Detector ring, computed tomography equipment and method for determining sampling parameters of computed tomography equipment

Abstract

The detector ring of the computed tomography equipment is formed by arranging a plurality of detector units (10) in the circumferential direction of the detector ring, and the detection face of each detector unit (10) is parallel to the axis (L) of the detector ring. Adjacent sides (11) of two adjacent detection surfaces are arranged parallel to each other and opposite to each other, and the sides are inclined relative to the axis of the detector ring. According to the detector ring, the computed tomography equipment can effectively eliminate ring artifacts. The invention further provides computed tomography equipment comprising the detector ring and a method for determining sampling parameters of the computed tomography equipment.

Description

Technical Field

[0001] This invention relates to the field of computed tomography (CT) technology, and more particularly to a detector ring, a computed tomography device including the detector ring, and a method for determining the sampling parameters of the computed tomography device. Background Technology

[0002] Computed tomography (CT), a non-invasive imaging technique, has become a core tool in modern medical diagnosis and industrial testing since its invention by Hounsfield in 1971. Early circular computed tomography (RCT) required a source-detector ring to rotate around the object to acquire data, followed by stepping movement of the examination table along the Z-axis. While suitable for static imaging, this was inefficient. Helical computed tomography (HCT), introduced in the 1990s, combined the rotation of the source-detector ring with continuous movement of the examination table to create a helical trajectory, achieving faster data acquisition and continuous volumetric imaging. Multi-source static computed tomography (MSSCT) represents a more advanced architecture, employing multiple fixed X-ray sources (e.g., 24 or more) distributed around the circumference of the source ring. Combined with examination table movement and X-ray source activation sequences, it achieves parallel acquisition without mechanical rotation, thus reducing motion-induced image blurring and making it suitable for dynamic imaging.

[0003] To meet the demands of large field-of-view imaging, detector stitching technology has gradually become a core means of expanding the performance of computed tomography (CT) equipment. This technology cleverly circumvents the technological and cost bottlenecks of manufacturing giant single detectors by precisely arranging multiple standard-sized detector units to form a large-scale array.

[0004] In existing equipment, as such Figure 1 Taking MSSCT as an example, several X-ray sources are evenly arranged to form a source ring, which is coaxial with the detector ring. Their axis L coincides with the Z-axis in the spatial rectangular coordinate system O-XYZ. The origin of the spatial rectangular coordinate system is a fixed point relative to the examination table, such as the geometric center of the object being examined. The X-axis is parallel to the width direction of the examination table, and the Y-axis is perpendicular to both the X-axis and the Z-axis. Detector units are usually formed by vertically splicing them together to form a detector ring. That is, in the detector ring, each detector unit is vertically arranged along the circumference of the detector ring, such as... Figure 1 The diagram in the lower right corner shows a partial unfolded view of the five detector units, with the side 11 of each detector unit parallel to the Z-axis. This layout is simple and easy to integrate.

[0005] However, as Figure 1As shown, the vertically spliced ​​layout of the detector rings results in gaps G between adjacent sides of two adjacent detector surfaces, preventing the reception of X-rays. These gaps G are formed by the frames of adjacent detector units and gaps caused by assembly errors, creating fixed, vertically penetrating linear sampling missing bands in the projection space. When the device rotates to scan, these fixed missing bands appear as periodic stripes, which are then amplified by backprojection in the reconstructed image, forming ring-shaped artifacts centered on the axis. Such artifacts severely reduce the quantitative accuracy of the image and destroy the image structure, potentially masking minute lesions or structural defects in high-precision medical diagnosis and industrial non-destructive testing. Summary of the Invention

[0006] The purpose of this invention is to provide a detector ring for a computed tomography (CT) scanner that enables the CT scanner to effectively eliminate ring artifacts.

[0007] Another object of the present invention is to provide a computed tomography device including the above-described detector ring, which can effectively eliminate ring artifacts.

[0008] Another objective of this invention is to provide a method for determining the sampling parameters of a computed tomography (CT) scanner, which can easily and conveniently determine the sampling parameters of the CT scanner and determine whether the CT scanner can effectively eliminate ring artifacts.

[0009] The present invention provides a detector ring for a computed tomography (CT) scanner, comprising multiple detector units arranged circumferentially. The detection surface of each detector unit is parallel to the axis of the detector ring. Adjacent sides of two adjacent detection surfaces are parallel to each other and arranged opposite to each other, and these sides are inclined relative to the axis of the detector ring.

[0010] By tilting the detector units, the computed tomography equipment, including the aforementioned detector ring, can effectively eliminate ring artifacts.

[0011] In another illustrative embodiment of the detector ring of a computed tomography (CT) scanner, the tilt angle of the side relative to the axis... Less than or equal to 45°.

[0012] The present invention also provides a computed tomography (CT) scanner, including the detector ring described above. This CT scanner can effectively eliminate ring artifacts.

[0013] In another illustrative embodiment of the computed tomography (CT) scanner, the CT scanner is an RCT, HCT, or MSSCT. The normalized pitch of the CT scanner... The result is obtained by calculation using equation (1): Equation (1) in, The Z-axis represents the distance the examination table moves along the Z-axis during one scan cycle. The Z-axis is a coordinate axis in the spatial rectangular coordinate system O-XYZ that is parallel to the axis of the detector ring and passes through the center of the X-ray source ring. The origin of the spatial rectangular coordinate system is fixed relative to the position of the examination table, and the X-axis is parallel to the width direction of the examination table. The maximum coverage height of the ray along the Z-axis during one scan cycle is calculated using equation (2): Equation (2) In equation (2), Let be the radius of the circle containing the rotation trajectory of the ray source. Let be the theoretical radius of the detector ring, and be the radius of the circle containing the center of each detector element. The effective height of each detector unit along the Z-axis direction. ,in, This represents the number of pixels in each detector unit. The height of a single pixel in the detector unit along the Z-axis when it is not tilted.

[0014] In another illustrative embodiment of the computed tomography (CT) device, when the CT device is an RCT, the normalized pitch is 0. When the computed tomography (CT) device is HCT, the normalized pitch is... , in, This represents the coverage height of the ray at X-axis coordinate R along the Z-axis during one scan cycle. The result is obtained by calculation using equation (3): Equation (3); or When the computed tomography (CT) device is MSSCT, the normalized pitch is... , in, This represents the coverage height of the ray at X-axis coordinate R along the Z-axis during one scan cycle. The result is obtained by calculation using equation (4): Equation (4) In equation (4), It represents the offset distance along the Z-axis between the plane containing the rotation trajectory of the X-ray source and the plane containing the center of each detector unit.

