Radiation imaging apparatus

Abstract

To enable offset correction capable of reducing a residual image and a random noise.SOLUTION: A radiation imaging apparatus includes: image acquisition means that alternately acquires a radiation image obtained by imaging with radiation emitted and an offset image obtained by imaging with radiation not emitted; and offset correction means that uses a plurality of offset images acquired by the image acquisition means to correct one radiation image acquired by the image acquisition means.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a radiation imaging device, a radiation imaging system, a processing method of a radiation imaging device, and a program.

Background Art

[0002] As a radiation imaging device that captures a radiation image using radiation (such as X-rays) transmitted through a subject, a radiation imaging device capable of displaying a radiation image in real time has become widespread. In addition, a radiation imaging device using an FPD (Flat Panel Detector) has been proposed.

[0003] In an FPD, a minute radiation detector in which a solid-state photodetector sandwiching an amorphous semiconductor between a transparent conductive film and a conductive film and a scintillator that converts radiation into visible light are stacked is arranged in a matrix on a quartz glass substrate. Further, as the solid-state photodetector, those using a photodetector such as a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) are known. In addition, as a radiation detector, there is known one that directly detects radiation with a solid-state photodetector without using a scintillator.

[0004] The FPD detects the amount of radiation irradiated during an arbitrary accumulation time as an electric charge amount. Therefore, when a charge unrelated to the radiation irradiation exists in the radiation detector during the imaging of a radiation image of a subject, this charge is superimposed on the radiation image as noise, leading to a deterioration in the image quality of the radiation image.

[0005] For example, as an example of a charge that becomes noise, there is a residual charge that remains based on the characteristics of a solid-state photodetector or a scintillator after the imaging of a previously captured radiation image. Another example of a charge that becomes noise is a dark current caused by a charge generated in the solid-state photodetector mainly due to the influence of temperature. In addition, the image quality of the radiation image also deteriorates due to fixed noise caused by defects inherent in the radiation detector.

[0006] When taking a radiation image of a subject, charges of residual charge and dark current components are also accumulated in proportion to the accumulation time of the image irradiated with radiation, and the image quality of the radiation image deteriorates. Therefore, in taking a radiation image of a subject, offset correction is performed to correct offset components due to residual charge, dark current charge, and fixed noise accumulated during imaging. Generally, offset correction is performed by using an image (non-exposure image) obtained by imaging in a state where no radiation is irradiated as an offset image and subtracting the offset image from the radiation image.

[0007] There are a plurality of such offset correction methods. For example, (1) there is a method (fixed offset correction) of performing offset correction by subtracting non-exposure image data obtained before taking a radiation image of a subject from the radiation image as an offset image.

[0008] Also, (2) there is a method (intermittent offset correction) of performing offset correction by alternately taking a radiation image of a subject and obtaining a non-exposure image (offset image) and subtracting the offset image from the radiation image.

[0009] Here, when listing the features of the method (1) and the method (2), in the method (1), since a plurality of offset images are obtained and averaged before taking a radiation image of a subject, it is possible to reduce random noise. Therefore, imaging at a low dose is possible.

[0010] However, in the method (1), since an offset image is obtained before radiation irradiation, there is a problem that afterimages cannot be sufficiently corrected. In addition, the dark current charge accumulated during imaging changes due to the influence of the temperature of the radiation detector, imaging conditions, or deterioration of the sensor over time. Therefore, when an offset image is obtained before taking a radiation image of a subject as in the method (1), there is a problem that sufficient accuracy of offset correction cannot be obtained.

[0011] In the method of (2), the taking of a radiation image of a subject and the acquisition of a non-exposure image (offset image) are alternately performed, and since subtraction is performed using the non-exposure image including an afterimage, the afterimage can be reduced. However, in the method of (2), since subtraction is performed using one non-exposure image from the radiation image, there is a problem that random noise is large.

[0012] As a technique for maintaining the accuracy of offset correction, the technique disclosed in Patent Document 1 has been proposed. Patent Document 1 discloses a technique for selecting an optimal offset correction method according to whether or not a stabilization mechanism for suppressing the temperature change of an FPD functions effectively.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0014] When the technique described in Patent Document 1 is applied to a radiation imaging apparatus, optimization can be achieved by switching between fixed offset correction and intermittent offset correction according to the state. However, reduction of random noise itself, which is an original problem of intermittent offset correction, is not achieved.

[0015] An object of the present disclosure is to enable offset correction capable of reducing an afterimage and random noise.

Means for Solving the Problems

[0016] The radiation imaging apparatus includes image acquisition means for alternately acquiring a radiation image captured while radiation is being irradiated and an offset image captured while no radiation is being irradiated, and offset correction means for correcting one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means.

Advantages of the Invention

[0017] According to the present disclosure, it is possible to perform offset correction capable of reducing afterimages and random noise.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments will be described with reference to the drawings.

[0020] (First Embodiment) FIG. 1 is a diagram showing a configuration example of a radiation imaging system 150 according to the first embodiment. The radiation imaging system 150 includes a radiation imaging apparatus 100, a radiation generator 300, a radiation source 301, an operation UI 302, a control device 400, a display unit 406, and an operation UI 407.

[0021] The radiation imaging device 100 includes a radiation detection unit 200. The radiation source 301 irradiates radiation. The radiation generation device 300 controls the radiation source 301. The operation UI 302 is connected to the radiation generation device 300. Note that radiation includes not only X-rays but also α-rays, β-rays, γ-rays, and various particle beams.

[0022] The control device 400 has a radiation imaging application 404. The radiation imaging application 404 controls the radiation imaging device 100 and the radiation generation device 300, and is capable of collecting and displaying captured images from the radiation imaging device 100.

