Geometric parameter acquisition method and device, terminal, storage medium and planar CT system

Abstract

The invention provides a geometric parameter acquisition method and device, a terminal, a storage medium and a plane CT system, and the geometric parameter acquisition method comprises the steps: obtaining the space coordinates of each test die body in a preset space coordinate system, and obtaining the scanning circular trajectory of each test die body on a detection plane; based on the circle center coordinates of the scanning circle trajectories and in combination with the space coordinates of the test die bodies, geometric projection coefficients of the corresponding test die bodies are obtained; on the basis of the geometric projection coefficient of each test die body and in combination with the scanning radius of each scanning circular trajectory, constructing an equation set, and obtaining the radiation source motion radius and the detector motion radius of the plane CT system; wherein the geometric projection coefficient is used for representing a conversion relation for converting the space coordinate and the scanning circular track on the detection plane based on the geometric projection relation of the plane CT system, and an equation or an equation set is constructed through the geometric projection coefficient to solve the accurate value of each geometric parameter, so that the image reconstruction effect of the plane CT system is improved.

Description

Technical Field

[0001] This application belongs to the field of ray imaging, and relates to a ray imaging system, in particular to a method and device for obtaining geometric parameters, a terminal, a storage medium, and a planar CT system. Background Art

[0002] CT (Computed Tomography) is an imaging technology that obtains projection data of an object from multiple angles and uses a reconstruction algorithm to generate a three-dimensional internal structure image of the object. It should be noted that the process of image reconstruction requires the participation of various geometric parameters of the CT system to assist in constructing the three-dimensional image. Among them, due to mechanical errors and other reasons of the system, the geometric parameters of the CT system may deviate from the set values. In order to improve the image reconstruction effect of the CT system, it is necessary to obtain the accurate values of the geometric parameters.

[0003] Planar CT is a CT imaging technology based on a planar detector. For planar structures such as PCB boards and chips, planar CT can generate images with higher resolution, thereby clearly presenting the internal details of the planar structure. However, the geometric relationship between the detector and the ray source in the planar CT system is significantly different from that in the traditional CT system. For example, Figure 1-2 As shown, where Figure 1 shows a schematic structural diagram of a traditional CT system. The black dot is the rotation center, and both the detector and the ray source rotate in a circular motion around it. Moreover, the diameter of the motion usually is equal to the sum of IDD (Imager to Detector Distance) and SID (Source to Imager Distance). Figure 2 shows a schematic structural diagram of a planar CT system. The detector and the ray source rotate in a circular motion around their respective rotation centers, and the ratio of the diameters of their motions is equal to the ratio of IDD and SID, but it is not equal to IDD and SID. This difference in geometric relationship causes the method for obtaining geometric parameters of the traditional CT system to be inapplicable to the planar CT system, and currently, there is no method for obtaining geometric parameters that can be effectively applied to the planar CT system to obtain high-precision geometric parameters. Summary of the Invention

[0004] The purpose of this application is to provide a method and device for obtaining geometric parameters, a terminal, a storage medium, and a planar CT system, which are used to solve the problem that there is still a lack of a method for accurately obtaining various geometric parameters of the planar CT system in the prior art.

[0005] In a first aspect, the present application provides a method for obtaining geometric parameters, which is applied to a planar CT system and includes: obtaining the spatial coordinates of each test phantom in a preset spatial coordinate system, and obtaining the scanning circle trajectories of each of the test phantoms on the detection plane; based on the center coordinates of each of the scanning circle trajectories, and in combination with the spatial coordinates of each of the test phantoms, obtaining the geometric projection coefficients of the corresponding test phantoms; based on the geometric projection coefficients of each of the test phantoms, and in combination with the scanning radii of each of the scanning circle trajectories, constructing a system of equations to obtain the moving radius of the ray source and the moving radius of the detector of the planar CT system; wherein, the geometric projection coefficient is used to represent the conversion relationship for converting the spatial coordinates and the scanning circle trajectories on the detection plane based on the geometric projection relationship of the planar CT system.

[0006] In an embodiment of the present application, the obtaining method of a single scanning circle trajectory includes: collecting the projection data of the current test phantom corresponding to the scanning circle trajectory on the detection plane at each acquisition moment; based on the projection data, obtaining the detection coordinates of the current test phantom at the corresponding acquisition moment; the detection coordinates are used to represent the projection position of the current test phantom on the detection plane; performing trajectory fitting on each of the detection coordinates to obtain the scanning circle trajectory of the current test phantom on the detection plane.

[0007] In an embodiment of the present application, the performing trajectory fitting on all of the detection coordinates to obtain the scanning circle trajectory of the test phantom on the detection plane includes: based on all of the detection coordinates, obtaining the scanning circle trajectory of the test phantom on the detection plane by the least squares method; or, based on all of the detection coordinates, obtaining the mean coordinates as the center coordinates of the scanning circle trajectory; taking the mean distance between the mean coordinate point and each of the detection coordinate points as the scanning radius of the scanning circle trajectory; based on the center coordinates and the scanning radius, obtaining the scanning circle trajectory of the test phantom on the detection plane.

[0008] In an embodiment of the present application, the geometric projection coefficient is characterized as the ratio of the opposite number of a first distance value to a second distance value; wherein, the first distance value is the sum of the distance from the system rotation center to the detection plane and the distance from the system rotation center to the test phantom plane, and the second distance value is the difference between the distance from the system rotation center to the ray source plane and the distance from the system rotation center to the test phantom plane.

[0009] In an embodiment of the present application, constructing a system of equations based on the geometric projection coefficients of each of the test phantoms and combining the scanning radii of each of the scanning circle trajectories to obtain the ray source movement radius and the detector movement radius of the planar CT system includes: obtaining the scanning radius corresponding to each of the scanning circle trajectories; based on each of the geometric projection coefficients, combining the pre-constructed conversion relationship between the scanning radius, the ray source movement radius, and the detector movement radius to establish a system of linear equations; and solving the ray source movement radius and the detector movement radius based on the system of linear equations.

