A helical CBCT geometry phantom device and correction method

Abstract

This invention discloses a spiral CBCT geometric phantom device and its calibration method, relating to the field of computed tomography (CT) imaging technology. The method includes: S1: acquiring projection data of the spiral CBCT geometric phantom device; S2: performing image segmentation on the acquired projection data and extracting the projection center coordinates of markers; S3: decoding and mapping the position of markers based on their projection size; S4: calculating the geometric parameters of the spiral CBCT system according to an optimization formula and performing spiral CBCT reconstruction. By utilizing distinguishable markers and efficient evolutionary optimization, high-precision adaptive calibration of spiral CBCT geometric parameters is achieved, significantly suppressing artifacts, improving image fidelity, and eliminating the need for complex calibration devices. It possesses advantages such as intelligence, strong practicality, and ease of promotion.

Description

Technical Field

[0001] This invention relates to the field of computed tomography imaging technology, specifically to a spiral CBCT geometric phantom device and calibration method. Background Technology

[0002] Cone-beam computed tomography (CBCT) systems acquire projection data by rotating an X-ray source and a flat / curved detector around the object being examined in a circular motion, enabling direct 3D image reconstruction. However, traditional circular orbit scanning introduces cone angle artifacts, which can be completely eliminated using a helical scanning trajectory, making helical CBCT a current research hotspot. Because the continuous movement of the bed during helical scanning causes the object to gradually move beyond the X-ray field, geometric correction of the helical CBCT system becomes a key technical challenge that must be addressed before image reconstruction. Currently, helical CBCT systems mainly employ two geometric correction methods:

[0003] The first method is to obtain all the geometric parameters of the spiral scan at once by scanning the long correction phantom. However, the long correction phantom has hundreds of geometric markers that are closely arranged, and their projections will mostly overlap, leading to misidentification and increasing the error in the calculation of geometric parameters.

[0004] The second correction scheme uses a segmented circular track scanning short correction phantom, calculates the rotational geometric parameters and the bed feed geometric parameters separately, and then derives the geometric parameters of the spiral scanning through fitting.

[0005] However, this calibration process is not only complex to operate, but the final calibration accuracy is also difficult to meet clinical needs. Summary of the Invention

[0006] Based on the shortcomings of the prior art described above, the purpose of this invention is to provide a spiral CBCT geometric phantom device and calibration method to solve the above-mentioned technical problems.

[0007] To achieve the above objectives, the present invention provides the following apparatus: a spiral CBCT geometric phantom apparatus, the apparatus comprising:

[0008] Markers and supporting cylindrical tubes;

[0009] After being encoded, the markers are embedded and arranged in a specific manner on the surface of the supporting cylindrical tube to form a spiral CBCT geometric phantom device.

[0010] The spiral CBCT geometric phantom device can be placed horizontally on the scanning bed of the spiral CBCT system.

[0011] The present invention is further configured such that the markers are available in two sizes;

[0012] The supporting cylindrical tube is hollow inside, and its surface is provided with two specifications of cylindrical holes, the diameter of which is the same as the size of the marker.

[0013] The cylindrical hole is perpendicular to the outer surface and is used to embed markers of two different sizes;

[0014] There are four axial laser grooves spaced 90 degrees apart and one radial laser groove at the intersection of the three central axial surfaces of the supporting cylindrical tube with the outer surface;

[0015] Encode markers of different specifications;

[0016] Based on the marker codes, the markers are embedded in the surface of the supporting cylinder in a spiral arrangement. After being embedded in the supporting cylinder, the markers are flush with its outer surface, forming a spiral CBCT geometric phantom device.

[0017] The present invention also provides a helical CBCT geometric correction method, the method comprising:

[0018] S1: Acquire projection data of the spiral CBCT geometric phantom device;

[0019] S2: Perform image segmentation on the collected projection data and extract the projection center coordinates of the markers;

[0020] S3: Decode and map the position and coordinates of the markers based on their projected size;

[0021] S4: Calculate the geometric parameters of the spiral CBCT system according to the optimization formula, and perform spiral CBCT reconstruction.

[0022] The present invention is further configured such that S1 includes:

[0023] The X-ray generator and the flat panel detector rotate synchronously around the center of the slip ring for scanning, and the imaging bed is controlled to move at a preset speed along the axis at a uniform speed to form a spiral trajectory during the scanning process.

[0024] While forming the spiral trajectory, a flat panel detector is used to continuously acquire X-ray projection images passing through the spiral CB CT geometric phantom device, forming an X-ray projection image sequence.

