Calibration device for a radiological imaging system
By using multi-layered symmetrical/asymmetrically distributed marker calibration bodies in radiographic imaging systems, the problems of high cost and poor adaptability in existing technologies are solved, achieving low-cost and highly robust geometric calibration, which is applicable to CBCT systems and C-arm X-ray machines.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SHENZHEN INST OF ARTIFICIAL INTELLIGENCE & ROBOTICS FOR SOC
- Filing Date
- 2025-07-10
- Publication Date
- 2026-06-16
AI Technical Summary
Existing geometric calibration techniques for radiographic imaging systems are costly and have poor adaptability to calibration bodies, failing to meet the requirements for long-term, effective, high-precision calibration.
A calibration device for a radiographic imaging system is provided, comprising a hollow calibration phantom and multiple layers of markers arranged in a symmetrical or asymmetrical distribution, for geometric calibration of a CBCT system or a C-arm X-ray machine, reducing equipment costs and improving robustness.
It ensures the uniqueness and coverage of the projected trajectory, reduces operational difficulty, is suitable for offset detector systems and C-arm systems with high mechanical flexibility, effectively controls calibration errors, and improves computational robustness.
Smart Images
Figure CN224357615U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of medical imaging technology, and in particular to a calibration device for a radiographic imaging system. Background Technology
[0002] CBCT (Cone-Beam Computed Tomography) and C-arm X-ray machines are widely used in medical and industrial non-destructive testing fields. They acquire two-dimensional projection data by rotating the X-ray source and detector, thereby achieving three-dimensional reconstruction or real-time two-dimensional imaging. CBCT often employs an offset detector design to expand the field of view, while C-arm X-ray machines, due to their open structure, offer greater flexibility in intraoperative guidance. However, image quality is highly dependent on the accuracy of geometric parameters, including the X-ray source position, detector position, puncture coordinates, and detector rotation angle. If these geometric parameters are not calibrated, image distortion, artifacts, or reduced resolution can occur, thus affecting imaging accuracy.
[0003] Existing geometric calibration methods mainly include online calibration and offline calibration. Online calibration can dynamically adapt to C-arm deformation or target motion in practical applications and does not require a dedicated calibration body, thus reducing preparation time. However, this calibration method introduces additional hardware dependencies, requiring additional equipment (e.g., cameras), has lower robustness, and is not suitable for low-cost CBCT or portable C-arm X-ray machines. Offline calibration, on the other hand, suffers from limitations in calibration bodies, poor long-term stability, poor adaptability to offset detectors, and weak dynamic adaptability, failing to meet the requirements for long-term effective high-precision calibration.
[0004] Therefore, existing technologies still need improvement. Summary of the Invention
[0005] The technical problem to be solved by this utility model is to provide a calibration device for a radiographic imaging system, in order to address the shortcomings of existing technologies, such as high cost and poor adaptability of calibration bodies.
[0006] The technical solution adopted by this utility model to solve the technical problem is as follows:
[0007] This utility model provides a calibration device for a radiographic imaging system, comprising:
[0008] A calibration phantom, which is a hollow structure, is used to provide the spatial reference required for calibration at different projection angles;
[0009] The calibration model has multiple layers of markers embedded in its inner wall. Each layer of markers consists of markers of the same size or markers of different sizes, and the markers in each layer are arranged in a symmetrical or pre-defined asymmetrical distribution to form the code required for calibration.
[0010] In one implementation, the calibration model is a cylinder or a regular polygonal prism, and the marking point is a metal point.
[0011] In one implementation, when the calibration mold is a cylinder, the arrangement of the metal points in each layer includes:
[0012] The metal points in each layer are arranged in a symmetrical distribution, and the metal points in each layer are evenly distributed along the circumference.
[0013] In one implementation, when the calibration mold is a cylinder, the arrangement of the metal points in each layer further includes:
[0014] The metal points in each layer are arranged in a preset asymmetrical distribution, and the metal points in each layer are increased sequentially according to a specified angle or the spacing between the metal points in each layer is set according to an increasing rule.
[0015] In one implementation, when the calibration mold is a cylinder, the side of the calibration mold is provided with at least one flat part, the flat part has a planar structure, and the flat part is parallel to the tangent of the nearest metal point in the mold.