[0010] In an embodiment of the present application, after obtaining the ray source movement radius and the detector movement radius of the planar CT system, it further includes: obtaining the total system distance based on the ray source movement radius and the detector movement radius and combining the pre-constructed calculation formula for the total system distance; and obtaining the first system distance based on the total system distance and combining the geometric relationship between the first system distance and the total system distance; where the total system distance is the distance from the detection plane to the ray source plane; and the first system distance is the distance from the system rotation center to the ray source plane.

[0011] In a third aspect, the present application provides a planar CT system, including: a detector and a ray source; the detector makes a circular motion around the detector rotation center, and at the same time the ray source makes a circular motion around the ray source rotation center, and the ray source and the detector rotate synchronously around the system rotation center; where the planar CT system obtains each geometric parameter through the geometric parameter obtaining method as described above.

[0012] In a third aspect, the present application provides a geometric parameter obtaining device, including a coordinate and trajectory obtaining module, a geometric projection coefficient obtaining module, and a geometric parameter obtaining module; the coordinate and trajectory obtaining module is configured to obtain the spatial coordinates of each test phantom in a preset spatial coordinate system and obtain the scanning circle trajectory of each test phantom on the detection plane; the geometric projection coefficient obtaining module is configured to obtain the geometric projection coefficient of the corresponding test phantom based on the center coordinates of each of the scanning circle trajectories and combining the spatial coordinates of each of the test phantoms; the geometric parameter obtaining module is configured to construct a system of equations based on the geometric projection coefficients of each of the test phantoms and combining the scanning radii of each of the scanning circle trajectories to obtain the ray source movement radius and the detector movement radius of the planar CT system; where the geometric projection coefficient is used to represent the conversion relationship for converting the spatial coordinates and the scanning circle trajectory on the detection plane based on the geometric projection relationship of the planar CT system.

[0013] In a fourth aspect, the present application provides a terminal, including: a processor and a memory, and the memory is communicatively connected to the processor;

[0014] The memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory, so that the terminal executes the geometric parameter acquisition method as described above.

[0015] In a fifth aspect, the present application provides a computer storage medium storing a computer program, and when the computer program is executed by a processor, the geometric parameter acquisition method as described above is implemented.

[0016] As described above, the present application provides a geometric parameter acquisition method, device, terminal, storage medium, and planar CT system. Mathematical calculations are performed through geometric projection coefficients to obtain various geometric parameters, so as to achieve precise calculation of various geometric parameters, facilitate image reconstruction of the planar CT system, and effectively improve the quality of the reconstructed images of the planar CT system, which is beneficial to the practical application of the planar CT system. Description of the Drawings

[0017] Figure 1 It shows a schematic structural diagram of a traditional CT system.

[0018] Figure 2 It shows a schematic structural diagram of a planar CT system according to an embodiment of the present application.

[0019] Figure 3 It shows a schematic flowchart of a geometric parameter acquisition method according to an embodiment of the present application.

[0020] Figure 4 It shows a schematic flowchart of a scanning circle trajectory acquisition method according to an embodiment of the present application.

[0021] Figure 5 It shows schematic diagrams of each scanning circle trajectory of a trajectory fitting according to an embodiment of the present application.

[0022] Figure 6 It shows a schematic flowchart of a method for obtaining the moving radius of a ray source and the moving radius of a detector according to an embodiment of the present application.

[0023] Figure 7 It shows a schematic flowchart of a method for obtaining the total system distance and the first system distance according to an embodiment of the present application.

[0024] Figure 8 It shows a schematic flowchart of a trajectory fitting method for the scanning circle trajectory according to an embodiment of the present application.

[0025] Figure 9 It shows a schematic structural diagram of a geometric parameter acquisition device according to an embodiment of the present application.

[0026] Figure 10It is a schematic structural diagram of a terminal according to an embodiment of the present application.

[0027] Description of the reference numerals in the drawings

[0028] 11: Detector; 12: Radiation source; 13: Detector rotation center; 14: Radiation source rotation center; 15: System rotation center; 20: Test phantom; 41: Coordinate and trajectory acquisition module; 42: Geometric projection coefficient acquisition module; 43: Geometric parameter acquisition module; 50: Terminal; 51: Processor; 52: Memory; 521: Operating system; 522: Application program; 53: User interface; 54: Network interface; 55: Bus system. Specific embodiments

[0029] The following specific examples illustrate the implementation manners of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific implementation manners. 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 application. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0030] It should be noted that the drawings provided in the following embodiments only schematically illustrate the basic concept of the present application. Therefore, only the components related to the present application are shown in the drawings, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, number, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0031] The method for obtaining geometric parameters of a traditional CT system is to construct a mathematical equation based on the geometric relationship between the radiation source, the detector, and the rotation center to calculate each geometric parameter in the CT system, so as to avoid the deviation of each geometric parameter from the set value due to the mechanical error of the system and affect the effect of image reconstruction. However, since the geometric relationship of each structure in the planar CT system is different from that of the traditional CT, the existing method for obtaining geometric parameters cannot be applied to the planar CT system, resulting in poor image quality of the planar CT system.

[0032] In view of the technical problems existing in the prior art, the following embodiments of the present application provide a method, device, terminal, storage medium, and planar CT system for obtaining geometric parameters. By obtaining the conversion relationship between the scanning circle trajectory and the spatial coordinates, the spatial geometric structure of the planar CT system is characterized, so as to construct an equation or a system of equations for each geometric parameter and perform calculations, thereby obtaining accurate values of each geometric parameter, so as to avoid problems such as artifacts, blurring, and position deviation of the reconstructed image caused by the mechanical error of the system, and effectively improve the detection effect of the planar CT system.

