Geometric parameter calibration method and device of cone beam industrial CT, terminal and storage medium

Abstract

The application provides a kind of cone beam industrial CT geometry parameter calibration method, device, terminal and storage medium, it adopts flat plate geometry correction phantom, the flat plate geometry correction phantom includes metal mark point part, metal mark point part includes plastic support structure, and the plastic support structure is embedded with 1 center metal mark point and multiple sets of concentric square metal mark points;Any one group of square metal mark points includes four metal mark points, and the four metal mark points are arranged at the four vertices of square with the center metal mark point as the symmetry center.Setting up the flat plate geometry correction phantom can effectively correct the geometry parameter of cone beam industrial CT.Specifically, only need to use the phantom to shoot two positions or two angles of CT, more accurate geometry parameter can be obtained, so that the final error of the geometry parameter of CT system can be kept within the level of micro nanometer.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a method, apparatus, terminal, and storage medium for calibrating the geometric parameters of a cone-beam industrial CT. Background Technology

[0002] Industrial CT (Industrial Computed Tomography) is a non-destructive testing method based on X-rays and computer image reconstruction technology. It is widely used in industrial fields for quality inspection, defect analysis, dimensional measurement, and reverse engineering of mechanical workpieces. Industrial CT typically needs to achieve micron or even nanometer-level spatial resolution and measurement accuracy to meet the high-precision inspection requirements of complex industrial parts.

[0003] Industrial CT includes circular industrial CT and horizontal industrial CT, among others. Horizontal industrial CT can be further categorized by size into large cabinet CT and small desktop CT. Large cabinet industrial CT is typically used in factories or quality inspection centers for high-precision, high-resolution scanning and analysis of samples. It is suitable for testing batteries, automotive parts, engines, turbine blades, etc. Small desktop CT is generally used in laboratories or testing institutions. Its core feature is its micrometer (μm) or even submicrometer (<1μm) spatial resolution, and it has been used in materials science, biomedicine, and electronics manufacturing.

[0004] Because the scenes and objects captured by industrial CT equipment are uncertain, and the objects being inspected cover a multi-scale range from micrometer-level precision chips to meter-level large-scale processed parts, it is necessary to adjust the object distance and image distance to achieve different magnifications for uncertain objects. For example, high magnification is used for microstructure analysis, while low magnification is used for overall evaluation of macroscopic components. Different magnifications, or after each magnification adjustment, require corresponding geometric parameter calibration to ensure imaging accuracy. Furthermore, industrial CT systems commonly suffer from system hardware errors, such as mechanical installation deviations and insufficient precision. These errors are positively correlated with hardware costs and are difficult to completely eliminate, ultimately leading to significant imaging deviations. For instance, the single-pixel resolution of a detector is typically around 50μm, and if the geometric parameter error exceeds one unit pixel, visible artifacts will form in the reconstructed image, severely affecting the accuracy of the detection results.

[0005] Existing technologies for calibrating cone-beam CT systems, especially industrial cone-beam CT systems, suffer from problems such as long calibration times, complex operations, stringent requirements for phantom positioning, size, and field of view (FOV) matching, and the potential for calibration failure due to magnification changes or local projection loss in practical applications. For example, in current small desktop CT scanners, different magnification ratios are achieved by changing the turntable position (SID) within the system. In this case, geometric correction needs to be performed again after each turntable movement. Traditional small desktop CT scanners use a single-row steel ball cylindrical phantom, but this phantom suffers from long calibration times and inability to calibrate at high magnifications. The single-row steel ball cylindrical phantom essentially calculates the geometric parameters of the CT system by fitting the rotational trajectories of multiple small balls on the projected image. Therefore, it is necessary to ensure that the ball trajectory is a complete 360-degree circle, calculate the coordinates of each ball in the projected image, ensure that at least 4 to 5 ball trajectories exist, and that the balls are not too close to the center of rotation. These requirements are difficult to meet at high magnification. In addition, the frequent movement of the turntable and the long calibration time will also increase the waiting time before each CT scan.

[0006] Therefore, given the limitations of existing geometric parameter calibration methods, developing an efficient, accurate, and adaptable geometric calibration method is crucial for improving the stability of cone-beam industrial CT inspection and reducing reliance on high-cost hardware. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a geometric parameter calibration method, device, terminal and storage medium for cone-beam CT, which solves the problems of long calibration time and inaccurate calibration at different magnifications in the geometric calibration process of existing cone-beam industrial CT.

[0008] To achieve the above and other related objectives, the present invention is implemented by including the following technical solutions.

[0009] The first aspect of the present invention provides a flat geometric correction phantom for cone-beam industrial CT, the flat geometric correction phantom including a metal marking point part, the metal marking point part including a plastic support structure, the plastic support structure having a central metal marking point and multiple sets of concentric square metal marking points embedded thereon; any set of square metal marking points includes four metal marking points, and the four metal marking points are located at the four vertices of the square with the central metal marking point as the center of symmetry.

[0010] In one embodiment, the flat geometric correction mold further includes an extension portion connected to the lower end of the metal marking point portion and a turntable docking base.