[0023] The radiation imaging device 100 includes a control unit 101, a power supply unit 114, and a radiation detection unit 200. The control unit 101 controls imaging and communication. The radiation detection unit 200 detects radiation and generates image data.

[0024] The radiation detection unit 200 has two-dimensionally distributed imaging elements and a scintillator. The scintillator converts the radiation (e.g., X-rays) that reaches the radiation detection unit 200 into light. Then, the imaging elements detect the two-dimensional distribution of the light converted by the scintillator and generate radiation image data.

[0025] This radiation detection unit 200 is a flat panel detector (FPD). Here, as an example, it is assumed that the scintillator emits light in proportion to the intensity of the incident radiation, and the imaging elements output high pixel values in proportion to the emission intensity of the scintillator.

[0026] The control unit 101 includes an image acquisition unit 102 that acquires a radiation image from the radiation detection unit 200, an image processing unit 103, a storage unit 107, and a communication unit 113.

[0027] The image acquisition unit 102 reads charges from each imaging element of the radiation detection unit 200, and when the reading of charges from all the imaging elements is completed, the acquisition of the radiation image is completed. The image acquisition unit 102 stores the acquired radiation image 108 in the storage unit 107.

[0028] The image processing unit 103 includes an offset correction unit 104, a gain correction unit 105, and an offset change amount determination unit 106.

[0029] The offset correction unit 104 performs offset correction on the radiation image 108 acquired by the image acquisition unit 102 and stored in the storage unit 107. The gain correction unit 105 performs gain correction. The offset change amount determination unit 106 determines the magnitude of the change amount of the immediately post-capture offset image 111.

[0030] Note that the image processing unit 103 may have a correction unit that performs correction processing other than these. Also, the offset correction unit 104 may execute generation processing of an offset image. Further, the gain correction unit 105 may perform generation processing of gain correction data 110.

[0031] The storage unit 107 stores the radiation image 108 acquired by the image acquisition unit 102 and the pre-offset image 109 when performing offset correction on the radiation image 108. Here, it is assumed that the pre-offset image 109 is an image generated in advance before the imaging is performed. Also, the pre-offset image 109 is not necessarily limited to one, and may be stored, for example, for each imaging image size or radiation accumulation time at the time of imaging.

[0032] Furthermore, the storage unit 107 holds the gain correction data 110 generated in advance by the gain correction unit 105. Note that the gain correction data 110 is not necessarily limited to one, and may be held, for example, for each imaging image size at the time of imaging.

[0033] Furthermore, the storage unit 107 stores the immediately post-capture offset image 111. The immediately post-capture offset image 111 is an image captured by the image acquisition unit 102 immediately after radiation imaging under no radiation exposure.

[0034] The control device 400 includes a radiation imaging device control unit 401, a radiation generating device control unit 402, a communication control unit 403, a radiation imaging application 404, and a power supply 405. The radiation generating device 300, a display unit 406, and an operation UI (such as a keyboard and a mouse) 407 are connected to the control device 400.

[0035] The radiation imaging device control unit 401 controls the image acquisition timing, conditions, etc. of the radiation imaging device 100. The radiation generating device control unit 402 controls the radiation irradiation conditions, etc. of the radiation generating device 300. The communication control unit 403 controls the communication with respect to the radiation imaging device 100 and the radiation generating device 300. The radiation imaging application 404 is as described above.

[0036] The display unit 406 displays the captured image and capture information. The operation UI 407 is a UI for operating the radiation imaging application 404.

[0037] Information communication is possible between the control device 400 and the radiation imaging device 100, and between the control device 400 and the radiation generating device 300 by any one or a plurality of means such as cable connection communication using standards such as RS232C, USB, and Ethernet, a dedicated signal line, and wireless communication.

[0038] Between the control device 400 and the radiation imaging device 100, for example, control communication such as image data, image acquisition condition setting, and device state acquisition is performed. Also, between the control device 400 and the radiation generating device 300, for example, control communication such as radiation irradiation condition setting, device state acquisition, and actual irradiation information is performed.

[0039] The radiation generating device 300 controls the radiation source 301 and generates radiation. The radiation imaging device 100 is communicably connected to the radiation generating device 300 via the control device 400.

[0040] FIG. 2 is a diagram showing an intermittent offset correction method of the radiation imaging apparatus 100. Intermittent offset correction is a correction method in which, for each frame during moving image shooting, a radiation image 108 and an immediately after imaging offset image 111 immediately after it are alternately acquired, the offset correction unit 104 takes the difference between the above two images, and generates an offset-corrected radiation image.

[0041] The image acquisition unit 102 acquires, for each frame, a radiation image 108 generated by the radiation detection unit 200 when irradiating radiation (X-rays), and an immediately after imaging offset image 111 generated by the radiation detection unit 200 when not irradiating radiation (X-rays) immediately after that. Then, the image acquisition unit 102 stores the acquired radiation image 108 and immediately after imaging offset image 111 in the storage unit 107.

[0042] The offset correction unit 104 generates, for each frame, the difference between the radiation image 108 and the immediately after imaging offset image 111 as an offset-corrected radiation image.

[0043] FIG. 3 is a diagram showing averaging intermittent offset correction using a plurality of frames of the radiation imaging apparatus 100. In the averaging intermittent offset correction using a plurality of frames, similar to the intermittent offset correction during moving image shooting, the radiation image 108 and the immediately after imaging offset image 111 are alternately acquired.