[0033] For ease of understanding, as Figure 2 shown, this embodiment exemplarily provides a planar CT system, including: a detector 11 and a radiation source 12. Among them, the detector 11 makes a circular motion around the detector rotation center 13, and at the same time the radiation source 12 makes a circular motion around the radiation source rotation center 14. The radiation source 11 and the detector 12 rotate synchronously around the system rotation center 15, that is, the angular velocities of the radiation source 11 and the detector 12 are the same, and the geometric center of the detector 11, the radiation source 12 and the system rotation center 15 are always on the same straight line. Specifically, when the detector 11 rotates from the Figure 2 solid line position in to the dashed line position, the radiation source 12 rotates from the Figure 2 solid line position in to the dashed line position. It should be noted that the detector rotation center 13, the radiation source rotation center 14 and the system rotation center 15 are actually virtual points for ease of understanding, rather than actual existing points.

[0034] Next, the technical solutions in the embodiments of the present application will be described in detail with reference to the accompanying drawings in the embodiments of the present application.

[0035] As Figure 3 shown, this embodiment provides a method for obtaining geometric parameters, which is applied to a planar CT system and includes:

[0036] S100, obtaining the spatial coordinates of each test phantom 20 in a preset spatial coordinate system, and obtaining the scanning circle trajectory of each test phantom 20 on the detection plane.

[0037] Among them, the test phantom 20 is arranged between the detector 11 and the radiation source 12 of the planar CT system, and is used to form corresponding projection data on the detector 11 based on the scanning process of the planar CT system. Exemplarily, as Figure 2 shown, each test phantom 20 is a steel ball, so as to form a relatively clear circular contour on the detector 11, which is convenient for improving the accuracy of the obtained scanning circle trajectory.

[0038] Furthermore, in this embodiment, the number of test phantoms 20 is at least two or more.

[0039] The spatial coordinates of the test phantom 20 are used to characterize the spatial position of the test phantom 20 in the planar CT system. For ease of understanding and to simplify subsequent calculations, in some alternative embodiments, with the system rotation center 15 of the planar CT as the origin, and the direction from the system rotation center 15 to the radiation source rotation center 14 as the positive y-axis direction, a spatial coordinate system is established, and the coordinates of the test phantom 20 in this spatial coordinate system are used as the spatial coordinates.

[0040] Further, the detection plane is the plane where the detector 11 is located, that is, in the spatial coordinate system, it is parallel to the x-z plane and passes through the detector 11.

[0041] The test phantom 20 is irradiated by the radiation beam emitted by the radiation source 12, as Figure 2 shown, and a projection is formed on the detection plane, so that the detector 11 collects the projection data to record the projection. When the planar CT system performs a scan, the radiation source 12 makes a circular motion around the radiation source rotation center 14, and the projection of the test phantom 20 on the detection plane also moves to form a circular trajectory, that is, the scan circular trajectory, and the scan circular trajectory is used to characterize the motion of the test phantom 20 on the detection plane during the scan and shooting process of the planar CT system.

[0042] In some alternative embodiments, as Figure 4 shown, the method for obtaining the scan circular trajectory includes:

[0043] S110, collecting the projection data of the current test phantom 20 on the detection plane at each acquisition moment corresponding to the scan circular trajectory.

[0044] Specifically, the test phantom 20 is scanned by the planar CT system, and each image formed by the detector 11 is used as the projection data of the test phantom 20 on the detection plane and saved.

[0045] S120, based on the projection data, obtaining the detection coordinates of the current test phantom 20 at the corresponding acquisition moment.

[0046] Among them, the detection coordinates are used to characterize the projection position of the test phantom 20 on the detection plane. Exemplarily, as Figure 2 shown, taking the geometric center of the detector 11 as the origin, taking the direction parallel to the z-axis of the spatial coordinate system as the z-axis, and taking the direction parallel to the x-axis of the spatial coordinate system as the x-axis, a detection plane coordinate system is established, and the coordinates of the projection of the test phantom 20 in this detection plane coordinate system are used as the detection coordinates.

[0047] Specifically, the geometric center of the detector 11 is actually the geometric center point of the image in each of the projection data, that is, taking the geometric center of the image of each of the projection data as the origin, obtaining the coordinates of the projection point in the image as the detection coordinates.

[0048] S130, performing trajectory fitting on each of the detection coordinates to obtain the scan circular trajectory of the current test phantom 20 on the detection plane.

[0049] Specifically, based on all the detected coordinates, trajectory fitting is performed by the least squares method to obtain the scanning circle trajectories of each test phantom 20 on the detection plane; alternatively, the mean coordinates are obtained based on all the detected coordinates as the center coordinates of the scanning circle trajectories; the mean distance between the mean coordinates and each of the detected coordinates is used as the scanning radius of the scanning circle trajectories; and based on the center coordinates and the scanning radius, the scanning circle trajectories of the test phantom 20 on the detection plane are obtained. As long as the scanning circle trajectories can be fitted and obtained, this embodiment does not make specific limitations here.

[0050] Among them, the x-axis coordinate of the mean coordinates is the mean of the x-axis coordinates of all the detected coordinates, and the y-axis coordinate is the mean of the y-axis coordinates of all the detected coordinates; the mean coordinate point is the point represented by the mean coordinates in the detection plane coordinate system, and each of the detected coordinate points is the point represented by the corresponding detected coordinates in the detection plane coordinate system; the mean distance is the mean of the distances between the mean coordinate point and each of the detected coordinate points.

[0051] It should be noted that the obtained scanning circle trajectories are actually the scanning circle trajectories corresponding to a single test phantom 20. In this embodiment, multiple test phantoms 20 actually need to be scanned and photographed to obtain the corresponding scanning circle trajectories, that is, each test phantom 20 is scanned and photographed synchronously, and based on all the projection data corresponding to each test phantom 20, the scanning circle trajectories corresponding to each test phantom 20 are obtained. As Figure 5 shown, it shows the images of the corresponding scanning circle trajectories obtained after trajectory fitting of the projection data of each test phantom 20 in practical applications, where a single circle trajectory is the trajectory image formed by scanning the corresponding single test phantom 20.

[0052] S200. Based on the center coordinates of each of the scanning circle trajectories and in combination with the spatial coordinates of each of the test phantoms, the geometric projection coefficients of the corresponding test phantoms are obtained.