[0015] This invention also provides a method for determining sampling parameters of a computed tomography (CT) scanner. The CT scanner is the aforementioned CT scanner. The method includes: establishing a spatial rectangular coordinate system, where the origin of the spatial rectangular coordinate system is fixed relative to the examination table; the coordinate axis passing through the center of the circle containing the X-ray source's rotation trajectory and parallel to the axis of the detector ring is the Z-axis; and the axis parallel to the width direction of the examination table is the X-axis; and obtaining the sampling parameters based on the spatial rectangular coordinate system through a constructed X-ray parameter equation.

[0016] This method can easily and conveniently determine the sampling parameters of a computed tomography (CT) scanner and whether the CT scanner can effectively eliminate ring artifacts.

[0017] In another illustrative embodiment of the method for determining sampling parameters in a computed tomography (CT) scanner, the sampling parameters are the number of effective viewing angles and angular sparsity. The steps are as follows: Based on a spatial rectangular coordinate system, the sampling parameters are obtained through a constructed ray parameter equation. Specifically, this includes: based on a spatial rectangular coordinate system, constructing and solving the ray parameter equation to obtain a set of effective viewing angle indices. The elements in the effective viewing angle index set represent the effective viewing angles. Under these effective viewing angles, a point on the inspected object... x Rays that can be hit and emitted can hit effective pixels of the detector unit to generate scan data for imaging; and the effective viewpoint number and angular sparsity are calculated based on the effective viewpoint index set, where the effective viewpoint number is the number of effective viewpoints hit by all pixels in the effective viewpoint index set. x The number of effective viewing angles for a point, and the angular sparsity is the normalized variance of the angular interval between two adjacent effective viewing angles. This facilitates the calculation and determination of the sampling parameters of the computed tomography (CT) scanner.

[0018] In another illustrative embodiment of the method for determining the sampling parameters of a computed tomography (CT) scanner, the ray parameter equation... Equation (5) represents: Equation (5) in, An isometric perspective The position of the corresponding ray source in the spatial rectangular coordinate system is represented by equation (6): Equation (6), In equation (6), Let be the radius of the circle containing the rotation trajectory of the ray source. An isometric perspective The angle between the line connecting the corresponding ray source and the origin O and the positive X-axis. This is the s-th iso-angle viewpoint in the c-th scan cycle. For the scan week number, The number of isoangular viewpoints per scan cycle. Equation (7) represents: Equation (7), In equation (7), The starting angle for cycle 0. The angular step size of adjacent viewpoints within each scan cycle. This represents the overall rotation increment between two adjacent scan cycles. An isometric perspective The corresponding Z-axis coordinate of the ray source, For RCT, , For HCT, , For MSSCT, , in: An isometric perspective The corresponding Z-axis coordinate of the ray source at the starting position, To check the distance the bed moves along the Z-axis during one scan cycle; For the first i Each detector unit at an equal angle Next The center coordinates of each pixel are represented by equation (8): Equation (8) In equation (8), To be able to be viewed from the same angle The corresponding radiation source emitted a ray that struck the first i The center position coordinates of each detector element are represented by equation (9): Equation (9) In equation (9), Let be the theoretical radius of the detector ring, and be the radius of the circle containing the center of each detector element. For the first in the XOY plane, i The azimuth angle of the center of the first detector unit is the first... i The line connecting the center of each detector unit and the origin O, and the iso-angle viewpoint The angle between the line connecting the corresponding ray source and the origin O. The offset distance along the Z-axis between the plane containing the rotation trajectory of the X-ray source and the plane containing the center of each detector unit. For the first i The pixel index at the center of each detector unit. The width of each pixel in the detector unit along the direction perpendicular to the Z-axis when it is not tilted. The height of each pixel in the detector unit along the Z-axis when it is not tilted. For the tilted detector unit along the width direction The unit step size vector, For the tilted detector unit along the height direction The unit step size vector, The tilt angle, and Expressed by equations (10) and (11) respectively: Equation (10) Equation (11) in, It is a tangential unit vector, with the tangential direction perpendicular to the Z-axis. , It is a unit vector along the axial direction, and the unit vector along the axial direction is parallel to the Z-axis. .

[0019] In another illustrative embodiment of the method for determining the sampling parameters of a computed tomography (CT) scanner, the effective viewpoint index set... Equation (12) represents: Equation (12) in, i This is the index sequence of the detector elements on the detector ring. For each detector element, the pixel index is... For the position located at the i The pixel in the m-th row and n-th column of a detector element Indicates a perspective at the same angle Below, at equal angles The corresponding radiation source emits radiation capable of hitting the first... i Pixels of each detector unit ; For the first i The set of valid pixel indices for each detector unit; To be at the same angle Below, from the same angle perspective The corresponding ray source points to the first i Pixels of each detector unit The ray parameter equation, For length, This indicates whether points on the inspected object can be viewed from the same angle. The solution is to be found by being hit below.

[0020] In another illustrative embodiment of the method for determining the sampling parameters of a computed tomography (CT) scanner, the effective field of view number... The number of elements in the effective view index set is represented by equation (13): Equation (13).

[0021] In another illustrative embodiment of the method for determining the sampling parameters of a computed tomography (CT) scanner, angular sparsity... Equation (14) represents: Equation (14) in, For ideal uniform sampling, the angular interval between two adjacent effective viewpoints is... ; When sampling is non-ideal uniform, the angular interval between two adjacent effective viewpoints is expressed by equation (15): Equation (15) In equation (15), Apply points to the subject of the examination The i An effective perspective ,in . Attached Figure Description

[0022] The following figures are for illustrative purposes only and do not limit the scope of the invention.

[0023] Figure 1 This is a schematic diagram illustrating the structure of the detector ring in an existing computed tomography (CT) scanner.

[0024] Figure 2 This is a schematic diagram illustrating the tilted arrangement of detector elements in a detector ring.

[0025] Figure 3 Used to illustrate the movement trajectory of the X-ray source during a scan cycle of three computed tomography (CT) devices.

[0026] Figure 4Used to illustrate the geometric relationship between the X-ray source and the detector unit.

[0027] Figure 5 A schematic flowchart illustrating one embodiment of a method for determining sampling parameters of a computed tomography (CT) scanner.

[0028] Figure 6 for Figure 5 The diagram shows a partial flowchart of one illustrative implementation of the determination method.

[0029] Figure 7 This is used to illustrate the method for constructing ray parameter equations.

[0030] Figure 8 This is an example diagram showing the distribution of the effective field of view for three types of computed tomography (CT) scanners.

