Spiral CBCT geometric die body device and correction method

Abstract

The invention discloses a spiral CBCT (Cone Beam Computed Tomography) geometric die body device and a correction method, and relates to the technical field of computed tomography. The method comprises the following steps: S1, acquiring projection data of a spiral CBCT geometric die body device; s2, performing image segmentation on the acquired projection data, and extracting projection center coordinates of the marker; s3, performing decoding identification and coordinate mapping on the position of the marker according to the projection size of the marker; and S4, geometric parameters of the spiral CBCT system are calculated according to the optimization formula, and spiral CBCT reconstruction is carried out. By using distinguishable markers and efficient evolution optimization, high-precision self-adaptive correction of spiral CBCT geometric parameters is realized, artifacts are remarkably inhibited, image fidelity is improved, a complex calibration device is not needed, and the method has the advantages of being intelligent, high in practicability, easy to popularize and the like.

Description

Technical Field

[0001] The present invention relates to the field of computer tomography technology, and in particular to a spiral CBCT geometric phantom device and a correction method. Background Art

[0002] The cone beam tomography system collects projection data by rotating the X-ray source and flat panel / curved detector around the object to be inspected, which can directly realize three-dimensional image reconstruction. However, the traditional circular orbit scanning method introduces cone angle artifacts, while the use of spiral scanning trajectory can completely eliminate such artifacts, making spiral CBCT technology a current research hotspot. Since the continuous movement of the bed during the spiral scanning process will cause the object to be inspected to gradually exceed the range of the radiation irradiation field, this characteristic makes the geometric correction of the spiral CBCT system a key technical problem that must be solved before image reconstruction. Currently, the spiral CBCT system mainly uses two geometric correction methods:

[0003] The first method is to obtain all the geometric parameters of the spiral scan at one time by scanning a long calibration phantom. However, the number of geometric markers on the long calibration phantom is as high as hundreds and they are densely arranged. Most of their projections will overlap, resulting in incorrect recognition, which in turn increases the error in the calculation of the geometric parameters.

[0004] The second correction scheme uses a segmented circular orbit to scan the short correction phantom, calculates the rotation geometric parameters and bed entry geometric parameters respectively, and then derives the geometric parameters of the spiral scanning by fitting.

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

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

[0007] To achieve the above-mentioned object, the present invention provides the following device: a spiral CBCT geometric phantom device, comprising:

[0008] marker and support cylinders;

[0009] The markers are encoded and embedded in a specific manner on the surface of the supporting cylinder 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 marker is provided with two sizes;

[0012] The supporting cylinder is hollow inside and has two sizes of cylindrical holes on its surface. The diameters of the cylindrical holes are the same as the size of the markers.

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

[0014] The intersection of the three central axis surfaces and the outer surface of the supporting cylinder has four axial laser grooves and one radial laser groove spaced 90 degrees apart;

[0015] Coding of markers of different specifications;

[0016] The markers are embedded in the surface of the supporting cylinder in a spiral arrangement according to the marker coding. After the markers are embedded in the supporting cylinder, they are flush with the outer surface of the supporting cylinder to form a spiral CBCT geometric phantom device.

[0017] The present invention also provides a spiral 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 marker;

[0020] S3: Decode and identify the position of the marker and map its coordinates according to the projection size of the marker;

[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 ray generator and the flat-panel detector perform synchronous rotation scanning around the center of the slip ring, and during the scanning process, the imaging bed is controlled to move uniformly along the axial direction at a preset speed to form a spiral trajectory;

[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 to form 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 projection image to extract the mask image of the marker;

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

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

[0029] Markers of different sizes are decoded and identified based on the area differences of the marker regions in the mask image, 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 the three-dimensional space and its two-dimensional coordinates in the projection image based on the decoded sequence and compared with the known sequences in the decoded library.

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

[0032] A loss function is constructed based on the mapping relationship, and the loss function is used 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.

[0033] The present invention is further configured to perform fitting optimization on key geometric parameters in the geometric projection matrix by using a covariance matrix adaptive evolution strategy to obtain an optimized geometric parameter set;

[0034] The optimized geometric parameters include: the distance from the ray source to the detector, the distance from the ray source to the system rotation center, the pitch corresponding to each rotation, the horizontal and vertical offset of the detector, 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 geometric parameter set to obtain a corrected spiral CBCT image.

[0036] The present invention provides a spiral CBCT geometric phantom device and correction method. The method comprises the following steps: S1: acquiring projection data of the spiral CBCT geometric phantom device; S2: performing image segmentation on the acquired projection data to extract the projection center coordinates of markers; S3: decoding and identifying the positions of the markers based on their projection sizes and performing coordinate mapping; and S4: calculating the geometric parameters of the spiral CBCT system according to an optimization formula and performing spiral CBCT reconstruction. The method achieves the following beneficial effects: significantly improving the estimation accuracy of the geometric parameters of the spiral CBCT system, reducing geometric distortion introduced by mechanical device manufacturing tolerances, installation errors, and motion inconsistencies, and ensuring accurate matching of various system 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 the geometric fidelity of the reconstructed image, thereby enhancing the diagnostic value and stability of spiral CBCT imaging results.

