An image reconstruction method and processing device

Abstract

The embodiment of the application provides a kind of image reconstruction method and processing device, it is related to tomography field.The method is applied to the processing device in detection system, system also includes turntable, ray source and detector;Turntable is located between ray source and detector, and the center point of turntable, the center ray of ray source and the center point of detector are collinear;Turntable can rotate around its central axis;The object to be examined is placed on the turntable;The projection image obtained by the detector detecting the object to be examined is obtained;Based on the projection image, the offset of the center point of the object to be examined relative to the image reconstruction center point is determined;The offset direction and offset value are used to correct the image reconstruction center point, to obtain the corrected image reconstruction center point;The projection image of the object to be examined is reconstructed using the corrected image reconstruction center point, to obtain the reconstructed image of the object to be examined. By using the offset of the center point of the object to be examined to correct the image reconstruction center, the image reconstruction efficiency can be improved.

Description

Technical Field

[0001] This application relates to the field of computed tomography technology, and in particular to an image reconstruction method and processing device. Background Technology

[0002] CT (Computed Tomography) technology uses an X-ray source to perform tomographic scanning of the object being examined, which can quickly and clearly image the object and is widely used in security inspections, object detection, disease diagnosis, etc.

[0003] When performing a CT scan on an object, the central axis of the object is usually aligned with the central axis of the turntable in order to make full use of the detector to image the object. However, due to factors such as human operation error and the shape of the object, the central axis of the object often deviates from the central axis of the turntable, resulting in the object being imaged at different positions on the detector as the rotation angle changes, and the position changes are relatively large.

[0004] When the central axis of the object being inspected coincides with the central axis of the turntable, image reconstruction of the object only requires establishing a coordinate system with the intersection of the central ray of the X-ray source and the central axis of the turntable as the origin. Image reconstruction is then performed based on the dimensions of the object, and the resulting reconstructed image contains all the information of the object. However, when the object being inspected is misaligned and its central axis does not coincide with the central axis of the turntable, image reconstruction requires considering the offset of the object relative to the origin. This offset increases the size of the reconstructed image, leading to reduced image reconstruction efficiency. Summary of the Invention

[0005] The purpose of this application is to provide an image reconstruction method and processing device to improve image reconstruction efficiency. The specific technical solution is as follows:

[0006] In a first aspect, embodiments of this application provide an image reconstruction method, the method being applied to a processing device in a detection system, the system further comprising a turntable, an X-ray source, and a detector; the turntable is located between the X-ray source and the detector, and the center point of the turntable, the central ray of the X-ray source, and the center point of the detector are collinear; the turntable is rotatable about its central axis; the object to be inspected is placed on the turntable; the method includes:

[0007] Acquire the projected image obtained by the detector detecting the object under test;

[0008] Based on the projected image, the offset of the center point of the object under inspection relative to the image reconstruction center point is determined, wherein the image reconstruction center point is the intersection of the central axis of the turntable and the central ray of the X-ray source; the offset includes the offset direction and the offset value.

[0009] Using the offset direction and the offset value, the image reconstruction center point is corrected to obtain the corrected image reconstruction center point;

[0010] Using the corrected image to reconstruct the center point, the projected image of the object under test is reconstructed to obtain the reconstructed image of the object under test.

[0011] Secondly, embodiments of this application provide a processing apparatus, including:

[0012] Memory, used to store computer programs;

[0013] When a processor executes a program stored in memory, it implements any of the methods described in the first aspect above.

[0014] Thirdly, embodiments of this application provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements any of the methods described in the first aspect above.

[0015] Fourthly, embodiments of this application also provide a computer program product containing instructions that, when run on a computer, cause the computer to perform any of the methods described in the first aspect above.

[0016] Beneficial effects of the embodiments in this application:

[0017] The technical solution provided in this application embodiment involves a processing device acquiring a projected image of the object being inspected by a detector; determining the offset of the center point of the object being inspected relative to the image reconstruction center point based on the projected image, wherein the image reconstruction center point is the intersection of the central axis of the turntable and the central ray of the X-ray source; the offset includes the offset direction and the offset value; correcting the image reconstruction center point using the offset direction and the offset value to obtain the corrected image reconstruction center point; and reconstructing the projected image of the object being inspected using the corrected image reconstruction center point to obtain the reconstructed image of the object being inspected.

[0018] By determining the offset of the center point of the object under inspection relative to the image reconstruction center point, and using this offset to correct the image reconstruction center point, the corrected image reconstruction center point is actually the location of the center point of the object under inspection. Therefore, when reconstructing the image using this corrected image reconstruction center point, only the spatial portion containing the object under inspection needs to be reconstructed. There is no need to consider enlarging the size of the reconstructed image due to the offset between the object's center point and the image reconstruction center point. This solves the problems of increased memory and video memory, increased image reconstruction time, and increased invalid image information caused by enlarging the size of the reconstructed image, thus improving image reconstruction efficiency. Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above simultaneously. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0020] Figure 1 A flowchart illustrating an image reconstruction method provided in an embodiment of this application;

[0021] Figure 2(a) is a schematic diagram of a tomographic imaging detection scenario provided in an embodiment of this application;

[0022] Figure 2(b) is a schematic diagram of another tomographic imaging detection scenario provided by an embodiment of this application;

[0023] Figure 3(a) is a schematic diagram of a reconstructed image size provided in an embodiment of this application;

[0024] Figure 3(b) is a schematic diagram of another reconstructed image size provided in an embodiment of this application;

[0025] Figure 3(c) is a schematic diagram of the offset of the center point of the object relative to the center point of the image reconstruction provided in the embodiment of this application;

[0026] Figure 4 This is a schematic diagram illustrating the relationship between the target distance between the center point of the object under test and the X-ray source and the magnitude of the column span corresponding to the object under test in the projection image, as provided in the embodiments of this application.

[0027] Figure 5(a) is a schematic diagram of the relative positional relationship between the object under test and the center of the detector provided in an embodiment of this application;

[0028] Figure 5(b) is another schematic diagram showing the relative positional relationship between the object under test and the center of the detector provided in the embodiment of this application;

[0029] Figure 5(c) is another schematic diagram of the relative positional relationship between the object under test and the center of the detector provided in the embodiment of this application;

[0030] Figure 6 A schematic flowchart illustrating an example of image reconstruction provided in an embodiment of this application;

[0031] Figure 7 This is a schematic diagram of the structure of an image reconstruction apparatus provided in an embodiment of this application;

[0032] Figure 8 This is a schematic diagram of the structure of a processing device provided in an embodiment of this application. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0034] To improve image reconstruction efficiency, embodiments of this application provide an image reconstruction method, apparatus, processing device, computer-readable storage medium, and computer program product. The image reconstruction method provided in this application embodiment is described below.

[0035] The image reconstruction method provided in this application can be applied to any processing device capable of image reconstruction, such as the background processor, image processor, or image processing unit of a CT scanner, etc., without specific limitations. For clarity, it will be referred to as a processing device herein.

[0036] like Figure 1 As shown, an image reconstruction method is applied to a processing device in a detection system. The system further includes a turntable, a radiation source, and a detector. The turntable is located between the radiation source and the detector, and the center point of the turntable, the central ray of the radiation source, and the center point of the detector are collinear. The turntable is rotatable about its central axis. The object to be inspected is placed on the turntable. The method includes:

[0037] S101: Obtain the projected image obtained by the detector detecting the object under test.

[0038] S102: Based on the projected image, determine the offset of the center point of the object under inspection relative to the center point of the image reconstruction.

[0039] Wherein, the image reconstruction center point is the intersection of the central axis of the turntable and the central ray of the ray source; the offset includes the offset direction and the offset value.

[0040] S103: Using the offset direction and the offset value, the image reconstruction center point is corrected to obtain the corrected image reconstruction center point.

[0041] S104: Using the corrected image to reconstruct the center point, the projected image of the object under test is reconstructed to obtain the reconstructed image of the object under test.

[0042] As can be seen, the technical solution provided in this application involves a processing device acquiring a projected image of the object being inspected by a detector; determining the offset of the center point of the object being inspected relative to the image reconstruction center point based on the projected image, wherein the image reconstruction center point is the intersection of the central axis of the turntable and the central ray of the X-ray source; the offset includes the offset direction and the offset value; correcting the image reconstruction center point using the offset direction and the offset value to obtain the corrected image reconstruction center point; and reconstructing the projected image of the object being inspected using the corrected image reconstruction center point to obtain the reconstructed image of the object being inspected.

[0043] By determining the offset of the center point of the object under test relative to the center point of the image reconstruction, and using this offset to correct the center point of the image reconstruction, the corrected center point of the image reconstruction is actually the location of the center point of the object under test. Therefore, when using the corrected center point of the image reconstruction to perform image reconstruction, only the spatial part where the object under test is located needs to be reconstructed. There is no need to consider expanding the size of the reconstructed image due to the offset between the center point of the object under test and the center point of the image reconstruction. This solves the problems of increased memory and video memory, increased image reconstruction time, and increased invalid image information caused by expanding the size of the reconstructed image, thus improving the efficiency of image reconstruction.

[0044] In computed tomography (CT) testing, taking conventional CBCT (cone beam CT) testing as an example, the testing system includes a radiation source, a turntable, and a detector. The turntable is located between the radiation source and the detector, and the center point of the turntable, the center ray of the radiation source, and the center point of the detector are collinear. The turntable can rotate around its central axis, and the object to be examined is placed on the turntable and can rotate with the turntable.

[0045] As shown in Figure 2(a), when inspecting an object, the operator usually places the object in the center of the turntable, aligning the central axis of the object with the central axis of the turntable, so as to make full use of the X-ray source S and detector D to image it. When the object is placed in the center of the turntable, as the turntable rotates, the X-ray source S emits X-rays, and the image of the object on detector D is concentrated around the center of detector D.

[0046] However, in actual use of CBCT equipment for object inspection, on the one hand, due to the influence of the staff and the object being inspected, the object may not be placed exactly in the center of the turntable, that is, the object may be placed off-center; on the other hand, in order to improve inspection efficiency, two or more objects may be placed on the turntable for scanning and imaging at the same time. Therefore, the object will inevitably be placed off-center, that is, the central axis of the object may not coincide with the central axis of the turntable, but may be at a certain distance from the central axis of the turntable. The image on the detector will be projected onto different positions on the detector as the rotation angle changes, and the position changes significantly.

[0047] Figure 2(b) shows a schematic diagram of the scanning imaging after the object is deflected. S represents the X-ray source, D represents the detector, A is the initial position of the object, and A' represents the image of the object on detector D when it is located at A. B' and C' represent the images of the object on detector D after the turntable rotates to B and C, respectively. It can be seen that when the object is deflected, its image on detector D is no longer concentrated at the center of detector D, but is imaged at different positions on detector D as the turntable rotates.

[0048] In CT image reconstruction, a coordinate system XYZ is typically established with the intersection of the central ray of the X-ray source and the central axis of the turntable as the origin. This intersection is also used as the center point for subsequent image reconstruction data processing. Based on the imaging scenarios in Figures 2(a)-2(b), as shown in Figure 3(a), when the object is placed at the center of the turntable, image reconstruction of the object's cross-section only requires reconstructing an image of size img(x,y). Image reconstruction is performed with the origin O as the center of the reconstructed image. If the length, width, and height of the reconstructed voxel are p, q, and n millimeters respectively, the reconstructed image mapped in the coordinate system is... The image information within the specified range can contain all the information of the cross-section of the object under inspection. However, when the object under inspection is misaligned, as shown in Figures 3(b) and 3(c), in order to reconstruct all the information of the object, an image of size Img(X,Y) needs to be reconstructed. When the pixel size of the reconstructed images is consistent, the number of voxels in Img(X,Y) is greater than that in img(x,y). A higher number of voxels requires more memory and computational resources for image reconstruction, resulting in longer computation time. Furthermore, in the enlarged reconstructed image, only a small portion contains useful object information; the rest is essentially useless data, leading to wasted memory and reduced image processing efficiency.

[0049] The image size of the reconstructed image of the object under inspection is determined based on the size of the object. For the same object, its size does not change with its spatial position during data acquisition. That is, regardless of where the object is placed on the turntable, as long as the amount of information in the original data obtained during the data acquisition process is consistent, the scanned cross-sectional information can be reconstructed using the image size of img(x,y) without needing to enlarge the reconstructed image, thus avoiding memory and time consumption.

