CT image reconstruction device, CT image reconstruction method, and CT image reconstruction program

Abstract

To specify the size of an object area existing inside a sample when a CT image of the inside of the sample is reconstituted by using a measuring system for irradiating the sample with X-rays from a part of all directions.SOLUTION: The CT image reconstruction device reconstructs a CT image having a defect. A CT image reconstruction device detects an artifact shape determined according to a measurement system representing an X-ray source and a detector from a CT image having a defect. The CT image reconstruction device specifies the size of the target existing inside the sample according to the artifact shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a CT image reconstruction device, a CT image reconstruction method, and a CT image reconstruction program. [Background technology]

[0002] Patent Document 1 discloses an X-ray system that can improve imaging speed and / or reduce radiation dose compared to conventional imaging techniques such as CT. The system disclosed in Patent Document 1 can identify a volume of interest within a subject.

[0003] Furthermore, Patent Document 2 discloses a CT image reconstruction system for obtaining CT images with reduced defects in a linear CT system. The reconstruction unit of the CT image reconstruction device in this CT image reconstruction system reconstructs a defective CT image of a sample based on detection data detected by multiple detectors. The defective CT image has a smaller amount of defect than a conventional defective CT image reconstructed based on detection data obtained by irradiating a sample with X-rays from a single X-ray source so that the sample receives X-rays from one direction. The image restoration unit of the CT image reconstruction device inputs the defective CT image into a trained learning device to obtain a restored CT image in which the defect has been restored.

[0004] Furthermore, Patent Document 3 discloses a tomography method and device for pipe inspection that can perform image reconstruction calculations only from incomplete projection data within a very small angle range, in cases such as on-site plant piping photography, where it is difficult to obtain the complete data required with conventional CT, and can create high-quality tomographic images that can visualize minute defects such as shallow wall thinning inside the object.

[0005] Furthermore, Patent Document 4 discloses a computed tomography apparatus that creates radiographic images of defects viewed from multiple directions based on the respective radiographic transmission data output by multiple detectors in a detector group, and also creates size information and position information of the defects.

[0006] Furthermore, Patent Document 5 discloses an X-ray CT system that realizes spectral CT that overcomes defects identified in the spectral CT configuration. This X-ray CT system uses a trained model to generate images with reduced streak artifacts.

[0007] Patent Document 6 also discloses a medical device that includes a processing circuit that acquires a sinogram representing the intensity of radiation detected by a detector, acquires a neural network, applies the acquired sinogram to the neural network, thereby outputting indicators of two or more artifacts from the neural network, determines whether or not a first artifact is present in the acquired sinogram and whether or not a second artifact is present in the acquired sinogram based on the indicators from the neural network, and, when it is determined that one or more artifacts are present in the acquired sinogram, generates a corrected sinogram in which the artifacts are corrected and performs reconstruction processing, and when it is determined that no artifacts are present, performs reconstruction processing using the sinogram.

[0008] Furthermore, Patent Document 7 discloses a method and system for CT imaging using a distributed X-ray source and interpolation-based reconstruction, which achieves high spatial resolution, high temporal resolution, good image quality, and sufficient imaging range using a standard or relatively small detector. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2023-503638 [Patent Document 2] Japanese Patent Application Publication No. 2022-158299 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-107298 [Patent Document 4] Japanese Patent Application Publication No. 3-100405 [Patent Document 5] Japanese Patent Publication No. 2020-99667 [Patent Document 6] Patent Publication No. 2021-13726 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-297083 Summary of the Invention [Problem to be solved by the invention]

[0010] Incidentally, when inspecting whether or not voids or other objects exist inside a sample, it is necessary to use X-ray CT measurement or ultrasonic measurement, as disclosed in the above-mentioned Patent Documents 1 to 7. For example, consider the case of inspecting whether or not casting cavities exist inside a product. In such a case, imaging the inside of the product using X-ray CT measurement is essentially required to measure the inside of the product nondestructively and noncontactly, measure multiple voids or objects present inside the product, and estimate the size of voids or other objects present inside the product.

[0011] When attempting to image the inside of a product using conventional X-ray CT measurement, it is necessary to irradiate the sample with X-rays from all around the product and obtain a transmission image of the inside of the product.

[0012] However, for example, when inspecting the inside of a product on a production line, a problem arises in that it takes time to irradiate the sample with X-rays from all around the product.

[0013] In particular, in the case of linear CT measurement, which has no resolution in the depth direction corresponding to the direction in which X-rays are irradiated onto the product, it is not possible to identify whether the position of a void or other object present inside the product is at a critical position on the sample.