[0025] The present invention is further configured such that S2 includes:

[0026] Based on the X-ray projection image sequence, image segmentation processing is performed on each frame of the projection image to extract the mask image of the marker;

[0027] Based on the pixel distribution of the marker region in the mask image, the coordinates of the marker projection center are determined, and the coordinates of the projection center are extracted.

[0028] The present invention is further configured such that S3 includes:

[0029] Based on the area differences of the marker regions in the mask image, markers of different sizes are decoded and identified, and a decoding sequence is constructed.

[0030] The present invention is further configured to establish a mapping relationship between the actual coordinates of the marker in three-dimensional space and its two-dimensional coordinates in the projected image based on the decoded sequence and by comparing it with the known sequences in the decoder library.

[0031] The present invention is further configured such that S4 includes:

[0032] A loss function is constructed based on the mapping relationship. The geometric projection matrix is ​​optimized by using the loss function to minimize the difference between the estimated projection center point coordinates of the marker and the actual extracted projection center point coordinates.

[0033] The present invention is further configured to fit and optimize the key geometric parameters in the geometric projection matrix through an adaptive evolution strategy of the covariance matrix to obtain an optimized set of geometric parameters;

[0034] The optimized geometric parameters include: the distance from the X-ray source to the detector, the distance from the X-ray source to the rotation center of the system, the pitch corresponding to each rotation, the offset of the detector in the lateral and longitudinal directions, and the deflection angle of the system in the three coordinate axes.

[0035] The present invention is further configured to apply the geometric parameters to the reconstruction process of the spiral CBCT image based on the optimized set of geometric parameters, thereby obtaining the corrected spiral CBCT image.

[0036] This invention provides a spiral CBCT geometric phantom device and calibration method. The method comprises: S1: acquiring projection data of the spiral CBCT geometric phantom device; S2: performing image segmentation on the acquired projection data and extracting the projection center coordinates of markers; S3: decoding and mapping the position of markers based on their projection size and coordinates; S4: calculating the geometric parameters of the spiral CBCT system according to an optimized formula and performing spiral CBCT reconstruction. The beneficial effects include: significantly improving the estimation accuracy of the geometric parameters of the spiral CBCT system, reducing geometric distortion introduced by manufacturing tolerances, installation errors, and motion inconsistencies in mechanical devices, and ensuring accurate matching of various parameters during spiral trajectory scanning. The optimized geometric parameters can be directly applied to the subsequent image reconstruction process, effectively suppressing artifacts, improving spatial resolution, and enhancing the geometric fidelity of the reconstructed image, thereby improving the diagnostic value and stability of spiral CBCT imaging results.

[0037] Compared with existing technologies, this method does not require additional complex physical calibration devices. By utilizing the distinguishability of markers of different sizes inside the geometric phantom and combining them with efficient evolutionary optimization algorithms, it can automatically complete the parameter fitting process, reducing manual intervention. It has high intelligence and practicality, and is suitable for geometric correction and long-term maintenance of spiral CBCT systems, with broad prospects for promotion and application.

[0038] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0040] Figure 1 A schematic diagram of a spiral CBCT geometric phantom device is shown as an exemplary embodiment of the present invention;

[0041] Figure 2 A flowchart illustrating a spiral CBCT geometric correction method as an exemplary embodiment of the present invention;

[0042] Figure 3 A schematic diagram of a spiral CBCT scanning system structure is shown as an exemplary embodiment of the present invention;

[0043] Figure 4 A schematic diagram of a spiral CBCT projection image shown as an exemplary embodiment of the present invention;

[0044] 101: Marker; 102: Supporting cylinder; 103a: Axial laser groove; 103b: Radial laser groove; 30: Spiral CBCT acquisition system; 301: X-ray generator; 302: Flat panel detector; 303: Imaging bed; 304: Slip ring; 10: Spiral CBCT geometric phantom device. Detailed Implementation

[0045] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. 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 understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0046] 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.

[0047] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0048] Example 1:

[0049] Please see Figure 1 The exemplary spiral CBCT geometric phantom device includes:

[0050] Markers and supporting cylindrical tubes;

[0051] After being encoded, the markers are embedded and arranged in a specific manner on the surface of the supporting cylindrical tube to form a spiral CBCT geometric phantom device.

[0052] The spiral CBCT geometric phantom device can be placed horizontally on the scanning bed of the spiral CBCT system.