[0050] Based on this, when the inspected object is offset from the turntable center, to reconstruct all its cross-sectional information using the image size of the inspected object when it is not offset, the offset of the inspected object relative to the turntable center axis can be determined, that is, the offset offset(X,Y,Z) of the image reconstruction center point relative to the algorithm coordinate system, which is the offset of O' relative to O as shown in Figure 3(c). Thus, by using the offset-corrected image reconstruction center point as the center of the reconstructed image, a reconstructed image of size img(x,y) can reconstruct all the information of the inspected object without expanding the reconstruction range.

[0051] In step S101 above, the processing device can acquire the projected image obtained by the detector detecting the object under test.

[0052] The object to be inspected is placed on a turntable. During the scanning process, the positions of the X-ray source and detector remain unchanged, while the object rotates with the turntable around a central axis perpendicular to the horizontal plane. Thus, the projected image of the object can be denoted as... Among them, row pixels , column pixels Projection angle , This represents the number of channels for the row pixels of the detector. This represents the number of channels for each column of pixels in the detector. This represents the maximum value of the projection angle. The horizontal axis represents the projection angle interval. The direction is the row pixel direction of the detector, and the vertical axis is... The direction is the direction of the array pixels of the detector.

[0053] In other words, the center of the projected image of the object being inspected coincides with the center point of the detector, and the number of column pixels in the projected image is equal to the number of channels of the column pixels of the detector, and the number of row pixels is equal to the number of channels of the row pixels of the detector.

[0054] Furthermore, the projected images of the inspected object acquired by the processing device can be multiple projected images of the inspected object collected at intervals according to the projection angle, or they can be a portion of the multiple projected images mentioned above, without any specific limitation here.

[0055] After acquiring the projected image of the object under inspection, the processing device can perform the above step S102, that is, based on the projected image, determine the offset of the center point of the object under inspection relative to the center point of the image reconstruction.

[0056] As mentioned earlier, the center point of image reconstruction is the intersection of the central axis of the turntable and the central ray of the X-ray source.

[0057] Since the object being examined is three-dimensional, the offset of its center point relative to the image reconstruction center point is a vector, including the offset direction and offset value. Furthermore, this offset includes the offset of the center point along the three coordinate axes of a preset initial image reconstruction coordinate system established with the image reconstruction center point as the origin.

[0058] Then the processing device can execute step S103, using the determined offset direction and offset value to correct the image reconstruction center point, that is, the position point whose positional relationship with the image reconstruction center point satisfies the above offset direction and offset value is used as the corrected image reconstruction center point.

[0059] Then, after correcting the image reconstruction center, the processing device can use the corrected image reconstruction center point to reconstruct the projected image of the object under inspection, and obtain the reconstructed image of the object under inspection, that is, to perform the above step S104.

[0060] The processing device can process each projected image of the object under inspection, and use the corrected image to reconstruct the center point, reconstruct each projected image after processing, and reconstruct the cross-sectional information of the object under inspection to obtain the reconstructed image of the object under inspection.

[0061] As can be seen, in this embodiment, without the need for mechanical control or software assistance, the processing device analyzes the original projection data and determines the offset of the center point of the object under inspection relative to the image reconstruction center point. It then uses this offset to correct the image reconstruction center point. The corrected image reconstruction center point is actually the location of the center point of the object under inspection. Therefore, when using the corrected image reconstruction center point for image reconstruction, only the spatial portion where the object under inspection is located needs to be reconstructed. There is no need to consider expanding the size of the reconstructed image due to the offset between the center point of the object under inspection and the image reconstruction center point. This solves the problems of increased memory and video memory, increased image reconstruction time, and increased invalid image information caused by expanding the size of the reconstructed image, thereby improving the efficiency of image reconstruction.

[0062] As one embodiment of this application, step S102, namely the step of determining the offset of the center point of the inspected object relative to the image reconstruction center point based on the projected image, may include:

[0063] In the projected image, determine the maximum and minimum column number of the object under test in the column pixel direction of the detector, and the maximum and minimum row number of the object under test in the row pixel direction of the detector.

[0064] Based on the maximum and minimum target ordinal numbers, the offset of the center point of the inspected object relative to the image reconstruction center point is determined along the first coordinate axis of the preset initial image reconstruction coordinate system; or, based on the maximum and minimum column ordinal numbers, the offset of the center point of the inspected object relative to the image reconstruction center point is determined along the first coordinate axis of the preset initial image reconstruction coordinate system; wherein, the initial image reconstruction coordinate system is established with the image reconstruction center point as the origin, and the first coordinate axis is the coordinate axis where the central ray of the ray source is located;

[0065] Based on the maximum row number and the minimum row number, the offset of the center point of the inspected object relative to the image reconstruction center point is determined in the direction of the second coordinate axis of the initial image reconstruction coordinate system, wherein the second coordinate axis is the coordinate axis where the center axis of the turntable is located;

[0066] Based on the maximum column number and the minimum column number, the offset of the center point of the object being inspected relative to the center point of the image reconstruction is determined in the direction of the third coordinate axis of the initial image reconstruction coordinate system, wherein the third coordinate axis is a coordinate axis perpendicular to the first coordinate axis and the second coordinate axis.

[0067] Since the center point of the turntable, the central ray of the X-ray source, and the center point of the detector are collinear, the image reconstruction center point is the intersection of the central axis of the turntable and the central ray of the X-ray source. The center point of the projected image coincides with the center point of the detector. Therefore, the image reconstruction center point corresponds to the center point of the detector, and consequently, it corresponds to the center point of the projected image. Specifically, the center point of the turntable is the intersection of the central axis of the turntable and the central ray of the X-ray source, which is the image reconstruction center point.

[0068] After acquiring the projected image of the object to be detected, in order to determine the offset of the center point of the object relative to the image reconstruction center point, the image area occupied by the object can be determined in the projected image, that is, the maximum and minimum column number of the object in the column pixel direction of the projected image, and the maximum and minimum row number of the object in the row pixel direction of the projected image.

[0069] Since the number of column pixels in the projected image is equal to the number of channels in the column pixels of the detector, and the number of row pixels is equal to the number of channels in the row pixels of the detector, the maximum and minimum column numbers of the inspected object in the column pixel direction of the projected image are also the maximum and minimum column numbers of the inspected object in the column pixel direction of the detector; the maximum and minimum row numbers of the inspected object in the row pixel direction of the projected image are also the maximum and minimum row numbers of the inspected object in the row pixel direction of the detector.

[0070] According to the principle of X-ray imaging, the size of the image area of ​​an object in the projected image is related to the size of the object and its position during imaging. That is, the maximum and minimum column numbers of the object in the column pixel direction of the detector, and the maximum and minimum row numbers of the object in the row pixel direction of the detector, are related to the offset of the center point of the object relative to the center point of the image reconstruction.

[0071] Therefore, the processing device can determine the offset of the center point of the object under inspection relative to the center point of the image reconstruction based on the maximum column number, minimum column number, maximum row number, and minimum row number.

[0072] Since the object being inspected is three-dimensional, the preset initial image reconstruction coordinate system used to reconstruct the image of the object being inspected, which is established with the center point of image reconstruction as the origin, is a three-dimensional coordinate system. Therefore, in this initial image reconstruction coordinate system, the object being inspected may be offset from the center point of image reconstruction in all three coordinate axes.

[0073] In the initial image reconstruction coordinate system, the first coordinate axis is the coordinate axis where the central ray of the ray source is located, the second coordinate axis is the coordinate axis where the central axis of the turntable is located, and the third coordinate axis is the coordinate axis perpendicular to the first and second coordinate axes. For example, the initial image reconstruction coordinate system is shown in Figure 3(c). The origin of this initial image reconstruction coordinate system is the intersection point of the central axis of the turntable and the central ray of the ray source S, i.e., the image reconstruction center point O. The first coordinate axis is the X-axis where the central ray of the ray source S is located, the second coordinate axis is the Z-axis where the central axis of the turntable is located, and the third coordinate axis is the Y-axis perpendicular to the X-axis and Z-axis.

[0074] The offset of the center point of the object under inspection relative to the center point of the image reconstruction includes the offset of the center point of the object under inspection relative to the center point of the image reconstruction in the first coordinate axis direction, the offset of the center point of the object under inspection relative to the center point of the image reconstruction in the second coordinate axis direction, and the offset of the center point of the object under inspection relative to the center point of the image reconstruction in the third coordinate axis direction.

[0075] Furthermore, based on the correspondence between the initial image reconstruction coordinate system and the pixel channel direction of the detector and the pixel direction of the projected image, it can be seen that the second coordinate axis direction corresponds to the row pixel channel direction of the detector and the row pixel direction of the projected image, and the third coordinate axis direction corresponds to the column pixel channel direction of the detector and the column pixel direction of the projected image.

[0076] When the center point of the object being inspected is not offset relative to the center point of the image reconstruction, the center point of the object being inspected coincides with the center point of the image reconstruction and the center point of the projected image; however, when the center point of the object being inspected is offset relative to the center point of the image reconstruction, the center point of the object being inspected is offset from the center point of the image reconstruction, and the center point of the object being inspected is also offset from the center point of the image.

[0077] In other words, the offset of the center point of the object under inspection relative to the center point of the image reconstruction will affect the image position of the center point of the object under inspection in the projected image. Specifically, the offset of the center point of the object under inspection relative to the center point of the image reconstruction in the second coordinate axis direction can affect the position of the object under inspection in the row pixel direction corresponding to the second coordinate axis direction of the projected image; the offset of the center point of the object under inspection relative to the center point of the image reconstruction in the third coordinate axis direction can affect the position of the object under inspection in the column pixel direction corresponding to the third coordinate axis direction of the projected image.

[0078] Furthermore, the offset of the center point of the object relative to the image reconstruction center point in the first coordinate axis direction indicates whether the center point of the object is closer to or farther from the X-ray source. According to the imaging principle of near-large and far-small in transmission imaging, the closer the object is to the X-ray source, the larger the corresponding image area of ​​the object in the projected image; conversely, the farther the object is from the X-ray source, the smaller the corresponding image area of ​​the object in the projected image. Therefore, the offset of the center point of the object relative to the image reconstruction center point in the first coordinate axis direction can affect the position of the object in the row pixel direction corresponding to the second coordinate axis direction and the column pixel direction corresponding to the third coordinate axis direction of the projected image.

[0079] Accordingly, the processing device can calculate the offset of the center point of the inspected object relative to the image reconstruction center point in the second coordinate axis direction based on the position of the inspected object in the row pixel direction of the projected image; calculate the offset of the center point of the inspected object relative to the image reconstruction center point in the third coordinate axis direction based on the position of the inspected object in the column pixel direction of the projected image; and calculate the offset of the center point of the inspected object relative to the image reconstruction center point in the first coordinate axis direction based on the position of the inspected object in the row pixel direction or the position of the inspected object in the column pixel direction of the projected image.

[0080] Furthermore, since the position of the inspected object in the row pixel direction of the projected image can be represented by the maximum and minimum row number corresponding to the inspected object, and the position of the inspected object in the column pixel direction of the projected image can be represented by the maximum and minimum column number corresponding to the inspected object, the processing device can also determine the offset of the center point of the inspected object relative to the image reconstruction center point in the second coordinate axis direction based on the maximum and minimum row number; determine the offset of the center point of the inspected object relative to the image reconstruction center point in the third coordinate axis direction based on the maximum and minimum column number; and determine the offset of the center point of the inspected object relative to the image reconstruction center point in the first coordinate axis direction based on the maximum and minimum row number, or the maximum and minimum column number.

[0081] As can be seen, in this embodiment, the processing device can quickly and accurately calculate the offset of the center point of the inspected object relative to the center point of the image reconstruction in each coordinate axis direction of the initial image reconstruction coordinate system based on the maximum row number, minimum row number, maximum column number, and minimum column number, thereby improving the image reconstruction efficiency.

[0082] As one embodiment of this application, determining the offset of the center point of the inspected object relative to the image reconstruction center point along the first coordinate axis direction may include:

[0083] Based on the magnitude relationship between the first image distance and the second image distance in the target pixel direction of the projected image, and the first correspondence between the target distance and the image distance in the target pixel direction corresponding to the object in the projected image, the first offset direction of the center point of the object relative to the image reconstruction center point is determined in the first coordinate axis direction of the preset initial image reconstruction coordinate system.

[0084] Based on the first image distance, the second image distance, and the second correspondence, a first offset value of the center point of the inspected object relative to the center point of the image reconstruction is determined.