[0014] The present disclosure has been made in consideration of the above circumstances, and provides a CT image reconstruction device, a CT image reconstruction method, and a CT image reconstruction program that can identify the size of a target area present inside a sample when reconstructing a CT image inside the sample using a measurement system that irradiates X-rays onto the sample from some of the all directions. [Means for solving the problem]

[0015] A first aspect of the present disclosure is a CT image reconstruction device in a CT image reconstruction system including an X-ray source that irradiates X-rays onto a sample from some of all directions, a detector that detects the X-rays irradiated from the X-ray source and transmitted through the sample, and a CT (Computed Tomography) image reconstruction device, the CT image reconstruction device including: a reconstruction unit that reconstructs a CT image having a defect based on detection data detected by the detector; a detection unit that detects an artifact shape from the CT image having a defect, the artifact shape being determined according to a measurement system representing the X-ray source and the detector; and an identification unit that identifies the size of an object present inside the sample according to the artifact shape.

[0016] The second aspect is a CT image reconstruction method executed by a CT image reconstruction device in a CT image reconstruction system including an X-ray source that irradiates X-rays onto a sample from some of all directions, a detector that detects the X-rays irradiated from the X-ray source and transmitted through the sample, and a CT (Computed Tomography) image reconstruction device, in which a computer constituting the CT image reconstruction device reconstructs a CT image with a defect based on detection data detected by the detector, detects an artifact shape from the CT image with a defect that is determined according to a measurement system representing the X-ray source and the detector, and identifies the depth-wise size of an object present inside the sample according to the artifact shape.

[0017] The third aspect is a CT image reconstruction program executed by a CT image reconstruction device in a CT image reconstruction system including an X-ray source that irradiates X-rays onto a sample from some of all directions, a detector that detects the X-rays irradiated from the X-ray source and transmitted through the sample, and a CT (Computed Tomography) image reconstruction device, the CT image reconstruction program causing a computer constituting the CT image reconstruction device to perform the following processes: reconstruct a CT image having a defect based on detection data detected by the detector, detect an artifact shape from the CT image having a defect that is determined according to a measurement system representing the X-ray source and the detector, and identify the depth-wise size of an object present inside the sample according to the artifact shape. [Effects of the Invention]

[0018] According to the present disclosure, when a CT image of the inside of a sample is reconstructed using a measurement system that irradiates the sample with X-rays from some of the all directions, the size of the target area present inside the sample can be identified. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating an example of a CT image reconstruction system according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of the functional configuration of CT image reconstruction according to the first embodiment. [Figure 3] FIG. 2 is a block diagram showing an example of the configuration of a computer that functions as a CT image reconstruction device according to the first embodiment. [Figure 4] FIG. 10 is a diagram for explaining a transmission image of a linear CT. [Figure 5] FIG. 10 is a diagram for explaining streak artifacts that occur in a reconstructed image obtained by linear CT. [Figure 6] FIG. 10 is a diagram for explaining streak artifacts in more detail. [Figure 7] FIG. 10 is a diagram for explaining streak artifacts in more detail. [Figure 8] FIG. 10 is a diagram for explaining a method for calculating the size of a rhombus. [Figure 9] FIG. 10 is a diagram showing an example of an image obtained by calculating the difference between an image showing an ideal sample and an actually captured reconstructed image. [Figure 10] 10 is a flowchart showing an example of the processing flow of a CT image reconstruction program according to the first embodiment. [Figure 11] FIG. 10 is a diagram illustrating an example of a CT image reconstruction system 210 according to a second embodiment. [Figure 12] FIG. 1 shows an example of a CT image with a defect obtained by a laminography measurement system. [Figure 13] FIG. 10 is a diagram showing an example of a streak artifact that occurs in a CT image obtained by a measurement system for laminography. [Figure 14] FIG. 10 is a diagram showing an example of an image obtained by calculating the difference between an image showing an ideal sample and a CT image with a defect. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the technology of the present disclosure will be described in detail with reference to the drawings. Note that in the present embodiment, components and processes that perform the same actions and functions are assigned the same reference numerals throughout the drawings, and duplicated descriptions may be omitted as appropriate. Each drawing is merely a schematic illustration to allow a sufficient understanding of the technology of the present disclosure. Therefore, the technology of the present disclosure is not limited to only the illustrated examples. Furthermore, in the present embodiment, descriptions of configurations that are not directly related to the technology of the present disclosure or well-known configurations may be omitted.