[0011] In one embodiment, the metal marker portion is X-shaped, and the metal marker is located on the X-shaped metal marker portion.

[0012] In one embodiment, the thickness of the plastic support structure is 3 to 5 mm.

[0013] In one embodiment, the difference in side length of the square formed by any two adjacent sets of square metal markers is 2 to 200 mm.

[0014] In one embodiment, the number of concentric square metal markers is 2 to 10 sets.

[0015] In one embodiment, the X-shaped metal marker part has four arms, and the width of any arm is 3 to 5 mm.

[0016] In one embodiment, the metal marker is a small metal ball with a diameter of 1 mm.

[0017] In one embodiment, the height of the elongated portion is 50–90 mm.

[0018] In one embodiment, the turntable docking base has threaded holes through which screws pass to secure it to the turntable.

[0019] A second aspect of the present invention provides a method for calibrating the geometric parameters of a cone-beam industrial CT, wherein a flat geometric correction phantom as described above is used to correct the geometric parameters required for the reconstruction of the cone-beam industrial CT.

[0020] The geometric parameter calibration method includes:

[0021] Acquire two DR scan projection images of the flat geometric correction phantom body position (0°) and the corresponding position rotated 180° relative to the body position;

[0022] The projected coordinates of the metal marker points are obtained based on the DR scan projection image;

[0023] Filter out the projected coordinates that can form the vertices of a square;

[0024] Geometric data is calculated based on the selected projection coordinates.

[0025] In one implementation, the method for selecting the projected coordinates that can constitute the vertices of a square includes:

[0026] For the projected coordinates of two positions, the radius of the circumcircle corresponding to each square is obtained based on the magnification and the side length of the square;

[0027] Starting from each metal marker point as the center point, and within the same radius, iterate through the Euclidean distances between the projected coordinates of all square metal marker points and the coordinates of the current metal marker point to obtain the projected coordinates of the center point and the projected coordinates of the metal marker points that are valid squares. A valid square metal marker point is defined as one whose error between the Euclidean distance to the corresponding metal marker point and the radius of the corresponding circumcircle does not exceed the number of pixels corresponding to the diameter of one metal marker point.

[0028] If there are fewer than four vertices with coordinates under the same radius, then all coordinates of the corresponding square metal marker point under that radius are discarded.

[0029] In one implementation, calculating geometric data based on the selected projected coordinates includes: reordering the coordinates of the four vertices of the selected square so that the directions represented by the signs of the geometric parameters are consistent with the directions represented by the reconstruction parameters of the CT system; and then calculating the geometric parameters.

[0030] A third aspect of the present invention also provides a geometric parameter calibration device for cone-beam industrial CT, which uses a flat geometric correction phantom as described in any of the above description to correct the geometric parameters required for cone-beam industrial CT reconstruction; the geometric parameter calibration device includes:

[0031] DR scanning projection image acquisition module: used to acquire DR scanning projection images of two positions of the flat geometric correction model, including the main body position (0°) and the corresponding position rotated 180° relative to the main body position;

[0032] Projection coordinate acquisition module: used to acquire the projection coordinates of metal marker points based on the DR scan projection image;

[0033] Valid coordinate filtering module: used to classify the projected coordinates to filter out the projected coordinates that can form the vertices of a square;

[0034] Calculation module: Used to calculate geometric parameters based on the selected projected coordinates.

[0035] In one implementation, the module for filtering valid coordinates includes:

[0036] Square circumcircle radius calculation module: used to obtain the radius of the circumcircle corresponding to each square based on the magnification and the side length of the square;

[0037] The effective square projection coordinate filtering module is used to traverse all square metal markers with the same radius, taking each metal marker as the center point, and calculate the Euclidean distance between the projection coordinates of all square metal markers and the coordinates of the current metal marker. It then obtains the projection coordinates of the center point and the projection coordinates of the metal markers that are valid squares. A valid square metal marker is defined as one where the error between the Euclidean distance to the metal marker and the radius of the corresponding circumcircle does not exceed the number of pixels corresponding to the diameter of the metal marker.

[0038] In one embodiment, the computing module includes:

[0039] Sorting module: used to reorder the coordinates of the four vertices of the selected square so that the direction represented by the positive and negative signs of the geometric parameters can be consistent with the direction represented by the reconstruction parameters of the CT system;

[0040] Geometric parameter calculation module: Calculates geometric parameters based on the coordinates obtained from the sorting module.

[0041] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the geometric parameter calibration method as described above.

[0042] A fifth aspect of the present invention provides a terminal, comprising: a processor and a memory; the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory to cause the terminal to perform any of the geometric parameter calibration methods described above.