[0053] Among them, the geometric projection coefficients are used to characterize the conversion relationship for converting the spatial coordinates and the scanning circle trajectories on the detection plane based on the geometric projection relationship of the planar CT system. The geometric projection relationship refers to the geometric relationship that maps the spatial coordinates to the detection plane based on the spatial geometric structure of the planar CT system.

[0054] It should be noted that the scanning circular trajectory is a set of projection points of the spatial coordinates on the detection plane, that is, a set of projection points obtained by projecting the spatial coordinates onto the detection plane based on the spatial geometric structure of the planar CT system. Based on this, the spatial geometric structure of the planar CT system can be characterized by the conversion relationship between the scanning circular trajectory and the spatial coordinates, that is, based on the conversion relationship between the scanning circular trajectory and the spatial coordinates, the spatial geometric structure of the planar CT system can be obtained, so as to obtain the geometric parameters of the planar CT system.

[0055] In this embodiment, the geometric projection coefficient is used to convert the spatial coordinates and the scanning circular trajectory. It should be noted that since the geometric projection coefficient is used to characterize the geometric projection relationship of the planar CT system, the expression of the geometric projection coefficient is actually constructed by the geometric parameters of the planar CT system. At the same time, since the spatial coordinates and the scanning circular trajectory have been obtained through test calculations, the geometric projection coefficient can be obtained based on the conversion relationship between the spatial coordinates and the scanning circular trajectory obtained above. Based on this, an equation or a system of equations can be constructed based on the geometric projection coefficients obtained by these two methods, so as to solve the accurate values of the geometric parameters of the planar CT system.

[0056] In some alternative embodiments, for the convenience of subsequent calculations, the geometric projection coefficient is characterized as the ratio of the opposite of the first distance value to the second distance value; wherein, the first distance value is the sum of the distance from the system rotation center 15 to the detection plane and the distance from the system rotation center 15 to the test phantom plane, and the second distance value is the difference between the distance from the system rotation center 15 to the ray source plane and the distance from the system rotation center 15 to the test phantom plane.

[0057] It should be noted that the above expression of the geometric projection coefficient is obtained based on the conversion relationship between the spatial coordinates and the circular trajectory on the detection plane. In the actual calculation process, the geometric projection coefficient is obtained by: based on the spatial coordinates and the scanning circular trajectory corresponding to the test phantom 20, and combining the pre-constructed geometric projection coefficient calculation formula, the geometric projection coefficient is obtained. To facilitate the understanding of the geometric projection coefficient described in this embodiment by those skilled in the art, the construction principle of the geometric projection coefficient expression will be explained below, and the geometric projection coefficient calculation formula will be given exemplarily.

[0058] Wherein, the test phantom plane passes through the test phantom 20 and is a plane parallel to the x-z plane of the spatial coordinate system, that is, the distance from the system rotation center 15 to the test phantom plane is actually the y-axis value of the spatial coordinates; the ray source plane passes through the ray source 12 and is a plane parallel to the x-z plane of the spatial coordinate system.

[0059] As shown Figure 2 in the figure, the rays emitted by the ray source 12 project the test phantom 20 onto the detection plane. Let the coordinates of the test phantom 20 in the spatial coordinate system be (x0, y0, z0), that is, the spatial coordinates of the test phantom 20 are (x0, y0, z0).

[0060] It should be noted that since the detection coordinate is actually the intersection point of the straight line formed by the test phantom 20 and the ray source 12, that is, the phantom-ray source straight line, and the detection plane. In order to obtain the detection coordinate, based on the spatial coordinates, the equation of the phantom-ray source straight line is obtained as follows:

[0061]

[0062] where r is the ray source movement radius, the ray source movement radius is the radius of the circular movement of the ray source 12 around the ray source rotation center 14, R is the detector movement radius, the detector movement radius is the radius of the circular movement of the detector 11 around the detector rotation center 13, θ is the rotation angle of the ray source 12 corresponding to this detection coordinate, SID is the distance from the system rotation center 15 to the ray source plane, the ray source plane is the plane where the ray source 12 is located, that is, in the spatial coordinate system, it is parallel to the x-z plane and passes through the ray source rotation center 14. Based on this, the coordinates of the ray source 12 can be expressed as: (r sinθ, SID, r cosθ). By obtaining the direction vector through the coordinate difference between this ray source coordinate and the spatial coordinate, the equation of the phantom-ray source straight line is determined.

[0063] Furthermore, since the y-axis coordinates of any point on the detection plane are equal in the spatial coordinate system, and are all negative values of the distance from the system rotation center to the detection plane. Based on this, the coordinates of the intersection point of the phantom-ray source straight line and the detection plane in the spatial coordinate system are:

[0064]

[0065] The origin of the detection plane coordinate system, that is, the coordinates of the geometric center of the detector 11 can be expressed as:

[0066] (-R sinθ, -IDD, -R cosθ)

[0067] where IDD is the distance from the system rotation center 15 to the detection plane.

[0068] Based on this, the detection coordinate can be expressed as:

[0069]

[0070] Based on the detection coordinates, the expression of the scanning circle trajectory can be obtained as follows:

[0071]

[0072] It should be noted that the expression of the above scanning circle trajectory is constructed based on the geometric relationship between the detector 11 and the radiation source 12 in the planar CT system, and is expressed by the geometric parameters of the planar CT system, that is, it can reflect the geometric projection relationship of the planar CT system. Since the expression of this scanning circle trajectory and the scanning circle trajectory obtained by fitting based on the projection data actually represent the same trajectory, based on the scanning circle trajectories obtained by these two methods, that is, the geometric parameters of the planar CT system can be measured and calculated based on the test phantom 20 and its actual projection data.

[0073] Furthermore, from the expression of the above scanning circle trajectory, it can be seen that the center coordinates and scanning radius of the scanning circle trajectory can both be represented by the sum of the distance from the system rotation center to the detection plane and the distance from the system rotation center to the test phantom plane, and the second distance value is the difference between the distance from the system rotation center to the radiation source plane and the distance from the system rotation center to the test phantom plane. Based on this, for the convenience of subsequent calculations, the sum of the distance from the system rotation center to the detection plane and the distance from the system rotation center to the test phantom plane is used as the first distance value, and the second distance value is the difference between the distance from the system rotation center to the radiation source plane and the distance from the system rotation center to the test phantom plane. Then the geometric projection coefficient can be expressed as the ratio of the opposite number of the first distance value to the second distance value.