[0021] [First embodiment] FIG. 1 is a diagram showing an example of a CT image reconstruction system 10 according to the first embodiment. As shown in FIG. 1, the CT image reconstruction system 10 includes an X-ray source 11, a detector 12, a conveyor belt 13, and a CT image reconstruction device 14. The X-ray source 11, the detector 12, and the CT image reconstruction device 14 are communicably connected. The z-axis in FIG. 1 is set along the direction from the back to the front of the paper. sd represents the distance between the X-ray source 11 and the detector 12. so represents the distance between the X-ray source 11 and the conveyor belt 13. o represents the length of the conveyor belt 13.

[0022] The X-ray source 11 irradiates the sample S with X-rays R.

[0023] The detector 12 detects the X-rays that are emitted from the X-ray source 11 and transmitted through the sample S.

[0024] The conveyor belt 13 operates to move the sample S in a direction D.

[0025] As shown in Fig. 1, an X-ray source 11 irradiates a sample S with X-rays R from some of all directions. Therefore, the measurement system representing the X-ray source 11 and detector 12 in the CT image reconstruction system 10 shown in Fig. 1 is a measurement system that acquires an image with so-called defects (hereinafter also simply referred to as an incomplete CT image). Specifically, the measurement system representing the X-ray source 11 and detector 12 in the CT image reconstruction system 10 shown in Fig. 1 is configured such that the X-ray source 11 and detector 12 are installed on both sides of the sample S moving on a conveyor belt 13.

[0026] The CT image reconstruction device 14 determines the size in the depth direction of an object present inside the sample S based on the detection data detected by the detector 12. The object present inside the sample S may be, for example, a void or another object. Hereinafter, the other object will also be referred to as an inclusion.

[0027] 2 is a block diagram showing an example of the functional configuration of the CT image reconstruction device 14 according to the first embodiment. As shown in FIG. 2, the CT image reconstruction device 14 functionally includes a data storage unit 140, a reconstruction unit 142, a detection unit 144, and an identification unit 146.

[0028] 3, the CT image reconstruction device 14 is realized by a computer 50 including a CPU 51, a memory 52 as a temporary storage area, and a non-volatile storage unit 53. The computer 50 of the CT image reconstruction device 14 also includes an input / output interface (I / F) 54 to which external devices, output devices, etc. are connected, and a read / write (R / W) unit 55 that controls reading and writing of data from and to a recording medium 59. The computer also includes a network I / F 56 that is connected to a network such as the Internet. The CPU 51, memory 52, storage unit 53, input / output I / F 54, R / W unit 55, and network I / F 56 are connected to one another via a bus 57.

[0029] The storage unit 53 can be realized by a hard disk drive (HDD), a solid state drive (SSD), a flash memory, etc. The storage unit 53 as a storage medium stores a program for causing the computer to function. The CPU 51 reads the program from the storage unit 53, loads it into the memory 52, and sequentially executes the processes contained in the program.

[0030] In the measurement system shown in Figure 1, X-rays R are irradiated onto the sample S from one direction of the sample S while the sample S is moving in a linear motion. For this reason, the image of the inside of the sample S obtained by such a measurement system is also called linear CT.

[0031] A measurement system using linear CT, such as that shown in Figure 1, can only obtain an incompletely reconstructed image of the interior of the sample S. As a result, the shape of voids or inclusions inside the sample S is unclear in the incompletely reconstructed image of the interior of the sample S.

[0032] FIG. 4 is a diagram illustrating the transmission images of the linear CT. IM1 shown in FIG. 4 is a transmission image based on detection data obtained when the sample S was located at the left end of the conveyor belt 13. IM2 shown in FIG. 4 is a transmission image based on detection data obtained when the sample S was located at the center of the conveyor belt 13. IM3 shown in FIG. 4 is a transmission image based on detection data obtained when the sample S was located at the right end of the conveyor belt 13. As shown in FIG. 4, the transmission images IM1 and IM3 are less clear than the transmission image IM2. An image of the interior of the sample S is reconstructed using these less clear transmission images. However, if a void or inclusion exists inside the sample S, a streak artifact appears in the reconstructed image of the linear CT. Therefore, even if only these transmission images are used, it is not possible to detect the shape of a void in the depth direction (Y direction), which is the direction in which the X-rays are irradiated.

[0033] An artifact is a phenomenon in which an image that does not actually exist inside the sample S is captured in the reconstructed image. A streak artifact is a phenomenon in which noise appears in a consistent direction in the reconstructed image due to insufficient information when generating the reconstructed image.

[0034] Figure 5 is a diagram illustrating streak artifacts that occur in reconstructed images obtained by linear CT. Image A shown in Figure 5 is a cross-sectional image of a true numerical phantom inside a sample, and image B shown in Figure 5 is a reconstructed image of a real sample using linear CT. A void is present in the center of image A, and a void also exists in the center of the real sample. However, the shape of the void in the center of image B is distorted and significantly different from the shape of the void in the cross-sectional image of the true numerical phantom.