[0085] As mentioned earlier, the first coordinate axis of the initial image reconstruction coordinate system established with the image reconstruction center point as the origin is the coordinate axis where the central ray of the X-ray source is located. Therefore, determining the offset of the center point of the object under inspection relative to the image reconstruction center point in the direction of the first coordinate axis is to determine whether the center point of the object under inspection is offset towards the X-ray source or away from the X-ray source relative to the image reconstruction center point.

[0086] According to the imaging principle of near-large and far-small in transmission imaging, the closer the object is to the X-ray source, the larger the corresponding image area of ​​the object on the projected image. Conversely, the farther the object is from the X-ray source, the smaller the corresponding image area of ​​the object on the projected image. The offset of the center point of the object relative to the image reconstruction center point in the first coordinate axis direction of the preset initial image reconstruction coordinate system affects the position of the object in the row pixel direction corresponding to the second coordinate axis direction and the column pixel direction corresponding to the third coordinate axis direction of the projected image.

[0087] Therefore, the processing device can determine the offset of the center point of the inspected object relative to the image reconstruction center point along the first coordinate axis of the preset initial image reconstruction coordinate system based on the maximum and minimum column numbers. Alternatively, the processing device can determine the offset of the center point of the inspected object relative to the image reconstruction center point along the first coordinate axis of the preset initial image reconstruction coordinate system based on the maximum and minimum row numbers.

[0088] Specifically, the processing equipment can determine a first correspondence between the target distance between the center point of the object under inspection and the X-ray source and the image distance in the direction of the target pixel corresponding to the object in the projected image, based on the principle of transmission imaging. This first correspondence indicates that the larger the target distance between the center point of the object under inspection and the X-ray source, the smaller the image distance in the direction of the target pixel corresponding to the object in the projected image; conversely, the smaller the target distance between the center point of the object under inspection and the X-ray source, the larger the image distance in the direction of the target pixel corresponding to the object in the projected image.

[0089] The target pixel direction corresponds to the target ordinal number. When the target ordinal number is the row ordinal number, the target pixel direction is the row pixel direction. When the target ordinal number is the column ordinal number, the target pixel direction is the column pixel direction.

[0090] In the direction of the first coordinate axis, when the center point of the object being inspected shifts towards the direction closer to the X-ray source relative to the center point of the image reconstruction, the image distance of the object being inspected in the direction of the target pixel in the projected image increases compared to the case where the center point of the object being inspected does not shift from the center point of the image reconstruction. When the center point of the object being inspected shifts away from the X-ray source relative to the center point of the image reconstruction, the image distance of the object being inspected in the direction of the target pixel in the projected image decreases compared to the case where the center point of the object being inspected does not shift from the center point of the image reconstruction.

[0091] Since it is impossible to obtain the image image of the inspected object in the projection image when the center point of the inspected object is not offset from the center point of the image reconstruction, it is impossible to determine the change of the image distance of the inspected object in the target pixel direction of the projection image by directly comparing the projection image obtained when the center point of the inspected object is offset from the center point of the image reconstruction with the projection image obtained when the center point of the inspected object is not offset from the center point of the image reconstruction. Based on the change of the image distance in the target pixel direction, the offset direction of the center point of the inspected object relative to the center point of the image reconstruction in the first coordinate axis direction can be determined.

[0092] Since the object being inspected can rotate around the central axis of the turntable, the detector can detect the object during the rotation process and obtain projected images of the object at different rotation angles. Therefore, the projected images of the object obtained by the processing device can include the projected images detected by the detector when the object rotates at different angles.

[0093] As the object is rotated, the spatial position of the object's center point relative to the image reconstruction center point changes; that is, the offset direction and offset value of the object's center point relative to the image reconstruction center point also change accordingly.

[0094] For example, such as Figure 4 As shown, the object 400 is placed on a turntable. In the first coordinate axis, i.e., the X-axis, its center point O1' shifts relative to the image reconstruction center point O towards the X-ray source S. In the projected image 401, the first image distance of the object in the column pixel direction is L1. When the turntable is rotated 180 degrees, in the X-axis direction, its center point O2' shifts relative to the image reconstruction center point O towards the direction away from the X-ray source S. In the projected image 402, the second image distance of the object in the column pixel direction is L2, which is significantly smaller than L1. It can be seen that as the object rotates 180 degrees with the turntable, the direction of the shift of its center point relative to the image reconstruction center point changes in the first coordinate axis direction, and its image distance in both the column pixel direction and the row pixel direction of the projected image changes.

[0095] Based on this, the processing device can determine the first image distance of the inspected object in the target pixel direction in the first projection image and the second image distance of the inspected object in the target pixel direction in the second projection image, wherein the first image distance is the image distance corresponding to the maximum target ordinal number and the minimum target ordinal number of the inspected object in the first projection image, and the second image distance is the image distance corresponding to the maximum target ordinal number and the minimum target ordinal number of the inspected object in the second projection image.

[0096] The angle difference between the second projected image and the first projected image is a preset angle. This preset angle can be set according to actual needs. In order to avoid the situation where the center point of the object before and after rotation is located in the same quadrant of the first coordinate axis, for example, the center point of the object before and after rotation is located in the first quadrant and the fourth quadrant of the positive direction of the first coordinate axis, the value range of the preset angle is set to [90, 270], for example, 90 degrees, 120 degrees, 180 degrees, etc., which are not specifically limited here.

[0097] In one implementation, the preset angle is 180 degrees, so the acquisition angle difference between the first and second projected images is 180 degrees. Therefore, the two center points of the object under inspection before and after rotation correspond about the central axis of the turntable, and their offset directions relative to the image reconstruction center point are opposite in the first coordinate axis direction. The following explanation uses a preset angle of 180 degrees as an example.

[0098] Furthermore, the processing device can utilize the relationship between the first image distance and the second image distance, and the first correspondence between the target distance between the center point of the object under inspection and the X-ray source and the image distance in the direction of the target pixel corresponding to the object under inspection in the projected image, to determine the first offset direction of the center point of the object under inspection relative to the image reconstruction center point in the first coordinate axis direction of the preset initial image reconstruction coordinate system. Here, the target distance is the distance between the center point of the object under inspection and the X-ray source in the first coordinate axis direction.

[0099] Since the target pixel direction can be either the column pixel direction or the row pixel direction, the first image distance and the second image distance can be the image distance in the column pixel direction or the image distance in the row pixel direction.

[0100] In one implementation, the processing device can determine the magnitude relationship between the first image distance and the second image distance in the column pixel direction, and based on the magnitude relationship between the first image distance and the second image distance, and the first correspondence between the target distance between the center point of the object under inspection and the X-ray source and the image distance in the column pixel direction corresponding to the object under inspection in the projected image, determine the first offset direction of the center point of the object under inspection relative to the image reconstruction center point in the first coordinate axis direction of the initial image reconstruction coordinate system.

[0101] In one implementation, the processing device can determine the magnitude relationship between a first image distance and a second image distance in the row pixel direction, and based on the magnitude relationship between the first image distance and the second image distance, and the first correspondence between the target distance between the center point of the object under inspection and the X-ray source and the image distance in the row pixel direction corresponding to the object under inspection in the projected image, determine the first offset direction of the center point of the object under inspection relative to the image reconstruction center point in the first coordinate axis direction of the initial image reconstruction coordinate system.

[0102] By comparing the changes in the image distance in the direction of the target pixel corresponding to the object in the first and second projected images acquired during the rotation process, based on the first correspondence between the target distance between the center point of the object and the X-ray source and the image distance in the direction of the target pixel corresponding to the object in the projected image, the first offset direction of the center point of the object relative to the image reconstruction center point in the first coordinate axis direction when acquiring a certain projected image can be determined.

[0103] For example, such as Figure 4 As shown, since the first image distance L1 of the object 400 in the column pixel direction in the projection image 401 is greater than the second image distance L2 of the object 400 in the column pixel direction in the projection image 402, according to the relationship between L1 and L2, and the first correspondence between the target distance between the center point of the object and the X-ray source and the image distance in the column pixel direction corresponding to the object in the projection image, when acquiring the projection image 401, in the first coordinate axis direction, the center point of the object is shifted towards the X-ray source S relative to the image reconstruction center point; when acquiring the projection image 402, in the first coordinate axis direction, the center point of the object is shifted away from the X-ray source S relative to the image reconstruction center point.

[0104] Furthermore, since the first image distance reflects the image area corresponding to the inspected object in the target pixel direction in the first projected image; the second image distance reflects the image area corresponding to the inspected object in the target pixel direction in the second projected image; and the image distance in the target pixel direction corresponding to the inspected object in the projected image is related to the width of the inspected object in the target pixel direction and the offset of the inspected object relative to the image reconstruction center point in the first coordinate axis direction, the processing device can determine the first offset value of the center point of the inspected object relative to the image reconstruction center point and the second correspondence between the image distance in the target pixel direction corresponding to the inspected object in the projected image, and determine the first offset value of the center point of the inspected object relative to the image reconstruction center point in the first coordinate axis direction of the initial image reconstruction coordinate system based on the first image distance, the second image distance and the second correspondence.

[0105] In one implementation, the processing device can determine a first offset value of the center point of the inspected object relative to the center point of the image reconstruction based on a first image distance, a second image distance, and a second correspondence in the column pixel direction.

[0106] In one implementation, the processing device can determine a first offset value of the center point of the inspected object relative to the center point of the image reconstruction based on a first image distance, a second image distance, and a second correspondence in the row pixel direction.

[0107] As can be seen, in this embodiment, the processing device can quickly and accurately determine the first offset direction and the first offset value of the center point of the inspected object relative to the center point of image reconstruction in the first coordinate axis direction based on the first image distance and the second image distance, thereby improving the offset determination efficiency and thus improving the image reconstruction efficiency.

[0108] As one embodiment of this application, the step of determining the first offset direction of the center point of the inspected object relative to the image reconstruction center point in the first coordinate axis direction of the preset initial image reconstruction coordinate system, based on the magnitude relationship between the first image distance and the second image distance in the target pixel direction of the projected image, and the first correspondence between the target distance between the center point of the inspected object and the X-ray source and the image distance in the target pixel direction corresponding to the inspected object in the projected image, may include:

[0109] When the first image distance in the direction of the target pixel in the projected image is greater than the second image distance, when acquiring the first projected image, the center point of the object being inspected is offset towards the ray source relative to the center point of the image reconstruction in the direction of the first coordinate axis of the preset initial image reconstruction coordinate system.

[0110] When the distance between the first image and the second image is less than the distance between the second image and the first projection image is acquired, the center point of the object being inspected is offset away from the X-ray source in the direction of the first coordinate axis relative to the center point of the image reconstruction.

[0111] When the first image distance is equal to the second image distance, the center point of the object being inspected does not shift relative to the image reconstruction center point in the direction of the first coordinate axis when the first projected image is acquired.

[0112] Since the target pixel direction is either row pixel direction or column pixel direction, the processing device can determine the first offset direction of the center point of the object relative to the image reconstruction center point in the first coordinate axis direction of the preset initial image reconstruction coordinate system based on the image distance of the object in the row pixel direction or column pixel direction in the projected image.

[0113] The following explanation uses the target pixel direction as the column pixel direction as an example to illustrate how to determine the first offset direction.

[0114] When the target pixel direction is the column pixel direction, the first image distance is the image distance in the column pixel direction, and the second image distance is the image distance in the column pixel direction. When the first image distance in the projected image is greater than the second image distance, when acquiring the first projected image, the center point of the object being inspected shifts towards the X-ray source relative to the image reconstruction center point along the first coordinate axis direction of the preset initial image reconstruction coordinate system; when the first image distance is less than the second image distance, when acquiring the first projected image, the center point of the object being inspected shifts away from the X-ray source relative to the image reconstruction center point along the first coordinate axis direction; when the first image distance is equal to the second image distance, the center point of the object being inspected does not shift relative to the image reconstruction center point along the first coordinate axis direction when acquiring the first projected image.

[0115] As mentioned above, the first offset direction of the center point of the object under inspection relative to the image reconstruction center point can be determined based on the magnitude relationship between the first image distance and the second image distance, as well as the first correspondence between the target distance between the center point of the object under inspection and the X-ray source and the image distance of the object under inspection in the column pixel direction in the projected image.