[0074] Even further, in order to construct an equation or a system of equations for the geometric projection coefficient to facilitate the solution of the geometric parameters of the planar CT system, in this embodiment, it is also necessary to obtain the geometric projection coefficient based on the spatial coordinates corresponding to the test phantom 20 and the scanning circle trajectory.

[0075] Specifically, if the expression of the scanning circle trajectory obtained based on steps S110 - S130 is:

[0076] (X - X0) 2 +(Z - Z0) 2 =f 2

[0077] where X0 is the x-axis value of the center of the scanning circle trajectory in the detection plane coordinate system, Z0 is the y-axis value of the center of the scanning circle trajectory in the detection plane coordinate system, and f is the scanning radius of the scanning circle trajectory.

[0078] Then the calculation method of the geometric projection coefficient is:

[0079]

[0080] or,

[0081]

[0082] Where, is the geometric projection coefficient.

[0083] That is, the geometric projection coefficient calculation formula is:

[0084]

[0085] or,

[0086]

[0087] Wherein, k is the geometric projection coefficient.

[0088] Specifically, the expression of the aforementioned scanning circle trajectory is compared and calculated with the expression of the scanning circle trajectory obtained based on steps S110-S130, that is, the center coordinates obtained by the two methods are combined and converted to obtain the calculation method of the above-mentioned geometric projection coefficient. This embodiment will not be explained in detail here.

[0089] S300 , constructing a set of equations based on the geometric projection coefficients of each test phantom and the scanning radius of each scanning circular trajectory to obtain the ray source motion radius and the detector motion radius of the planar CT system.

[0090] The ray source motion radius is the radius of the circular motion of the ray source 12 around the ray source rotation center 14, and the detector motion radius is the radius of the circular motion of the detector 11 around the detector rotation center 13. It should be noted that the ray source motion radius and the detector motion radius are both geometric parameters of the planar CT system. In this embodiment, the accurate values of the ray source motion radius and the detector motion radius are obtained by constructing a set of equations to assist in the image reconstruction process of the planar CT system.

[0091] Specifically, based on each of the geometric projection coefficients, combined with the expression of the geometric projection coefficient with respect to each geometric parameter, mathematical calculations are performed using simultaneous equations to obtain precise values of each geometric parameter, thereby calibrating the mechanical errors of the system to assist the image reconstruction process in the planar CT system, thereby effectively improving the quality of the reconstructed image and enabling the planar CT system to achieve better detection effects.

[0092] For ease of calculation, in some optional implementations, such as Figure 6As shown, the method for obtaining the moving radius of the ray source and the moving radius of the detector includes:

[0093] S310. Obtain the scanning radius corresponding to each of the scanning circle trajectories.

[0094] S320. Based on each of the geometric projection coefficients, and in combination with the pre-established conversion relationship among the scanning radius, the moving radius of the ray source, and the moving radius of the detector, establish a system of linear equations.

[0095] Among them, the conversion relationship among the scanning radius, the moving radius of the ray source, and the moving radius of the detector is a linear equation based on the geometric projection coefficients. Based on each of the geometric projection relationships, multiple linear equations are constructed to form a system of linear equations.

[0096] In some alternative embodiments, the conversion relationship among the scanning radius, the moving radius of the ray source, and the moving radius of the detector is:

[0097] kr + R = f

[0098] Among them, k is the geometric projection coefficient, that is

[0099] Specifically, by comparing and calculating the expression of the aforementioned scanning circle trajectory with the expression of the scanning circle trajectory obtained based on steps S110 - S130, the calculation method of the above geometric projection coefficient can be obtained, and specific explanations are not given in this embodiment.

[0100] S330. Based on the system of linear equations, solve for the moving radius of the ray source and the moving radius of the detector.

[0101] Exemplarily, the system of linear equations is:

[0102] k1r + R = f1

[0103] k2r + R = f2

[0104] ……

[0105] k n r + R = f n

[0106] Among them, k1, k2... k n are the geometric projection coefficients corresponding to each of the test phantoms 20; f1, f2... f n are the scanning radii corresponding to each of the test phantoms 20.

[0107] Solve based on this system of linear equations to calculate the moving radius r of the ray source and the moving radius R of the detector.

[0108] Specifically, based on the solution method of the linear equations, the moving radius of the ray source and the moving radius of the detector can be obtained. Those skilled in the art should know the specific solution method of the linear equations, and this embodiment does not make specific limitations here.

[0109] Further, the geometric parameters of the planar CT system further include the total system distance and the first system distance. Among them, the total system distance is the distance from the detection plane to the ray source plane; the first system distance is the distance from the system rotation center to the ray source plane. In order to further improve the image reconstruction effect of the planar CT system, after obtaining the moving radius of the ray source and the moving radius of the detector of the planar CT system, this embodiment also obtains the total system distance and the first system distance. Specifically, as Figure 7 shown, the obtaining methods of the total system distance and the first system distance include:

[0110] S340, based on the moving radius of the ray source and the moving radius of the detector, and combining the pre-constructed calculation formula of the total system distance, obtain the total system distance.

[0111] It should be noted that the calculation formula of the ray source-detector plane distance is constructed based on the geometric relationship of the planar CT system, and is a calculation formula regarding the moving radius of the ray source and the moving radius of the detector, for calculating the ray source-detector plane distance based on the moving radius of the ray source and the moving radius of the detector.

[0112] In some alternative embodiments, the calculation formula of the ray source-detector plane distance is:

[0113]

[0114] Among them, SDD is the total system distance, that is, the distance from the ray source plane to the detection plane.

[0115] Further, in order to facilitate those skilled in the art to understand the above calculation formula of the ray source-detector plane distance, the principle thereof is explained below.