[0035] 6 and 7 are diagrams for explaining the streak artifact in more detail. Inside the sample S shown in FIG. 6, there are voids T A ,T BThe xyz coordinate system in Fig. 6 corresponds to the xyz coordinate system in Fig. 1. The Z cross section in Fig. 6 is B It is positioned so that it slices the image into slices.

[0036] Figure 7 shows an example of a reconstructed image of the linear CT of the sample S in Figure 6. The images shown in the left column of Figure 7 are cross-sectional images of the correct numerical phantom inside the sample, and the images shown in the right column of Figure 7 are reconstructed images of the actual sample S by linear CT.

[0037] The inventors of the present invention conducted a simulation as shown in Fig. 7 and found that streak artifacts occur not only at the outer boundary of the sample S but also at the boundaries of voids or inclusions present inside the sample S. As shown in image B of Fig. 5, it can be seen that streak artifacts occur around voids. Note that, as shown in image B of Fig. 5, streak artifacts occur along the depth direction (Y direction) in which X-rays are irradiated into the sample.

[0038] Therefore, in this embodiment, the shape of the streak artifact is regarded as a diamond, and the size in the depth direction of the voids or inclusions present inside the sample S is calculated. Although the shape of the streak artifact is, strictly speaking, different from a diamond, for ease of explanation, hereinafter the shape of the streak artifact will also be simply referred to as a "diamond."

[0039] Fig. 8 is a diagram for explaining a method for calculating the size of a diamond. A diamond-shaped streak artifact that appears in a reconstructed image of a linear CT can be decomposed into its components as shown in Fig. 8.

[0040] For this reason, first, the length c of the longer diagonal of the rhombus shown in Figure 8 is measured using known image processing technology. Then, the length a of the shorter diagonal of the rhombus shown in Figure 8 is measured using known image processing technology. Note that the acute angle θ of the rhombus shown in Figure 8 corresponds to the imaging angle θ of the linear CT shown in Figure 8. Therefore, the following equation (1) holds between the length c of the longer diagonal of the rhombus, the length a of the shorter diagonal of the rhombus, and the acute angle θ of the rhombus. Therefore, the dimension b of a predetermined point of the rhombus shown in Figure 8 is calculated according to the following equation (1).

[0041]

number

[0042] The following formula (2) holds between the length c of the longer diagonal of the rhombus, the depth length d of the void or inclusion in the rhombus, and the acute angle θ of the rhombus. Therefore, the depth length d of the void or inclusion in the rhombus shown in Figure 8 is calculated according to the following formula (2).

[0043]

number

[0044] In order to make the diamonds in the reconstructed image clearer, the diamonds in the reconstructed image may be detected by calculating the difference between an image of an ideal sample that does not contain voids or inclusions inside and an actually captured reconstructed image.

[0045] Fig. 9 shows an example of an image obtained by calculating the difference between an image of an ideal sample and an actually captured reconstructed image. As shown in Fig. 9, the diamond-shaped portion is emphasized, making it possible to more accurately calculate the depth length d of the void or inclusion within the diamond.

[0046] The values ​​of each diamond shown in Figure 9 are as follows:

[0047]

number

[0048] Each part of the CT image reconstruction device 14 will be described below.

[0049] The data storage unit 140 stores the detection data detected by the detector 12.

[0050] The reconstruction unit 142 reconstructs a CT image having a defect using a known method based on the detection data stored in the data storage unit 140. A CT image having a defect is a CT image obtained by irradiating a sample with X-rays from only a portion of all directions. CT images having a defect have artifacts such as those shown in FIG. 5. Irradiating a sample with X-rays from only a portion of all directions is also called incomplete CT.

[0051] The detector 144 detects an artifact shape determined according to the measurement system representing the X-ray source 11 and the detector 12 from the CT image having a defect obtained by the reconstructor 142 .

[0052] The measurement system of this embodiment is a linear CT measurement system that generates a CT image by irradiating X-rays from one direction while the sample S travels straight ahead. As described above, the artifact shape determined by the linear CT measurement system is a diamond. For example, the detection unit 144 detects the diamond artifact shape using the following method.

[0053] <Example of image processing procedure for mechanically extracting diamonds> As described above, if it is possible to prepare a numerical phantom image that is an image of an ideal sample that does not contain voids or inclusions, it is possible to extract the diamond shape with higher accuracy using the numerical phantom image. Therefore, if it is possible to prepare a numerical phantom image, for example, the detection unit 144 detects the diamond shape, which is an artifact shape, using the following method.