[0016] In one implementation, when the calibration mold is a cylinder and has the flat portion, the thickness of the sidewall of the calibration mold is greater than the thickness of the calibration mold without the flat portion, and the arrangement of the metal points in each layer is as follows:
[0017] The metal points in each layer are arranged in a symmetrical distribution, and the metal points in each layer are evenly distributed along the circumference.
[0018] In one implementation, when the calibration mold is a cylinder and has the flat portion, the thickness of the sidewall of the calibration mold is the same as the thickness of the calibration mold without the flat portion, and the arrangement of the metal points in each layer is as follows:
[0019] The metal points in each layer are arranged in a symmetrical distribution, and the metal points in each layer are evenly distributed circumferentially. Compared with the calibration mold without the flat position, the diameter of the circle formed by the metal points in each layer is reduced.
[0020] In one implementation, the axial spacing between the multiple layers of metal points on the calibration mold is equal, and the distance between each layer of metal points is greater than N times the diameter of the circle formed by each layer of metal points.
[0021] In one implementation, the number of metal points in each layer is greater than or equal to 6. When the metal points in each layer are metal points of different sizes, at least one of any three consecutive metal points has a size that is different from the sizes of the other two metal points.
[0022] In one implementation, when the metal points in each layer are of different sizes, the sizes of the metal points set at the same position in any two adjacent layers are different.
[0023] The present invention, by adopting the above-described technical solution, has the following advantages:
[0024] This invention proposes a calibration body comprising multiple layers of symmetrical / asymmetrically distributed marker points for geometric calibration of CBCT systems or C-arm X-ray machines. Compared to traditional calibration bodies, this invention ensures the uniqueness and coverage of the projection trajectory, reduces equipment costs for geometric calibration, and significantly improves computational robustness. Furthermore, the calibration body provided by this invention does not require precise placement, reducing operational complexity and making it particularly suitable for offset detector systems and C-arm systems with high mechanical flexibility, thereby effectively controlling calibration errors. Attached Figure Description
[0025] To more clearly illustrate the technical solutions in the embodiments of this utility model 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 utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0026] Figure 1 This is a schematic diagram of the calibration device for the radiographic imaging system in this utility model.
[0027] Figure 2 This is a schematic diagram of the standard mold body in this utility model, which is a cylinder or a regular polygonal prism.
[0028] Figure 3 This is a schematic diagram (even number) of a regular polygonal prism in this utility model.
[0029] Figure 4 This is a schematic diagram showing the distribution of steel balls in calibration molds of different thicknesses in this utility model.
[0030] Figure 5 This is a schematic diagram showing the distribution of steel balls of different sizes in this utility model.
[0031] Figure 6 This is a schematic diagram of a regular polyhedron (odd number) in this utility model.
[0032] The purpose, features, and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0033] To make the objectives, technical solutions, and advantages of this utility model clearer and more explicit, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.
[0034] Exemplary device
[0035] CBCT (Cone-Beam Computed Tomography) and C-arm X-ray machines are widely used in medical and industrial non-destructive testing fields. They acquire two-dimensional projection data by rotating the X-ray source and detector, thereby achieving three-dimensional reconstruction or real-time two-dimensional imaging. CBCT often employs an offset detector design to expand the field of view, while C-arm X-ray machines, due to their open structure, offer greater flexibility in intraoperative guidance. However, image quality is highly dependent on the accuracy of geometric parameters, including the X-ray source position, detector position, puncture coordinates, and detector rotation angle. If these geometric parameters are not calibrated, image distortion, artifacts, or reduced resolution can occur, thus affecting imaging accuracy.
[0036] Existing geometric calibration methods mainly include online calibration and offline calibration. Online calibration can dynamically adapt to C-arm deformation or target motion in practical applications and does not require a dedicated calibration body, thus reducing preparation time. However, this calibration method introduces additional hardware dependencies, requiring additional equipment (e.g., cameras), has lower robustness, and is not suitable for low-cost CBCT or portable C-arm X-ray machines. Offline calibration, on the other hand, suffers from limitations in calibration bodies, poor long-term stability, poor adaptability to offset detectors, and weak dynamic adaptability, failing to meet the requirements for long-term effective high-precision calibration.