[0116] When the distance between the first and second images in the projection image is greater than the distance between the second and third images, the center point of the object being inspected shifts towards the direction closer to the X-ray source relative to the image reconstruction center point in the direction of the first coordinate axis when the first projection image is acquired.

[0117] When the distance between the first image and the second image is less than the distance between the second image and the first projection image is acquired, the center point of the object being inspected shifts away from the X-ray source relative to the image reconstruction center point in the direction of the first coordinate axis.

[0118] When the distance between the first image and the second image is equal, the center point of the object being inspected does not shift relative to the center point of the image reconstruction in the direction of the first coordinate axis when the first projected image is acquired.

[0119] The image distance in the column pixel direction can be calculated based on the maximum and minimum column ordinal numbers of the object in the projected image, and the image distance in the column pixel direction can be represented by the column span of the ordinal number.

[0120] For example, the first projected image in the projected image is obtained, denoted as P0. o (i,j); Take the second projected image acquired after the turntable rotates 180 degrees, denoted as P. 180 o(i,j), here and It represents the pixel sequence of the projected image, not the coordinates.

[0121] Determine at P0 respectively o (i,j) and P 180 o In (i,j), the minimum column index (ordinal number) J corresponding to the column pixel direction of the object in the detector. min and the maximum column ordinal number indexJ max Among them, in P0 o The minimum and maximum column indexes corresponding to the inspected items in (i,j) are index J and index J, respectively. max_0 o and indexJ min_0 o In P 180 o The minimum and maximum column indexes corresponding to the inspected items in (i,j) are index J and index J, respectively. max_180 o and indexJ min_180 o .

[0122] Calculate the test sample at P0 o The first image distance indexJ corresponding to (i,j) max_0 o - indexJ min_0 o And calculate the value of the tested item at P. 180 o The second image distance indexJ corresponding to (i,j) max_180 o - indexJ min_180 o The magnitudes of the first image distance and the second image distance are compared, and based on the magnitudes of the first image distance and the second image distance, as well as the first correspondence between the target distance between the center point of the object being inspected and the X-ray source and the image distance of the object being inspected in the column pixel direction in the projected image, the position of the object being inspected at P0 is determined. o In (i,j), the first offset direction symbolx is relative to the image reconstruction center point along the first coordinate axis.

[0123] Set the first coordinate axis as the X-axis, with the positive direction of the X-axis representing the direction closer to the ray source and the negative direction representing the direction farther away from the ray source. (indexJ) max_0o - indexJ min_0 o (indexJ) max_180 o - indexJ min_180 o In the case of (indexJ), the inspected object is shifted in the positive direction of the X-axis, symbolx=1; max_0 o - indexJ min_0 o )<(indexJ max_180 o -indexJ min_180 o In the case of (indexJ), the object being inspected shifts to the negative X-axis, symbolx = -1; max_0 o -indexJ min_0 o = (indexJ) max_180 o - indexJ min_180 o In the case of ), the object being inspected is located on the X-axis and is not offset relative to the X-axis, so symbolx=0.

[0124] When the target pixel direction is the row pixel direction, the method of determining the first offset direction of the center point of the inspected object in the first coordinate axis direction of the preset initial image reconstruction coordinate system relative to the image reconstruction center point is similar to the method of determining the first offset direction of the center point of the inspected object in the first coordinate axis direction relative to the image reconstruction center point when the target pixel direction is the column pixel direction, and will not be repeated here.

[0125] As can be seen, in this embodiment, the processing device can quickly and accurately determine the first offset direction of the center point of the inspected object relative to the image reconstruction center point in the first coordinate axis direction based on the relationship between the first image distance and the second image distance.

[0126] As one embodiment of this application, the step of determining the first offset value of the center point of the inspected object relative to the image reconstruction center point based on the first image distance, the image distance, and the second correspondence includes:

[0127] Calculate the sum of the distances between the first image distance and the second image distance, and calculate the first difference between the first image distance and the second image distance;

[0128] Calculate the first product of the first distance from the X-ray source to the central axis of the turntable and the first difference;

[0129] Calculate the ratio of the first product to the sum of the distances to obtain the first offset value of the center point of the object being inspected relative to the center point of the image reconstruction.

[0130] When the center point of the object being inspected has no offset relative to the center point of the image reconstruction in the direction of the first coordinate axis of the initial image reconstruction coordinate system, the image position of the object being inspected in the projected image does not change as the object rotates with the turntable, and the distance between the first image and the distance between the second image are equal.

[0131] For example, if the target pixel direction is the column pixel direction, and the center point of the object being inspected has no offset relative to the image reconstruction center point in the first coordinate axis direction of the initial image reconstruction coordinate system, then the first image distance indexJ of the object being inspected in the first projected image is... max_0 o - indexJ min_0 o The distance indexJ between the inspected object and the second image in the first projection image. max_180 o - indexJ min_180 o equal.

[0132] When the center point of the object being inspected is offset relative to the center point of the image reconstruction in the first coordinate axis direction of the initial image reconstruction coordinate system, the image position of the object being inspected in the projected image changes as the turntable rotates. The first image distance and the second image distance can be calculated based on the width of the object being inspected in the target pixel direction, the offset of the object being inspected relative to the center point of the image reconstruction in the first coordinate axis direction, the first distance from the X-ray source to the central axis of the turntable, the second distance from the X-ray source to the center point of the detector, and the pixel size of the detector.

[0133] For example, if the target pixel direction is the column pixel direction, the first image distance of the object in the first projection image and the second image distance of the object in the second projection image are respectively related to the width of the object in the third coordinate axis direction (column pixel direction), the first offset of the object relative to the image reconstruction center point in the first coordinate axis direction, the first distance from the X-ray source to the central axis of the turntable, the second distance from the X-ray source to the center point of the detector, and the pixel size of the detector as follows:

[0134] L × SDD / (SOD - offsetX) = (indexJ max_180 o - indexJ min_180 o )×detpixelJ;

[0135] L × SDD / (SOD + offsetX) = (indexJ max_0 o - indexJ min_0 o )×detpixelJ;

[0136] Where L is the width of the object under inspection in the direction of the target pixel; SDD is the second distance from the X-ray source to the center point of the detector; SOD is the first distance from the X-ray source to the central axis of the turntable; offsetX is the first offset of the object under inspection relative to the center point of image reconstruction in the direction of the first coordinate axis; and detpixelJ is the pixel size of the detector in the image channel.

[0137] Based on the above relationship, the processing device can calculate: indexJ max_180 o - indexJ min_180 o and indexJ max_0 o indexJ min_0 o .

[0138] By combining the formulas, when the center point of the object being inspected shifts towards the X-ray source, the first shift of the object relative to the image reconstruction center point along the first coordinate axis is:

[0139] OffsetX = SOD × | (indexJ) max_180 o - indexJ min_180 o )-(indexJ max_0º - indexJ min_0 o )| / ((indexJ) max_180 o - indexJ min_180 o )+(indexJ max_0º- indexJ min_0 o ));

[0140] That is, the processing device can calculate the sum of the distances between the first image distance and the second image distance, and calculate the first difference between the first image distance and the second image distance; calculate the first product of the first distance from the X-ray source to the center axis of the turntable and the first difference; and calculate the ratio of the first product to the sum of the distances to obtain the first offset value of the center point of the inspected object relative to the center point of the image reconstruction, and obtain the first offset value of the inspected object relative to the center point of the image reconstruction in the direction of the first coordinate axis.

[0141] When the first offset of the object relative to the image reconstruction center point is shifted towards the direction closer to the X-ray source along the first coordinate axis direction, that is, when the direction closer to the X-ray source is taken as the positive direction of the first coordinate axis, and the first offset of the object relative to the image reconstruction center point is shifted in the positive direction of the first coordinate axis direction, the first offset value of the object relative to the image reconstruction center point along the first coordinate axis direction is:

[0142] SOD×((indexJ) max_180 o - indexJ min_180 o )-(indexJ max_0 o - indexJ min_0 o )) / (indexJ max_180 o - indexJ min_180 o )+(indexJ max_0 o - indexJ min_0 o );

[0143] In the direction of the first coordinate axis, the first offset of the inspected object relative to the image reconstruction center point is:

[0144] OffsetX=symbolx×SOD×((indexJ max_0 o - indexJ min_0 o )-(indexJ max_180 o -indexJ min_180 o)) / (indexJ max_180 o - indexJ min_180 o )+(indexJ max_0 o - indexJ min_0 o );

[0145] Here, symbolx represents the offset direction, which is 1 in this case;

[0146] When the first offset of the object relative to the image reconstruction center point in the direction of the first coordinate axis shifts away from the X-ray source, that is, when the direction closer to the X-ray source is taken as the positive direction of the first coordinate axis, and the first offset of the object relative to the image reconstruction center point shifts in the negative direction of the first coordinate axis, the first offset value of the object relative to the image reconstruction center point in the direction of the first coordinate axis is:

[0147] SOD×((indexJ) max_180 o - indexJ min_180 o )-(indexJ max_0 o - indexJ min_0 o )) / (indexJ max_180 o - indexJ min_180 o )+(indexJ max_0 o - indexJ min_0 o );

[0148] In the direction of the first coordinate axis, the first offset of the inspected object relative to the image reconstruction center point is:

[0149] OffsetX=symbolx×SOD×((indexJ max_180 o - indexJ min_180 o )-(indexJ max_0 o -indexJ min_0 o)) / (indexJ max_180 o - indexJ min_180 o )+(indexJ max_0 o - indexJ min_0 o );

[0150] Here, symbolx is -1.

[0151] As can be seen, in this embodiment, the processing device can use the first image distance and the second image distance to quickly and accurately calculate the first offset value of the center point of the inspected object relative to the center point of image reconstruction, thereby improving the image reconstruction efficiency.

[0152] As one embodiment of this application, the target coordinate axis includes at least one of a second coordinate axis and a third coordinate axis. Determining the offset of the center point of the inspected object relative to the image reconstruction center point in the target coordinate axis direction of the initial image reconstruction coordinate system includes:

[0153] Based on the relative positional relationship between the object under test and the center of the detector, represented by the maximum and minimum target ordinal numbers corresponding to the object under test in the third projection image of the projection image, the second offset direction of the center point of the object under test relative to the image reconstruction center point in the direction of the target coordinate axis is determined.

[0154] Based on the relative positional relationship and the pixel size of the detector in the target pixel direction, the target image offset value of the center point of the object under test relative to the image center point in the third projected image is determined. Based on the conversion relationship between the image offset value and the actual offset value and the target image offset value, a second offset value of the center point of the object under test relative to the image reconstruction center point in the target coordinate axis direction is determined. The target pixel direction includes at least one of row pixel direction and column pixel direction. When the target coordinate axis is the second coordinate axis, the target pixel direction is the row pixel direction. When the target coordinate axis is the third coordinate axis, the target pixel direction is the column pixel direction.

[0155] As mentioned earlier, based on the correspondence between the initial image reconstruction coordinate system and the detector's pixel channel direction (projection image's pixel direction), the second coordinate axis direction corresponds to the detector's row pixel channel direction (projection image's row pixel direction), and the third coordinate axis direction corresponds to the detector's column pixel channel direction (projection image's column pixel direction).

[0156] When the center point of the object being inspected coincides with the center point of the image reconstruction, the center point of the object being inspected also coincides with the center point of the detector. Since both the center point of the image reconstruction and the center point of the detector correspond to the center point of the image, and the center point of the image corresponds to the median of the ordinal number of the projected image in the direction of the target pixel, the center point of the object being inspected corresponds to the median of the ordinal number of the projected image in the direction of the target pixel. The sum of the maximum and minimum target ordinal numbers corresponding to the object being inspected is equal to the sum of the ordinal numbers in the direction of the target pixel.

[0157] For example, if the sum of column ordinal numbers is 20 and the sum of row ordinal numbers is 30, and the center point of the object being examined coincides with the center point of the image reconstruction, the column ordinal number of the column containing the image center point is 10, and the column ordinal number of the corresponding row is 15. The sum of the maximum column ordinal number 12 and the minimum column ordinal number 8 corresponding to the object being examined equals the sum of column ordinal numbers 20; the sum of the maximum row ordinal number 20 and the minimum row ordinal number 15 corresponding to the object being examined equals the sum of row ordinal numbers 30.