[0031] Figure 9 This is an example diagram showing the angular sparsity distribution of three computed tomography (CT) devices.

[0032] Figure 10 and Figure 11 This is used to illustrate the effect of tilted detector units on eliminating ring artifacts.

[0033] Figure 12 This is a grayscale curve used to illustrate CT images from three different computed tomography (CT) devices.

[0034] Figure 13 This is used to illustrate the iterative reconstruction results of the resolution test card under different tilt angles.

[0035] Figure 14 Used to illustrate modulation transfer function curves at different tilt angles.

[0036] Figure 15 This is used to illustrate the iterative reconstruction results under the combination of gap width and tilt angle.

[0037] Figure 16 For illustrative purposes Figure 15 Line graphs showing the peak signal-to-noise ratio, structural similarity, and root mean square error of the iterative reconstruction results.

[0038] Label Explanation 10 detector units 11 Side L-axis Angle of tilt G gap. Detailed Implementation

[0039] To provide a clearer understanding of the technical features, objectives, and effects of the invention, specific embodiments of the invention are now described with reference to the accompanying drawings, in which the same reference numerals denote the same parts.

[0040] In this document, “illustrative” means “serving as an example, illustration or description”, and any illustration or implementation described herein as “illustrative” should not be construed as a more preferred or advantageous technical solution.

[0041] In this article, terms such as "up," "down," "front," "back," "inner," and "outer" are used only to indicate the relative positional relationship between related parts, rather than to define the absolute position of these related parts.

[0042] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention and does not represent the actual structure of the product. The nouns and pronouns used to refer to people in this patent application are not limited to specific genders.

[0043] Figure 2 This is a schematic diagram illustrating the tilted arrangement of detector elements in a detector ring. See also... Figure 2 The detector ring provided in this illustrative embodiment and Figure 1 The difference in the detector ring shown is that, as Figure 2 The detector elements 10 of the detector ring shown are inclined, and the adjacent sides 11 of two adjacent detector surfaces are parallel to each other and opposite to each other. These sides 11 are parallel to the axis L of the detector ring (as shown in the figure). Figure 2 The dashed line (shown as b) is inclined at an angle of . .

[0044] It should be noted that when the detector unit 10 is tilted, its effective area for receiving X-rays decreases to the following size: Figure 2 The red area is shown. In this illustrative embodiment, the detector unit 10 is rectangular; however, it is not limited to this. In other illustrative embodiments, the detector unit 10 can also be a parallelogram, trapezoid, or other shape, as long as the gap G between two adjacent detector units 10 is ensured to be relative to the axis L of the detector ring (parallel to the axis L). Figure 2 The dotted line shown is slanted.

[0045] By arranging the detector units at an angle, the computed tomography equipment, including the aforementioned detector ring, can effectively eliminate ring artifacts.

[0046] Specifically, in the illustrative embodiment, the tilt angle of the side relative to the axis For an angle less than or equal to 45°, there is a gap G between the adjacent sides 11 of two adjacent detection surfaces.

[0047] The present invention also provides a computed tomography (CT) device, including the detector ring described above. The CT device is an RCT, HCT, or MSSCT.

[0048] See Figure 3 , Figure 3 Figures a, b, and c schematically illustrate the trajectory of the X-ray source during one scan cycle for RCT, HCT, and MSSCT, respectively. The fields of view extending along the Z-axis formed by these three computed tomography (CT) devices are contained within three cylinders. The dashed circle represents the X-ray source at the beginning of one scan cycle, and the black circle represents the X-ray source at the end of one scan cycle. During one scan cycle of RCT, the examination table remains stationary, and the trajectory of its X-ray source is a circle, as shown in the figure. Figure 3 As shown by the dashed line in diagram a, the black circle coincides with the dashed circle. In HCT, the examination table moves at a constant speed along the Z-axis during one scan cycle, and the trajectory of the X-ray sources is a spiral around the cylinder. In MSSCT, the examination table moves at a constant speed along the Z-axis during one scan cycle, with several X-ray sources forming a ring around the X-ray source (…). Figure 3 In (only one of them is schematically drawn in c), each X-ray source deflects by only one angle, and the total angle of deflection of several X-ray sources is 360°, which is equivalent to each X-ray source deflecting by one angle. The X-ray source ring can complete a 360° scan of the object under inspection.

[0049] Figure 4 Used to illustrate the geometric relationship between the X-ray source and detector units. See also Figure 4 In the illustrative embodiment, Figure 4 Figures a, b, and c all show a rectangle, and these rectangles are... Figure 3 The projection of the cylinder onto the XOZ plane, where R is the radius of the cylinder. The normalized pitch of the computed tomography (CT) scanner. The result is obtained by calculation using equation (1): Equation (1) in, The Z-axis is the distance the examination table moves along the Z-axis during one scan cycle. The Z-axis is the coordinate axis parallel to the axis L of the detector ring in the spatial rectangular coordinate system O-XYZ and passes through the center of the circle containing the rotation trajectory of the X-ray source. The origin of the spatial rectangular coordinate system is fixed relative to the position of the examination table. The X-axis is parallel to the width direction of the examination table, and the Y-axis is perpendicular to both the X-axis and the Z-axis. The maximum coverage height of the ray along the Z-axis during one scan cycle, such as Figure 4 As shown by the purple line segments in a, b, and c, based on the geometric relationship of similar triangles, The result is obtained by calculation using equation (2): Equation (2) In equation (2), Let be the radius of the circle containing the rotation trajectory of the ray source. Let be the theoretical radius of the detector ring, and be the radius of the circle containing the center of each detector element. The effective height of each detector unit 10 along the Z-axis direction. ,in, This represents the number of pixels in each detector unit 10 along the Z-axis direction. The height of a single pixel in detector unit 10 along the Z-axis when it is not tilted. for Figure 2 The length of the middle side 11.

[0050] When the computed tomography (CT) device is an RCT, such as Figure 4 In the diagram, 'a' represents the start and end points of a full scan, indicated by a solid black line, while the midpoint is represented by a dashed gray line. The moving bed remains stationary, therefore... Normalized pitch =0. The coverage area of ​​the RCT along the Z-axis during one scan cycle is as follows: Figure 4 The blue area is shown as 'a'. The red line segment represents the coverage height of the ray at X-axis coordinate R along the Z-axis. It refers to the effective imaging range along the Z-axis direction at point R on the X-axis after one scan. This is based on the geometric relationship of similar triangles. The result is obtained by calculation using equation (3): Equation (3) Therefore, as shown in equation (3), the coverage height of the RCT along the Z-axis is determined by the geometric relationship between the X-ray source and the detector unit 10. The dimension of the reconstructed volume along the Z-axis cannot exceed [the specified value]. The reconstructed volume refers to the three-dimensional spatial range reconstructed from the original acquired data by a computed tomography (CT) scanner, that is, the three-dimensional space covered by the final generated three-dimensional CT image.