[0053] The present invention is further configured such that the markers are available in two sizes;

[0054] The supporting cylindrical tube is hollow inside, and its surface is provided with two specifications of cylindrical holes, the diameter of which is the same as the size of the marker.

[0055] The cylindrical hole is perpendicular to the outer surface and is used to embed markers of two different sizes;

[0056] There are four axial laser grooves spaced 90 degrees apart and one radial laser groove at the intersection of the three central axial surfaces of the supporting cylindrical tube with the outer surface;

[0057] Encode markers of different specifications;

[0058] Based on the marker codes, markers are embedded in a spiral arrangement on the surface of a supporting cylinder. After embedding, the markers are flush with the outer surface of the cylinder, forming a spiral CBCT geometric phantom device. Specifically, such as... Figure 1 As shown, 101 is a marker, 102 is a supporting cylindrical tube, 103a is an axial laser groove, and 103b is a radial laser groove; wherein, the marker 101 is embedded and arranged in a spiral pattern after being encoded on the surface of the supporting cylindrical tube 102; as shown... Figure 3 As shown, 30 represents the spiral CBCT system, and 10 represents the spiral CBCT assembly phantom device. The supporting cylindrical tube can be placed horizontally on the scanning bed of the spiral CBCT system. The marker material is ordinary metal steel balls, which can meet most X-ray application scenarios; for high-energy X-rays such as megavolt-level rays, the material can be replaced with tungsten carbide. In this embodiment, for ease of explanation, the markers are set in two sizes, with diameters of 1.2 mm and 2.5 mm respectively. The supporting cylindrical tube is made of acrylic, with a length of 245 mm, a hollow interior, a wall thickness of 5 mm, and cylindrical holes of 1.2 mm and 2.5 mm in diameter distributed on its surface. The cylindrical holes are perpendicular to the outer surface, allowing for the embedding of markers of both sizes. After the markers are embedded in the supporting cylindrical tube 102, they are flush with its outer surface, thus ensuring accurate and consistent embedding depth. At the intersection of the three central axial planes of the supporting cylindrical tube with the outer surface, there are four axial laser grooves 103a spaced 90 degrees apart and one radial laser groove 103b.

[0059] Further explanation is needed, such as Figure 1 As shown, the markers can be encoded according to their size, with 1 representing a large-diameter marker and 0 representing a small-diameter marker. The purpose of encoding the markers is to establish a mapping relationship between their three-dimensional spatial coordinates and two-dimensional coordinates. In this embodiment, binary encoding is used, but this is not intended to limit the scope of this application. Therefore, those skilled in the art can easily modify the system to use other number systems for encoding, such as ternary, i.e., using three different sizes of markers, which is also within the scope of this application.

[0060] The embedding and arrangement method of markers 101 in this embodiment is described in detail below: The supporting cylindrical tube is divided into 36 equal parts along the axial direction, each part being 7 mm thick. Then, markers are placed one by one in each part in a front-to-back sequence. Therefore, in this embodiment, a total of 36 markers can be placed. On the surface of the supporting cylindrical tube, each marker is staggered by 20 degrees from adjacent markers. When placing each marker, the following formula is used to check whether the projection of the marker will overlap with the projection of the already placed markers. Estimated projection coordinate calculation formula: Where u and v represent the estimated projection center coordinates of the marker; x, y, and z are the three-dimensional spatial coordinates occupied by the marker; D is the distance from the X-ray source to the detector, the specific value depends on the equipment size, usually ranging from 1000 mm to 1200 mm, and is set to 1050 mm in this embodiment; S is the distance from the X-ray source to the rotation center, the specific value depends on the equipment structure design, usually ranging from 600 mm to 700 mm, and is set to 640 mm in this embodiment; P is the pitch generated per revolution, the specific value is set according to the imaging requirements, usually ranging from 50 mm to 500 mm, and is set to 100 mm in this embodiment; θ z The rotation angle along the z-axis is determined by the installation tilt and ranges from -2° to +2°; in this embodiment, it is set to 0°. The projected coordinates are the coordinates of the three-dimensional spatial coordinates magnified proportionally by similar triangles and falling within the detector.