[0158] Correspondingly, when the center point of the object being inspected is offset from the center point of the image reconstruction, the center point of the object being inspected is also offset from the center of the detector. In the second coordinate axis direction, if the center point of the object being inspected is offset relative to the image reconstruction center point, then the center point of the object being inspected no longer corresponds to the median of the row number in the projected image. Similarly, in the third coordinate axis direction, if the center point of the object being inspected is offset relative to the image reconstruction center point, then the center point of the object being inspected no longer corresponds to the median of the column number in the projected image. Consequently, the sum of the maximum and minimum row numbers corresponding to the object being inspected is not equal to the sum of the row numbers, but rather depends on the specific offset direction and is related to the sum of the row numbers. Likewise, the sum of the maximum and minimum column numbers corresponding to the object being inspected is not equal to the sum of the column numbers, but rather depends on the specific offset direction and is related to the sum of the column numbers.

[0159] Specifically, in the direction of the second or third coordinate axis, when the center point of the object being inspected shifts in the direction of increasing ordinal number relative to the center point of the image reconstruction, the object being inspected shifts in the direction of increasing ordinal number relative to the center point of the detector. Compared to the case where the center point of the object being inspected coincides with the center point of the image reconstruction, the maximum and minimum target ordinal numbers corresponding to the object being inspected are increased overall. When the center point of the object being inspected shifts in the direction of decreasing ordinal number relative to the center point of the image reconstruction, the object being inspected shifts in the direction of decreasing ordinal number relative to the center point of the detector. Compared to the case where the center point of the object being inspected coincides with the center point of the image reconstruction, the maximum and minimum target ordinal numbers corresponding to the object being inspected are decreased overall.

[0160] As shown in Figure 5(a), i represents the row pixel direction, and j represents the column pixel direction. When the center point of the object being inspected coincides with the center point of the image reconstruction, the median index (ordinal number) J of the column ordinal number of the projected image (P(1,1), P(I,J)) corresponding to the image center point is... mid Then, the median index (ordinal number) of the column ordinal number of the projected image corresponding to the center point of the inspected object is J. mid The index (ordinal number) of the largest column corresponding to the inspected item. max and the minimum column ordinal index (ordinal number) J min The sum of the values ​​is equal to the sum of the column ordinal numbers.

[0161] Based on Figure 5(a), as shown in Figure 5(b), in the direction of the third coordinate axis, when the center point of the object shifts relative to the image reconstruction center point in the direction of increasing column ordinal number, the object shifts relative to the detector center in the direction of increasing column ordinal number. Compared to the case where the center point of the object coincides with the image reconstruction center point, the maximum column ordinal number J corresponding to the object is... max and the minimum column ordinal index (ordinal number) J min Overall increase.

[0162] Based on Figure 5(a), as shown in Figure 5(c), in the direction of the third coordinate axis, when the center point of the object being inspected shifts relative to the image reconstruction center point in the direction of decreasing column ordinal number, the object being inspected shifts relative to the detector center in the direction of decreasing column ordinal number. Compared to the case where the center point of the object being inspected coincides with the image reconstruction center point, the maximum column ordinal number J corresponding to the object being inspected is... max and the minimum column ordinal index (ordinal number) J min Overall reduction.

[0163] Therefore, at least one of the row ordinal number and the column ordinal number can be used as the target ordinal number, and at least one of the second coordinate axis and the third coordinate axis can be used as the target coordinate axis. When the target ordinal number is the row ordinal number, the target coordinate axis is the second coordinate axis, the maximum target ordinal number is the maximum row ordinal number, and the minimum target ordinal number is the minimum row ordinal number. When the target ordinal number is the column ordinal number, the target coordinate axis is the third coordinate axis, the maximum target ordinal number is the maximum column ordinal number, and the minimum target ordinal number is the minimum column ordinal number.

[0164] Based on the relative positional relationship between the object and the detector center, represented by the maximum and minimum target ordinal numbers corresponding to the object in the third projection image, the processing device can determine the second offset direction of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction.

[0165] The third projected image can be any of the projected images, and the third projected image can be the same image as the first projected image or a different image. If the third projected image is not the same image as the first projected image, the third projected image can be the same image as the second projected image or a different image, without any specific limitation.

[0166] Furthermore, based on the relative positional relationship between the inspected object and the detector center, represented by the maximum and minimum target ordinal numbers corresponding to the inspected object in the third projected image, and the pixel size in the direction of the detected target pixel, the processing device can determine the target image offset value of the center point of the inspected object relative to the image center point in the third projected image; and based on the conversion relationship between the image offset value and the actual offset value and the target image offset value, it can determine the second offset value of the center point of the inspected object in the direction of the target coordinate axis relative to the image reconstruction center point.

[0167] The target cell direction includes at least one of the row cell direction and the column cell direction. When the target ordinal number is the row ordinal number, the target cell direction is the row cell direction. When the target ordinal number is the column ordinal number, the target cell direction is the column cell direction.

[0168] For a ray passing through the center point of the object being inspected, the ray, the line segment from the ray source to the central axis of the turntable, and the actual offset value form a triangle. Furthermore, the ray, the line segment from the ray source to the center point of the detector, and the image offset value form another triangle. Since the two triangles are similar, the ratio of the distance from the ray source to the central axis of the turntable to the distance from the ray source to the center point of the detector is equal to the ratio of the actual offset value to the image offset value. Therefore, the conversion relationship between the actual offset value and the image offset value can be obtained.

[0169] The relative positional relationship between the inspected object and the center of the detector, represented by the maximum and minimum target ordinal numbers, is the offset of the inspected object relative to the center of the detector in the target ordinal dimension. Since each ordinal number corresponds to a pixel size, the product of this relative positional relationship and the pixel size is the target image offset value of the center point of the inspected object relative to the center point of the image.

[0170] Since the target image offset value corresponds to the second offset value of the center point of the object to be inspected relative to the center point of the image reconstruction in the direction of the target coordinate axis, the two satisfy the conversion relationship between the image offset value and the actual offset value. Therefore, the second offset value can be obtained based on the target image offset value and the conversion relationship between the image offset value and the actual offset value.

[0171] In one case, the target ordinal number is the row ordinal number, and the target coordinate axis is the second coordinate axis.

[0172] The processing device can determine the second offset direction of the center point of the inspected object relative to the image reconstruction center point in the second coordinate axis direction based on the relative positional relationship between the inspected object and the detector center in the third projected image, which is represented by the maximum and minimum row numbers corresponding to the inspected object. Based on the relative positional relationship and the pixel size in the row pixel direction of the detector, the processing device can determine the target image offset value of the center point of the inspected object relative to the image center point in the third projected image. Based on the conversion relationship between the image offset value and the actual offset value and the row image offset value, the processing device can determine the second offset value of the center point of the inspected object relative to the image reconstruction center point in the second coordinate axis direction.

[0173] In another case, the target ordinal number is the column ordinal number, and the target coordinate axis is the third coordinate axis.

[0174] The processing device can determine the second offset direction of the center point of the inspected object relative to the image reconstruction center point in the third coordinate axis direction based on the relative positional relationship between the inspected object and the detector center in the third projection image, represented by the maximum and minimum column numbers corresponding to the inspected object. Based on the relative positional relationship and the pixel size in the column pixel direction of the detector, the processing device can determine the target image offset value of the center point of the inspected object relative to the image center point in the third projection image. Based on the conversion relationship between the image offset value and the actual offset value and the row image offset value, the processing device can determine the second offset value of the center point of the inspected object relative to the image reconstruction center point in the second coordinate axis direction.

[0175] As can be seen, in this embodiment, the processing device can quickly and accurately determine the second offset direction and the second offset value of the center point of the inspected object relative to the image reconstruction center point in the direction of the target coordinate axis based on the maximum target ordinal number and the minimum target ordinal number corresponding to the inspected object in the third projected image.

[0176] As one embodiment of this application, the target coordinate axis is a second coordinate axis; the image reconstruction method provided in this application embodiment may further include:

[0177] The average projection image of multiple projection images obtained by the detector from detecting the object at various preset acquisition angles is calculated and used as the third projection image in the projection image.

[0178] The detector can acquire multiple projected images of the object being inspected as the turntable rotates. However, once the object is placed on the turntable, its offset relative to the image reconstruction center point along the second coordinate axis does not change with the turntable's rotation. Furthermore, due to the change in the object's offset direction relative to the image reconstruction center point along the first coordinate axis during rotation, the maximum and minimum row numbers of the object in each projected image are inconsistent. This makes it difficult to determine the actual maximum and minimum row numbers of the object, thus making it impossible to accurately determine the object's actual height and its offset relative to the image reconstruction center point along the second coordinate axis.

[0179] Therefore, in order to accurately determine the offset of the object under test relative to the image reconstruction center point along the second coordinate axis, the processing device can calculate the average projection image of multiple projection images obtained by the detector at each preset acquisition angle of the object under test, and use it as the third projection image in the projection image.

[0180] The processing device can calculate the mean projected image P of multiple projected images using the following formula. mean (i,j):

[0181]

[0182] in, For the projected image, I represents the number of row pixel channels of the detector, and J represents the number of column pixel channels of the detector. , For scanning angle, The interval is the angle.

[0183] As can be seen, in this embodiment, the processing device can fully consider the height information of the inspected object, which can improve the accuracy of the offset of the inspected object relative to the image reconstruction center point in the direction of the determined second coordinate axis.

[0184] As one embodiment of this application, the step of determining the second offset direction of the center point of the inspected object relative to the image reconstruction center point in the target coordinate axis direction, based on the relative positional relationship between the inspected object and the center of the detector represented by the maximum and minimum target ordinal numbers corresponding to the inspected object in the third projection image of the projection image, includes:

[0185] Calculate the sum of the maximum and minimum target ordinal numbers corresponding to the inspected object in the third projection image of the projected image; if the sum of the ordinal numbers is greater than the number of pixels of the detector in the target pixel direction, the center point of the inspected object shifts in the target coordinate axis direction relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector increases; if the sum of the ordinal numbers is less than the number of pixels, the center point of the inspected object shifts in the target coordinate axis direction relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector decreases; if the sum of the ordinal numbers is equal to the number of pixels, the center point of the inspected object does not shift in the target coordinate axis direction relative to the image reconstruction center point.

[0186] As mentioned earlier, the maximum and minimum target ordinal numbers corresponding to the object in the third projection image can characterize the relative positional relationship between the object and the center of the detector. Based on this relative positional relationship, the second offset direction of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction can be determined.

[0187] Specifically, the processing device can calculate the ordinal number and value of the maximum and minimum target ordinal numbers corresponding to the inspected object in the third projection image of the projection image.

[0188] When the sum of the ordinal numbers is greater than the number of pixels in the detector along the target pixel direction, the center point of the object being inspected shifts relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector increases along the target coordinate axis direction; when the sum of the ordinal numbers is less than the number of pixels, the center point of the object being inspected shifts relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector decreases along the target coordinate axis direction; when the sum of the ordinal numbers is equal to the number of pixels, the center point of the object being inspected does not shift relative to the image reconstruction center point along the target coordinate axis direction.

[0189] Scenario 1: When the target ordinal number is the column ordinal number and the target coordinate axis is the third coordinate axis, the processing device can calculate the ordinal number and value of the maximum and minimum column ordinal numbers corresponding to the inspected object in the third projection image of the projection image.

[0190] When the sum of the ordinal numbers is greater than the number of pixels in the detector along the column direction, the center point of the object being inspected shifts relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector increases along the third coordinate axis; when the sum of the ordinal numbers is less than the number of pixels, the center point of the object being inspected shifts relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector decreases along the third coordinate axis; when the sum of the ordinal numbers is equal to the number of pixels, the center point of the object being inspected does not shift relative to the image reconstruction center point along the third coordinate axis.

[0191] Exemplarily, determine the third projection image P0 o The minimum column ordinal number indexJ of (i,j) min_0 o and the maximum column ordinal number indexJ max_0 o , determine the offset direction of the center point of the inspected object relative to the image reconstruction center point on the third coordinate axis, i.e., the Y-axis. The positive direction of the Y-axis is the direction in which the column pixel ordinal number increases, and the negative direction of the Y-axis is the direction in which the column pixel ordinal number decreases. The number of pixels J in the column direction.

[0192] If (indexJ max_0 o - indexJ min_0 o ) > J, the inspected object is offset in the positive direction of the Y-axis, symboly = 1;

[0193] If (indexJ max_0 o - indexJ min_0 o ) < J, the inspected object is offset in the negative direction of the Y-axis, symboly = -1;

[0194] If (indexJ max_0 o - indexJ min_0 o ) = J, the inspected object is located on the Y-axis and is not offset relative to the image reconstruction center point, symboly = 0.