[0043] As described above, the flat geometric correction phantom, cone-beam CT geometric parameter calibration method, apparatus, device, and storage medium of the present invention have the following beneficial effects:

[0044] This invention provides a novel flat-panel geometric correction phantom and method. Using this phantom, the geometric parameters of cone-beam industrial CT can be effectively corrected. Specifically, by using this phantom to capture CT images at two positions or two angles, the algorithm accuracy can be effectively improved, and more precise geometric parameters can be obtained. This allows the final error of the CT system's geometric parameters to be kept within the micro-nano meter level, such as below 10 μm. Attached Figure Description

[0045] Figure 1 The diagram shown is a three-dimensional structural schematic of the geometric correction mold of the present invention.

[0046] Figure 2 The diagram shown is a structural schematic corresponding to the main view of the geometric correction mold of the present invention.

[0047] Figure 3The diagram shows a partial structural schematic of the square metal marker points in the geometric correction mold of the present invention.

[0048] Figure 4 The diagram shown is a structural schematic corresponding to the side view of the geometric correction mold of the present invention.

[0049] Figure 5 The diagram shown is a top view of the geometric correction mold of the present invention.

[0050] Figure 6 The diagram shown is a flowchart illustrating the geometric parameter calibration method of the present invention.

[0051] Figure 7 This diagram illustrates the specific method for selecting the projected coordinates that can form the vertices of a square in this invention.

[0052] Figure 8 The diagram shows a flowchart illustrating a specific method for calculating geometric parameters in this invention.

[0053] Figure 9 This is a schematic diagram illustrating a specific process for calculating various geometric parameters in this invention.

[0054] Figure 10 The image shown is a DR scan projection image of the flat geometric correction phantom in this invention at a magnification of 3x.

[0055] Figure 11 The image shown is a DR scan projection image of the flat geometric correction phantom in this invention at a magnification of 6x.

[0056] Figure 12 The diagram shown is a schematic representation of the geometric parameter calibration device in this invention.

[0057] Figure 13 The diagram shown is a frame structure diagram of the geometric parameter calibration terminal in the invention. Detailed Implementation

[0058] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0059] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0060] Explanation of technical terms in this application:

[0061] CT: Computed Tomography.

[0062] SDD: Source-to-Detector Distance, is one of the core geometric parameters of an industrial CT system, directly affecting image resolution, magnification, signal-to-noise ratio, and scanning efficiency.

[0063] SID: Source-to-Iso Distance, the distance from the source focal point to the center of the rotation axis. Together with SDD, it constitutes the geometric magnification model of the CT system, directly affecting resolution, scanning field of view, and image quality. Industrial CT scanners can generally move the stage position (center of rotation axis) according to the object under test, thus changing its magnification.

[0064] Δu: Col Offset, the lateral offset between the actual midpoint and the theoretical center (geometric center of the detector) of the central ray emitted from the X-ray source after passing the center of rotation. This error can originate from mechanical installation deviations after assembling or transporting new equipment, detector displacement caused by reinstallation after maintenance, or thermal deformation of the mechanical structure due to prolonged operation. It is crucial for the geometric calibration of the CT system and directly affects the accuracy and symmetry of the reconstructed images.

[0065] Δv: Row Offset, the longitudinal offset between the actual midpoint and the theoretical center (geometric center of the detector) of the central ray emitted from the X-ray source after passing the rotation center. This error can originate from detector tilt caused by mechanical assembly errors, rotation axis tilt caused by structural deformation due to system vibration or long-term use, X-ray source offset caused by recalibrating the source position after maintenance, and micro-deformation of the mechanical structure caused by temperature changes. It is one of the core parameters of system geometric calibration and directly affects the vertical alignment and three-dimensional accuracy of the reconstructed image.

[0066] Φ, Slant Angle, refers to the angle by which the detector plane rotates around its middle column, which is the longitudinal axis of the detector; that is, the tilt angle between the detector plane and its ideal vertical position (strictly parallel to the axis of rotation). This parameter is one of the core parameters of CT system geometric calibration, directly affecting the symmetry of the projection data and the accuracy of the reconstructed image.

[0067] θ, Tilt Angle, refers to the angle by which the detector plane rotates along the middle row direction, which is the transverse central axis of the detector;

[0068] ΔD, the correction offset from the center of the light source to the center of rotation to the center of the detector;

[0069] η, Skew Angle, refers to the rotation angle between the central axis of the detector plane and the axis of rotation, that is, the angle of twist of the detector about its normal axis (usually the direction perpendicular to the detector plane). This parameter is an advanced parameter for the geometric calibration of the CT system, which directly affects the orthogonality of the projected data and the geometric accuracy of the reconstructed image.

[0070] FOV, or Field-Of-View, refers to the physical space within which an X-ray beam illuminates and forms an effective image. The size of the FOV depends on factors such as the emission angle of the X-ray source, the size of the detector, and its geometric configuration.

[0071] DR scan projection image: A DR scan projection image is generated by the detector receiving the attenuated signal after X-rays penetrate the object being measured.

[0072] The technical solution of this invention is applicable to cone-beam CT equipment, and is particularly proposed to address the problem of decreased accuracy in industrial cone-beam CT equipment due to overall system errors, including motion control errors, mechanical precision errors of the phantom and equipment, and assembly errors.