[0054] [When the difference between the numerical phantom and the reconstructed image can be calculated] First, the detection unit 144 thins the lines in the difference image by performing erosion processing, a morphological operation, on the difference image between the numerical phantom image and the CT image with defects. Then, the detection unit 144 extracts the contours of the thinned difference image using the marching squares method or the like, thereby making it possible to highlight the locations of voids or inclusions.

[0055] If it is not possible to prepare a numerical phantom image, the detection unit 144 detects the diamond shape, which is an artifact shape, using the following method, for example.

[0056] [When the difference between the numerical phantom and the reconstructed image cannot be calculated] (Example 1) The detection unit 144 performs Canny binarization on the CT image with defects, and then extracts, by probabilistic straight-line Hough detection, a diamond-shaped shape or a line of a streak artifact that occurs depending on the imaging angle θ of the incomplete CT.

[0057] (Example 2) A template image containing a diamond shape expected to occur due to a streak artifact is prepared in advance. Then, the detection unit 144 scans the template against a CT image containing a defect and determines that a void or inclusion exists in a location where the similarity is higher than a threshold (so-called template matching).

[0058] (Example 3) The detection unit 144 performs semantic segmentation using deep learning on the CT image with defects and extracts diamond-shaped streak artifacts that are thought to contain voids.

[0059] The identifying unit 146 identifies the depth size of a void or inclusion, which is an example of an object present inside the sample, according to the artifact shape detected by the detecting unit 144. Specifically, as described above, the identifying unit 146 calculates the depth length d of the void or inclusion within the diamond by identifying the length of each point of the diamond using a known image processing technique. The identifying unit 146 may further identify the position of the void or inclusion present inside the sample using the above method. For example, the identifying unit 146 may identify the midpoint of the depth length d of the void or inclusion within the diamond as the position of the void or inclusion.

[0060] Next, the operation of the CT image reconstruction device 14 according to the first embodiment will be described with reference to Fig. 10. Fig. 10 is a flowchart showing an example of the processing flow of the CT image reconstruction program according to the first embodiment.

[0061] First, in step S100, the reconstruction unit 142 reconstructs a CT image having a defect based on the detection data stored in the data storage unit 140 using a known method.

[0062] In step S101, the detection unit 144 acquires a Z cross-sectional image from the CT image having a defect obtained in step S100.

[0063] In step S102, the detection unit 144 detects the position of a diamond, which is an example of an artifact shape determined according to the measurement system representing the X-ray source 11 and the detector 12, from the Z cross-sectional image acquired in step S101.

[0064] In steps S104 to S110, the identifying unit 146 identifies the size in the depth direction of a void or an inclusion, which is an example of an object present inside the sample S, according to the diamond detected in step S102.

[0065] Specifically, in step S104, the identification unit 146 measures the length c of the longer diagonal line of the diamond detected in step S102. Specifically, the identification unit 146 acquires the length c by measuring the number of pixels corresponding to the length of the longer diagonal line of the diamond.

[0066] In step S106, the identification unit 146 measures the length a of the shorter diagonal line of the diamond detected in step S102. Specifically, the identification unit 146 acquires the length a by measuring the number of pixels corresponding to the length of the shorter diagonal line of the diamond.

[0067] In step S108, the identification unit 146 calculates the dimension b of a predetermined location as shown in FIG. 8 in accordance with the above formula (1) based on the length c of the longer diagonal measured in step S104, the length a of the shorter diagonal measured in step S106, and the imaging angle θ.

[0068] In step S110, the identification unit 146 calculates the depth direction length d of the void or inclusion in the diamond shown in FIG. 8 according to the above formula (2) based on the dimension b of the predetermined location obtained in step S108 and the length c of the longer diagonal measured in step S104.

[0069] In step S112, the identifying unit 146 outputs the depth direction length d of the void or inclusion obtained in step S110 as a result, and ends the process.

[0070] As described above, the CT image reconstruction system of the first embodiment includes an X-ray source that irradiates a sample with X-rays from some of all directions, a detector that detects the X-rays irradiated from the X-ray source and transmitted through the sample, and a CT image reconstruction device. The CT image reconstruction device in the CT image reconstruction system reconstructs a CT image with a defect (incomplete CT) based on detection data detected by the detector. The CT image reconstruction device detects an artifact shape determined according to a measurement system representing the X-ray source and the detector from the CT image with a defect. The CT image reconstruction device identifies the size of an object (void or inclusion) present inside the sample according to the artifact shape. This makes it possible to identify the size of an object present inside the sample when reconstructing a CT image of the sample using a measurement system that irradiates the sample with X-rays from some of all directions.