[0195] Case 2: When the target ordinal number is the row ordinal number and the target coordinate axis is the second coordinate axis, the processing device can calculate the ordinal sum value of the maximum row ordinal number and the minimum row ordinal number corresponding to the inspected object in the third projection image of the projection image.

[0196] When the ordinal sum value is greater than the number of pixels of the detector in the row direction, the center point of the inspected object is in the direction of the second coordinate axis and is offset relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector increases; when the ordinal sum value is less than the number of pixels, the center point of the inspected object is in the direction of the second coordinate axis and is offset relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector decreases; when the ordinal sum value is equal to the number of pixels, the center point of the inspected object is not offset relative to the image reconstruction center point in the direction of the second coordinate axis.

[0197] Exemplarily, determine the third projection image P mean The minimum row ordinal number indexI in (i,j)min_0 o and the maximum column ordinal number indexI max_0 o , determine the offset direction of the center point of the inspected object relative to the image reconstruction center point on the second coordinate axis, i.e., the Z-axis. The positive direction of the Z-axis is the direction in which the row pixel ordinal number increases, and the negative direction of the Z-axis is the direction in which the row pixel ordinal number decreases. The number of pixels I in the row direction.

[0198] At (indexJ max_0 o - indexJ min_0 o ) > I, the inspected object is offset in the positive direction of the Z-axis, symbolz = 1;

[0199] At (indexJ max_0 o - indexJ min_0 o ) < I, the inspected object is offset in the negative direction of the Z-axis, symbolz = -1;

[0200] At (indexJ max_0 o - indexJ min_0 o ) = I, the inspected object is located on the Z-axis and is not offset relative to the image reconstruction center point, symbolz = 0.

[0201] It can be seen that in this embodiment, the processing device can quickly and accurately determine the offset direction of the center point of the inspected object relative to the image reconstruction center point in the target coordinate axis direction according to the above calculation method.

[0202] As an implementation manner of the embodiment of the present application, the step of determining the target image offset value of the center point of the inspected object relative to the image center point in the third projection image based on the relative position relationship and the pixel size of the detector in the target pixel direction, and determining the second offset value of the center point of the inspected object relative to the image reconstruction center point in the target coordinate axis direction based on the conversion relationship between the image offset value and the actual offset value and the target image offset value includes:

[0203] Calculate the sum of the ordinal values ​​of the maximum and minimum target ordinal numbers, and calculate the second difference between the sum of the ordinal values ​​and the number of pixels of the detector; calculate the second product of the second difference and the pixel size of the detector in the target pixel direction, and take half of the second product as the target image offset value of the center point of the object under inspection in the third projected image relative to the image center point; calculate the first ratio of the first distance from the X-ray source to the central axis of the turntable to the second distance from the X-ray source to the center point of the detector; calculate the second ratio of the target image offset value to the first ratio to obtain the second offset value of the center point of the object under inspection in the target coordinate axis direction relative to the image reconstruction center point.

[0204] As mentioned earlier, the maximum and minimum target ordinal numbers corresponding to the object in the third projection image can characterize the relative positional relationship between the object and the center of the detector. Based on this relative positional relationship, the second offset value of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction can be determined.

[0205] The processing device can calculate the sum of the ordinal numbers of the maximum and minimum target ordinal numbers, and calculate the second difference between the sum of the ordinal numbers and the number of pixels of the detector; calculate the second product of the second difference and the pixel size of the detector in the target pixel direction, and take half of the second product as the target image offset value of the center point of the object being inspected relative to the center point of the image in the third projected image.

[0206] The processing equipment can then calculate the first ratio of the first distance from the X-ray source to the central axis of the turntable to the second distance from the X-ray source to the center point of the detector, and obtain the conversion relationship; and calculate the second ratio of the target image offset value to the first ratio, and obtain the second offset value of the center point of the inspected object in the target coordinate axis direction relative to the image reconstruction center point.

[0207] Case 1: When the target ordinal number is the column ordinal number and the target coordinate axis is the third coordinate axis, the processing device can calculate the sum of the ordinal numbers of the maximum and minimum column ordinal numbers, and calculate the second difference between the sum of the ordinal numbers and the number of column pixels of the detector; calculate the second product of the second difference and the pixel size of the detector in the column direction, and take half of the second product as the target image offset value of the center point of the object being inspected relative to the center point of the image in the third projected image.

[0208] The processing device can then calculate the first ratio of the first distance from the X-ray source to the central axis of the turntable to the second distance from the X-ray source to the center point of the detector; and calculate the second ratio of the target image offset value to the first ratio, to obtain the second offset value of the center point of the inspected object relative to the image reconstruction center point in the direction of the third coordinate axis.

[0209] For example, the processing device can calculate the ordinal sum value indexJ of the maximum and minimum column ordinal numbers. max_0 o + indexJ min_0 o And calculate the second difference between the ordinal sum and the number of column pixels of the detector; calculate the second difference indexJ. max_0 o + indexJ min_0 o -J is the second product of the detector's pixel size detpixelJ in the column direction (indexJ). max_0 o +indexJ min_0 o -J)×detpixelJ, and take half of the second product (indexJ) max_0 o +indexJ min_0 o -J)×detpixelJ / 2 is the target image offset value of the center point of the object being inspected relative to the center point of the image in the third projection image.

[0210] Calculate the first ratio of the first distance SOD from the X-ray source to the central axis of the turntable to the second distance SDD from the X-ray source to the center point of the detector, SOD / SDD; and calculate the second ratio of the target image offset value to the first ratio to obtain the second offset value of the center point of the inspected object relative to the image reconstruction center point in the direction of the third coordinate axis:

[0211]

[0212] Furthermore, it can be expressed as offsetY of the center point of the inspected object in the direction of the third coordinate axis, relative to the center point of the image reconstruction:

[0213]

[0214] Case 2: When the target ordinal number is the row ordinal number and the target coordinate axis is the second coordinate axis, the processing device can calculate the sum of the ordinal numbers of the maximum and minimum row ordinal numbers, and calculate the second difference between the sum of the ordinal numbers and the number of row pixels of the detector; calculate the second product of the second difference and the pixel size of the detector in the row direction, and take half of the second product as the target image offset value of the center point of the object being inspected relative to the center point of the image in the third projected image.

[0215] The processing device can then calculate a first ratio of the first distance from the X-ray source to the central axis of the turntable to the second distance from the X-ray source to the center point of the detector; and calculate a second ratio of the target image offset value to the first ratio, to obtain a second offset value of the center point of the inspected object relative to the image reconstruction center point in the direction of the second coordinate axis.

[0216] For example, the processing device can calculate the ordinal sum of the maximum and minimum row ordinal numbers. And calculate the second difference between the ordinal sum value and the number of row pixels of the detector. ; Calculate the second difference and the pixel size of the detector in the row direction. The second product and half of the second product This serves as the target image offset value relative to the center point of the object being inspected in the third projected image.

[0217] Calculate the first ratio of the first distance SOD from the X-ray source to the central axis of the turntable to the second distance SDD from the X-ray source to the center point of the detector, SOD / SDD; and calculate the second ratio of the target image offset value to the first ratio to obtain the second offset value of the center point of the inspected object relative to the image reconstruction center point in the second coordinate axis direction:

[0218]

[0219] Furthermore, this can be represented as the offset of the center point of the inspected object relative to the center point of the image reconstruction along the second coordinate axis. :

[0220] );

[0221] As can be seen in this embodiment, based on the above calculation method, the processing device can quickly and accurately determine the offset value of the center point of the inspected object relative to the center point of the image reconstruction in the direction of the target coordinate axis.

[0222] As one embodiment of this application, the target ordinal number includes the row ordinal number and the column ordinal number; the maximum target ordinal number includes the maximum row ordinal number and the maximum column ordinal number, and the minimum target ordinal number includes the minimum row ordinal number and the minimum column ordinal number; the determination method of the maximum target ordinal number and the minimum target ordinal number includes:

[0223] Calculate the average pixel grayscale of the pixel value corresponding to each target ordinal number in the projected image;

[0224] According to the data in ascending order of target ordinal numbers, each target ordinal number is traversed sequentially. The first target ordinal number whose average pixel gray value is greater than the preset pixel gray value is taken as the minimum target ordinal number corresponding to the object in the projected image, and the last target ordinal number whose average pixel gray value is greater than the preset pixel gray value is taken as the maximum target ordinal number corresponding to the object in the projected image. The preset pixel gray value is determined based on the average pixel gray value of the pre-acquired air image.

[0225] The target ordinal number includes at least one of the row ordinal number and the column ordinal number. When the target ordinal number is the row ordinal number, the maximum target ordinal number is the maximum row ordinal number and the minimum target ordinal number is the minimum row ordinal number. When the target ordinal number is the column ordinal number, the maximum target ordinal number is the maximum column ordinal number and the minimum target ordinal number is the minimum column ordinal number.

[0226] The maximum and minimum target ordinal numbers corresponding to the inspected object are the target ordinal regions where the inspected object is located in the image area of ​​the projected image. When the target ordinal number is a row ordinal number, the minimum and maximum row ordinal numbers constitute the pixel row range occupied by the inspected object in the image area of ​​the projected image. Furthermore, each pixel row within this pixel row range contains at least one imaging pixel corresponding to the inspected object. Therefore, the average pixel grayscale of the pixel value of each pixel in each pixel row within this pixel row range is greater than the preset pixel grayscale.

[0227] The preset pixel grayscale is based on the average pixel grayscale of the pixels in the pre-acquired air image AirImg(i,j):

[0228] ;

[0229] Similarly, the maximum and minimum target ordinal numbers corresponding to the inspected object are the target ordinal regions where the inspected object is located in the image area of ​​the projected image. When the target ordinal number is a column ordinal number, the minimum and maximum column ordinal numbers constitute the pixel column range occupied by the inspected object in the image area of ​​the projected image. Furthermore, each pixel column within this pixel column range contains at least one imaging pixel corresponding to the inspected object. Therefore, the average pixel grayscale of the pixel value of each pixel column within this pixel column range is greater than the preset pixel grayscale.

[0230] Therefore, for each projected image, the processing device can determine the maximum and minimum target ordinal numbers corresponding to the inspected object in the projected image based on the average pixel grayscale of the pixels in the aforementioned air image.

[0231] Specifically, the processing device can calculate the average pixel gray level of the pixel value corresponding to each target ordinal number in the projected image;

[0232] Then, according to the data in ascending order of target ordinal numbers, each target ordinal number is traversed sequentially. The first target ordinal number whose average pixel gray value is greater than the preset pixel gray value is taken as the minimum target ordinal number corresponding to the object in the projected image, and the last target ordinal number whose average pixel gray value is greater than the preset pixel gray value is taken as the maximum target ordinal number corresponding to the object in the projected image.

[0233] When the maximum target ordinal number is the maximum column ordinal number and the minimum column ordinal number includes the minimum column ordinal number, the processing device can calculate the average pixel gray level of the pixel value corresponding to each column ordinal number in the projected image; then, according to the data of the column ordinal numbers in ascending order, it traverses each column ordinal number in turn, takes the first column ordinal number whose average pixel gray level is greater than the preset pixel gray level as the minimum column ordinal number corresponding to the object in the projected image, and takes the last column ordinal number whose average pixel gray level is greater than the preset pixel gray level as the maximum column ordinal number corresponding to the object in the projected image.

[0234] With projected image P0 o Taking (i,j) as an example, calculate the projected image P0 column by column. o Average pixel gray level of (i,j):

[0235]

[0236] Iterate through each column index in turn, and then iterate through the indexes. By comparing with the air threshold (preset pixel grayscale), find the minimum and maximum column sequences of the projected image.

[0237]

[0238] ;

[0239] When the maximum target sequence number is the maximum row sequence number and the minimum row sequence number includes the minimum row sequence number, the processing device can calculate the average pixel gray level of the pixel value corresponding to each row sequence number in the projected image; then, according to the data in ascending order of row sequence number, it traverses each row sequence number in turn, takes the first row sequence number whose average pixel gray level is greater than the preset pixel gray level as the minimum row sequence number corresponding to the object in the projected image, and takes the last row sequence number whose average pixel gray level is greater than the preset pixel gray level as the maximum row sequence number corresponding to the object in the projected image.