[0051] When the computed tomography (CT) device is HCT, such as Figure 4 For b, during a scan cycle, the end point of the previous week's scan (the starting point of this week's scan) is represented by a black dashed line, the end point of this week's scan is represented by a black solid line, and the midpoint of the scan is represented by a gray dashed line. During a scan cycle, the inspection bed moves a distance along the Z-axis. ,like Figure 4 As shown by the green line segment in b. The coverage height of the ray at X-axis coordinate R along the Z-axis during one scan cycle is... , like Figure 4 The red line segment in b represents this.

[0052] The coverage area along the Z-axis from last week's scan is represented by green, and the coverage area along the Z-axis from this week's scan is represented by blue. For example... Figure 4 As shown in b, the blue and green areas have partially overlapped. To ensure there are no gaps between the blue and green areas after two weeks of scanning, the blue and green areas... At least they should be interconnected, that is Cannot exceed At this point, the normalized pitch Based on the geometric relationships of similar triangles, It can also be calculated using equation (3): Equation (3).

[0053] From equation (3), it can be seen that, given In the case of R, the upper limit of the normalized pitch of HCT is determined solely by geometry: as R approaches R... The smaller the allowed normalized pitch, the more restricted the field of view along the Z-axis.

[0054] When the computed tomography (CT) scanner is MSSCT, during one scan cycle, the end point of the previous scan (start point of this scan cycle) from the left-hand X-ray source is represented by a black dashed line, the end point of this scan cycle from the left-hand X-ray source is represented by a black solid line, and both scan cycles from the right-hand X-ray source are represented by gray dashed lines. During one scan cycle, the examination table moves a distance along the Z-axis of [distance missing]. ,like Figure 4 As shown by the green line segment in c. The coverage height of the ray at X-axis coordinate R along the Z-axis during one scan cycle is... , like Figure 4 The red line segment in c represents this.

[0055] The coverage area along the Z-axis from last week's scan is represented by green, and the coverage area along the Z-axis from this week's scan is represented by blue. Similarly, as... Figure 4 As shown in Figure c, the blue and green areas partially overlap. To ensure there is no gap between the blue and green areas after two adjacent scan cycles, the blue and green areas... At least they should be interconnected, that is Cannot exceed At this point, the normalized pitch Using the similar triangle method, The result is obtained by calculation using equation (4): Equation (4) In equation (4), The offset distance along the Z-axis between the plane containing the rotation trajectory of the X-ray source and the plane containing the center of each detector unit 10.

[0056] As can be seen from equation (4), under the same R, the normalized pitch allowed by MSSCT is... The upper limit depends not only on and the dimensions of detector unit 10 along the Z-axis direction It also depends on Through reasonable design While maintaining data integrity, normalized pitch The upper limit can be relaxed, thereby allowing for... Under the same conditions, a larger field of view along the Z-axis can be obtained.

[0057] Figure 5 This is a schematic flowchart illustrating one embodiment of a method for determining sampling parameters of a computed tomography (CT) scanner. The CT scanner is an RCT, HCT, or MSSCT including the aforementioned detector ring. This method is applicable to the CT scanner claimed in this invention. This method can, for example, serve as a method for evaluating or optimizing the sampling performance of a CT scanner, providing a quantitative tool for assessing the core advantages of the CT scanner claimed in this invention. See also Figure 5 In the illustrative embodiment, the determination method includes steps S10 and S20.

[0058] S10: Establish a spatial rectangular coordinate system. The spatial rectangular coordinate system is as follows: Figure 1 As previously mentioned, this will not be repeated here.

[0059] S20: Based on a spatial rectangular coordinate system, sampling parameters are obtained through the constructed ray parameter equation.

[0060] In the illustrative implementation, the sampling parameters are the number of effective viewpoints and angular sparsity. Step S20: Based on the spatial rectangular coordinate system, the sampling parameters are obtained through the constructed ray parameter equation, specifically including steps S21 and S22, as follows... Figure 6 As shown.

[0061] S21: Based on a spatial rectangular coordinate system, construct the ray parametric equation and solve it to obtain the effective viewpoint index set. The elements in the effective viewpoint index set are the effective viewpoints. Under a certain effective viewpoint, a certain point on the inspected object... x The rays that can be hit and emitted by the rays can hit the effective pixels of the detector unit 10 to generate scan data for imaging.

[0062] Figure 7 This is used to illustrate the method for constructing the ray parameter equations. See also Figure 7 In the illustrative embodiment, the projection of the trajectory of the ray source onto the XOY plane is represented by a pink dashed line. Figure 7 The gray dots shown in figure 'a' represent the X-ray sources for RCT and HCT. Figure 7 The gray dots shown in b represent the uniformly distributed X-ray sources of MSSCT. Figure 7 (One of them is marked schematically in b), sampling the subject from different perspectives.

[0063] The ring coaxial with the pink dashed line is the projection of the detector ring onto the XOY plane, and the black dashed circle coaxial with the pink dashed line is... Figure 3 The projection of the cylinder shown onto the XOY plane has a radius of R.

[0064] In the illustrative embodiment, the ray parameter equation Equation (5) represents: Equation (5) in, An isometric perspective The position of the corresponding ray source in the spatial rectangular coordinate system is represented by equation (6): Equation (6), In equation (6), This is the s-th iso-angle viewpoint in the c-th scan cycle. , For the scan week number, The number of isoangular viewpoints per scan cycle. Let be the radius of the circle containing the rotation trajectory of the ray source. An isometric perspective The angle between the line connecting the corresponding ray source and the origin O and the positive X-axis is expressed by equation (7): Equation (7), In equation (7), The starting angle for cycle 0 can be defined in any degree based on the actual application scenario. The angular step size of adjacent viewpoints within each scan cycle. This represents the overall rotation increment between two adjacent scan cycles. An isometric perspective The corresponding Z-axis coordinate of the ray source, For RCT, , For HCT, , For MSSCT, , in: An isometric perspective The Z-axis coordinate of the corresponding ray source at the starting position can be determined according to the actual application scenario. To check the distance the bed moves along the Z-axis during one scan cycle; For the first i Each detector unit at an equal angle Next The center coordinates of each pixel are represented by equation (8): Equation (8) In equation (8), To be able to be viewed from the same angle The corresponding radiation source emitted a ray that struck the first i The center position coordinates of each detector element are represented by equation (9): Equation (9) In equation (9), Let be the theoretical radius of the detector ring, and be the radius of the circle containing the center of each detector element. For the first in the XOY plane, i The azimuth angle of the center of the first detector unit is the first... i The line connecting the center of each detector unit and the origin O, and the isotropic viewing angle The angle between the line connecting the corresponding ray source and point O. The offset distance along the Z-axis between the plane containing the rotation trajectory of the X-ray source and the plane containing the center of each detector unit. For the first i The pixel index at the center of each detector unit. The width of each pixel in the detector unit along the direction perpendicular to the Z-axis when it is not tilted. The height of each pixel in the detector unit along the Z-axis when it is not tilted. For the tilted detector unit along the width direction The unit step size vector, For the tilted detector unit along the height direction The unit step size vector, The tilt angle, and Expressed by equations (10) and (11) respectively: Equation (10) Equation (11) in, Let r be a tangential unit vector, parallel to the width direction of the detector panel when it is not tilted, such as... Figure 1 As shown, , It is a unit vector along the axial direction, and the unit vector along the axial direction is parallel to the Z-axis. .