[0116] Specifically, as Figure 2 shown, based on geometric principles, it can be known that the moving radius of the ray source and the first system distance, and the moving radius of the detector and the distance from the system rotation center 15 to the detection plane are actually in a relationship of proportional magnification, that is:

[0117]

[0118] Since the total system distance is actually the sum of the first system distance and the distance from the system rotation center 15 to the detection plane, that is:

[0119] SID + IDD = SDD

[0120] The following relationship exists between the moving radius of the radiation source and the moving radius of the detector:

[0121] kr + R = f

[0122] Based on the above three relational expressions, mathematical transformation is performed to obtain the calculation formula for the total system distance. Specifically, those skilled in the art should know the specific methods and principles of performing mathematical transformation on the above relational expressions, and this embodiment does not specifically explain them here.

[0123] S350. Based on the radiation source-detector plane distance and in combination with the geometric relationship between the first system distance and the total system distance, the first system distance is obtained.

[0124] Specifically, since the total system distance is the sum of the first system distance and the distance from the system rotation center 15 to the detection plane, and there is a relationship of geometric magnification in proportion between the moving radius of the radiation source and the first system distance, and between the moving radius of the detector and the distance from the system rotation center 15 to the detection plane. Based on these two geometric relationships, mathematical operations are performed to obtain the relational expression of the first system distance with respect to the radiation source-detector plane distance, so as to solve for the first system distance.

[0125] Exemplarily, the relational expression of the first system distance with respect to the radiation source-detector plane distance is:

[0126]

[0127] Based on this, in this embodiment, through the geometric projection coefficient, an equation or a system of equations is constructed based on the geometric relationship of the planar CT system for solution, so as to calculate and obtain the first system distance, the total system distance, the moving radius of the radiation source, and the moving radius of the detector, thereby obtaining the accurate values of the geometric parameters of the planar CT system.

[0128] It should be noted that in this embodiment, the geometric projection coefficient is obtained through the scanning circle trajectory obtained from the projection data for use in the subsequent calculation of each geometric parameter. Based on this, the accuracy of the scanning circle trajectory has a great influence on the precision of each geometric parameter obtained. Therefore, in order to improve the accuracy of the scanning circle trajectory obtained by trajectory fitting, in some alternative embodiments, the least squares method is used to obtain the scanning circle trajectory to reduce errors and improve the accuracy of the scanning circle trajectory. Specifically, as Figure 8 shown, the trajectory fitting method of the scanning circle trajectory is:

[0129] S131. Based on a preset circular trajectory equation and in combination with each of the detection coordinates, obtain the sum of squared errors of the scanning circular trajectory.

[0130] Wherein, the preset circular trajectory equation refers to a general equation used to represent a circular trajectory.

[0131] Specifically, substitute each of the detection coordinates into the preset circular trajectory equation. Due to the existence of factors such as measurement errors, there may be a certain error between the detection coordinates and the scanning circular trajectory. Therefore, there is also a certain error between the value obtained by substituting each of the detection coordinates into the circular trajectory equation and the value that should be obtained theoretically.

[0132] In order to obtain the circular trajectory closest to each of the detection coordinates, it is necessary to minimize the error after substituting each of the detection coordinates into the circular trajectory equation. Based on this, in this embodiment, obtain the sum of squared errors corresponding to each of the detection coordinates. When the sum of squared errors is the smallest, the circular trajectory closest to each of the detection coordinates, that is, the scanning circular trajectory, can be obtained.

[0133] S132. Based on the sum of squared errors and in combination with Fermat's theorem, construct a circular trajectory equation when the sum of squared errors is the smallest as the scanning circular trajectory.

[0134] Specifically, according to Fermat's theorem, when the sum of squared errors is the smallest, its first-order derivatives with respect to the center coordinates and the radius must be zero. Based on this, take the partial derivatives of the sum of squared errors with respect to the center coordinate values and the radius, and calculate the values when the partial derivatives are zero to obtain the center coordinates and the scanning radius of the scanning circular trajectory, and further obtain the scanning circular trajectory.

[0135] To facilitate those skilled in the art to understand this embodiment, a specific process for solving the scanning circular trajectory is given below.

[0136] In some alternative embodiments, the preset circular trajectory equation is:

[0137] (x - C x ) 2 +(z - C z ) 2 =f 2

[0138] Wherein, C x is the coordinate value of the center on the x-axis, and C z is the coordinate value of the center on the z-axis.

[0139] If the error after substituting the i-th detection coordinate into the preset circular trajectory equation is denoted as s i , that is:

[0140] (X i - C x) 2 +(Z i -C z ) 2 =f 2 +s i

[0141] where X i is the coordinate value of the i-th detection coordinate on the x-axis, and Z i is the coordinate value of the i-th detection coordinate on the y-axis.

[0142] Based on this, the sum of squared errors is:

[0143]

[0144] where N is the number of detection coordinates, F is the square of the scanning radius, i.e., F = f 2 , and S is the sum of squared errors, i.e.,

[0145] Next, take the partial derivatives of S with respect to C x , C z and F, and we get:

[0146]

[0147] For the convenience of understanding and simplifying the calculation process, let

[0148]

[0149] Based on this, the partial derivatives of S with respect to C x and C z can be simplified to

[0150]

[0151] When the partial derivatives of S with respect to C x and C z are zero, we get the matrix equation:

[0152]

[0153] Solving this matrix equation, we get

[0154]

[0155] Based on this, the center coordinates of the scanning circle trajectory can be obtained.

[0156] Based on the partial derivative expression of S with respect to F, we get

[0157]

[0158] Substitute Cx and C z By the value of, the scanning radius of the scanning circular trajectory can be obtained as

[0159]

[0160] Based on the center coordinates and the scanning radius, the scanning circular trajectory can be obtained.

[0161] In some other alternative embodiments, in order to reduce the calculation amount of T mn During the calculation, in order to simplify the calculation process and improve the calculation efficiency, the respective detection coordinates in the barycentric coordinate system can be used, that is, with the barycenter of the respective detection coordinates as the origin, a coordinate system is constructed, and then the respective detection coordinates are

[0162]

[0163] where g xi is the coordinate value of the i-th detection coordinate on the x-axis in the barycentric coordinate system, and g zi is the coordinate value of the i-th detection coordinate on the y-axis in the barycentric coordinate system.