[0044] In intermittent offset correction, one immediately after imaging offset image 111 is used for offset correction, whereas in averaging intermittent offset correction, an immediately after imaging offset image obtained by averaging a plurality of immediately after imaging offset images 111 acquired in the past is used.

[0045] The image acquisition unit 102 acquires, for each frame, a radiation image 108 generated by the radiation detection unit 200 when irradiating radiation (X-rays), and an immediately after imaging offset image 111 generated by the radiation detection unit 200 when not irradiating radiation (X-rays) immediately after that. Then, the image acquisition unit 102 stores the acquired radiation image 108 and immediately after imaging offset image 111 in the storage unit 107.

[0046] The offset correction unit 104 obtains an immediately after imaging offset image obtained by averaging the immediately after imaging offset images 111 of a plurality of past frames. Then, the offset correction unit 104 generates, for each frame, a difference between the radiation image 108 and the averaged immediately after imaging offset image as an offset-corrected radiation image.

[0047] FIG. 4 is a flowchart showing a processing method of the radiation imaging apparatus 100 according to the present embodiment. Hereinafter, an example of averaging intermittent offset correction using a plurality of frames in FIG. 3 will be shown.

[0048] In step S500, the control unit 101 sets the frame number n and the number m of immediately after imaging offset images to be stored to 0.

[0049] In step S501, the control unit 101 controls the radiation detection unit 200 to start video shooting.

[0050] In step S502, the image acquisition unit 102 acquires the n-th frame radiation image 108 generated by the radiation detection unit 200 when radiation is irradiated, and stores it in the storage unit 107.

[0051] In step S503, the image acquisition unit 102 acquires the n-th frame immediately after imaging offset image 111 generated by the radiation detection unit 200 when radiation is not irradiated, and stores it in the storage unit 107 so that the past history remains. Here, as an example, the image acquisition unit 102 stores the immediately after imaging offset image 111 so that the history of the immediately after imaging offset images 111 for the past 5 frames remains. Next, the control unit 101 increments the number m of immediately after imaging offset images to be stored. As an example, the maximum value of m is 5.

[0052] In step S504, the offset change amount determination unit 106 determines whether the change amount between the past immediately after imaging offset image 111 and the latest immediately after imaging offset image 111 is smaller than the first threshold value. For example, when the offset change amount determination unit 106 is shooting the fourth frame in FIG. 3, it compares the fourth immediately after imaging offset image with the third immediately after imaging offset image, or compares the fourth immediately after imaging offset image with the second immediately after imaging offset image.

[0053] Note that the above-mentioned latest immediately after imaging offset image 111 is not limited to the latest one, and may be, for example, one frame before the latest. The above-mentioned latest immediately after imaging offset image 111 is the immediately after imaging offset image 111 captured at the first time, and the above-mentioned past immediately after imaging offset image 111 may be the immediately after imaging offset image 111 captured at the second time before the first time.

[0054] If it is determined that the change amount is smaller than the first threshold value, the process proceeds to step S505. If it is determined that the change amount is not smaller than the first threshold value, the process proceeds to step S507.

[0055] In step S505, the offset correction unit 104 generates an integrated image obtained by adding the immediately after imaging offset images 111 for m frames including the latest immediately after imaging offset image 111 acquired in step S503 and the past immediately after imaging offset image 111.

[0056] In step S506, the offset correction unit 104 first divides the integrated image by m to calculate an averaged offset image. Next, the offset correction unit 104 obtains the difference between the averaged offset image and the radiation image 108 of the nth frame as the offset-corrected radiation image of the nth frame. Then, the process proceeds to step S508.

[0057] However, immediately after imaging, the offset image 111 may change significantly due to the occurrence of afterimages caused by high radiation exposure or temperature changes within the radiation imaging apparatus 100. In the averaged image of multiple frames using the immediately after-imaging offset image 111 with a large amount of change, a correct averaged offset image cannot be generated. Therefore, in step S504, if it is determined that the amount of change is not less than the first threshold value, the process proceeds to step S507.

[0058] In step S507, the offset correction unit 104 corrects the number m of immediately after-imaging offset images stored to 1. Thereafter, the process proceeds to step S505. In that case, in step S505, since m is 1, the offset correction unit 104 sets the immediately after-imaging offset image 111 of the latest nth frame as the integrated image and proceeds to step S506.

[0059] In that case, in step S506, the offset correction unit 104 first divides the integrated image by m = 1 to calculate the averaged offset image. The averaged offset image becomes the same as the immediately after-imaging offset image 111 of the nth frame. Next, the offset correction unit 104 obtains the difference between the immediately after-imaging offset image 111 of the nth frame and the radiation image 108 of the nth frame as the offset-corrected radiation image of the nth frame. This process is equivalent to the intermittent offset correction in FIG. 2.

[0060] In step S508, the control unit 101 determines whether or not the shooting has ended. If it is determined that the shooting has not ended, the control unit 101 increments the frame number n, returns to step S502, and repeats the above process. If it is determined that the shooting has ended, the process of the flowchart in FIG. 4 ends.

[0061] FIG. 5 is a diagram showing an example in which the storage unit 107 has five storage areas. The five storage areas are the first to fifth storage areas, and can store five immediately after-imaging offset images 111.

[0062] The upper part of FIG. 5 corresponds to step S502 in FIG. 4. The radiation generator 300 controls the radiation source 301 to irradiate radiation. In this state, the radiation detection unit 200 accumulates charges based on the radiation. The image acquisition unit 102 reads out the charges accumulated in the radiation detection unit 200 and records the radiation image 108 in the storage unit 107.