[0061] It should be noted that since the three-dimensional spatial coordinates occupied by the marker are infinitely divisible, this embodiment uses a uniform sampling method to uniformly extract 1000 grid points from this three-dimensional space to roughly represent the three-dimensional area occupied by the marker. Therefore, the obtained estimated projection center point coordinates are also 1000. These 1000 estimated projection center point coordinates form a continuous two-dimensional region. If the projections of two markers overlap, the calculated estimated projection center point coordinates or the projection regions they represent will intersect. The intersection discrimination method can be determined by whether the connected regions represented by the two-dimensional regions are connected. If the connected regions are connected, it means that the projections have intersected; otherwise, no intersection has occurred. By continuously adjusting the position of the marker, the projection of the marker does not overlap with the projections of the placed markers during the entire helical scan. The above placement process is repeated so that the projections of all markers do not overlap during the entire helical scan. It should be further explained that the arrangement method shown in this embodiment is a general arrangement method, which sacrifices some efficiency, but does not limit the arrangement of markers in this application. Therefore, those skilled in the art can also use some special rules, such as spiral lines and single inclined lines, to ensure that the projections do not intersect, thereby accelerating the design process of marker arrangement for spiral CBCT geometric phantom devices, which is also within the scope of protection of this application.

[0062] Example 2:

[0063] A spiral CBCT geometric correction method, such as Figure 2 As shown, it includes:

[0064] S1: Acquire projection data of the spiral CBCT geometric phantom device;

[0065] S2: Perform image segmentation on the collected projection data and extract the projection center coordinates of the markers;

[0066] S3: Decode and map the position and coordinates of the markers based on their projected size;

[0067] S4: Calculate the geometric parameters of the spiral CBCT system according to the optimization formula, and perform spiral CBCT reconstruction.

[0068] The present invention is further configured such that S1 includes:

[0069] The X-ray generator and the flat panel detector rotate synchronously around the center of the slip ring for scanning, and the imaging bed is controlled to move at a preset speed along the axis at a uniform speed to form a spiral trajectory during the scanning process.

[0070] While forming the spiral trajectory, a flat panel detector continuously acquires X-ray projection images passing through the spiral CB CT geometric phantom device, forming an X-ray projection image sequence. Specifically, such as... Figure 3 As shown, 30 is the spiral CBCT acquisition system, 301 is the X-ray emission device, 302 is the flat panel detector, 304 is the imaging bed, 305 is the slip ring, and 10 is the spiral CBCT geometric phantom device. The spiral CBCT acquisition system includes: a X-ray emission device, a flat panel detector, an imaging bed, and a slip ring. The distance between the X-ray emission device and the flat panel detector is 1050 mm, and the distance between the X-ray emission device and the center of the slip ring is 640 mm. The X-ray emission device and the flat panel detector are connected to the slip ring, and both rotate around the center point of the slip ring. Since the slip ring does not have a winding problem, the X-ray emission... The X-ray generator and flat panel detector rotate continuously until the X-ray beam stops exiting. Simultaneously, while they rotate, the imaging bed carrying the object being imaged advances linearly at a constant speed of 25 mm / s. For every revolution of the X-ray generator and flat panel detector, the imaging bed advances 100 mm. The rotational motion of the X-ray generator and flat panel detector, combined with the uniform linear motion of the imaging bed, forms a helical scanning motion. During this motion, the X-rays emitted by the X-ray generator pass through the helical CBCT geometric phantom device and the imaging bed, where they are partially attenuated. Ultimately, they are captured by the flat panel detector and converted into image signals, forming projection data, denoted as I. n Where n = 1, 2, 3, ..., N, n is the current image frame, and N is the total number of projected images acquired. By default, N = 720. Figure 4 One frame of the projected data image is shown, clearly showing the arrangement of markers on the spiral CBCT geometric phantom device.

[0071] The present invention is further configured such that S2 includes:

[0072] Based on the X-ray projection image sequence, image segmentation processing is performed on each frame of the projection image to extract the mask image of the marker;

[0073] Based on the pixel distribution of the marker region in the mask image, the coordinates of the marker projection center are determined, and the projection center coordinates are extracted. Specifically, for the collected projection data I... n Perform image segmentation and extract the coordinates of the actual projection center point of the marker. This invention does not limit the image segmentation algorithm used; it can be a classical thresholding algorithm, a maximum entropy adaptive thresholding algorithm, a random walk segmentation algorithm, or a neural network segmentation algorithm. After processing by the image segmentation algorithm, a mask image of the marker can be obtained, denoted as M. n In the mask image M n In the diagram, the region marked by the marker is denoted as Ω. The logic for calculating the coordinates of the center point of the marker's projection is as follows: in, Let i and j be the actual projection center point coordinates, i and j be the pixel coordinates within region Ω, and r(i, j) be the pixel coordinates within region Ω. n The projected pixel values ​​within region Ω. Based on the above formula, the actual projection center point coordinates of the markers in all projection data can be calculated.