[0073] In this invention, a flat geometric phantom with multiple embedded metal spheres is used as the object to be scanned, and a flat panel detector is used as the radiographic imaging system for acquisition. The geometric parameters of the CT device are calculated through the projected images.

[0074] Geometric parameters of a CT system are crucial for CT image reconstruction; sufficiently accurate geometric parameters are fundamental to ensuring that subsequent image algorithms can obtain high-resolution, low-artifact images. The flat geometric phantom described in this invention enables rapid and accurate calculation of geometric parameters at any magnification.

[0075] Compared to other phantoms that require scanning the entire circle of data, the flat geometric phantom of this application saves calibration time. This time saving stems from the smaller data volume; only DR projection is needed, significantly reducing scanning time. The number of small spheres to be located in each projection image is also smaller, resulting in less overall computation. The final geometric parameter error can reach the micro-nano level, achieving an accuracy below 10 μm.

[0076] This application provides a specific example such as... Figures 1-5The flat geometric model shown is improved compared to the prior art in that it has a central metal marker and multiple sets of concentric square metal markers that can be adapted for different magnification ratios.

[0077] The metal marker in this application meets the general requirements of the CT equipment field, such as: 1) having a high X-ray absorption rate relative to the plastic support structure; 2) having physicochemical stability and not deforming under changes in temperature and humidity; 3) requiring high processing precision, typically being a regularly shaped sphere with a diameter of 0.5–2 mm and a smooth surface to reduce scattering artifacts; and 4) avoiding interference with electromagnetic components of the CT system, such as detection circuits. Specifically, tungsten, tantalum, and stainless steel can be used.

[0078] These metallic markers typically need to be embedded in a low-density substrate to avoid artifact interference. The low-density substrate can be something like acrylic, and the embedding depth should remain consistent. In a... Figures 1-5 In the specific embodiment shown, this application provides a specific flat-panel geometric correction phantom for cone-beam industrial CT, which includes a metal marking point part 1. The metal marking point part 1 includes a plastic support structure 15, on which a central metal marking point 11 and multiple sets of concentric square metal marking points (such as 12, 13, and 14) are embedded. Any set of square metal marking points, such as 12, includes four metal marking points (such as 121 / 122 / 123 / 124), and the four metal marking points are located at the four vertices of the square with the central metal marking point 11 as the center of symmetry. The difference in the side length of the square (the distance between two steel balls) of two adjacent sets of concentric square metal marking points can be equal or unequal, such as a difference of 2 to 200 mm. In other words, the spacing of the metal marking points on a single arm can be the same or different. The specific number of groups and settings can be adjusted according to the specific circumstances. For example, considering the magnification of the CT scan, at the maximum magnification, all metal markers on the phantom can be seen; at the minimum magnification, at least 5 metal markers (i.e., 11 and 12) can be seen.

[0079] In a more specific case, Figure 1 In the illustrated embodiment, the flat geometric correction mold further includes an extension 2 connected to the lower end of the metal marker point portion and a turntable docking base 3. The turntable docking base 3 is used to dock with the turntable for fixation. The fixation method can be screw fixing, such as forming screw holes 31 as shown in the figure, or snap-fit ​​fixing, etc.; this fixation ensures the stability of the connection. The extension 2 is to ensure that the metal marker point portion 1 appears within the field of view (FOV). Figure 1As shown, the turntable docking base 3 at the bottom of the flat geometric correction mold in this application is fixed on the turntable to drive the entire flat geometric correction mold to rotate. In use, the metal marker point is located within the FOV to form a DR scan projection image using the CT equipment.

[0080] like Figures 1-5 As shown, the metal marker part 1 of the flat geometric correction mold is X-shaped, meaning its overall outline is X-shaped. The X-shaped structure is designed to reduce the attenuation rate of the metal markers in the projection domain, avoiding inconsistent attenuation of X-rays entering from the sides and front due to the plastic support structure itself. The included angle between the four arms of the X-shape can be 90° to facilitate the formation of multiple sets of square metal markers. The metal markers on any arm are distributed along the centerline of the arm's extension direction, also considering processing accuracy, stability, and ensuring relatively consistent X-ray attenuation rates in all directions.

[0081] In one specific embodiment, the thickness of the plastic support structure can be 3-5 mm, and the X-shaped metal marker has four arms, the width of any arm being 3-5 mm. This width and thickness are to ensure that it has a certain strength and is not easily broken; too wide a width would affect the attenuation rate of the projection field.

[0082] In this application, the number of concentric square metal markers is not limited and can be set according to specific circumstances and requirements. For example, the number of groups can be set according to the device size and variable magnification. In a specific embodiment, the number of concentric square metal markers is 2 to 10 groups, such as 2 groups, or... Figures 1-5 The diagram shows 3 groups, but it can also show 5, 7, 8, or 10 groups, etc.

[0083] In one specific embodiment, the metal markers in this application are small metal balls with a diameter of 1 mm. If the diameter of the metal ball is too small, its processing accuracy cannot be guaranteed; if it is too large, the shape and size of the plastic support structure are insufficient.