[0065] Based on the constructed ray parameter equations, the effective viewpoint index set... Equation (12) represents: Equation (12) in, This is the index sequence of the detector elements on the detector ring. For each detector element, the pixel index is... For the position located at the i The pixel in the m-th row and n-th column of a detector element Indicates a perspective at the same angle Below, at equal angles The corresponding radiation source emits radiation capable of hitting the first... i Pixels of each detector unit ; For the first i The set of effective pixel indices for each detector unit, which contains all effective pixel indices. Effective pixels are pixels that are theoretically capable of receiving X-rays and outputting electrical signals. To be at the same angle Below, from the same angle perspective The corresponding ray source points to the first i Pixels of each detector unit The ray parameter equation, For length, This indicates whether points on the inspected object can be viewed from the same angle. The solution is performed based on the hit condition. The solution results are based on... Whether it is greater than or equal to 0 and pixels Determine whether it is within the set of valid pixel indices.

[0066] S22: Calculate the number of effective viewpoints and angle sparsity based on the effective viewpoint index set, where the number of effective viewpoints is the sum of all hits in the effective viewpoint index set. x The number of effective viewpoints, angular sparsity is the normalized variance of the angular interval between two adjacent effective viewpoints, used to measure the hit rate. x The uniformity of the distribution of the effective viewing angle of a point within the range of 0° to 360°.

[0067] Effective number of viewpoints The number of elements in the effective view index set is represented by equation (13): Equation (13).

[0068] Angular sparsity Equation (14) represents: Equation (14) in, For ideal uniform sampling, the angular interval between two adjacent effective viewpoints is... ; When sampling is non-ideal uniform, the angular interval between two adjacent effective viewpoints is expressed by equation (15): Equation (15), In equation (15), Apply points to the subject of the examination The i An effective perspective ,in , It represents all equal-angle viewpoints within its set. of It is a set The elements. Due to It is a set The elements that make Combining equation (15) yields Applying it to equation (14) makes it easier to solve. .

[0069] This method can easily and conveniently determine the sampling parameters of a computed tomography (CT) scanner and whether the CT scanner can effectively eliminate ring artifacts.

[0070] Another point worth mentioning is that for any isotropic viewpoint... The radiation source is located at... The ray from the ray source to the origin is denoted as . As for the same angle perspective The three-dimensional coordinates of the two rows of pixels in the detector unit corresponding to the lower boundary ray can be obtained by equation (8) and denoted as: ,like Figure 7 As shown in a, the figure is located in The detector unit hit by the ray source is covered by a red arc. The direction of the ray from the ray source to these edge pixels is... Then the half-sector angle corresponding to the boundary ray. Calculate using equation (16): Equation (16) in, and For set and The model.

[0071] For a boundary ray that hits one pixel, the perpendicular distance from the origin to that ray is the radius R of the black dashed circle. This can be obtained from simple geometric relationships. .

[0072] In the tilting assembly of detector units, multiple detector units are arranged at an angle along the detector ring. The arrangement is such that the angular interval between the centers of two adjacent detector units is... Calculated using equation (17): Equation (17) in, This is the angular interval between the centers of two adjacent detector elements when the detector elements are not tilted; it is a constant. With a radius of... On the detector ring, the arc length between the centers of two adjacent detector elements It can be approximately calculated using equation (18): Equation (18) As can be seen from equation (18), compared to the untilted case, the distance between the centers of two adjacent detector units varies with the tilt angle. The number of detector elements in the detector ring increases with the increase of the detector ring radius, so the tilted layout can reduce the number of detector elements in the detector ring without changing the detector ring radius.

[0073] Figure 8 This is an example diagram showing the distribution of the effective field of view for three types of computed tomography (CT) scanners. Figure 9 This is an example diagram showing the angular sparsity distribution of three computed tomography (CT) scanners. In a specific embodiment, the three CT scanners... It is 600mm. The diameter is 400mm. The detector ring is composed of multiple detector units arranged at an angle, with an angle of [missing information]. The angle is 20°. Each detector element has a size of 240*130 pixels within the detector ring plane, and the pixel size is... A physical seam is reserved between the two detector units to simulate the gaps caused by the actual assembly process. The gap width is perpendicular to the Z-axis direction and is 4.8mm.

[0074] RCT acquires data during the scanning process. Equally spaced perspectives. HCT in Helical scanning is completed with constant bed displacement during constant angle rotation, and data is collected weekly. Each angle has a normalized pitch of 0.6. MSSCT is set with... A series of equally spaced radiation sources were used to sequentially collect radiation samples. The normalized pitch of the screw is 0.6, and the initial position is... It is 100mm.

[0075] This invention employs two algorithms—FDK analytical reconstruction and SIRT iterative reconstruction—to reconstruct scan data. These two algorithms are well-known to those skilled in the art and will not be elaborated upon here. The reconstruction is achieved through the aforementioned geometric parameter configuration, scan parameter settings, and algorithmic reconstruction. Figure 8 and Figure 9 The data.

[0076] exist Figure 8 The top, middle, and bottom rows represent data acquired from RCT, HCT, and MSSCT, respectively. Columns 1 to 4 represent, respectively, the central layer of the object under examination when the detector unit is not tilted, the central layer of the object under examination when the detector unit is tilted by 20°, the offset layer of the object under examination when the detector unit is not tilted, and the offset layer of the object under examination when the detector unit is tilted by 20°. The central layer is the layer containing the XOY plane in the spatial rectangular coordinate system, and the offset layer is the layer that deviates from the XOY plane along the Z-axis in the spatial rectangular coordinate system. The color bands on the right indicate the number of effective viewing angles; the yellow ring corresponds to areas with a large number of effective viewing angles, and the blue-green ring corresponds to areas with a small number of effective viewing angles.