[0074] The present invention is further configured such that S3 includes:

[0075] Based on the area differences of marker regions in the mask image, markers of different sizes are decoded and identified, and a decoding sequence is constructed;

[0076] Based on the decoded sequence, and compared with known sequences in the decoding library, a mapping relationship is established between the actual coordinates of the marker in three-dimensional space and its two-dimensional coordinates in the projected image. Specifically, in the mask image, the size of the region formed by markers of different sizes varies; the area formed by larger markers is significantly larger than the area formed by smaller markers. Therefore, the position of the marker can be decoded and identified based on the size of the area, such as... Figure 4 The markers shown can form a decoding sequence: 10111001010011000100000. By comparing with the known sequences in the decoding library, the serial number of each marker and its position in three-dimensional space can be found, thus establishing a mapping relationship between three-dimensional space coordinates and two-dimensional coordinates.

[0077] The present invention is further configured such that S4 includes:

[0078] A loss function is constructed based on the mapping relationship. The geometric projection matrix is ​​optimized by using the loss function to minimize the difference between the estimated projection center point coordinates of the marker and the actual extracted projection center point coordinates.

[0079] The key geometric parameters in the geometric projection matrix are fitted and optimized by an adaptive evolution strategy of covariance matrix to obtain an optimized set of geometric parameters.

[0080] The optimized geometric parameters include: the distance from the X-ray source to the detector, the distance from the X-ray source to the rotation center of the system, the pitch corresponding to each rotation, the offset of the detector in the lateral and longitudinal directions, and the deflection angle of the system in the three coordinate axes.

[0081] Based on the optimized set of geometric parameters, these parameters are applied to the reconstruction process of helical CBCT images to obtain corrected helical CBCT images. Specifically, the loss function calculation logic is as follows: Where E is the loss function, which measures the sum of squared deviations between the "estimated projection position" and the "actual extracted position"; is the geometric projection matrix; u and v are the coordinates of the estimated projection center point; The coordinates of the actual projection center point are calculated in step S3. The optimized geometric projection matrix can be obtained by minimizing the loss function E. The geometric parameters of the helical scan are obtained by solving. The relationship between the estimated projection center point coordinates and the geometric projection matrix can be described by the following formula:

[0082] Where x, y, and z are the three-dimensional spatial coordinates occupied by the marker; w is the normalization factor, which is essentially the perspective depth scaling amount generated when this spatial coordinate is projected onto the detector plane. It is calculated by considering the distance from the source point to the rotation center, the spatial position of the marker, and the rotation attitude, and is used for homogeneous coordinate normalization of the perspective projection; D is the distance from the ray source to the detector; S is the distance from the ray source to the rotation center; P is the pitch generated per revolution; u0 and v0 are the lateral and longitudinal offsets of the detector center, respectively, introduced by mechanical assembly errors, with values ​​ranging from -10 to +10, and a default initial value of 0; θ x′ θ y′ θ z This represents the rotation angle of the helical CBCT system along the x, y, and z axes, with a default initial value of 0. It's important to note that the 3D spatial coordinates x, y, and z are different from the actual projection center point coordinates. There is a mapping relationship, which has been given in step S3. For example, based on the three-dimensional spatial coordinates x, y, z of the first marker, the estimated projection center point coordinates u, v of the first marker can be calculated according to the above formula. The actual projection center point coordinates are then subtracted from these estimated projection center point coordinates u, v. It should also be extracted from the projection area of ​​the first marker, which is a one-to-one correspondence; ideally, u0 = 0, v0 = 0, θ x =0, θ y =0, the above formula will degenerate into the formula for calculating the estimated projection coordinates of the spiral CBCT geometric phantom device in the first embodiment.

[0083] It should be further explained that the covariance matrix adaptive evolution strategy used in this invention is a highly efficient optimizer, suitable for solving complex nonlinear optimization problems with multiple parameters as described in this embodiment, and is an existing technology. After optimization by the algorithm, eight key geometric parameters of the helical CBCT system can be obtained: D, S, P, u0, v0, θ x θ y ,θ z Based on the aforementioned key geometric parameters, an optimized set of geometric parameters is constructed. This optimized set of geometric parameters forms a 3×4 geometric projection matrix using the relationship formula between the estimated projection center point coordinates and the geometric projection matrix described above, and is then used in the reconstruction of helical CBCT.

