TIFF2025065993000014.tif5073. (Item 9) 9. The information processing device according to any one of items 1 to 8, wherein the correction means performs correction on the radiation image corrected using the correction coefficient to reduce grid stripes caused by the anti-scatter grid. (Item 10) a radiation imaging apparatus that simultaneously drives and resets consecutive n rows of a plurality of pixels arranged in a matrix, and detects the start of irradiation of radiation based on signals read out from the pixels, thereby performing radiation imaging; an information processing device including a storage unit for storing a radiation image captured by the radiation imaging device; The information processing device, a generating means for generating a binned image by combining the n consecutive rows of the radiation image into one row using a weighting factor that suppresses the influence of an anti-scatter grid; an acquisition means for acquiring a correction coefficient for correcting pixel values ​​of a row to be corrected in the binning image based on pixel values ​​of rows adjacent to the row to be corrected in the binning image; a correction unit that corrects n rows of the radiation image corresponding to the row to be corrected based on the correction coefficient. (Item 11) a radiation image captured by a radiation imaging device that performs radiation imaging by simultaneously driving and resetting consecutive n rows of a plurality of pixels arranged in a matrix, and detecting the start of irradiation of radiation based on a signal that is read out from the pixels; generating a binned image by combining the n consecutive rows of the radiological image into one row using a weighting factor that reduces the effect of an anti-scatter grid; obtaining a correction coefficient for correcting pixel values ​​of a row to be corrected in the binned image based on pixel values ​​of rows adjacent to the row to be corrected in the binned image; A method for controlling an information processing apparatus, comprising: correcting n rows of the radiographic image corresponding to the row to be corrected based on the correction coefficient, thereby correcting the radiographic image. (Item 12) A program for causing an information processing device to function as each of the means of the information processing device described in any one of items 1 to 9.

[0054] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0055] 100: Radiation imaging system, 101: Radiation generation unit, 102: FPD, 103: Subject, 104: Radiation generation device, 105: FPD control unit, 106: Monitor, 107: Operation unit, 108: Image storage unit, 109: Correction coefficient calculation unit, 110: Correction unit, 111: Post-processing unit

Claims

1. a holding means for holding a radiation image captured by a radiation imaging apparatus which performs radiation imaging by simultaneously driving and resetting consecutive n rows of a plurality of pixels arranged in a matrix, every n rows being equal to each other, and detecting the start of irradiation of radiation based on a signal read out from the pixels; a generating means for generating a binned image by combining the n consecutive rows of the radiation image into one row using a weighting factor that suppresses the influence of an anti-scatter grid; an acquisition means for acquiring a correction coefficient for correcting pixel values ​​of a row to be corrected in the binning image based on pixel values ​​of rows adjacent to the row to be corrected in the binning image; and a correction unit configured to correct n rows of the radiation image corresponding to the row to be corrected based on the correction coefficient.

2. The information processing apparatus according to claim 1 , wherein the correction coefficient is a coefficient for correcting pixel values ​​of each column in the row to be corrected so as to approach an average value of pixel values ​​of corresponding columns in rows on both sides of the row to be corrected.

3. The information processing apparatus according to claim 1 , wherein the rows to be corrected are rows on which the reset has been executed, from the row on which the start of irradiation of the radiation was detected to a row going back a predetermined number of rows in the order in which the reset was executed.

4. 2 . The information processing device according to claim 1 , wherein the rows to be corrected are rows on which the reset was performed, going back in order of the resetting from the row on which the start of the radiation irradiation was detected to the row on which the reset was performed immediately after the row adjacent to the detected row.

5. n is an integer of 3 or more, 2. The information processing device according to claim 1, wherein the generating means obtains pixel values ​​of the binned image by combining values ​​of n pixels arranged in the same column of the n consecutive rows of the radiographic image or values ​​of n pixels arranged in a diagonal direction of the n consecutive rows of the radiographic image using the weighting coefficient.

6. 2. The information processing device according to claim 1, wherein the generating means generates the binned image by weighting and adding n pixel values ​​using a weighting coefficient that sets an amplitude response of a grid frequency in a radiation image obtained by radiation imaging using the anti-scatter grid to approximately 0.

7. The weighted sum is calculated by dividing the values ​​of three consecutive pixels by V ｉ＋ｋ (k=0, 1, 2), g is the density of the grid (lines / cm), and S is the sampling pitch of the pixels (mm), the pixel value B of the binned image is expressed as follows: The information processing apparatus according to claim 6 , wherein the information is acquired by

8. The weighted sum is calculated by dividing the values ​​of three consecutive pixels by V ｉ＋ｋ (k=0, 1, 2), and the grid frequency in the radiation image is fg (rad / sample), the pixel value B of the binned image is expressed as The information processing apparatus according to claim 6 , wherein the information is acquired by

9. The information processing apparatus according to claim 1 , wherein the correction means performs a correction for reducing grid stripes caused by the anti-scatter grid on the radiation image corrected using the correction coefficient.

10. a radiation imaging apparatus that simultaneously drives and resets consecutive n rows of a plurality of pixels arranged in a matrix, and detects the start of irradiation of radiation based on signals read out from the pixels, thereby performing radiation imaging; an information processing device including a storage unit for storing a radiation image captured by the radiation imaging device; The information processing device, a generating means for generating a binned image by combining the n consecutive rows of the radiation image into one row using a weighting factor that suppresses the influence of an anti-scatter grid; an acquisition means for acquiring a correction coefficient for correcting pixel values ​​of a row to be corrected in the binning image based on pixel values ​​of rows adjacent to the row to be corrected in the binning image; a correction unit that corrects n rows of the radiation image corresponding to the row to be corrected based on the correction coefficient.

11. a radiation image captured by a radiation imaging device that performs radiation imaging by simultaneously driving and resetting consecutive n rows of a plurality of pixels arranged in a matrix, and detecting the start of irradiation of radiation based on a signal read out from the pixels; generating a binned image by combining the n consecutive rows of the radiological image into one row using a weighting factor that reduces the effect of an anti-scatter grid; obtaining a correction coefficient for correcting pixel values ​​of a row to be corrected in the binned image based on pixel values ​​of rows adjacent to the row to be corrected in the binned image; A method for controlling an information processing apparatus, comprising: correcting n rows of the radiographic image corresponding to the row to be corrected based on the correction coefficient.

12. A program for causing an information processing device to function as each of the means of the information processing device according to any one of claims 1 to 9.

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