[0071] Specifically, the measurement system of the first embodiment is a measurement system related to linear CT, which irradiates a sample with X-rays from one direction while moving the sample in a straight line, thereby generating a CT image with defects. In this case, the detection unit detects a diamond, which is an artifact shape determined according to the measurement system related to linear CT, and identifies the size in the depth direction of an object (void or object) present inside the sample according to the diamond.

[0072] As described above, linear CT can only obtain transmission images from a limited imaging angle, resulting in the reconstruction of a CT image with defects. In a CT image with defects, streak artifacts appear from the edges of voids or inclusions present inside the sample, depending on the imaging angle. The shape of this streak artifact is determined by the imaging angle. Therefore, in this embodiment, the imaging angle θ, a parameter related to the linear CT measurement system, is used to calculate the depth length d of the void or inclusion within the diamond shape of the streak artifact. This makes it possible to estimate the depth dimension of the void or inclusion inside the sample, which was previously unknown, despite linear CT measurement only being able to obtain transmission images from a limited angle.

[0073] [Second embodiment] Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that the X-ray CT measurement system is a measurement system related to laminography. The measurement system related to laminography is an example of a measurement system for incomplete CT.

[0074] 11 is a diagram showing an example of a CT image reconstruction system 210 according to the second embodiment. As shown in FIG. 11, the CT image reconstruction system 210 includes an X-ray source 11, a detector 12, a turntable (not shown) for rotating the sample S, and a CT image reconstruction device 214.

[0075] The measurement system shown in FIG. 11 is a measurement system for laminography in which a sample S rotates in a direction E on the xy plane.

[0076] Figure 12 shows an example of a CT image with a defect obtained by a laminography measurement system. The image on the left side of Figure 12 is a numerical phantom image, the image in the center of Figure 12 is an actually obtained CT image with a defect, and the image on the right side of Figure 12 is a difference image between the numerical phantom image and the CT image with a defect.

[0077] The horizontal arrow in the center image of Figure 12 corresponds to the y-axis direction, and the vertical arrow corresponds to the z-axis direction. As shown in the center image of Figure 12, laminography often has high resolution in the y-axis direction but low resolution in the z-axis direction. For this reason, streak artifacts such as those shown in Figure 13 occur in laminography measurement systems.

[0078] As shown in FIG. 13 , streak artifact lines J1, J2, J3, J4, J5, J6, J7, and J8 appear in a laminography measurement system. In this case, the z-direction dimension L of the void T can be calculated from the position coordinates of the intersections K1, K2, K3, and K4 of the streak artifact lines J1, J2, J3, J4, J5, J6, J7, and J8. Specifically, because the y-direction resolution of a CT image with defects is high, it is possible to detect the boundaries of the left and right ends of the void T. Therefore, the detection unit 144 of the second embodiment detects the intersections K1, K2, K3, and K4 where the streak artifacts meet. The intersections K1, K2, K3, and K4 are considered to be the upper and lower ends of the void T, respectively. Therefore, the z-direction dimension of the void T can be calculated from the difference in the z-direction position coordinates of these intersections K1, K2, K3, and K4. Furthermore, the angle θ of the streak artifact lines J1, J2, J3, J4, J5, J6, J7, and J8 relative to the horizontal line corresponds to the imaging angle, so it is possible to extract the artifact lines based on this information.

[0079] Therefore, when the measurement system for X-ray CT is a measurement system for laminography, the detection unit 144 of the CT image reconstruction device 214 of the second embodiment detects the artifact shape determined according to the measurement system for laminography. Specifically, the detection unit 144 of the CT image reconstruction device 214 of the second embodiment calculates the position coordinates of the intersections K1, K2, K3, and K4 of the lines J1, J2, J3, J4, J5, J6, J7, and J8 of the streak artifact using a known image processing technique.

[0080] Then, the identifying unit 146 of the CT image reconstruction device 214 of the second embodiment identifies the size of the void or inclusion present inside the sample according to the artifact shape. Specifically, the identifying unit 146 of the CT image reconstruction device 214 of the second embodiment identifies the size of the void or inclusion present inside the sample based on the position coordinates of the intersections K1, K2, K3, and K4 of the lines J1, J2, J3, J4, J5, J6, J7, and J8 of the treaky artifact.

[0081] As in the first embodiment, in order to make artifacts in a CT image with a defect clearer, the artifacts in the CT image with a defect may be detected by calculating the difference between an image of an ideal sample that does not contain voids or inclusions and an actually captured reconstructed image.