[0037] To address the above technical problems, this utility model provides a calibration device for a radiographic imaging system. The device includes: a calibration phantom, which is a hollow structure used to provide spatial reference for calibration at different projection angles; and multiple layers of steel balls embedded in the inner wall of the calibration phantom, with each layer of steel balls arranged symmetrically or in a pre-set asymmetrical distribution to form the required calibration code. This utility model proposes a calibration body containing multiple layers of symmetrical / asymmetrically distributed markers for geometric calibration of CBCT systems or C-arm X-ray machines. Compared to traditional calibration bodies, this utility model ensures the uniqueness and coverage of the projection trajectory, reduces the equipment cost of geometric calibration, and significantly improves computational robustness.
[0038] like Figure 1 As shown, this utility model embodiment provides a calibration device for a radiographic imaging system, including: a calibration phantom 1, which is a hollow structure used to provide spatial reference for calibration at different projection angles; and multiple layers of marker points 2, which are embedded in the inner wall of the calibration phantom 1. Each layer of marker points 2 consists of marker points of the same size or marker points of different sizes, and the marker points 2 in each layer are arranged in a symmetrical or preset asymmetrical distribution to form the code required for calibration.
[0039] In this embodiment, the marking point is a marking structure formed by a metal point or other marking material. The following description uses a steel ball as an example of a metal point.
[0040] The principle of the calibration device for the radiographic imaging system is as follows: When performing geometric calibration on a CBCT system or a C-arm X-ray machine, the calibration device is used as a spatial reference. A detector acquires a projection image of the calibration device under X-ray illumination. Software is used to detect and preprocess the marker points (i.e., the steel balls in the calibration device) in this projection image (i.e., extracting the centroid coordinates of the marker points and correcting the center coordinates of the marker points) to obtain the projection coordinates of the marker points in the projection image. Then, based on these projection coordinates, the geometric parameters of the radiographic imaging system are analyzed to obtain geometric parameters such as the X-ray source position, detector position, puncture point coordinates, and detector rotation angle. Finally, the positions in the geometric parameters are compared with the expected positions in historical calibration data, and combined with IMU sensor data and dynamically adjusted deviation detection thresholds, the geometric deviation of the radiographic imaging system is calculated. This geometric deviation is then used to dynamically compensate for the analyzed geometric parameters, thereby realizing the calibration process of the radiographic imaging system.
[0041] In this embodiment, the calibration model is a cylinder or a regular polygonal prism, and the calibration model has a hollow structure; in actual application scenarios, the corresponding structure can be selected according to the actual processing or imaging requirements.
[0042] like Figure 2 As shown, as an example, the calibration model in this embodiment can be set as a cylinder or a regular polygonal prism. Figure 2 Examples (a) through (c) are all cylindrical structures. Figure 2 Image (a) shows a schematic diagram of the steel ball distribution in a cylinder composed of two layers of small steel balls. Figure 2 (b) is a schematic diagram of the steel ball distribution in a cylinder composed of two layers of different steel balls (each layer contains small and large steel balls). Figure 2 (c) is a schematic diagram of the steel ball distribution in a cylinder composed of three layers of small steel balls; Figure 2 In the middle (d), there is a regular polygonal prism structure.
[0043] In this embodiment, when the calibration mold is a cylinder, the arrangement of the steel balls in each layer includes: the steel balls in each layer are arranged in a symmetrical distribution, and the steel balls in each layer are evenly distributed along the circumference.
[0044] like Figure 2 As shown, as an example, when the calibration model is a cylinder, Figure 2 In (a) to (c), the steel balls in each layer are arranged in a symmetrical distribution, that is, the steel balls in each layer are symmetrically distributed around the central axis of the cylinder, and the steel balls in each layer are evenly distributed along the circumference.
[0045] In this embodiment, when the calibration model is a cylinder, the arrangement of the steel balls in each layer further includes: the steel balls in each layer are arranged in a preset asymmetrical distribution, and the steel balls in each layer are increased sequentially according to a specified angle or the spacing between the steel balls in each layer is set according to an increasing rule; for example, the steel balls in each layer are increased sequentially according to a specified angle (i.e., the spacing between two steel balls is fixed, for example, 15°, 30°, 45°, etc.), or the spacing between the steel balls in each layer is set according to an increasing rule (for example, the first spacing is 15°, the second spacing is 30°, and the third spacing is 45°); these angle designs are only examples, and these angles can be adapted to the actual calibration scenario as needed.