[0063] The lower part of FIG. 5 corresponds to step S503 in FIG. 4. The radiation generator 300 controls the radiation source 301 not to irradiate radiation. In this state, the radiation detection unit 200 accumulates charges. The image acquisition unit 102 moves the immediately-after-imaging offset images 111 for the past 4 frames stored in the first to fourth storage areas of the storage unit 107 to the second to fifth storage areas. Then, the image acquisition unit 102 reads out the charges accumulated in the radiation detection unit 200 and records the immediately-after-imaging offset image 111 in the first storage area of the storage unit 107.

[0064] In step S505, the offset correction unit 104 generates an integrated image by adding the immediately-after-imaging offset images 111 for 5 frames stored in the first to fifth storage areas of the storage unit 107.

[0065] In step S506, the offset correction unit 104 first divides the integrated image by m = 5 to calculate an averaged offset image. Next, the offset correction unit 104 obtains the difference between the averaged offset image and the radiation image 108 as an offset-corrected radiation image.

[0066] The communication unit 113 transmits the offset-corrected radiation image to the control device 400.

[0067] Here, a configuration in which the storage unit 107 has 5 storage areas is shown, but it is not limited to 5. The storage unit 107 has a configuration for storing a plurality of immediately-after-imaging offset images 111. For example, in FIG. 5, the consecutive immediately-after-imaging offset images 111 have a first-in-first-out structure from the first storage area to the fifth storage area, and all storage areas are reset to 0 at the start of operation.

[0068] After the start of imaging, the image acquisition unit 102 records the latest immediately after imaging offset image 111 in the first storage area, moves the immediately after imaging offset image 111 originally in the first storage area to the second storage area, and moves the immediately after imaging offset image 111 in the second storage area to the third storage area. Then, the image acquisition unit 102 moves the immediately after imaging offset image 111 in the third storage area to the fourth storage area, and moves the immediately after imaging offset image 111 in the fourth storage area to the fifth storage area. Then, the image acquisition unit 102 deletes the oldest immediately after imaging offset image 111 recorded in the fifth storage area previously.

[0069] Note that the implementation means is an example and is not limited to this as long as images of a plurality of frames can be updated. For example, the storage unit 107 may use a ring buffer.

[0070] Finally, the offset correction unit 104 integrates the immediately after imaging offset images 111 for the acquired frames and performs division by the number of acquired frames to generate an averaged immediately after imaging offset image.

[0071] As described above, the image acquisition unit 102 alternately acquires the radiation image 108 imaged in the state where the radiation in step S502 is irradiated and the immediately after imaging offset image 111 imaged in the state where the radiation in step S503 is not irradiated.

[0072] First, the process when it is determined in step S504 that the amount of change is small will be described. In that case, in steps S505 and S506, the offset correction unit 104 corrects one radiation image 108 acquired by the image acquisition unit 102 using an image obtained by averaging a plurality of immediately after imaging offset images 111 acquired by the image acquisition unit 102.

[0073] Specifically, the offset correction unit 104 obtains the difference between one radiation image 108 acquired by the image acquisition unit 102 and an image obtained by averaging a plurality of immediately after imaging offset images 111 acquired by the image acquisition unit 102 as the radiation image after offset correction.

[0074] Next, the processing when it is determined in step S504 that the amount of change is not small will be described. In that case, in steps S505 and S506, the offset correction unit 104 corrects one radiation image 108 acquired by the image acquisition unit 102 using one immediately-after-imaging offset image 111 acquired by the image acquisition unit 102.

[0075] As described above, according to the present embodiment, when the amount of change between the past immediately-after-imaging offset image 111 and the latest immediately-after-imaging offset image 111 is smaller than the threshold value, the offset correction unit 104 performs the averaging intermittent offset correction of FIG. 3. On the other hand, when the amount of change between the past immediately-after-imaging offset image 111 and the latest immediately-after-imaging offset image 111 is not smaller than the threshold value, the offset correction unit 104 performs the intermittent offset correction of FIG. 2.

[0076] Since the intermittent offset correction uses only the immediately-after-imaging offset image 111 for one frame, there is a problem that the random noise is large. According to the present embodiment, the radiation imaging apparatus 100 can achieve both reduction of afterimages and reduction of random noise by the above-described processing.

[0077] (Second Embodiment) FIG. 6 is a diagram showing a processing method of the radiation imaging apparatus 100 according to the second embodiment. Hereinafter, a method of dividing the pixel region of the radiation detection unit 200 into regions and checking the amount of change in each region will be shown.

[0078] FIG. 6 shows a case where the pixel region of the radiation detection unit 200 is divided into four regions. The offset change amount determination unit 106 generates a difference image between the immediately-after-imaging offset image 111 of the past (n - 1)-th frame and the immediately-after-imaging offset image 111 of the latest n-th frame, calculates the average value, the maximum value, or the minimum value in each region of the difference image, and determines the offset change amount.

[0079] The offset change amount determination unit 106 can make the determination in step S504 based on the average value. For example, in step S504, the offset change amount determination unit 106 generates a difference image between the latest immediately-after-imaging offset image 111 and the past immediately-after-imaging offset image 111. Then, the offset change amount determination unit 106 compares, for each region, the average value of each of the plurality of regions obtained by dividing the above difference image with 1% of the average value of each of the plurality of regions obtained by dividing one of the radiographic images 108 in step S502. 1% of the average value of each of the plurality of regions obtained by dividing the above radiographic image 108 is an example of a second threshold value, and it may be a value based on the average value of each of the plurality of regions obtained by dividing the above radiographic image 108.