[0084] In a specific embodiment, such as Figure 1As shown, to ensure that the metal marker is located within the projection area, there is generally a certain height from the base fixed to the turntable to the projection area. This height can be set according to specific circumstances and needs, as long as it ensures that the flat geometric correction mold can be rotated by the turntable and that the metal marker remains within the projection area. In a more specific embodiment, the height of the elongated portion 2 can be 50–100 mm, such as 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm. Furthermore, to provide stable support and form an effective projection, the upper section of the elongated portion can be thinned to form a thickness consistent with the metal marker, as shown in [reference needed]. Figure 1 The diagram shows a section that has been thinned.

[0085] Based on such Figures 1-5 The applicant proposes a method for calibrating cone-beam industrial CT using a flat plate geometric correction phantom. This method obtains the final geometric parameters by filtering and calculating the coordinates of metal marker points in the projection images of the phantom at two locations. The method acquires DR scan projection images of the metal marker points at 0° and 180° positions, effectively improving algorithm accuracy; furthermore, different numbers of metal marker points ensure that effective data is available for calculation at different magnifications.

[0086] Generally, a cone-beam industrial CT system includes a flat panel detector, a turntable, and an X-ray source. Specifically, this application may describe a horizontal cone-beam industrial CT. The X-ray source, used to emit a cone-shaped X-ray beam, is located on one side of the system, opposite the flat panel detector. The flat panel detector, installed directly opposite the X-ray source, receives the X-rays penetrating the sample and converts them into digital signals. The turntable, located between the X-ray source and the flat panel detector, is used to place and rotate the sample, with its rotation axis perpendicular to the plane of the flat panel detector. The turntable is fixedly mounted, such as on the system's base. The X-ray source and the flat panel detector can be fixed using a bracket or robotic arm, ensuring alignment of their central axes. The X-ray source and the flat panel detector are connected to a computer via cables, and the turntable is driven by a motor, rotating synchronously with data acquisition. In actual operation, the process includes the following steps: 1) Sample placement: Fix the sample to be tested in the center of the turntable, ensuring it is within the X-ray beam coverage area; 2) Parameter setting: Set the voltage, current, exposure time, rotation step angle, and number of scans; 3) Scanning and acquisition: The turntable rotates in steps, pausing at each angle for X-ray exposure. The flat panel detector acquires the projected images, completing the scan of the required angle and obtaining hundreds to thousands of projected images; 4) Image reconstruction: Reconstruct the projected data into 3D volume data using computer software; 5) Analysis and application: Perform analysis such as defect detection, dimensional measurement, or reverse engineering. In actual operation, coaxial calibration is crucial. Specifically, ensure that the X-ray source focal point, the turntable central axis, and the detector center are strictly aligned. Also, ensure that the turntable rotation and detector acquisition are precisely synchronized to avoid motion blur.

[0087] This application uses the above-mentioned methods as described above. Figures 1-5 The method described above calculates the geometric parameters of the CT system based on the projected image of the defined flat geometric correction phantom under a CT system. These geometric parameters are crucial for reconstruction in CT imaging systems, as image reconstruction requires geometric parameters to construct stereoscopic data. Sufficiently accurate geometric parameters are fundamental to ensuring that subsequent image algorithms can obtain high-resolution, low-artifact images. Furthermore, the method provided by this invention can achieve fast and accurate geometric parameter calculation at any magnification.

[0088] Specifically, it will be like Figures 1-5The aforementioned flat-panel geometric correction phantom is placed on a turntable, and a flat-panel detector acquires a two-dimensional projection image of the geometric correction for system performance calibration. In this application, DR data from two positions (0° and 180°) of the phantom are selected. This data is a 2D grayscale image, and the pixel values ​​reflect the attenuation distribution after X-rays penetrate the phantom. This is used to correct the non-uniformity of the flat-panel detector response or to verify the geometric alignment of the X-ray source, detector, and turntable to avoid projection offset. The process of acquiring DR data includes: 1) Placing the phantom: Fixing the geometric correction phantom at the center of the turntable, ensuring it is parallel to the plane of the flat-panel detector; 2) Setting parameters: Selecting appropriate X-ray energy, current, and exposure time; 3) Acquiring images: Keeping the turntable stationary at the 0° and 180° positions, triggering X-ray exposure and acquiring DR images; 4) Analyzing data: Using software tools to analyze the data to obtain geometric parameters, including Φ, θ, η, Δu, Δv, SID, and SDD.

[0089] This invention provides a method such as... Figure 6 The geometric parameter calibration method for cone-beam industrial CT shown includes:

[0090] S10: Acquire two DR scan projection images (0° and 180° positions) of the flat geometric correction model body position and the corresponding position after rotating 180° relative to the body position.

[0091] S20: Obtain the projection coordinates of the metal marker points based on the DR scan projection image;

[0092] S30: Filter out the projected coordinates that can form the vertices of a square;

[0093] S40: Calculate geometric parameters based on the selected projected coordinates.