[0046] In this embodiment, the uniqueness and coverage of the projection trajectory are ensured through the aforementioned asymmetric angle distribution, supporting complex geometric calibration of the offset detector and C-arm system. Furthermore, this calibration phantom can provide optimization for C-arm X-ray machines and CBCT systems.
[0047] In this embodiment, as Figure 2 As shown in (d), when the calibration mold is a cylinder, at least one flat part is provided on the side of the mold to facilitate the stable placement of the cylinder. The flat part has a planar structure and is parallel to the tangent of the nearest steel ball in the mold.
[0048] like Figure 3 As shown, in one implementation of this embodiment, the calibration phantom can be a polygonal prism structure, specifically:
[0049] The calibration mold is a regular square prism: it can be considered as a quadrilateral cross-section. Steel balls are distributed at eight equiangular positions, with the width of each side divided into three equal parts, arranged in a double layer. Figure 3 As shown in (d). Alternatively, the steel balls are distributed in a double layer at eight angular positions, including the corners and the center of each side, as shown in Figure d. Figure 3 As shown in (e).
[0050] The calibration mold is a regular hexagonal prism: steel balls are distributed at the points where the width of each side is divided into three equal parts, thus forming a track divided into twelve equal parts, such as... Figure 3 As shown in (a); or, the steel balls are distributed in the middle of each side, forming a six-part track, as shown in (a). Figure 3 As shown in (b).
[0051] The calibration mold is a regular octagonal prism: this further improves angular resolution, and steel balls can be arranged in eight equal positions at each corner or edge point, such as... Figure 3 As shown in (c).
[0052] The calibration mold is an octagonal prism or larger, and steel balls can be placed at each corner or edge point to achieve a positional arrangement of 12, 16, etc.
[0053] In this embodiment, as Figure 4 As shown, when the calibration mold is a cylinder and has a flat section, the thickness of the sidewall of the calibration mold has two forms: a normal thickness and an increased thickness. When the thickness is increased, the position of the steel balls remains unchanged, that is, the arrangement of the steel balls in each layer is as follows: the steel balls in each layer are arranged in a symmetrical distribution and are evenly distributed circumferentially. In this case, since the thickness of the sidewall of the calibration mold is increased, the diameter of the circle formed by the steel balls in each layer can remain unchanged.
[0054] It can be determined that, as the thickness increases, each layer of steel balls forms a circle around the center of the calibration mold, as shown below. Figure 4 As shown in (d); Comparison Figure 4 The distribution of the cylindrical calibration phantoms shown in (c) is as follows. Figure 4 The distribution of the flat calibration mold shown in (d) is such that the steel balls in both are circles and the diameters of the two circles remain unchanged.
[0055] In this embodiment, when the calibration mold is a cylinder and the flat part is provided, the thickness of the side wall of the calibration mold remains unchanged. When the thickness of the side wall of the calibration mold remains unchanged, the position of the steel balls is closer to the center. That is, the arrangement of the steel balls in each layer is as follows: the steel balls in each layer are arranged in a symmetrical distribution, and the steel balls in each layer are evenly distributed along the circumference. Compared with the arrangement where the thickness of the side wall increases, the diameter of the circle formed by the steel balls in each layer is reduced.
[0056] It can be determined that each layer of steel balls forms a smaller circle around the center of the calibration mold, such as... Figure 4 As shown in (b); Comparison Figure 4 The distribution of cylindrical calibration phantoms is shown in (a). Figure 4The distribution of the flattened calibration mold shown in (b) has different diameters of the circles formed by the steel balls in the two designs. Figure 4 The diameter of the circle formed by the steel balls shown in (b) is smaller.
[0057] In this embodiment, the flat position setting prevents the calibration model from rolling when placed and makes it easier to find the calibration zero position.
[0058] In this embodiment, the steel balls in the multiple layers are spaced equally axially in the calibration mold, and the distance between each layer of steel balls is greater than N times the diameter of the steel ball ring. To ensure the uniqueness of the steel ball code in the calibration mold, the number of steel ball layers in this embodiment is at least two. As an example, when the number of steel ball layers is two, the axial spacing between the two layers of steel balls in the calibration mold is equal, and the distance between each layer of steel balls is greater than N times the diameter of the steel ball ring. For example, two upper and lower tracks, each with N steel balls (e.g., 8), are arranged at equal angular intervals in space to form a closed circumference, with a fixed axial spacing between the upper and lower layers of steel balls, forming a three-dimensional geometric reference frame.