[0077] Figure 9 Data arrangement method and Figure 8 Same. Color represents local angular sparsity; higher values ​​indicate more uneven distribution of the effective viewing angle, which can be compared to... Figure 8 The low effective field of view number corresponds to the ring band in the middle.

[0078] For RCTs, the behavior differs between the central and offset layers. In the central layer, regardless of detector element tilt, a distinct low-value ring appears in the number of effective viewing angles, while a high-value ring appears in the same location for angular sparsity. These two rings almost overlap, indicating a region in the central layer with severely insufficient viewing angles and highly uneven angular distribution, where the tilting of the detector elements has virtually no effect. The circle containing the X-ray source's rotation trajectory is concentric with the circle containing the detector element's center. X-rays passing through the central layer primarily fall on the middle row of detector elements, and the projection of the slit onto this row always corresponds to a fixed ring with fewer effective viewing angles. Therefore, the distribution of effective viewing angles and angular sparsity remains essentially unchanged.

[0079] Conversely, on the offset layer, a clear annular band with a low effective viewing angle number and high angular sparsity is still visible when the detector elements are tilted. When the detector elements are tilted, the lowest effective viewing angle number of this annular band increases, the highest angular sparsity decreases, and the contrast of the annular stripes weakens, indicating that the tilted layout of the detector elements effectively eliminates the annular artifacts introduced by the gaps on the offset layer.

[0080] HCT and MSSCT show similar trends in the number of effective viewing angles and angular sparsity. Without tilting, a ring with relatively low effective viewing angles combined with high angular sparsity is observed in both the central and offset layers, but the contrast is weaker than that of RCT. When the detector elements are tilted, the effective viewing angles of their low-effective-viewing-angle rings increase, while the angular sparsity decreases significantly. This indicates that tilted detector element placement effectively eliminates ring artifacts introduced by gaps in both the central and offset layers of HCT and MSSCT. MSSCT, including the tilted detector ring, exhibits the highest effective viewing angles and the lowest angular sparsity among the three.

[0081] The following example demonstrates the effectiveness of three computed tomography (CT) devices, including the aforementioned detector ring, in eliminating ring artifacts. The experimental parameters used in this example are... Figure 8 and Figure 9 The experimental parameters are exactly the same, the difference is that Figure 8 and Figure 9 There were no subjects being tested.

[0082] Figure 10 and Figure 11 This is used to illustrate the effect of tilted detector units on eliminating ring artifacts. Figure 10 and Figure 11 The CT images were obtained using three types of computed tomography (CT) scanners, each equipped with both untilted and tilted detector units. Figure 10 and Figure 11 The subjects examined were all patients' chest and abdomen. Figure 10The SIRT iterative algorithm was used to reconstruct the scan results obtained from three types of computed tomography (RTC), including RCT, HCT, and MSSCT. Figure 11 The FDK parsing and reconstruction algorithm is used. Figure 10 and Figure 11 Cross sections of the central and offset layers, as well as the corresponding coronal and sagittal planes, are shown. Figure 10 and Figure 11 The regions defined by the small red, green, pink, and blue squares are the regions of interest. Their magnified views are the regions defined by the large red, green, pink, and blue squares, respectively.

[0083] exist Figure 10 In the RCT scans, when the detector units were not tilted, noticeable annular artifacts appeared on the transverse sections obtained by all three computed tomography (CT) devices. Vertical stripe artifacts were prevalent in the coronal and sagittal planes, indicating that missing data at the slits significantly affected the reconstruction homogeneity. When the detector units were tilted, it was observed in the magnified images that the annular artifacts on the transverse sections, as well as the vertical artifacts in the coronal and sagittal planes, were significantly eliminated, resulting in a more homogeneous background and clearer structural boundaries. It should be noted that for RCT, a certain degree of annular artifacts could still be observed in the central layer under the tilted configuration, while the annular artifacts in the non-central layers essentially disappeared. This is related to… Figure 8 and Figure 9 The results were consistent.

[0084] exist Figure 11 In the process, because the data collected at the gaps needs to be interpolated before analytical reconstruction, compared to... Figure 10 In the uninterpolated iteration results, the previously significant annular artifacts on the cross-section are generally weaker, but interpolation introduces new needle-like artifacts, which can be seen in the magnified images as localized sharp stripe structures. With the detector units tilted, the overall image quality obtained by the three computed tomography (CT) devices is still significantly better than the untilted images, while the annular artifacts are further reduced and the needle-like artifacts are also suppressed. The differences in slit-related artifacts are more intuitive in the coronal and sagittal planes. Without tilting, the magnified images of RCT, HCT, and MSSCT (marked with red, green, and yellow arrows, respectively) all show slit-related artifacts along... Figure 11 The vertical stripes extending in the vertical direction indicate that the missing data near the slit is concentrated and superimposed; however, under the tilted layout, these vertical stripes are significantly reduced or even almost disappear in the images obtained by the three computed tomography devices, and the background uniformity is significantly improved, indicating that the tilted layout of the detector unit is equally effective in eliminating the annular artifacts caused by the slit under analytical reconstruction.

[0085] Table 1 shows the index values ​​of CT images from three different computed tomography (CT) scanners. These CT images were obtained through SIRT iterative reconstruction (z=200) and FDK analytical reconstruction (z=179), respectively.

[0086] Table 1. CT image index values ​​of three types of computed tomography (CT) scanners As shown in Table 1, MSSCT outperforms HCT and RCT in all metrics: regardless of tilt, it consistently has the highest peak signal-to-noise ratio and structural similarity, and the lowest root mean square error. This is consistent with the previous qualitative observation that MSSCT has the weakest annular artifacts and the clearest structure.

[0087] Meanwhile, compared to the untilted case, the 20° tilt consistently improved image quality across different scanning modes of the three computed tomography (CT) scanners and two types of reconstruction algorithms: peak signal-to-noise ratio (PSNR) improved across the board (approximately 1 dB during iterations and 2 dB to 4 dB during analysis), structural similarity increased slightly, and root mean square error decreased significantly (approximately 10% to 30%). This result demonstrates that the tilted detector layout can stably improve image quality under different reconstruction algorithms, with the benefits primarily stemming from the geometric optimization of the slit-related sampling structure.