[0080] For example, the offset change amount determination unit 106 compares the average value of region 1 obtained by dividing the above difference image with 1% of the average value of region 1 obtained by dividing the above one radiographic image 108. Also, the offset change amount determination unit 106 compares the average value of region 2 obtained by dividing the above difference image with 1% of the average value of region 2 obtained by dividing the above one radiographic image 108. Also, the offset change amount determination unit 106 compares the average value of region 3 obtained by dividing the above difference image with 1% of the average value of region 3 obtained by dividing the above one radiographic image 108. Also, the offset change amount determination unit 106 compares the average value of region 4 obtained by dividing the above difference image with 1% of the average value of region 4 obtained by dividing the above one radiographic image 108.

[0081] If the average value of any of the regions among the average values of each of the plurality of regions obtained by dividing the above difference image is not less than 1% of the average value of each of the plurality of regions obtained by dividing the above one radiographic image 108, the offset change amount determination unit 106 proceeds to step S507. For example, if the average value of region 2 of the difference image in FIG. 6 is greater than 1% of the average value of region 2 of the radiographic image 108, the offset change amount determination unit 106 determines that there has been a large change in the latest immediately-after-imaging offset image 111 and proceeds to step S507.

[0082] Further, when the average value of all regions among the average values of the plurality of regions obtained by dividing the above differential image is less than 1% of the average value of the plurality of regions obtained by dividing the above one radiographic image 108, the offset change amount determination unit 106 proceeds to step S505.

[0083] Incidentally, the second threshold value described above may be 1% of the average value of the one radiographic image 108 in step S502. In that case, when the average value of all regions among the average values of the plurality of regions obtained by dividing the above differential image is less than the second threshold value, the offset change amount determination unit 106 proceeds to step S505. Further, when the average value of any one of the regions among the average values of the plurality of regions obtained by dividing the above differential image is not less than the second threshold value, the offset change amount determination unit 106 proceeds to step S507. Here, the second threshold value is, for example, 1% of the average value of the one radiographic image 108 as described above.

[0084] Further, the offset change amount determination unit 106 may make the determination in step S504 based on the minimum value and the maximum value. In step S504, the offset change amount determination unit 106 generates a differential image between the immediately post-capture offset image 111 and the past immediately post-capture offset image 111. Then, the offset change amount determination unit 106 compares, for each region, the difference between the minimum value and the maximum value of the plurality of regions obtained by dividing the above differential image with 1% of the average value of the plurality of regions obtained by dividing the one radiographic image 108 in step S502. 1% of the average value of the plurality of regions obtained by dividing the above radiographic image 108 is an example of a third threshold value, and may be a value based on the average value of the plurality of regions obtained by dividing the above radiographic image 108.

[0085] The offset change amount determination unit 106 proceeds to step S507 when the difference between the minimum value and the maximum value of any of the regions obtained by dividing the above differential image is not less than 1% of the average value of the regions obtained by dividing the above radiation image 108. For example, when the difference between the minimum value and the maximum value of region 3 in the differential image of FIG. 6 is greater than 1% of the average value of the radiation image 108, the offset change amount determination unit 106 determines that there has been a large change in the offset image 111 immediately after the latest imaging, and proceeds to step S507.

[0086] Also, when the differences between the minimum value and the maximum value of all of the regions obtained by dividing the above differential image are less than 1% of the average value of the regions obtained by dividing the above one radiation image 108, the offset change amount determination unit 106 proceeds to step S505.

[0087] Note that the above third threshold value may be 1% of the average value of one radiation image 108 in step S502. In that case, when the differences between the minimum value and the maximum value of all of the regions obtained by dividing the above differential image are less than the third threshold value, the offset change amount determination unit 106 proceeds to step S505. Also, when the difference between the minimum value and the maximum value of any of the regions obtained by dividing the above differential image is not less than the third threshold value, the offset change amount determination unit 106 proceeds to step S507. The third threshold value is, for example, 1% of the average value of one radiation image 108 in step S502 as described above.

[0088] (Third Embodiment) FIG. 7 is a diagram showing a processing method of the radiation imaging apparatus 100 according to the third embodiment. Hereinafter, an example of performing weighting and averaging on the offset image 111 immediately after past imaging will be shown.

[0089] In the offset change amount determination unit 106, even when it is determined that the offset change amount is small by comparing the latest immediately after imaging offset image 111 with the past immediately after imaging offset image 111, it is considered that the older the image, the more likely the deviation of the immediately after imaging offset image 111 is to increase. For this reason, when averaging a plurality of frames of consecutive past immediately after imaging offset images 111, by reducing the weighting coefficient for older images, it is possible to suppress random noise reduction during averaging and temporal changes.

[0090] In steps S505 and S506, the offset correction unit 104 multiplies each of the immediately after imaging offset images X1 to X5 for 5 frames by a weighting coefficient and adds them as follows to calculate the averaged offset image Y.

[0091] Y = X1×0.47 + X2×0.35 + X3×0.14 + X4×0.03 + X5×0.01

[0092] Here, the weighting coefficient is smaller for the older immediately after imaging offset image X5. Y is the weighted averaged offset image. X1 is the latest immediately after imaging offset image 111. X2 to X5 are the past immediately after imaging offset images 111.

[0093] For example, the weighting coefficient of the immediately after imaging offset image X1 is 0.47. The weighting coefficient of the immediately after imaging offset image X2 is 0.35. The weighting coefficient of the immediately after imaging offset image X3 is 0.14. The weighting coefficient of the immediately after imaging offset image X4 is 0.03. The weighting coefficient of the immediately after imaging offset image X5 is 0.01.