[0059] When the number of steel ball layers is three, the axial spacing of the steel balls in each layer on the calibration mold is equal, and the distance between the steel balls in each layer is greater than N times the diameter of the steel ball ring. For example, the distance between the steel ball rings is greater than 0.8 times the diameter of the steel ball ring. Figure 2 As shown in (c).
[0060] In this embodiment, the number of steel balls in each layer is greater than or equal to 6, and the steel balls in each layer are of the same size, such as... Figure 2 (a) Figure 2 As shown in (c); or the steel balls in each layer are steel balls of different sizes, such as... Figure 5 As shown. Moreover, when the steel balls in each layer are of different sizes, at least one of any three consecutive steel balls will have a different size from the other two.
[0061] like Figure 5 As shown, as an example, Figure 5 (a) shows the distribution of 5 large steel balls and 5 small steel balls. In any three consecutive steel balls, at least one is a large steel ball. Figure 5 (b) shows the distribution of 6 large steel balls and 6 small steel balls. In any three consecutive steel balls, there is at least one small steel ball. Figure 5 (c) shows the distribution of 7 large steel balls and 7 small steel balls. In any three consecutive steel balls, at least one of them is a large steel ball. Figure 5 The diagram in (d) shows the distribution of 8 large steel balls and 8 small steel balls. In any three consecutive steel balls, there is at least one small steel ball.
[0062] In this embodiment, when the steel balls in each layer are of different sizes, the steel balls at the same position in any two adjacent layers are of different sizes. That is, the steel ball at the 0° position in the first layer is different in size from the steel ball at the 0° position in the second layer. This ensures the uniqueness of the encoding.
[0063] In this embodiment, based on the structure of the calibration phantom and steel balls described above, and according to the steel ball diameter and mirroring rules, the visual encoding scheme for two different diameter steel balls is as follows:
[0064] Definition: Small steel ball represents 0, large steel ball represents 1.
[0065] Define a fixed encoding sequence in a clockwise direction (this is not a limitation in this embodiment, but only an example), for example:
[0066] The upper steel ball is coded as (0 1 0 0 1 0 1 1), and the lower track is coded according to the mirror coding rule, that is, the upper track is mirrored at the same angle position to obtain the lower steel ball code as (1 0 1 1 0 1 0 0). In this way, the codes of the upper and lower tracks have a mirror relationship, which can be effectively used for viewpoint recognition, direction judgment, and to eliminate 180-degree symmetry ambiguity in the image.
[0067] Therefore, the above coding rule is: among any three consecutive small steel balls, at least one is different in size from the other two, making it easier for the mold to distinguish the angular relationship; thus, the two small steel balls on a diameter are different in size, making it easier for the mold to find the zero position.
[0068] The structure and application scenarios of this embodiment have the following advantages:
[0069] The structure is regular and the manufacturing method is simple: the polygonal prism structure can be easily realized through 3D printing or machining.
[0070] Clear and highly distinguishable coding: Physical coding is achieved by utilizing the difference in steel ball diameter, making it easy to identify in X-ray images.
[0071] Angles are determinable and directions are unambiguous: Mirror encoding ensures that the orbital correspondence can be correctly resolved when viewed from any angle.
[0072] Highly scalable: 4, 6, or 8 prism structures can be selected as needed, and maintaining equiangular distribution ensures geometric stability and coding consistency.
[0073] In a variation of this embodiment, three or more layers of steel balls can be used. When three or more layers of steel balls are used, the distance between the steel ball rings is greater than 0.8 times the diameter of the steel ball ring. Simultaneously, a polygonal prism with an odd number of edges can be used. When the number of edges of the polygonal prism is odd, each track within the prism includes at least 6 steel balls, and the centers of the multiple steel balls must form a circle that is equally divided. Figure 6 As shown, Figure 6 In the middle (a), there is a calibration mold of a triangular prism, which is equipped with 6 steel balls (two steel balls are set on each prism face). Figure 6 In the middle (b), there is a calibration mold of a pentagonal prism, which is equipped with 10 steel balls (two steel balls are set on each prism face). Figure 6 The middle (c) is the calibration mold of the heptagonal prism, which is equipped with 7 steel balls (one steel ball at each corner).