[0088] Figure 12 This is a grayscale curve used to illustrate CT images from three different computed tomography (CT) scanners. From... Figure 10 A one-dimensional grayscale profile is extracted from the location indicated by the yellow dashed line, as shown below. Figure 12 The grayscale curve shown Figure 12 'a', 'b', and 'c' all include three curves: the true value, the untilted curve, and the tilted curve. In the pixel ranges corresponding to the annular artifacts at pixel indices 230 to 240 and 270 to 290, it can be seen that in all three scanning modes, there are obvious grayscale jumps when the curve is untilted, the curve produces local peak-valley oscillations, and there is a significant deviation from the true value curve.

[0089] In contrast, with the detector units tilted, the grayscale curves within the corresponding range remained relatively smooth, without any sharp fluctuations, and were generally closest to the true values. This result is consistent with... Figure 10 Consistent with the observations in the study, the tilted layout of the detector unit effectively eliminates ring artifacts by quantitatively verifying the effect of one-dimensional grayscale.

[0090] Figure 13 This is used to illustrate the iterative reconstruction results of the resolution test card under different tilt angles. Figure 14 Used to illustrate modulation transfer function curves at different tilt angles, based on Figure 13 The area within the green box was calculated. Figure 13Reconstructed images and magnified local areas are shown under tilt angles ranging from 0° to 25°, providing a visual comparison of the resolvability and sharpness of high-frequency line pairs at different tilt angles. From Figure 13 As can be seen from the magnified area, when the tilt angle increases from 0° to 25°, the resolvability of the high-frequency line pairs does not show a visible decrease; the edges of the high-frequency line pairs remain clear at each tilt angle, without significant blurring. Furthermore, with... Figure 13 The region within the green box represents the region of interest. Modulation transfer function curves were calculated at different tilt angles, and the results are shown below. Figure 14 As shown.

[0091] exist Figure 14 In the results, the modulation transfer function curves at various tilt angles almost completely overlap. In the high-frequency range close to the Nyquist frequency, the modulation transfer function curve of the 20° tilt layout is higher than that of the non-tilted case. Combining visual resolution and modulation transfer function analysis, it can be concluded that the tilted detector layout effectively reduces the ring artifacts caused by sampling dead zones without sacrificing spatial resolution.

[0092] Figure 15 This is used to illustrate the iterative reconstruction results under the combination of gap width and tilt angle. Figure 15 The regions defined by the small red squares are the regions of interest, and their magnified views are the regions defined by the large red squares located below them. Figure 16 For illustrative purposes Figure 15 Line plots showing the peak signal-to-noise ratio, structural similarity, and root mean square error of the iterative reconstruction results. See also... Figure 15 and Figure 16 In a vertical layout without tilt, image quality is highly sensitive to the width of the slit. As the slit increases from slit 1 (3.6 mm) to slit 4 (5.4 mm), Figure 15 The mid-band and annular artifacts are intensified. It should be noted here that the slit width is not limited to... Figure 15 The four values ​​shown indicate that the gap width is related to the detector unit's frame and assembly process. Quantitatively, Figure 16 Show gap 4 in The peak signal-to-noise ratio at =0 is about 1.5 dB lower than that at slot 1, and the root mean square error is significantly increased.

[0093] When tilt angle At angles ≥15°, the difference in gap widths decreases significantly. Even under the maximum gap condition, the difference decreases with increasing tilt angle. As the sample size increases, the strip artifacts decrease rapidly, the local structure gradually recovers, and the visual difference from the small slit sample is greatly reduced. Figure 16 As can be seen in a, the peak signal-to-noise ratio of the large slit group increases with... The rise was most pronounced; when At 20°, the peak signal-to-noise ratio difference between slit 4 and slit 1 has narrowed to approximately 0.2dB. At this point, it can effectively compensate for larger physical gaps caused by manufacturing process limitations or assembly errors, reducing the reliance on high-precision, narrow-bezel detector units, thereby potentially significantly reducing hardware costs.

[0094] Figure 16 The curve trend reveals the nonlinear law of image quality changing with tilt angle, when 0 < Within the ≤15° range, as the tilt angle increases, the number of effective viewing angles increases significantly, while the peak signal-to-noise ratio and structural similarity show an approximately linear improvement. When the angle is greater than 15°, the curve gradually flattens out, and further increasing the tilt angle has limited effect on eliminating ring artifacts. Figure 16 The structural similarity curve in b shows slight fluctuations around 20°, indicating that an excessively large tilt angle did not lead to a sustained improvement in structural similarity.

[0095] However, it is worth noting that when The artifact removal effect is poor when the temperature is close to 0°; however, when... When the angle is too large (e.g., greater than 45°), it is determined by equation (2). It can be seen that the effective height of the detector unit along the Z-axis Will because This will significantly reduce the Z-axis coverage of a single scan. This reduces (as can be seen from Equation 2), thereby compressing the field of view along the Z-axis.

[0096] When designing computed tomography (CT) equipment, this method can be used to pre-simulate and calculate the effective number of viewing angles and angular sparsity under different tilt angles and slit widths, thereby guiding the design and optimization of parameters such as the tilt angle of the detector unit, the number of detector units, and the normalized pitch, to ensure that the final equipment can effectively eliminate ring artifacts.

[0097] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0098] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent implementation schemes or modifications made without departing from the spirit of the present invention, such as combinations, divisions or repetitions of features, should be included within the scope of protection of the present invention.

Claims

1. A detector ring for a computed tomography (CT) scanner, characterized in that, The detector ring is composed of multiple detector units (10) arranged circumferentially. The detection surface of each detector unit (10) is parallel to the axis (L) of the detector ring. The adjacent sides (11) of two adjacent detection surfaces are parallel to each other and opposite to each other. These sides (11) are inclined relative to the axis of the detector ring.

2. The detector ring as described in claim 1, characterized in that, The angle of inclination of the side relative to the axis Less than or equal to 45°.

3. A computed tomography (CT) scanner, characterized in that, Includes the detector ring as described in any one of claims 1 to 2.