[0094] In a further such as Figure 7 In the illustrated embodiment, the method for filtering the projected coordinates that can form the vertices of a square includes:

[0095] S31: For the projected coordinates of two positions, obtain the radius of the circumcircle corresponding to each square based on the magnification and the side length of the square;

[0096] S32: Starting from each metal marker point as the center point, under the same radius, traverse the Euclidean distance between the projected coordinates of all square metal marker points and the coordinates of the current metal marker point, and obtain the projected coordinates of the center point and the projected coordinates of the metal marker points that are valid squares; the valid square metal marker point is the one whose error between the Euclidean distance corresponding to the metal marker point and the radius of the corresponding circumcircle does not exceed the number of pixels corresponding to the diameter of one metal marker point.

[0097] In the above steps, based on the magnification and the side length of the square, the magnification is the CT reading magnification corresponding to the DR scan projection image. When SID and SDD are fixed, it is a constant value, and the magnification = SDD / SID. As long as the relative position does not change, the magnification of DR and CT will not change. The side length of the square is the processing size of the phantom itself, which is known data.

[0098] It should be noted that in step S32, if there are fewer than 4 vertices with coordinates under the same radius, then all coordinates of the corresponding square metal marker point under that radius are discarded.

[0099] In a specific example Figure 8 In the illustrated embodiment, calculating geometric parameters based on the selected projected coordinates includes:

[0100] S41: Reorder the projected coordinates of the metal markers of the selected squares so that the direction represented by the positive and negative signs of the geometric parameters can remain consistent across different data.

[0101] S42: Calculate geometric parameters.

[0102] In a more specific embodiment, the geometric parameters are calculated for each valid square and then the average value of each geometric parameter is output.

[0103] In a specific example Figure 9 In the illustrated embodiment, for a given valid square, the calculation of geometric parameters includes: 1) calculating the lengths of the four sides of each square; 2) calculating Φ and θ; 3) calculating ΔD; and 4) calculating η, Δu, and Δv.

[0104] It should be noted that if no valid square is found, an error message will be output directly.

[0105] In the correction method of this application, the person skilled in the art understands that 0° and 180° are in the case of fixed equipment, where only the turntable rotates, and the DR scan projection image is fixed in other cases, and the image is obtained only at the two angles of 0° and 180°.

[0106] To further illustrate that the flat-plate geometric correction phantom provided in this application can respond better to variable magnification situations without having to change phantoms for different probes, the applicant provides further details as follows. See the DR scan projection image as shown below. Figure 10 and Figure 11 As shown, Figure 10 This is a DR projection of a flat geometric correction phantom at 3x magnification. Figure 11This is a DR projection of the flat geometric correction model at 6x magnification. It can be seen that due to the presence of multiple sets of concentric square metal markers, there are corresponding effective square DR projections for both magnifications. The appropriate center points are found, and the coordinates of the effective square vertices are ultimately determined. Figure 10 There are 3 squares in the middle, from which 3 sets of geometric parameters required for reconstruction are obtained. Then, two angles (0° and 180°) are superimposed to obtain a total of 2×3 sets of data. Figure 11 There are two valid squares in the image. Two sets of geometric parameters required for reconstruction are calculated for each square. These are then superimposed with two angles (0° and 180°) to produce 2×2 sets of data. One set of geometric parameters includes two offsets, three angles, and SID. Since the industrial CT in this application uses variable magnification, the calculated ΔD is used to correct the SID to obtain the true SID. In this application, a phantom composed of multiple concentric square metal markers made of steel balls is used as the scanned phantom. Compared to arranging metal points in a single square, this method can obtain many times more data in the same image. Figures 1-5 As shown, 3x data can be obtained; at the same time, effective data is guaranteed for calculation at different magnifications, thus avoiding the problem of no effective data for calculation at higher magnifications.

[0107] It should be further stated that the final target geometric parameters of the correction method in this application are seven, specifically: Δu (Col Offset), Δv (Row Offset), Φ (Slant Angle), θ (Tilt Angle), SID, and SDD. Among them, SID and SDD are used to calculate the magnification. Since the industrial CT in this application has a variable magnification, the calculated ΔD is used to correct SID to obtain the true magnification.

[0108] The method for calculating geometric parameters in this application can refer to existing methods. For example, the calculation method in Sun, Yiet al., "A calibration method for misaligned scanner geometry in cone-beam computed tomography," Ndt&E International 39 (2006):499-513, can be referenced. Compared to that paper, the accuracy of this application is greatly improved by using this phantom and specific method, especially considering the common issues of machine accuracy and phantom accuracy, where the algorithm in that paper cannot meet the requirements of practical industrial CT applications. Furthermore, compared to existing methods that use single-column or single-row 360° scanning to form circular or elliptical trajectories, requiring phantoms of different sizes for different magnifications and processing large amounts of data, this application not only eliminates the need to change the phantom for different subjects but also simplifies the process and reduces geometric calibration time.