[0094] Further, the offset correction unit 104 may use the latest immediately after imaging offset image X1 and the past immediately after imaging offset images X2 to X5, multiply each of the images X1 to X5 by a coefficient and calculate recursively (recursively), and generate an averaged offset image.

[0095] As described above, in steps S505 and S506, the offset correction unit 104 calculates the averaged offset image Y based on the above formula. The offset correction unit 104 corrects a single radiation image 108 acquired by the image acquisition unit 102 using the averaged offset image Y obtained by averaging a plurality of immediately-after-capture offset images X1 to X5 acquired by the image acquisition unit 102 with weighting factors. The weighting factors for the plurality of immediately-after-capture offset images X1 to X5 are smaller for older immediately-after-capture offset images X5.

[0096] Specifically, the offset correction unit 104 obtains, as the radiation image after offset correction, the difference between a single radiation image 108 acquired by the image acquisition unit 102 and the averaged offset image Y obtained by averaging a plurality of immediately-after-capture offset images X1 to X5 acquired by the image acquisition unit 102 with weighting factors.

[0097] As described above, according to the first to third embodiments, the radiation imaging apparatus 100 can reduce afterimages and further reduce random noise by the averaged intermittent offset correction of FIG. 3.

[0098] (Other Embodiments) The present disclosure can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

[0099] Note that the above-described embodiments are merely specific examples for implementing the present disclosure, and the technical scope of the present disclosure is not limitedly interpreted by these. That is, the present disclosure can be implemented in various forms without departing from its technical idea or its main features.

[0100] The disclosure of the present embodiment includes the following configurations, methods, and programs. (Configuration 1) Image acquisition means for alternately acquiring a radiation image captured while being irradiated with radiation and an offset image captured while not being irradiated with radiation; Offset correction means for correcting one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means; A radiation imaging apparatus, characterized by comprising: (Configuration 2) The offset correction means: In the first case, corrects one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means; In the second case, corrects one radiation image acquired by the image acquisition means using one offset image acquired by the image acquisition means. The radiation imaging apparatus according to Configuration 1, characterized by this. (Configuration 3) The offset correction means: When the amount of change between the offset image captured at the first time and the offset image captured at the second time before the first time is in the first case, corrects one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means; When the amount of change between the offset image captured at the first time and the offset image captured at the second time before the first time is in the second case, corrects one radiation image acquired by the image acquisition means using one offset image acquired by the image acquisition means. The radiation imaging apparatus according to Configuration 2, characterized by this. (Configuration 4) The offset correction means: When the amount of change between the latest offset image and the past offset image is in the first case, corrects one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means; When the amount of change between the latest offset image and the past offset image is in the second case, correcting one radiation image acquired by the image acquisition means using one offset image acquired by the image acquisition means, the radiation imaging apparatus according to Configuration 3. (Configuration 5) The offset correction means When the amount of change between the latest offset image and the past offset image is smaller than the first threshold value, correcting one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means, When the amount of change between the latest offset image and the past offset image is not smaller than the first threshold value, correcting one radiation image acquired by the image acquisition means using one offset image acquired by the image acquisition means, the radiation imaging apparatus according to Configuration 4. (Configuration 6) The offset correction means When a plurality of regions obtained by dividing a difference image between an offset image captured at a first time and an offset image captured at a second time before the first time are in the first case, correcting one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means, When a plurality of regions obtained by dividing a difference image between an offset image captured at a first time and an offset image captured at a second time before the first time are in the second case, correcting one radiation image acquired by the image acquisition means using one offset image acquired by the image acquisition means, the radiation imaging apparatus according to Configuration 2. (Configuration 7) The offset correction means When a plurality of regions obtained by dividing a difference image between the latest offset image and the past offset image are in the first case, correcting one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means, When a plurality of regions obtained by dividing the difference image between the latest offset image and the past offset image are in the second case, the radiation imaging apparatus according to configuration 6, characterized in that one radiation image obtained by the image acquisition means is corrected using one offset image obtained by the image acquisition means. (Configuration 8) The offset correction means When the average value of all regions among the average values of each of the plurality of regions obtained by dividing the difference image between the latest offset image and the past offset image is smaller than the second threshold value, one radiation image obtained by the image acquisition means is corrected using a plurality of offset images obtained by the image acquisition means. When the average value of any one of the average values of each of the plurality of regions obtained by dividing the difference image between the latest offset image and the past offset image is not smaller than the second threshold value, one radiation image obtained by the image acquisition means is corrected using one offset image obtained by the image acquisition means. The radiation imaging apparatus according to configuration 7, characterized in that (Configuration 9) The offset correction means Compares, for each region, the average value of each of the plurality of regions obtained by dividing the difference image with a value based on the average value of each of the plurality of regions obtained by dividing one radiation image obtained by the image acquisition means. When the average value of all regions among the average values of each of the plurality of regions obtained by dividing the difference image is smaller than the value based on the average value of each of the plurality of regions obtained by dividing the one radiation image, one radiation image obtained by the image acquisition means is corrected using a plurality of offset images obtained by the image acquisition means. When the average value of any one of the average values of each of the plurality of regions obtained by dividing the difference image is not smaller than the value based on the average value of each of the plurality of regions obtained by dividing the one radiation image, one radiation image obtained by the image acquisition means is corrected using one offset image obtained by the image acquisition means. The radiation imaging apparatus according to configuration 8, characterized in that (Configuration 10) The offset correction means When the difference between the minimum value and the maximum value for all regions among the differences between the minimum value and the maximum value for each of the plurality of regions obtained by dividing the difference image between the latest offset image and the past offset image is smaller than the third threshold value, one radiation image obtained by the image acquisition means is corrected using the plurality of offset images obtained by the image acquisition means. When the difference between the minimum value and the maximum value for any one of the regions among the differences between the minimum value and the maximum value for each of the plurality of regions obtained by dividing the difference image between the latest offset image and the past offset image is not smaller than the third threshold value, one radiation image obtained by the image acquisition means is corrected using one offset image obtained by the image acquisition means, which is a configuration of the radiation imaging apparatus according to claim 7. (Configuration 11) The offset correction means compares, for each region, the difference between the minimum value and the maximum value for each of the plurality of regions obtained by dividing the difference image with a value based on the average value for each of the plurality of regions obtained by dividing one radiation image obtained by the image acquisition means. When the difference between the minimum value and the maximum value for all regions among the differences between the minimum value and the maximum value for each of the plurality of regions obtained by dividing the difference image is smaller than the value based on the average value for each of the plurality of regions obtained by dividing the one radiation image, one radiation image obtained by the image acquisition means is corrected using the plurality of offset images obtained by the image acquisition means. When the difference between the minimum value and the maximum value for any one of the regions among the differences between the minimum value and the maximum value for each of the plurality of regions obtained by dividing the difference image is not smaller than the value based on the average value for each of the plurality of regions obtained by dividing the one radiation image, one radiation image obtained by the image acquisition means is corrected using one offset image obtained by the image acquisition means, which is a configuration of the radiation imaging apparatus according to claim 10. (Configuration 12) The offset correction means corrects one radiation image obtained by the image acquisition means using an image obtained by averaging the plurality of offset images obtained by the image acquisition means, which is a configuration of the radiation imaging apparatus according to any one of claims 1 to 11. (Configuration 13) The offset correction means obtains, as a radiation image after offset correction, a difference between one radiation image acquired by the image acquisition means and an image obtained by averaging a plurality of offset images acquired by the image acquisition means. The radiation imaging apparatus according to Configuration 12. (Configuration 14) The offset correction means corrects one radiation image acquired by the image acquisition means using an image obtained by averaging a plurality of offset images acquired by the image acquisition means with a weighting coefficient. The radiation imaging apparatus according to any one of Configurations 1 to 11. (Configuration 15) The offset correction means obtains, as a radiation image after offset correction, a difference between one radiation image acquired by the image acquisition means and an image obtained by averaging a plurality of offset images acquired by the image acquisition means with a weighting coefficient. The radiation imaging apparatus according to Configuration 14. (Configuration 16) The weighting coefficient of the plurality of offset images is such that an older offset image has a smaller value. The radiation imaging apparatus according to Configuration 14 or 15. (Configuration 17) A radiation generation device that generates radiation, A radiation imaging apparatus according to any one of Configurations 1 to 16, communicably connected to the radiation generation device, and A radiation imaging system characterized by including the above. (Method 1) An image acquisition step of alternately acquiring a radiation image captured while radiation is being irradiated and an offset image captured while radiation is not being irradiated, An offset correction step of correcting one radiation image acquired in the image acquisition step using a plurality of offset images acquired in the image acquisition step, and A processing method for a radiation imaging apparatus, characterized by including the above. (Program 1) A program for causing a computer to execute the processing method for a radiation imaging apparatus according to Method 1.