[0240] With projected image For example, calculate the projected image by row. Average pixel grayscale:

[0241] ;

[0242] Iterate through each row number in turn, and then... By comparing with the air threshold (preset pixel grayscale), find the minimum and maximum row order number of the projected image.

[0243]

[0244] ;

[0245] As can be seen, in this embodiment, the processing device can quickly and accurately determine the maximum and minimum target ordinal numbers corresponding to the inspected object in the projected image using the average pixel grayscale of the air image, and then use the maximum and minimum target ordinal numbers to perform offset calculation, thereby improving the offset calculation speed.

[0246] To facilitate understanding of the image reconstruction method provided in the embodiments of this application, the following is combined with... Figure 6 The provided specific example illustrates the execution flow of the image reconstruction method, which includes:

[0247] S601: Determine the relevant parameters for cone-beam CT scanning;

[0248] The processing equipment can determine cone-beam CT scanning parameters, such as voltage, current, scanning angle, scanning angle interval, distance SOD from the X-ray source focal spot to the rotation center, and distance SDD from the X-ray source focal spot to the detector center, based on the characteristics of the sample being tested (i.e., the object under test in this application).

[0249] S602: Acquire an air image;

[0250] The air image AirImg obtained by the detector is acquired, and the average gray value of the air image is calculated as the air threshold (i.e., the preset pixel gray value in this application).

[0251] S603: Obtain the projection data P0(i,j,k) of the sample being tested. θ );

[0252] Acquire the data P0(i,j,k) obtained by the detector detecting the sample. θ ).

[0253] S604: Analyze the sample projection data to obtain the sample's offset O' relative to the origin of the coordinate system;

[0254] Using the average gray value of the air image, find P0(i,j,k) θ Find the minimum and maximum column number in the column pixel direction and the minimum and maximum row number in the row pixel direction of the projection image, based on the span in the column pixel direction and the span in the row pixel direction of the detector.

[0255] Using P0 o (i,j) and P 180 o The minimum and maximum column numbers of (i,j) are used to determine the center point of the sample under test, and its offset relative to the center of the reconstructed image in the X-axis direction; using P0 o (i,j) or P 180 o The minimum and maximum column numbers of (i,j) are used to determine the center point of the sample, its offset relative to the center of the reconstructed image along the Y-axis, and the mean projection image P of each projection image is calculated. mean (i,j), using the mean-projected image P mean The minimum and maximum row numbers of (i,j) are used to determine the center point of the sample, and the offset of the sample relative to the center of the reconstructed image in the Z-axis direction is used to obtain the offset O'(offsetX,offsetY,offsetZ) of the sample relative to the origin of the coordinate system.

[0256] S605: Reconstruct the center of the image using O' correction;

[0257] Determine the offset of the sample's center relative to the origin, and use this offset O'(offsetX,offsetY,offsetZ) to update the center of the reconstructed image.

[0258] S606: Reconstruct CT images from the raw data to obtain slice images of the sample.

[0259] By using the updated reconstructed image center to process the original data, the sample's spatial range can be processed and analyzed without expanding the reconstructed image range, and its cross-sectional information can be fully reconstructed to obtain a slice image of the sample.

[0260] Corresponding to the image reconstruction method described above, this application also provides an image reconstruction apparatus. The image reconstruction apparatus provided in this application embodiment will be described below.

[0261] like Figure 7 As shown, an image reconstruction apparatus is used in a processing device within a detection system. The system further includes a turntable, a radiation source, and a detector. The turntable is located between the radiation source and the detector, and the center point of the turntable, the central ray of the radiation source, and the center point of the detector are collinear. The turntable is rotatable about its central axis. The object to be inspected is placed on the turntable. The apparatus includes:

[0262] Image acquisition module 701 is used to acquire the projected image obtained by the detector detecting the object under test;

[0263] Offset determination module 702 is used to determine the offset of the center point of the object under inspection relative to the image reconstruction center point based on the projected image, wherein the image reconstruction center point is the intersection of the central axis of the turntable and the central ray of the X-ray source; the offset includes the offset direction and the offset value;

[0264] The correction module 703 is used to correct the image reconstruction center point using the offset direction and the offset value to obtain the corrected image reconstruction center point;

[0265] The reconstruction module 704 is used to reconstruct the center point using the corrected image, and then reconstruct the projected image of the object under test to obtain the reconstructed image of the object under test.

[0266] As can be seen, the technical solution provided in this application involves a processing device acquiring a projected image of the object being inspected by a detector; determining the offset of the center point of the object being inspected relative to the image reconstruction center point based on the projected image, wherein the image reconstruction center point is the intersection of the central axis of the turntable and the central ray of the X-ray source; the offset includes the offset direction and the offset value; correcting the image reconstruction center point using the offset direction and the offset value to obtain the corrected image reconstruction center point; and reconstructing the projected image of the object being inspected using the corrected image reconstruction center point to obtain the reconstructed image of the object being inspected.

[0267] By determining the offset of the center point of the object under test relative to the center point of the image reconstruction, and using this offset to correct the center point of the image reconstruction, the corrected center point of the image reconstruction is actually the location of the center point of the object under test. Therefore, when using the corrected center point of the image reconstruction to perform image reconstruction, only the spatial part where the object under test is located needs to be reconstructed. There is no need to consider expanding the size of the reconstructed image due to the offset between the center point of the object under test and the center point of the image reconstruction. This solves the problems of increased memory and video memory, increased image reconstruction time, and increased invalid image information caused by expanding the size of the reconstructed image, thus improving the efficiency of image reconstruction.

[0268] As one embodiment of this application, the offset determination module 702 includes:

[0269] The first determining submodule is used to determine the maximum and minimum column number of the object under test in the column pixel direction of the detector, and the maximum and minimum row number of the object under test in the row pixel direction of the detector in the projected image.

[0270] The second determining submodule is used to determine, based on the maximum and minimum row ordinal numbers, the offset of the center point of the inspected object relative to the image reconstruction center point along the first coordinate axis of a preset initial image reconstruction coordinate system; or, based on the maximum and minimum column ordinal numbers, the offset of the center point of the inspected object relative to the image reconstruction center point along the first coordinate axis of a preset initial image reconstruction coordinate system; wherein, the initial image reconstruction coordinate system is established with the image reconstruction center point as the origin, and the first coordinate axis is the coordinate axis where the central ray of the ray source is located;

[0271] The third determining submodule is used to determine, based on the maximum row number and the minimum row number, the offset of the center point of the inspected object relative to the image reconstruction center point in the direction of the second coordinate axis of the initial image reconstruction coordinate system, wherein the second coordinate axis is the coordinate axis where the center axis of the turntable is located;

[0272] The fourth determining submodule is used to determine, based on the maximum column number and the minimum column number, the offset of the center point of the inspected object relative to the center point of the image reconstruction in the direction of the third coordinate axis of the initial image reconstruction coordinate system, wherein the third coordinate axis is a coordinate axis perpendicular to the first coordinate axis and the second coordinate axis.

[0273] As one embodiment of this application, the apparatus further includes a first offset determination module, the first offset determination module comprising:

[0274] The fifth determining submodule is used to determine, based on the magnitude relationship between the first image distance and the second image distance in the target pixel direction of the projected image, and the first correspondence between the target distance and the image distance in the target pixel direction corresponding to the inspected object in the projected image, the first offset direction of the center point of the inspected object relative to the image reconstruction center point in the first coordinate axis direction of the preset initial image reconstruction coordinate system, wherein the target distance is the distance between the center point of the inspected object and the X-ray source; the target pixel direction is the pixel direction corresponding to the target ordinal number; the first image distance is the maximum target ordinal number and the maximum target ordinal number of the inspected object in the first projected image. The image distance corresponding to the small target ordinal number, the second image distance is the image distance corresponding to the maximum target ordinal number and the minimum target ordinal number of the inspected object in the second projection image; the maximum target ordinal number is the maximum column ordinal number or the maximum row ordinal number, and when the maximum target ordinal number is the maximum column ordinal number, the minimum target ordinal number is the minimum column ordinal number; when the maximum target ordinal number is the maximum row ordinal number, the minimum target ordinal number is the minimum row ordinal number; the target distance is the distance between the center point of the inspected object and the X-ray source in the direction of the first coordinate axis; the acquisition angle difference between the first projection image and the second projection image is a preset angle;

[0275] The sixth determining submodule is used to determine a first offset value of the center point of the inspected object relative to the image reconstruction center point based on the first image distance, the second image distance, and the second correspondence relationship, wherein the second correspondence relationship is the relationship between the first offset value of the center point of the inspected object relative to the image reconstruction center point and the image distance in the direction of the target pixel corresponding to the inspected object in the projected image; the first offset value is the offset value of the center point of the inspected object relative to the image reconstruction center point in the direction of the first coordinate axis of the initial image reconstruction coordinate system.

[0276] As one embodiment of this application, the fifth determining submodule is specifically used for:

[0277] When the first image distance in the direction of the target pixel in the projected image is greater than the second image distance, when acquiring the first projected image, the center point of the object being inspected is offset towards the ray source relative to the center point of the image reconstruction in the direction of the first coordinate axis of the preset initial image reconstruction coordinate system.

[0278] When the distance between the first image and the second image is less than the distance between the second image and the first projection image is acquired, the center point of the object being inspected is offset away from the X-ray source in the direction of the first coordinate axis relative to the center point of the image reconstruction.

[0279] When the first image distance is equal to the second image distance, the center point of the object being inspected does not shift relative to the image reconstruction center point in the direction of the first coordinate axis when the first projected image is acquired.

[0280] As one embodiment of this application, the sixth determining submodule is specifically used for:

[0281] Calculate the sum of the distances between the first image distance and the second image distance, and calculate the first difference between the first image distance and the second image distance;

[0282] Calculate the first product of the first distance from the X-ray source to the central axis of the turntable and the first difference;

[0283] Calculate the ratio of the first product to the sum of the distances to obtain the first offset value of the center point of the object being inspected relative to the center point of the image reconstruction.

[0284] As one embodiment of this application, the target coordinate axis includes at least one of a second coordinate axis and a third coordinate axis;

[0285] The device further includes a second offset determination module, the second offset determination module comprising:

[0286] The seventh determining submodule is used to determine the second offset direction of the center point of the inspected object relative to the image reconstruction center point in the target coordinate axis direction, based on the relative positional relationship between the inspected object and the center of the detector represented by the maximum target ordinal number and the minimum target ordinal number corresponding to the inspected object in the third projection image of the projection image; wherein, when the target coordinate axis is the second coordinate axis, the maximum target ordinal number is the maximum row ordinal number and the minimum target ordinal number is the minimum row ordinal number; when the target coordinate axis is the third coordinate axis, the maximum target ordinal number is the maximum column ordinal number and the minimum target ordinal number is the minimum column ordinal number;

[0287] The eighth determining submodule is used to determine, based on the relative positional relationship and the pixel size of the detector in the target pixel direction, the target image offset value of the center point of the object under test relative to the image center point in the third projected image, and based on the conversion relationship between the image offset value and the actual offset value and the target image offset value, to determine the second offset value of the center point of the object under test relative to the image reconstruction center point in the target coordinate axis direction, wherein the target pixel direction includes at least one of row pixel direction and column pixel direction, and when the target coordinate axis is the second coordinate axis, the target pixel direction is the row pixel direction, and when the target coordinate axis is the third coordinate axis, the target pixel direction is the column pixel direction.

[0288] As one embodiment of this application, the target coordinate axis is a second coordinate axis; the device further includes:

[0289] The first calculation module is used to calculate the average projection image of multiple projection images obtained by the detector from detecting the object at various preset acquisition angles, and use it as the third projection image in the projection images.

[0290] As one embodiment of this application, the seventh determining submodule includes:

[0291] The first determining unit is used to calculate the ordinal number and value of the maximum target ordinal number and the minimum target ordinal number corresponding to the inspected object in the third projection image of the projection image;

[0292] The second determining unit is configured to, when the sum of the ordinal numbers is greater than the number of pixels of the detector in the target pixel direction, shift the center point of the object under test in the target coordinate axis direction relative to the image reconstruction center point towards the end of the detector with increasing pixel ordinal number.

[0293] The third determining unit is used to determine that, when the sum of the ordinal numbers and values ​​is less than the number of pixels, the center point of the object being inspected is shifted relative to the image reconstruction center point towards the end where the pixel ordinal number of the detector decreases in the direction of the target coordinate axis.