[0164] Based on the respective detection coordinates in the barycentric coordinate system, the sum of squared errors is obtained, and based on the center coordinates and radius value when the sum of squared errors is minimized, the scanning circular trajectory is obtained. Specifically, for the steps and principles of obtaining the center coordinates and radius value, please refer to the foregoing content and will not be elaborated here.

[0165] It should be noted that the center coordinates obtained at this time are actually the center coordinates in the barycentric coordinate system, and this center coordinate needs to be converted into the coordinates in the detection plane coordinate system, that is:

[0166]

[0167] where g x is the coordinate value of the center coordinate on the x-axis in the barycentric coordinate system, and g z is the coordinate value of the center coordinate on the y-axis in the barycentric coordinate system, G x is the coordinate value of the center coordinate on the x-axis in the detection plane coordinate system, and G z is the coordinate value of the center coordinate on the y-axis in the detection plane coordinate system.

[0168] Based on the center coordinates and the scanning radius in the detection plane coordinate system, the scanning circular trajectory in the detection plane coordinate system can be obtained.

[0169] Such as Figure 9As shown in the figure, the present embodiment further provides a geometric parameter acquisition device, including a coordinate and trajectory acquisition module 41, a geometric projection coefficient acquisition module 42, and a geometric parameter acquisition module 43.

[0170] Among them, the coordinate and trajectory acquisition module 41 is configured to acquire the spatial coordinates of each test phantom in a preset spatial coordinate system and acquire the scanning circle trajectory of each test phantom on the detection plane;

[0171] The geometric projection coefficient acquisition module 42 is configured to acquire the geometric projection coefficient of the corresponding test phantom based on the center coordinates of each of the scanning circle trajectories and in combination with the spatial coordinates of each of the test phantoms;

[0172] The geometric parameter acquisition module 43 is configured to construct an equation set based on the geometric projection coefficients of each of the test phantoms and in combination with the scanning radii of each of the scanning circle trajectories, and acquire the moving radius of the ray source and the moving radius of the detector of the planar CT system;

[0173] Based on the same inventive concept, the geometric parameter acquisition method for the planar CT system provided by the embodiments of the present invention can be implemented on the terminal side or the server side.

[0174] As Figure 10 shown, it is an optional hardware structure schematic diagram of a terminal provided by an embodiment of the present invention. The terminal 50 may be a mobile phone, a computer device, a tablet device, a personal digital processing device, a factory background processing device, etc. The terminal 50 includes: at least one processor 51, a memory 52, at least one network interface 54, and a user interface 53. Each component in the device is coupled together through a bus system 55. It can be understood that the bus system 55 is used to realize the connection and communication between these components. In addition to the data bus, the bus system 55 further includes a power bus, a control bus, and a status signal bus.

[0175] Among them, the user interface 53 may include a display, a keyboard, a mouse, a trackball, a click gun, a button, a button, a touchpad, or a touch screen, etc.

[0176] It can be understood that the memory 52 can be a volatile memory or a non-volatile memory, or can include both volatile and non-volatile memories. Among them, the non-volatile memory can be a read-only memory (ROM, Read Only Memory), a programmable read-only memory (PROM, Programmable Read-Only Memory), which is used as an external cache. By way of example but not limitation, many forms of RAM are available, such as static random access memory (SRAM, Static Random Access Memory), synchronous static random access memory (SSRAM, Synchronous Static Random Access Memory). The memory characterized in the embodiments of the present invention is intended to include but not limited to these and any other suitable categories of memories.

[0177] The memory 52 in the embodiments of the present invention is used to store various categories of data to support the operation of the terminal. Examples of these data include: any executable program for operating on the terminal 50, such as the operating system 521 and the application program 522; the operating system 521 contains various system programs, such as the framework layer, the core library layer, the driver layer, etc., for implementing various basic services and processing hardware-based tasks. The application program 522 can include various application programs, such as a media player (Media Player), a browser (Browser), etc., for implementing various application services. The method for obtaining the geometric parameters of the planar CT system provided in the embodiments of the present invention can be included in the application program 522.

[0178] The method disclosed in the above embodiments of the present invention can be applied to the processor 51 or implemented by the processor 51. The processor 51 may be an integrated circuit chip with signal processing capabilities. During implementation, each step of the above method can be completed by the integrated logic circuit in the hardware of the processor 51 or by instructions in software form. The above processor can be a general-purpose processor, a digital signal processor (DSP, Digital Signal Processor), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The processor 51 can implement or execute the various methods, steps, and logic block diagrams disclosed in the embodiments of the present invention. The processor 51 can be a microprocessor or any conventional processor, etc. Combining the steps of the accessory optimization method provided in the embodiments of the present invention can be directly embodied as being completed by a hardware decoding processor, or by a combination of hardware and software modules in the decoding processor. The software module can be located in a storage medium, and this storage medium is located in the memory. The processor reads the information in the memory and combines its hardware to complete the steps of the foregoing method.

[0179] In an exemplary embodiment, the terminal 50 may be one or more application specific integrated circuits (ASICs), DSPs, programmable logic devices (PLDs), or complex programmable logic devices (CPLDs) for performing the foregoing method.

[0180] An embodiment of the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when called by a processor, implements the method for obtaining geometric parameters of the planar CT system provided by the present invention.

[0181] Among them, the computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. The computer-readable storage medium may be, for example, (but not limited to) an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (non-exhaustive list) of the computer-readable storage medium include: portable computer disks, hard disks, random access memories (RAMs), read-only memories (ROMs), erasable programmable read-only memories (EPROMs or flash memories), static random access memories (SRAMs), portable compact disk read-only memories (CD-ROMs), digital versatile disks (DVDs), memory sticks, floppy disks, and mechanical encoding devices.