4. The computed tomography (CT) scanner as described in claim 3, characterized in that, The computed tomography (CT) scanner is a circular CT scanner, a spiral CT scanner, or a multi-source static CT scanner, and the normalized pitch of the CT scanner is... The result is obtained by calculation using equation (1): Equation (1) in, The Z-axis is the distance the examination table moves along the Z-axis during one scan cycle. The Z-axis is a coordinate axis in the spatial rectangular coordinate system O-XYZ that is parallel to the axis of the detector ring and passes through the center of the rotation trajectory of the X-ray source. The origin of the spatial rectangular coordinate system is fixed relative to the position of the examination table, and the X-axis is parallel to the width direction of the examination table. The maximum coverage height of the ray along the Z-axis during one scan cycle is calculated using equation (2): Equation (2) In equation (2), Let be the radius of the circle containing the rotation trajectory of the ray source. Let be the theoretical radius of the detector ring, and let be the radius of the circle containing the center of each detector unit (10). The effective height of each detector unit (10) along the Z-axis direction, ,in, The number of pixels in each detector unit (10) along the Z-axis direction. The height of a single pixel in the detector unit (10) along the Z-axis when it is not tilted.

5. The computed tomography (CT) scanner as described in claim 4, characterized in that, When the computed tomography (CT) device is a circular computed tomography (CT) device, the normalized pitch is 0; When the computed tomography (CT) device is a spiral CT device, the normalized pitch , in, This represents the coverage height of the ray at X-axis coordinate R along the Z-axis during one scan cycle. The result is obtained by calculation using equation (3): Equation (3); or When the computed tomography (CT) device is a multi-source static computed tomography (CT) device, the normalized pitch , in, This represents the coverage height of the ray at X-axis coordinate R along the Z-axis during one scan cycle. The result is obtained by calculation using equation (4): Equation (4) In equation (4), The offset distance along the Z-axis between the plane containing the rotation trajectory of the X-ray source and the plane containing the center of each detector unit (10).

6. A method for determining sampling parameters of a computed tomography (CT) scanner, wherein the CT scanner is the CT scanner as described in any one of claims 3 to 5, characterized in that, The determination method includes: A spatial rectangular coordinate system is established, wherein the origin of the spatial rectangular coordinate system is fixed relative to the examination table, the coordinate axis passing through the center of the circle containing the rotation trajectory of the X-ray source and parallel to the axis of the detector ring is the Z-axis, and the direction parallel to the width of the examination table is the X-axis; and Based on the aforementioned spatial rectangular coordinate system, sampling parameters are obtained through the constructed ray parameter equations.

7. The determination method as described in claim 6, characterized in that, The sampling parameters are the number of effective viewpoints and angular sparsity. The steps are as follows: Based on the spatial rectangular coordinate system, the sampling parameters are obtained through the constructed ray parameter equation, specifically including: Based on the aforementioned spatial rectangular coordinate system, ray parameter equations are constructed and solved to obtain an effective viewpoint index set. Elements in the effective viewpoint index set represent effective viewpoints. Under a given effective viewpoint, a point on the inspected object... x The emitted rays, capable of being hit by the rays, can strike the effective pixels of the detector unit to generate scan data for imaging; and Based on the effective viewpoint index set, calculate the number of effective viewpoints and angle sparsity, wherein the number of effective viewpoints is the number of all hits in the effective viewpoint index set. x The number of effective viewpoints of a point, wherein the angular sparsity is the normalized variance of the angular interval between two adjacent effective viewpoints.

8. The determination method as described in claim 7, characterized in that, The ray parameter equation Equation (5) represents: Equation (5) in, The isotropic viewpoint The position of the corresponding ray source in the spatial rectangular coordinate system is represented by equation (6): Equation (6), In equation (6), Let be the radius of the circle containing the rotation trajectory of the ray source. The isotropic viewpoint The angle between the line connecting the corresponding ray source and the origin O and the positive X-axis. This is the s-th iso-angle viewpoint in the c-th scan cycle. For the scan week number, The number of isoangular viewpoints per scan cycle, Equation (7) represents: Equation (7), In equation (7), The starting angle for cycle 0. The angular step size of adjacent viewpoints within each scan cycle, This is the overall rotation increment between two adjacent scan cycles. The isotropic viewpoint The corresponding Z-axis coordinate of the ray source, For circular computed tomography (CT) scanners , For spiral computed tomography (CT) equipment , For multi-source static computed tomography (CT) equipment , in: The isotropic viewpoint The corresponding Z-axis coordinate of the ray source at the starting position, The distance the examination bed moves along the Z-axis during one scan cycle; For the first i Each detector unit is at the equal angle view Next The center coordinates of each pixel are represented by equation (8): Equation (8) In equation (8), In order to be able to be viewed from the same angle The corresponding radiation source emitted a ray that struck the first i The center position coordinates of each detector unit are represented by equation (9): Equation (9) In equation (9), Let be the theoretical radius of the detector ring, and be the radius of the circle containing the center of each detector element. For the first in the XOY plane, i The azimuth angle of the center of the detector unit is the first... i The line connecting the center of each detector unit and the origin O, and the iso-angle viewpoint The angle between the line connecting the corresponding ray source and the origin O. The offset distance along the Z-axis between the plane containing the rotation trajectory of the X-ray source and the plane containing the center of each detector unit. For the first i The pixel index of the center of each of the detector units The width of each pixel in the detector unit along the direction perpendicular to the Z-axis when it is not tilted. The height of each pixel in the detector unit along the Z-axis when it is not tilted. The detector unit is tilted along the width direction The unit step size vector, The detector unit after tilting along the height direction The unit step size vector, The tilt angle is... and Expressed by equations (10) and (11) respectively: Equation (10) Equation (11) in, The vector is a tangential unit vector, and the tangential direction is perpendicular to the Z-axis. , This is a unit vector along the axial direction, which is parallel to the Z-axis. .

9. The determination method as described in claim 8, characterized in that, The effective view index set Equation (12) represents: Equation (12) in, i This refers to the index sequence of the detector elements on the detector ring. For each of the detector units, the pixel index is... For the position located at the i The pixel in the m-th row and n-th column of the detector unit. Indicated by the same angle view Below, the equal angle perspective The rays emitted by the corresponding ray source can hit the pixel of the i-th detector unit. ; For the first i The set of valid pixel indices for each of the detector units; To the iso-angle view Below, from the aforementioned angle perspective The corresponding ray source points to the first i Pixels of the detector unit The ray parameter equation, For length, This indicates whether a point on the inspected object can be viewed from the same angle. The solution is to be found by being hit below.

10. The determination method as described in claim 9, characterized in that, The number of effective viewpoints The number of elements in the effective view index set is represented by equation (13): Equation (13).

11. The determination method as described in claim 10, characterized in that, The angular sparsity Equation (14) represents: Equation (14) in, For ideal uniform sampling, the angular interval between two adjacent effective viewpoints is... ; When sampling is non-ideal uniform, the angular interval between two adjacent effective viewpoints is expressed by equation (15): Equation (15) In equation (15), Point on the object under inspection The i An effective perspective ,in .

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