[0074] This embodiment achieves the following technical effects through the above technical solution:
[0075] This embodiment proposes a calibration body containing multiple layers of symmetrical / asymmetrically distributed marker points for geometric calibration of CBCT systems or C-arm X-ray machines. Compared to traditional calibration bodies, the calibration body designed in this invention ensures the uniqueness and coverage of the projection trajectory during calibration, thus eliminating the need for additional equipment for auxiliary calibration, reducing the equipment cost of geometric calibration, and significantly improving computational robustness. Furthermore, the calibration body provided by this invention does not require precise placement, reducing operational difficulty, and is particularly suitable for offset detector systems and C-arm systems with high mechanical flexibility, thereby effectively controlling calibration errors.
[0076] In summary, this invention provides a calibration device for a radiographic imaging system, comprising: a calibration phantom, which is a hollow structure used to provide spatial reference for calibration at different projection angles; and multiple layers of steel balls embedded in the inner wall of the calibration phantom, with each layer of steel balls arranged in a symmetrical or pre-set asymmetrical distribution to form the required calibration code. This invention proposes a calibration body containing multiple layers of symmetrical / asymmetrically distributed markers for geometric calibration of CBCT systems or C-arm X-ray machines. Compared to traditional calibration bodies, this invention ensures the uniqueness and coverage of the projection trajectory, reduces the equipment cost of geometric calibration, and significantly improves computational robustness.
[0077] It should be understood that the application of this utility model is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. A calibration device for a radiographic imaging system, characterized in that, include: A calibration phantom, which is a hollow structure, is used to provide the spatial reference required for calibration at different projection angles; The calibration model has multiple layers of markers embedded in its inner wall. Each layer of markers consists of markers of the same size or markers of different sizes, and the markers in each layer are arranged in a symmetrical or pre-defined asymmetrical distribution to form the coding distribution required for calibration.
2. The calibration device for a radiographic imaging system according to claim 1, characterized in that, The calibration model is a cylinder or a regular polygonal prism, and the marking points are metal points.
3. The calibration device for a radiographic imaging system according to claim 2, characterized in that, When the calibration mold is a cylinder, the arrangement of the metal points in each layer includes: The metal points in each layer are arranged in a symmetrical distribution, and the metal points in each layer are evenly distributed along the circumference.
4. The calibration device for a radiographic imaging system according to claim 2, characterized in that, When the calibration mold is a cylinder, the arrangement of the metal points in each layer further includes: The metal points in each layer are arranged in a preset asymmetrical distribution, and the metal points in each layer are increased sequentially according to a specified angle or the spacing between the metal points in each layer is set according to an increasing rule.
5. The calibration device for a radiographic imaging system according to claim 2, characterized in that, When the calibration mold is a cylinder, the side of the calibration mold is provided with at least one flat part, the flat part has a planar structure, and the flat part is parallel to the tangent of the nearest metal point in the mold.
6. The calibration device for a radiographic imaging system according to claim 5, characterized in that, When the calibration mold is a cylinder and has the flat portion, the thickness of the sidewall of the calibration mold is greater than the thickness of the calibration mold without the flat portion, and the arrangement of the metal points in each layer is as follows: The metal points in each layer are arranged in a symmetrical distribution, and the metal points in each layer are evenly distributed along the circumference.
7. The calibration device for a radiographic imaging system according to claim 5, characterized in that, When the calibration mold is a cylinder and has the flat portion, the thickness of the sidewall of the calibration mold is the same as the thickness of the calibration mold without the flat portion, and the arrangement of the metal points in each layer is as follows: The metal points in each layer are arranged in a symmetrical distribution, and the metal points in each layer are evenly distributed circumferentially. Compared with the calibration mold without the flat position, the diameter of the circle formed by the metal points in each layer is reduced.
8. The calibration device for a radiographic imaging system according to claim 2, characterized in that, The axial spacing of the multiple layers of metal points on the calibration mold is equal, and the distance between each layer of metal points is greater than N times the diameter of the circle formed by each layer of metal points.
9. The calibration device for a radiographic imaging system according to claim 2, characterized in that, The number of metal points in each layer is greater than or equal to 6. When the metal points in each layer are metal points of different sizes, at least one of any three consecutive metal points has a size that is different from the other two metal points.
10. The calibration device for a radiographic imaging system according to claim 2, characterized in that, When the metal points in each layer are of different sizes, the sizes of the metal points set at the same position in any two adjacent layers are different.