[0082] Figure 14 shows an example of an image obtained by calculating the difference between an image of an ideal sample and a CT image with a defect. As shown in Figure 14, the artifact portion is emphasized, making it possible to calculate the size of voids or inclusions with greater accuracy. In particular, if the angle of the streak artifact coincides with the outline of a diamond-shaped void (the void at the bottom of the image), it is difficult to distinguish it from the shape of the void. In such cases, by taking the difference with the numerical phantom image and emphasizing the brightness, as shown in the right figure, it becomes possible to detect artifacts with greater accuracy.

[0083] The other configurations of the CT image reconstruction system 210 and the CT image reconstruction device 214 of the second embodiment are the same as those of the first embodiment, and therefore detailed description thereof will be omitted.

[0084] As described above, when the measurement system for X-ray CT is a measurement system for laminography, the CT image reconstruction device 14 of the second embodiment detects an artifact shape determined according to the measurement system for laminography. Then, the CT image reconstruction device 14 of the second embodiment identifies the size of an object (void or object) present inside the sample according to the artifact shape. This makes it possible to identify the size of a target region present inside the sample when reconstructing a CT image of the inside of the sample using a measurement system that irradiates the sample with X-rays from some of all directions.

[0085] [Other embodiments] The above describes an embodiment using a CT image reconstruction device as an example. The embodiment may be in the form of a program that causes a computer to function as each unit of the CT image reconstruction device. The embodiment may be in the form of a computer-readable storage medium that stores the program.

[0086] In the above embodiment, the incomplete CT scan corresponds to a linear CT scan or laminography, but the present invention is not limited to this. For example, the present invention can be applied to dimensional measurement in a direction with low resolution in a CT scan technique called circular tomosynthesis.

[0087] Furthermore, the configuration of the CT image reconstruction device described in the above embodiment is merely an example, and may be changed depending on the situation without departing from the spirit of the invention.

[0088] Furthermore, the processing flow of the program described in the above embodiment is also an example, and unnecessary steps may be deleted, new steps may be added, or the processing order may be rearranged within the scope of the main idea.

[0089] In the above embodiment, the processing according to the embodiment is realized by a software configuration using a computer by executing a program, but the present invention is not limited to this. The embodiment may be realized by, for example, a hardware configuration or a combination of a hardware configuration and a software configuration.

[0090] Furthermore, the processes in the above-described embodiments may be stored as a program on a storage medium such as an optical disk and distributed.

[0091] In the above embodiment, the term "CPU" refers to a processor in a broad sense, including general-purpose processors and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.).

[0092] In this case, the operations of the processors may not only be performed by a single processor, but may also be performed by multiple processors located at physically separate locations working together. Furthermore, the order of the operations of the processors is not limited to the order described in the above embodiments, and may be changed as appropriate.

[0093] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0094] (Implementation) The technology of the present disclosure may be implemented in the dependent relationships shown in the following appendices.

[0095] (Appendix 1) an X-ray source that irradiates a sample with X-rays from some of all directions, a detector that detects the X-rays that have been irradiated from the X-ray source and transmitted through the sample, and a CT (Computed Tomography) image reconstruction device; A CT image reconstruction device in a CT image reconstruction system comprising: a reconstruction unit that reconstructs a CT image having a defect based on the detection data detected by the detector; a detection unit that detects an artifact shape determined according to a measurement system representing the X-ray source and the detector from a CT image having a defect; an identification unit that identifies the size of an object present inside the sample according to the artifact shape; CT image reconstruction device including: (Appendix 2) The measurement system is a linear CT measurement system that moves the sample in a straight line and irradiates X-rays from one direction to generate a CT image with defects, the detection unit detects an artifact shape determined according to a measurement system related to the linear CT; the identifying unit identifies a size in a depth direction of an object present inside the sample according to the artifact shape. 10. The CT image reconstruction device according to claim 1. (Appendix 3) When the measurement system is a measurement system related to laminography, the detection unit detects an artifact shape determined according to a measurement system related to the laminography; the identifying unit identifies a size of an object present inside the sample according to the artifact shape. 10. The CT image reconstruction device according to claim 1. (Appendix 4) The identification unit further identifies the position of the target present inside the sample. CT image reconstruction device according to any one of Supplementary Note 1 to Supplementary Note 3. (Appendix 5) The object present inside the sample is a void or a body; 10. The CT image reconstruction device according to claim 1, wherein the CT image reconstruction device is a CT image reconstruction device. (Appendix 6) the detection unit detects the artifact shape by calculating a difference between an image of an ideal sample without the target therein and a CT image with the defect. 10. The CT image reconstruction device according to claim 1, wherein the first and second sub-components are arranged in a plane parallel to each other. (Appendix 7) an X-ray source that irradiates a sample with X-rays from some of all directions, a detector that detects the X-rays that have been irradiated from the X-ray source and transmitted through the sample, and a CT (Computed Tomography) image reconstruction device; A CT image reconstruction method executed by a CT image reconstruction device in a CT image reconstruction system comprising: a computer constituting the CT image reconstruction device, Reconstructing a CT image having a defect based on the detection data detected by the detector; Detecting an artifact shape determined according to a measurement system representing the X-ray source and the detector from the CT image having the defect; Identifying the size of the object present inside the sample in the depth direction according to the artifact shape; CT image reconstruction method to perform processing. (Appendix 8) an X-ray source that irradiates a sample with X-rays from some of all directions, a detector that detects the X-rays that have been irradiated from the X-ray source and transmitted through the sample, and a CT (Computed Tomography) image reconstruction device; A CT image reconstruction program executed by a CT image reconstruction device in a CT image reconstruction system comprising: A computer constituting the CT image reconstruction device includes: Reconstructing a CT image having a defect based on the detection data detected by the detector; Detecting an artifact shape determined according to a measurement system representing the X-ray source and the detector from the CT image having the defect; Identifying the size of the object present inside the sample in the depth direction according to the artifact shape; CT image reconstruction program for performing processing. [Explanation of symbols]