[0109] Existing similar methods generally assume an ideal situation where the phantom is located at the center of rotation. However, in practical applications, the phantom's position often deviates, causing the center of rotation and the phantom center to not completely coincide. Therefore, this application uses two projection angles, 0° and 180°, to acquire a DR image. Since the phantom positions in these two images are symmetrically distributed based on the center of rotation, this symmetry can be used to accurately calculate the true position of the center of rotation, thereby correcting the phantom offset. This method not only solves the problem of placing the phantom center at the center of rotation but also reduces errors caused by the phantom itself and its placement, making it of significant application value for high-precision CT imaging systems.

[0110] This application also discloses a method such as... Figure 12 The geometric parameter calibration device shown employs, for example... Figures 1-5 The flat geometric correction phantom shown corrects the geometric parameters required for cone-beam industrial CT reconstruction; the geometric parameter calibration device includes:

[0111] DR Scan Projection Image Acquisition Module 1: Used to acquire DR scan projection images of two positions of the flat geometric correction model, including the main body position and the corresponding position rotated 180° relative to the main body position;

[0112] Projection coordinate acquisition module 2: used to acquire the projection coordinates of the metal marker points based on the DR scan projection image;

[0113] Valid coordinate filtering module 3: used to classify the projected coordinates to filter out the projected coordinates that can form the vertices of a square;

[0114] Calculation module 4: Used to calculate geometric parameters based on the selected projected coordinates.

[0115] In one specific embodiment, the module for filtering valid coordinates includes:

[0116] Square circumcircle radius calculation module: used to obtain the radius of the circumcircle corresponding to each square based on the magnification and the side length of the square;

[0117] The effective square projection coordinate filtering module is used to traverse the Euclidean distances between the projection coordinates of all square metal markers and the coordinates of the central metal marker, assuming each metal marker is the center point, and within the same radius. It then obtains the projection coordinates of metal markers that are valid squares. A valid square metal marker is defined as one whose error between the Euclidean distance to the corresponding metal marker and the radius of its corresponding circumcircle does not exceed the number of pixels corresponding to the diameter of one metal marker.

[0118] In one specific embodiment, the computing module includes:

[0119] Sorting module: used to reorder the coordinates of the four vertices of the selected square so that the direction represented by the positive and negative signs of the geometric parameters is consistent with the direction represented by the reconstruction parameters of the CT system;

[0120] Geometric parameter calculation module: Calculates geometric parameters based on the coordinates obtained from the sorting module.

[0121] This invention also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the geometric parameter calibration method as described above.

[0122] It should be noted that the division of the various modules in the above device is merely a logical functional division. In actual implementation, they can be fully or partially integrated into a single physical entity, or they can be physically separated. Furthermore, these modules can be implemented entirely in software via processing element calls, entirely in hardware, or partially in software calls via processing element calls and partially in hardware. For example, any module can be a separate processing element or integrated into a chip within the device. Additionally, any module can be stored as program code in the device's memory, and its function can be called and executed by a processing element. The implementation of other modules is similar. These modules can be fully or partially integrated together or implemented independently. The processing element mentioned here can be an integrated circuit with signal processing capabilities. In the implementation process, each step of the above method or each of the above modules can be completed through integrated logic circuits in the hardware of the processor element or through software instructions. These modules can be one or more integrated circuits configured to implement the above methods, such as one or more Application Specific Integrated Circuits (ASICs), one or more Digital Signal Processors (DSPs), one or more Field Programmable Gate Arrays (FPGAs), etc. When a module is implemented through processing element scheduler code, the processing element can be a general-purpose processor, such as a Central Processing Unit (CPU) or other processor capable of calling program code. These modules can be integrated together to form a System-on-a-Chip (SOC).

[0123] A schematic diagram of another geometric parameter calibration terminal provided in this application embodiment is shown below. Figure 13 As shown. The geometric parameter terminal provided in this example includes: a processor, a memory, a transceiver, a communication interface and / or a system bus; the memory and the communication interface are connected to the processor and the transceiver through the system bus and complete mutual communication. The memory is used to store computer programs, the communication interface is used to communicate with other devices, and the processor and the transceiver are used to run the computer program, so that the geometric parameter calibration device performs the various steps of the geometric parameter calibration method described above.

[0124] The system bus mentioned above can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This system bus can be divided into address bus, data bus, control bus, etc. For ease of representation, only one thick line is used in the diagram, but this does not indicate that there is only one bus or one type of bus. The communication interface is used to enable communication between the database access device and other devices (such as clients, read-write libraries, and read-only libraries). Memory may include Random Access Memory (RAM) and may also include non-volatile memory, such as at least one disk drive.

[0125] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0126] Computer-readable storage media:

[0127] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented using computer program-related hardware. The aforementioned computer program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0128] The scope of protection of the geometric parameter calibration method described in this invention is not limited to the execution order of the steps listed in this embodiment. Any solution implemented by adding, subtracting, or replacing steps in the prior art based on the principles of this invention is included within the scope of protection of this invention.

[0129] The present invention also provides a geometric parameter calibration system, which can implement the geometric parameter calibration method described in the present invention. However, the implementation device of the geometric parameter calibration method described in the present invention includes, but is not limited to, the structure of the geometric parameter calibration system listed in this embodiment. All structural modifications and substitutions of the prior art made in accordance with the principles of the present invention are included within the protection scope of the present invention.