[0182] The computer-readable program characterized herein may be downloaded from the computer-readable storage medium to various computing / processing devices, or downloaded to an external computer or external storage device through a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network adapter or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0183] In summary, the present application characterizes the geometric projection relationship between the scanning circle trajectory and the spatial coordinates through the geometric projection coefficient, thereby constructing an equation or a system of equations for each of the geometric parameters based on the geometric projection coefficient to calculate each of the geometric parameters, with high calculation accuracy. Furthermore, it assists the planar CT system in image reconstruction, avoids the occurrence of artifact problems or poor spatial resolution, improves the image quality of the planar CT system, achieves a better detection effect, and has high industrial utilization value.

[0184] The descriptions of the processes or structures corresponding to the above-mentioned various drawings each have their own focuses. For parts not detailed in a certain process or structure, reference may be made to the relevant descriptions of other processes or structures.

[0185] The above embodiments are only illustrative of the principles and effects of the present application and are not intended to limit the present application. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present application should still be covered by the claims of the present application.

Claims

1. A geometric parameter acquisition method, applied to a planar CT system, includes: Obtaining the spatial coordinates of each test phantom in a preset spatial coordinate system, and obtaining the scanning circle trajectories of each of the test phantoms on the detection plane; Based on the center coordinates of each of the scanning circle trajectories, and in combination with the spatial coordinates of each of the test phantoms, obtaining the geometric projection coefficients of the corresponding test phantoms; Based on the geometric projection coefficients of each of the test phantoms, and in combination with the scanning radii of each of the scanning circle trajectories, constructing a system of equations to obtain the ray source movement radius and the detector movement radius of the planar CT system; Wherein, the geometric projection coefficient is used to represent the conversion relationship for converting the spatial coordinates and the scanning circle trajectories on the detection plane based on the geometric projection relationship of the planar CT system.

2. The geometric parameter acquisition method according to claim 1, characterized in that, The acquisition method of a single scanning circle trajectory includes: Collecting the projection data of the current test phantom corresponding to the scanning circle trajectory on the detection plane at each acquisition moment; Based on the projection data, obtaining the detection coordinates of the current test phantom at the corresponding acquisition moment; the detection coordinates are used to represent the projection position of the current test phantom on the detection plane; Performing trajectory fitting on each of the detection coordinates to obtain the scanning circle trajectory of the current test phantom on the detection plane.

3. The geometric parameter acquisition method according to claim 2, wherein The performing trajectory fitting on all of the detection coordinates to obtain the scanning circle trajectory of the test phantom on the detection plane includes: based on all of the detection coordinates, obtaining the scanning circle trajectory of the test phantom on the detection plane by the least squares method; Or, based on all of the detection coordinates, obtaining the mean coordinate as the center coordinate of the scanning circle trajectory; taking the mean distance between the mean coordinate point and each of the detection coordinate points as the scanning radius of the scanning circle trajectory; based on the center coordinate and the scanning radius, obtaining the scanning circle trajectory of the test phantom on the detection plane.

4. The geometric parameter acquisition method according to claim 1, characterized in that, The geometric projection coefficient is characterized as the ratio of the opposite number of the first distance value to the second distance value; wherein, the first distance value is the sum of the distance from the system rotation center to the detection plane and the distance from the system rotation center to the test phantom plane, and the second distance value is the difference between the distance from the system rotation center to the ray source plane and the distance from the system rotation center to the test phantom plane.

5. The geometric parameter obtaining method according to claim 1, characterized in that The based on the geometric projection coefficients of each of the test phantoms, and in combination with the scanning radii of each of the scanning circle trajectories, constructing a system of equations to obtain the ray source movement radius and the detector movement radius of the planar CT system includes: Obtaining the scanning radius corresponding to each of the scanning circle trajectories; Based on each of the geometric projection coefficients, and in combination with the pre-constructed conversion relationship of the scanning radius, the ray source movement radius, and the detector movement radius, establishing a system of linear equations; Based on the system of linear equations, solving for the ray source movement radius and the detector movement radius.

6. The geometric parameter acquisition method according to claim 5, wherein After obtaining the ray source movement radius and the detector movement radius of the planar CT system, it further includes: Based on the ray source movement radius and the detector movement radius, and in combination with the pre-constructed calculation formula of the total system distance, obtaining the total system distance; Based on the total system distance and combining the geometric relationship between the first system distance and the total system distance, obtain the first system distance; wherein, the total system distance is the distance from the detection plane to the ray source plane; the first system distance is the distance from the system rotation center to the ray source plane.

7. A planar CT system, characterized in that, Comprising: a detector and a ray source; the detector makes a circular motion around the detector rotation center, and at the same time the ray source makes a circular motion around the ray source rotation center, and the ray source and the detector rotate synchronously around the system rotation center; wherein, the planar CT system obtains each geometric parameter through the geometric parameter acquisition method according to any one of claims 1 to 7.

8. A geometric parameter acquisition device, characterized in that, Comprising a coordinate and trajectory acquisition module, a geometric projection coefficient acquisition module and a geometric parameter acquisition module; the coordinate and trajectory acquisition module is configured to acquire the spatial coordinates of each test phantom in a preset spatial coordinate system and acquire the scanning circle trajectory of each test phantom on the detection plane; the geometric projection coefficient acquisition module is configured to acquire the geometric projection coefficient of the corresponding test phantom based on the center coordinates of each of the scanning circle trajectories and combining the spatial coordinates of each of the test phantoms; the geometric parameter acquisition module is configured to construct an equation set based on the geometric projection coefficients of each of the test phantoms and combining the scanning radii of each of the scanning circle trajectories, and acquire the ray source movement radius and the detector movement radius of the planar CT system; wherein, the geometric projection coefficient is used to represent the conversion relationship for converting the spatial coordinates and the scanning circle trajectory on the detection plane based on the geometric projection relationship of the planar CT system.

9. A terminal, characterized in that, Comprising: a processor and a memory, and the memory is communicatively connected to the processor; the memory is used to store a computer program, and the processor is used to execute the computer program stored in the memory so that the terminal executes the geometric parameter acquisition method according to any one of claims 1 to 7.

10. A computer storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the geometric parameter acquisition method according to any one of claims 1 to 7.

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