[0096] 10 CT image reconstruction system 11 X-ray source 12 Detectors 13 Conveyor Belt 14 CT image reconstruction device 140 Data storage unit 142 Reconstruction part 144 Detector 146 Specific part 210 CT Image Reconstruction System 214 CT image reconstruction device

Claims

1. an X-ray source that irradiates a sample with X-rays from some of all directions; a detector that detects the X-rays that have been irradiated from the X-ray source and transmitted through the sample; and a CT (Computed Tomography) image reconstruction device; A CT image reconstruction device in a CT image reconstruction system comprising: a reconstruction unit that reconstructs a CT image having a defect based on the detection data detected by the detector; a detection unit that detects an artifact shape determined according to a measurement system representing the X-ray source and the detector from a CT image having a defect; an identification unit that identifies the size of an object present inside the sample according to the artifact shape; A CT image reconstruction device comprising:

2. When the measurement system is a measurement system for linear CT in which the sample is moved in a straight line and irradiated with X-rays from one direction to generate a CT image with defects, the detector detects an artifact shape determined according to a measurement system related to the linear CT; the identifying unit identifies a size in a depth direction of an object present inside the sample according to the artifact shape.

2. The CT image reconstruction device according to claim 1.

3. When the measurement system is a measurement system related to laminography, the detection unit detects an artifact shape determined according to a measurement system related to the laminography; the identifying unit identifies a size of an object present inside the sample according to the artifact shape.

2. The CT image reconstruction device according to claim 1.

4. The identification unit further identifies the position of the object present inside the sample.

4. A CT image reconstruction device according to claim 1.

5. The object present inside the sample is a void or a body; 4. A CT image reconstruction device according to claim 1.

6. the detection unit detects the artifact shape by calculating a difference between an image of an ideal sample without the target therein and a CT image of the defect.

4. A CT image reconstruction device according to claim 1.

7. an X-ray source that irradiates a sample with X-rays from some of all directions; a detector that detects the X-rays that have been irradiated from the X-ray source and transmitted through the sample; and a CT (Computed Tomography) image reconstruction device; A CT image reconstruction method executed by a CT image reconstruction device in a CT image reconstruction system comprising: a computer constituting the CT image reconstruction device, Reconstructing a CT image having a defect based on the detection data detected by the detector; Detecting an artifact shape determined according to a measurement system representing the X-ray source and the detector from the CT image having a defect; Identifying the size of the object present inside the sample in the depth direction according to the artifact shape; A CT image reconstruction method for performing the process.

8. an X-ray source that irradiates a sample with X-rays from some of all directions; a detector that detects the X-rays that have been irradiated from the X-ray source and transmitted through the sample; and a CT (Computed Tomography) image reconstruction device; A CT image reconstruction program executed by a CT image reconstruction device in a CT image reconstruction system comprising: A computer constituting the CT image reconstruction device includes: Reconstructing a CT image having a defect based on the detection data detected by the detector; Detecting an artifact shape determined according to a measurement system representing the X-ray source and the detector from the CT image having a defect; Identifying the size of the object present inside the sample in the depth direction according to the artifact shape; A CT image reconstruction program for executing the process.

Images