[0084] It should be noted that the spiral CBCT geometric phantom device provided in the above embodiments and the spiral CBCT geometric correction method provided in the above embodiments belong to the same concept. The specific operation methods of each module and unit have been described in detail in the method embodiments and will not be repeated here. In practical applications, the spiral CBCT geometric phantom device provided in the above embodiments can be assigned to different functional modules as needed, that is, the internal structure of the system can be divided into different functional modules to complete all or part of the functions described above. This is not a limitation here.

[0085] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more sets of available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.

[0086] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it may also indicate an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0087] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0088] It should be understood that in the various embodiments of this application, the order of the above-mentioned processes does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0089] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0090] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0091] In the several embodiments provided in this application, it should be understood that the disclosed system can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0092] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0093] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0094] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0095] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A helical CBCT geometry phantom apparatus, characterized by, include: Markers and supporting cylindrical tubes; The markers, after being encoded, are embedded and arranged in a specific manner on the surface of a supporting cylindrical tube to form a spiral CBCT geometric phantom device. This includes: two sizes of markers; a hollow supporting cylindrical tube with two sizes of cylindrical holes on its surface, the diameter of which is the same as the size of the markers; the cylindrical holes are perpendicular to the outer surface and used to embed the two sizes of markers; four axial laser grooves spaced 90 degrees apart and one radial laser groove at the intersection of the three central axial surfaces of the supporting cylindrical tube with the outer surface; encoding the markers of different sizes; and embedding the markers in a spiral arrangement on the surface of the supporting cylindrical tube according to the marker codes, so that the markers are flush with the outer surface of the supporting cylindrical tube after embedding, thus forming the spiral CBCT geometric phantom device. The spiral CBCT geometric phantom device can be placed horizontally on the scanning bed of the spiral CBCT system.

2. A spiral CBCT geometry correction method applied to the spiral CBCT geometry phantom device of claim 1, characterized in that, include: S1: Acquire projection data of the spiral CBCT geometric phantom device; S2: Perform image segmentation on the collected projection data and extract the projection center coordinates of the markers; S3: Decode and map the position and coordinates of the markers based on their projected size; S4: Calculate the geometric parameters of the spiral CBCT system according to the optimization formula, and perform spiral CBCT reconstruction; S4 specifically includes: constructing a loss function based on the mapping relationship, and using the loss function to optimize the geometric projection matrix with the goal of minimizing the difference between the estimated projection center point coordinates of the marker and the actual extracted projection center point coordinates; The key geometric parameters in the geometric projection matrix are fitted and optimized by the covariance matrix adaptive evolution strategy to obtain an optimized set of geometric parameters. The optimized geometric parameters include: the distance from the X-ray source to the detector, the distance from the X-ray source to the rotation center of the system, the pitch corresponding to each rotation, the offset of the detector in the lateral and longitudinal directions, and the deflection angle of the system in the three coordinate axes. Based on the optimized set of geometric parameters, the geometric parameters are applied to the reconstruction process of spiral CBCT images to obtain corrected spiral CBCT images.

3. The helical CBCT geometry correction method of claim 2, wherein, S1 includes: The X-ray generator and the flat panel detector rotate synchronously around the center of the slip ring for scanning, and the imaging bed is controlled to move at a preset speed along the axis at a uniform speed to form a spiral trajectory during the scanning process. While forming the spiral trajectory, a flat panel detector is used to continuously acquire X-ray projection images passing through the spiral CBCT geometric phantom device, forming an X-ray projection image sequence.

4. The helical CBCT geometry correction method of claim 2, wherein, S2 includes: Based on the X-ray projection image sequence, image segmentation processing is performed on each frame of the projection image to extract the mask image of the marker; Based on the pixel distribution of the marker region in the mask image, the coordinates of the marker projection center are determined, and the coordinates of the projection center are extracted.

5. The helical CBCT geometry correction method of claim 2, wherein, S3 includes: Based on the area differences of the marker regions in the mask image, markers of different sizes are decoded and identified, and a decoding sequence is constructed.

6. The helical CBCT geometry correction method of claim 5, wherein, Based on the decoded sequence, and by comparing it with the known sequences in the decoding library, a mapping relationship is established between the actual coordinates of the marker in three-dimensional space and its two-dimensional coordinates in the projected image.

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