[0294] The fourth determining unit is configured to ensure that, when the ordinal sum is equal to the number of pixels, the center point of the inspected object does not shift relative to the image reconstruction center point in the direction of the target coordinate axis.

[0295] As one embodiment of this application, the eighth determining submodule includes:

[0296] The first calculation unit is used to calculate the sum of the ordinal numbers of the maximum and minimum target ordinal numbers, and to calculate the second difference between the sum of the ordinal numbers and the number of pixels of the detector.

[0297] The second calculation unit is used to calculate the second product of the second difference and the pixel size of the detector in the target pixel direction, and to use half of the second product as the target image offset value of the center point of the object being inspected relative to the image center point in the third projected image.

[0298] The third calculation unit is used to calculate a first ratio between the first distance from the radiation source to the central axis of the turntable and the second distance from the radiation source to the center point of the detector;

[0299] The fourth calculation unit is used to calculate the second ratio of the target image offset value to the first ratio, and obtain the second offset value of the center point of the inspected object relative to the image reconstruction center point in the direction of the target coordinate axis.

[0300] As one embodiment of this application, the target ordinal number includes a row ordinal number and a column ordinal number; the device further includes an ordinal number determination module, which is specifically used for:

[0301] Calculate the average pixel grayscale of the pixel value corresponding to each target ordinal number in the projected image;

[0302] According to the data in ascending order of target ordinal numbers, each target ordinal number is traversed sequentially. The first target ordinal number whose average pixel gray value is greater than the preset pixel gray value is taken as the minimum target ordinal number corresponding to the object in the projected image, and the last target ordinal number whose average pixel gray value is greater than the preset pixel gray value is taken as the maximum target ordinal number corresponding to the object in the projected image. The preset pixel gray value is determined based on the average pixel gray value of the pre-acquired air image.

[0303] This application also provides a processing device, such as... Figure 8 As shown, it includes:

[0304] Memory 801 is used to store computer programs;

[0305] The processor 802, when executing the program stored in the memory 801, implements the image reconstruction method described in any of the above embodiments.

[0306] Furthermore, the aforementioned processing device may also include a communication bus and / or a communication interface, with the processor 802, the communication interface, and the memory 801 communicating with each other via the communication bus.

[0307] The communication bus mentioned in the above processing device can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of illustration, only one thick line is used to represent it in the diagram, but this does not indicate that there is only one bus or one type of bus.

[0308] The communication interface is used for communication between the aforementioned processing device and other devices.

[0309] The memory may include random access memory (RAM) or non-volatile memory (NVM), such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0310] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0311] In another embodiment provided in this application, a computer-readable storage medium is also provided, which stores a computer program that, when executed by a processor, implements the steps of any of the above-described image reconstruction methods.

[0312] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to perform any of the image reconstruction methods described above.

[0313] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a solid-state drive (SSD), etc.

[0314] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0315] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the embodiments of apparatus, processing devices, computer-readable storage media, and computer program products are basically similar to the method embodiments, and therefore the descriptions are relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0316] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A method of image reconstruction, characterized by, The method is applied to a processing device in a detection system, the system further comprising a turntable, a ray source and a detector; the turntable is located between the ray source and the detector, and a center point of the turntable, a center ray of the ray source and a center point of the detector are collinear; the turntable can rotate around a central axis thereof; The object under examination is placed on the turntable; the method comprises: Obtaining a projection image of the object under examination detected by the detector; Based on the projection image, determining an offset of the center point of the object under examination relative to an image reconstruction center point, wherein the image reconstruction center point is an intersection of the central axis of the turntable and the center ray of the ray source; the offset comprises an offset direction and an offset value; Using the offset direction and the offset value, correcting the image reconstruction center point to obtain a corrected image reconstruction center point, wherein the corrected image reconstruction center point is a position where the center point of the object under examination is located; Using the corrected image reconstruction center point, reconstructing the projection image of the object under examination to obtain a reconstructed image of the object under examination.

2. The method of claim 1, wherein, The step of determining the offset of the center point of the object under examination relative to the image reconstruction center point based on the projection image comprises: Determining a maximum column sequence number and a minimum column sequence number corresponding to the object under examination in a column pixel direction of the detector in the projection image, and a maximum row sequence number and a minimum row sequence number corresponding to the object under examination in a row pixel direction of the detector; Based on the maximum row sequence number and the minimum row sequence number, determining an offset of the center point of the object under examination relative to the image reconstruction center point in a first coordinate axis direction of a preset initial image reconstruction coordinate system; or, based on the maximum column sequence number and the minimum column sequence number, determining an offset of the center point of the object under examination relative to the image reconstruction center point in the first coordinate axis direction of the preset initial image reconstruction coordinate system; wherein the initial image reconstruction coordinate system is established with the image reconstruction center point as a coordinate origin, and the first coordinate axis is a coordinate axis where the center ray of the ray source is located; Based on the maximum row sequence number and the minimum row sequence number, determining an offset of the center point of the object under examination relative to the image reconstruction center point in a second coordinate axis direction of the initial image reconstruction coordinate system, wherein the second coordinate axis is a coordinate axis where the central axis of the turntable is located; Based on the maximum column sequence number and the minimum column sequence number, determining an offset of the center point of the object under examination relative to the image reconstruction center point in a third coordinate axis direction of the initial image reconstruction coordinate system, wherein the third coordinate axis is a coordinate axis perpendicular to the first coordinate axis and the second coordinate axis.

3. The method of claim 2, wherein, The manner of determining the offset of the center point of the object under examination relative to the image reconstruction center point in the first coordinate axis direction comprises: According to a size relationship between a first image distance and a second image distance in a target pixel direction in the projection image, and a first corresponding relationship between a target distance and an image distance in the target pixel direction corresponding to the object in the projection image, a first offset direction of a center point of the object in a first coordinate axis direction of a preset initial image reconstruction coordinate system relative to an image reconstruction center point is determined, wherein the target distance is a distance between the center point of the object and the ray source; the target pixel direction is a pixel direction corresponding to a target ordinal number; the first image distance is an image distance corresponding to a maximum target ordinal number and a minimum target ordinal number of the object in a first projection image, and the second image distance is an image distance corresponding to a maximum target ordinal number and a minimum target ordinal number of the object in a second projection image; the maximum target ordinal number is the maximum column ordinal number or the maximum row ordinal number; in a case where the maximum target ordinal number is the maximum column ordinal number, the minimum target ordinal number is the minimum column ordinal number; in a case where the maximum target ordinal number is the maximum row ordinal number, the minimum target ordinal number is the minimum row ordinal number; and a difference in an acquisition angle corresponding to the first projection image and the second projection image is a preset angle; According to the first image distance, the second image distance, and a second corresponding relationship, a first offset value of the center point of the object relative to the image reconstruction center point is determined, wherein the second corresponding relationship is a relationship between the first offset value of the center point of the object relative to the image reconstruction center point and the image distance in the target pixel direction corresponding to the object in the projection image; and the first offset value is an offset value of the center point of the object in the first coordinate axis direction of the initial image reconstruction coordinate system relative to the image reconstruction center point.

4. The method of claim 3, wherein, The step of determining, according to a size relationship between a first image distance and a second image distance in a target pixel direction in the projection image, and a first corresponding relationship between a target distance and an image distance in the target pixel direction corresponding to the object in the projection image, a first offset direction of a center point of the object in a first coordinate axis direction of a preset initial image reconstruction coordinate system relative to an image reconstruction center point, comprises: In a case where the first image distance is greater than the second image distance in the target pixel direction in the projection image, when the first projection image is acquired, the center point of the object in the first coordinate axis direction of the preset initial image reconstruction coordinate system is offset relative to the image reconstruction center point in a direction close to the ray source; In a case where the first image distance is less than the second image distance, when the first projection image is acquired, the center point of the object in the first coordinate axis direction is offset relative to the image reconstruction center point in a direction away from the ray source; In a case where the first image distance is equal to the second image distance, a center point of the object does not shift in the first coordinate axis direction relative to the image reconstruction center point when the first projection image is acquired.

5. The method of claim 3, wherein, The step of determining the first offset value of the center point of the object relative to the image reconstruction center point according to the first image distance, the image distance, and the second correspondence relationship comprises: calculating a sum of distances of the first image distance and the second image distance, and calculating a first difference value of the first image distance and the second image distance; calculating a first product of the first distance of the ray source to the central axis of the turntable and the first difference value; calculating a ratio of the first product to the sum of distances to obtain the first offset value of the center point of the object relative to the image reconstruction center point.

6. The method of claim 2, wherein, The target coordinate axis comprises at least one of a second coordinate axis and a third coordinate axis. The manner of determining the offset of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction of the initial image reconstruction coordinate system comprises: determining a second offset direction of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction according to a relative position relationship between the object and the center of the detector represented by a maximum target ordinal number and a minimum target ordinal number of the object in a third projection image of the projection images; wherein, in a case where the target coordinate axis is the second coordinate axis, the maximum target ordinal number is the maximum row ordinal number, and the minimum target ordinal number is the minimum row ordinal number; in a case where the target coordinate axis is the third coordinate axis, the maximum target ordinal number is the maximum column ordinal number, and the minimum target ordinal number is the minimum column ordinal number. determining a target image offset value of the center point of the object relative to the image center point in the third projection image based on the relative position relationship and a pixel size of the detector in a target pixel direction, and determining a second offset value of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction based on a conversion relationship between the image offset value and the actual offset value and the target image offset value, wherein the target pixel direction comprises at least one of a row pixel direction and a column pixel direction, in a case where the target coordinate axis is the second coordinate axis, the target pixel direction is the row pixel direction, and in a case where the target coordinate axis is the third coordinate axis, the target pixel direction is the column pixel direction.

7. The method of claim 6, wherein, The target coordinate axis is the second coordinate axis; and the method further comprises: calculating a mean projection image of a plurality of projection images of the object detected by the detector at each preset acquisition angle as the third projection image of the projection images.

8. The method of claim 6, wherein, The step of determining the second offset direction of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction, according to the relative position relationship between the object and the center of the detector represented by the maximum target serial number and the minimum target serial number corresponding to the object in the third projection image in the projection images, comprises: calculating the serial number sum of the maximum target serial number and the minimum target serial number corresponding to the object in the third projection image in the projection images; in the case that the serial number sum is greater than the number of pixels of the detector in the target pixel direction, the center point of the object in the target coordinate axis direction is offset relative to the image reconstruction center point to the end of the increasing pixel serial number of the detector; in the case that the serial number sum is less than the number of pixels, the center point of the object in the target coordinate axis direction is offset relative to the image reconstruction center point to the end of the decreasing pixel serial number of the detector; in the case that the serial number sum is equal to the number of pixels, the center point of the object in the target coordinate axis direction is not offset relative to the image reconstruction center point.

9. The method of claim 6, wherein, The step of determining the target image offset value of the center point of the object relative to the image center point in the third projection image based on the relative position relationship and the pixel size of the detector in the target pixel direction, and determining the second offset value of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction based on the conversion relationship between the image offset value and the actual offset value and the target image offset value, comprises: calculating the serial number sum of the maximum target serial number and the minimum target serial number, and calculating the second difference value between the serial number sum and the number of pixels of the detector; calculating the second product of the second difference value and the pixel size of the detector in the target pixel direction, and taking half of the second product as the target image offset value of the center point of the object relative to the image center point in the third projection image; calculating the first ratio of the first distance from the ray source to the central axis of the turntable and the second distance from the ray source to the center point of the detector; calculating the second ratio of the target image offset value and the first ratio, to obtain the second offset value of the center point of the object relative to the image reconstruction center point in the target coordinate axis direction.

10. The method according to any one of claims 2-9, characterized in that, The target serial number comprises a row serial number and a column serial number; the determination method of the maximum target serial number and the minimum target serial number comprises: calculating the average pixel gray value of the pixel value corresponding to each target serial number in the projection image; According to the data from small to large target serial numbers, each target serial number is sequentially traversed, a first target serial number with an average pixel gray level greater than a preset pixel gray level in the traversed target serial numbers is taken as a minimum target serial number corresponding to the detected object in the projection image, and a last target serial number with an average pixel gray level greater than the preset pixel gray level in the traversed target serial numbers is taken as a maximum target serial number corresponding to the detected object in the projection image, wherein the preset pixel gray level is determined based on an average pixel gray level of a pre-acquired air image.

11. A processing device, characterized by Comprising: a memory for storing a computer program; a processor for executing the program stored on the memory to implement the method of any one of claims 1-10.

Images