Explanation of Signs

[0101] 100: Radiation imaging device, 101: Control unit, 102: Image acquisition unit, 103: Image processing unit, 104: Offset correction unit, 105: Gain correction unit, 106: Offset change amount determination unit, 107: Memory unit, 108: Radiation image, 109: Pre-offset image, 110: Gain correction data, 111: Immediately after imaging offset image, 113: Communication unit, 200: Radiation detection unit, 300: Radiation generator, 301: Radiation source, 400: Control device

Claims

1. Image acquisition means for alternately acquiring a radiation image captured while being irradiated with radiation and an offset image captured while not being irradiated with radiation; Offset correction means for correcting one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means A radiation imaging apparatus, characterized by comprising the above.

2. The offset correction means is: In the first case, one radiation image acquired by the image acquisition means is corrected using a plurality of offset images acquired by the image acquisition means; In the second case, one radiation image acquired by the image acquisition means is corrected using one offset image acquired by the image acquisition means. The radiation imaging apparatus according to claim 1, characterized by this.

3. The offset correction means is: When the amount of change between the offset image captured at the first time and the offset image captured at the second time before the first time is in the first case, a plurality of offset images acquired by the image acquisition means are used to correct one radiation image acquired by the image acquisition means; When the amount of change between the offset image captured at the first time and the offset image captured at the second time before the first time is in the second case, one radiation image acquired by the image acquisition means is corrected using one offset image acquired by the image acquisition means. The radiation imaging apparatus according to claim 2, characterized by this.

4. The offset correction means is: When the amount of change between the latest offset image and the past offset image is in the first case, a plurality of offset images acquired by the image acquisition means are used to correct one radiation image acquired by the image acquisition means; When the amount of change between the latest offset image and the past offset image is in the second case, one radiation image acquired by the image acquisition means is corrected using one offset image acquired by the image acquisition means. The radiation imaging apparatus according to claim 3, characterized by this.

5. The offset correction means is: When the amount of change between the latest offset image and the past offset image is smaller than the first threshold value, a plurality of offset images acquired by the image acquisition means are used to correct one radiation image acquired by the image acquisition means; When the amount of change between the latest offset image and the past offset image is not less than a first threshold value, correcting one radiation image obtained by the image acquisition means using one offset image obtained by the image acquisition means, the radiation imaging apparatus according to claim 4.