[0130] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A flat geometric correction phantom for cone-beam industrial CT, characterized in that, The flat geometric correction model includes a metal marker part, which includes a plastic support structure. The plastic support structure is embedded with a central metal marker and multiple sets of concentric square metal markers. Each set of square metal markers includes four metal markers, and the four metal markers are located at the four vertices of the square with the central metal marker as the center of symmetry.

2. The flat geometric correction mold according to claim 1, characterized in that, The flat geometric correction mold further includes an extension portion connected to the lower end of the metal marking point portion and a turntable docking base; and / or, the metal marking point portion is X-shaped, and the metal marking point is located on the X-shaped metal marking point portion; and / or, the thickness of the plastic support structure is 3 to 5 mm; and / or, the difference in side length of the square formed by any two adjacent sets of square metal marking points is 2 to 200 mm; and / or, there are 2 to 10 sets of concentric square metal marking points.

3. The flat geometric correction mold according to claim 2, characterized in that, The X-shaped metal marker part has four arms, the width of any arm being 3-5 mm; and / or, the metal marker is a small metal ball with a diameter of 1 mm; and / or, the height of the elongated part is 50-90 mm; and / or, the turntable docking base has threaded holes for screws to pass through and fix it to the turntable.

4. A method for calibrating the geometric parameters of a cone-beam industrial CT, characterized in that, The geometric parameters required for cone-beam industrial CT reconstruction are corrected using the flat geometric correction phantom as described in any one of claims 1 to 3. The geometric parameter calibration method includes: Acquire two DR scan projection images of the main body position of the flat geometric correction model and the corresponding position of the model rotated 180° relative to the main body position; The projected coordinates of the metal marker points are obtained based on the DR scan projection image; Filter out the projected coordinates that can form the vertices of a square; Geometric parameters are calculated based on the selected projection coordinates.

5. The geometric parameter calibration method according to claim 4, characterized in that, Methods for selecting the projected coordinates that can form the vertices of a square include: For the projected coordinates of the two positions, the radius of the circumcircle corresponding to each square is obtained based on the magnification and the side length of the square. Assuming that each metal marker point is the center point and starts from the same radius, the Euclidean distance between the projected coordinates of all square metal marker points and the coordinates of the current metal marker point is traversed to obtain the projected coordinates of the center point and the projected coordinates of the metal marker points that have valid squares. The valid square metal marker point is defined as the metal marker point whose error between the Euclidean distance and the radius of the corresponding circumcircle does not exceed the number of pixels corresponding to the diameter of one metal marker point.

6. The geometric parameter calibration method according to claim 4, characterized in that, The calculation of geometric parameters based on the selected projection coordinates includes: reordering the projection coordinates of the selected square metal markers so that the direction indicated by the positive and negative signs of the geometric parameters is consistent with the direction indicated by the reconstruction parameters of the CT system; and then calculating the geometric parameters.

7. A geometric parameter calibration device for cone-beam industrial CT, characterized in that, The geometric parameters required for cone-beam industrial CT reconstruction are corrected using the flat geometric correction phantom as described in any one of claims 1 to 3. The geometric parameter calibration device includes: DR scanning projection image acquisition module: used to acquire DR scanning projection images of two positions of the flat geometric correction model, including the main body position and the corresponding position rotated 180° relative to the main body position; Projection coordinate acquisition module: used to acquire the projection coordinates of metal marker points based on the DR scan projection image; Valid coordinate filtering module: used to classify the projected coordinates to filter out the projected coordinates that can form the vertices of a square; Calculation module: Used to calculate geometric parameters based on the selected projected coordinates.

8. The geometric parameter calibration device according to claim 7, characterized in that, The module for filtering valid coordinates includes: Square circumcircle radius calculation module: used to obtain the radius of the circumcircle corresponding to each square based on the magnification and the side length of the square; The effective square projection coordinate filtering module is used to traverse the Euclidean distance between the projection coordinates of all square metal markers and the coordinates of the current metal marker, assuming each metal marker is the center point, and within the same radius. It obtains the projection coordinates of the center point and the projection coordinates of the metal markers that are effective squares. The effective square metal marker is defined as one whose error between the Euclidean distance to the corresponding metal marker and the radius of the corresponding circumcircle does not exceed the number of pixels corresponding to the diameter of one metal marker.

9. The geometric parameter calibration device according to claim 7, characterized in that, The computing module includes: Sorting module: used to reorder the coordinates of the four vertices of the selected square so that the direction represented by the positive and negative signs of the geometric parameters is consistent with the direction represented by the reconstruction parameters of the CT system; Geometric parameter calculation module: Calculates geometric parameters based on the coordinates obtained from the sorting module.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the geometric parameter calibration method according to any one of claims 4 to 6.

11. A terminal, characterized in that, include: Processor and memory; The memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory to cause the terminal to perform the geometric parameter calibration method as described in any one of claims 4 to 6.

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