6. The offset correction means When a plurality of regions obtained by dividing a difference image between an offset image captured at a first time and an offset image captured at a second time before the first time are in a first case, correcting one radiation image obtained by the image acquisition means using a plurality of offset images obtained by the image acquisition means, When a plurality of regions obtained by dividing a difference image between an offset image captured at a first time and an offset image captured at a second time before the first time are in a second case, correcting one radiation image obtained by the image acquisition means using one offset image obtained by the image acquisition means, the radiation imaging apparatus according to claim 2.

7. The offset correction means When a plurality of regions obtained by dividing a difference image between the latest offset image and the past offset image are in a first case, correcting one radiation image obtained by the image acquisition means using a plurality of offset images obtained by the image acquisition means, When a plurality of regions obtained by dividing a difference image between the latest offset image and the past offset image are in a second case, correcting one radiation image obtained by the image acquisition means using one offset image obtained by the image acquisition means, the radiation imaging apparatus according to claim 6.

8. The offset correction means When the average value of all regions among the average values of each of a plurality of regions obtained by dividing a difference image between the latest offset image and the past offset image is less than a second threshold value, correcting one radiation image obtained by the image acquisition means using a plurality of offset images obtained by the image acquisition means, When the average value of any one of the regions among the average values of each of a plurality of regions obtained by dividing a difference image between the latest offset image and the past offset image is not less than the second threshold value, correcting one radiation image obtained by the image acquisition means using one offset image obtained by the image acquisition means, the radiation imaging apparatus according to claim 7.

9. The offset correction means compares, for each of a plurality of regions obtained by dividing the difference image, an average value for each of the plurality of regions with a value based on an average value for each of a plurality of regions obtained by dividing one radiation image acquired by the image acquisition means, and when the average value of all regions among the average values for each of the plurality of regions obtained by dividing the difference image is smaller than the value based on the average value for each of the plurality of regions obtained by dividing the one radiation image, corrects the one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means, and when the average value of any one of the regions among the average values for each of the plurality of regions obtained by dividing the difference image is not smaller than the value based on the average value for each of the plurality of regions obtained by dividing the one radiation image, corrects the one radiation image acquired by the image acquisition means using one offset image acquired by the image acquisition means. The radiation imaging apparatus according to claim 8, characterized in that **Claim 10** The offset correction means compares, for each of a plurality of regions obtained by dividing a difference image between a latest offset image and a past offset image, the difference between the minimum value and the maximum value for all regions among the differences between the minimum value and the maximum value for each of the plurality of regions with a third threshold value, and when the difference between the minimum value and the maximum value for all regions among the differences between the minimum value and the maximum value for each of the plurality of regions is smaller than the third threshold value, corrects the one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means, and when the difference between the minimum value and the maximum value for any one of the regions among the differences between the minimum value and the maximum value for each of the plurality of regions obtained by dividing the difference image between the latest offset image and the past offset image is not smaller than the third threshold value, corrects the one radiation image acquired by the image acquisition means using one offset image acquired by the image acquisition means. The radiation imaging apparatus according to claim 7, characterized in that **Claim 11** The offset correction means compares, for each of a plurality of regions obtained by dividing the difference image, the difference between the minimum value and the maximum value for each of the plurality of regions with a value based on an average value for each of a plurality of regions obtained by dividing one radiation image acquired by the image acquisition means, and when the difference between the minimum value and the maximum value for all regions among the differences between the minimum value and the maximum value for each of the plurality of regions obtained by dividing the difference image is smaller than the value based on the average value for each of the plurality of regions obtained by dividing the one radiation image, corrects the one radiation image acquired by the image acquisition means using a plurality of offset images acquired by the image acquisition means, If the difference between the minimum value and the maximum value of any of the regions obtained by dividing the difference image is not smaller than the value based on the average value of the regions obtained by dividing the one radiographic image, the radiographic image obtained by the image acquisition means is corrected using the one offset image obtained by the image acquisition means. The radiographic imaging apparatus according to claim 10, characterized in that.

12. The offset correction means corrects one radiographic image obtained by the image acquisition means using an image obtained by averaging a plurality of offset images obtained by the image acquisition means. The radiographic imaging apparatus according to claim 1, characterized in that.

13. The offset correction means obtains, as a radiographic image after offset correction, the difference between one radiographic image obtained by the image acquisition means and an image obtained by averaging a plurality of offset images obtained by the image acquisition means. The radiographic imaging apparatus according to claim 12, characterized in that.

14. The offset correction means corrects one radiographic image obtained by the image acquisition means using an image obtained by averaging a plurality of offset images obtained by the image acquisition means with a weighting coefficient. The radiographic imaging apparatus according to claim 1, characterized in that.

15. The offset correction means obtains, as a radiographic image after offset correction, the difference between one radiographic image obtained by the image acquisition means and an image obtained by averaging a plurality of offset images obtained by the image acquisition means with a weighting coefficient. The radiographic imaging apparatus according to claim 14, characterized in that.

16. The weighting coefficient of the plurality of offset images is such that the older the offset image, the smaller it is. The radiographic imaging apparatus according to claim 14, characterized in that.

17. A radiation generation device that generates radiation, A radiographic imaging apparatus according to any one of claims 1 to 16, communicably connected to the radiation generation device A radiographic imaging system, characterized by comprising.

18. An image acquisition step of alternately acquiring a radiographic image taken while radiation is being irradiated and an offset image taken while radiation is not being irradiated; An offset correction step of correcting one radiographic image obtained by the image acquisition step using a plurality of offset images obtained by the image acquisition step A processing method for a radiation imaging apparatus, characterized by having [

19. ] A program for causing a computer to execute the processing method of the radiation imaging apparatus according to Claim 18.

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