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

[0038] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 inventive efforts. In the drawings:

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

[0041] Figure 2 A flowchart of a spiral CBCT geometric correction method according to an exemplary embodiment of the present invention is shown;

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

[0043] Figure 4 A schematic diagram of a spiral CBCT projection image is 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: ray generating device, 302: flat panel detector, 303: imaging bed, 304: slip ring, 10: spiral CBCT geometric phantom device. DETAILED DESCRIPTION

[0045] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0046] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0047] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the embodiments of the present 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 the embodiments of the present invention.

[0048] Example 1:

[0049] See also Figure 1 The exemplary spiral CBCT geometric phantom device includes:

[0050] marker and support cylinders;

[0051] The markers are encoded and embedded in a specific manner on the surface of the supporting cylinder 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 marker is provided with two sizes;

[0054] The supporting cylinder is hollow inside and has two sizes of cylindrical holes on its surface. The diameters of the cylindrical holes are the same as the size of the markers.

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

[0056] The intersection of the three central axis surfaces and the outer surface of the supporting cylinder has four axial laser grooves and one radial laser groove spaced 90 degrees apart;

[0057] Coding of markers of different specifications;

[0058] The markers are embedded in the surface of the supporting cylinder in a spiral arrangement according to the marker coding. After the markers are embedded in the supporting cylinder, they are flush with the outer surface of the supporting cylinder to form a spiral CBCT geometric phantom device. Figure 1 As shown, 101 is a marker, 102 is a supporting cylinder, 103a is an axial laser groove, and 103b is a radial laser groove; wherein the marker 101 is embedded and arranged on the surface of the supporting cylinder 102 in a spiral arrangement after being encoded; Figure 3 As shown, 30 represents the spiral CBCT system, and 10 represents the spiral CBCT phantom assembly. The supporting cylinder can be placed horizontally on the scanning bed of the spiral CBCT system. The marker material is ordinary metal steel balls, which are suitable for most X-ray applications. For high-energy X-rays, such as megavolt radiation, the material can be substituted with tungsten carbide. For ease of explanation, the markers in this embodiment are provided in two sizes, with diameters of 1.2 mm and 2.5 mm, respectively. The supporting cylinder is made of acrylic, 245 mm long, hollow inside, and 5 mm thick. Its surface is provided with cylindrical holes with diameters of 1.2 mm and 2.5 mm. The cylindrical holes are perpendicular to the outer surface and can accommodate markers of two sizes. After embedding the markers into the supporting cylinder 102, they are flush with the outer surface to ensure accurate and consistent embedding depth. Four axial laser grooves 103a and one radial laser groove 103b are cut at 90-degree intervals at the intersection of the three central axis surfaces of the supporting cylinder and the outer surface.

[0059] It needs further explanation that, Figure 1 As shown, the marker can be encoded according to its size, with 1 representing a marker with a large diameter and 0 representing a marker with a small diameter. The purpose of encoding the marker is to establish a mapping relationship between the three-dimensional spatial coordinates of the marker and the two-dimensional coordinates. In this embodiment, binary encoding is used, but this is not a limitation of this application. Therefore, those skilled in the art can easily modify it and use other bases for encoding, such as ternary encoding, that is, using three markers of different sizes, which is also within the scope of protection of this application.

[0060] The following is a detailed description of the embedding arrangement method of the marker 101 in this embodiment: the supporting cylindrical tube is divided into 36 equal parts along the axial direction, that is, each part is 7 mm thick, and then the markers are placed one by one in a front-to-back order, and only one marker is placed in each equal part. Therefore, in this embodiment, a total of 36 markers can be placed. On the surface where the supporting cylindrical tube is located, each marker is placed 20 degrees apart from the adjacent markers. Each time a marker is placed, the following formula is used to check whether the projection of the marker will overlap with the projection of the placed marker. Estimated projection coordinate calculation formula: Wherein, u and v represent the coordinates of the estimated projection center point of the marker; x, y, and z are the three-dimensional spatial coordinates occupied by the marker; D is the distance from the ray source to the detector, the specific value of which depends on the device size and is usually in the range of 1000 mm to 1200 mm. In this embodiment, it is set to 1050 mm; S is the distance from the ray source to the rotation center, the specific value of which depends on the device structure design and is usually in the range of 600 mm to 700 mm. In this embodiment, it is set to 640 mm; P is the pitch generated per rotation, the specific value is set according to the imaging requirements and is usually in the range of 50 mm to 500 mm. In this embodiment, it is set to 100 mm; θ z The rotation angle of the z-axis is determined by the installation tilt, and the rotation angle range is between -2° and +2°. In this embodiment, it is set to 0°. The projected coordinates are the coordinate points in the detector after the three-dimensional space coordinates are magnified by the similar triangle ratio.

[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 resulting estimated projection center coordinates are also 1000. These 1000 estimated projection center coordinates form a continuous two-dimensional area. If the projections of two markers overlap, the calculated estimated projection center coordinates or the projected areas they represent will intersect. The intersection determination method can determine whether the connected domains represented by the two-dimensional areas are connected. If the connected domains are connected, it indicates that the projections have intersected; otherwise, there is no intersection. By continuously adjusting the marker position, the projection of the marker does not overlap with the projections of the already placed markers during the entire spiral scan. This placement process is repeated until the projections of all markers do not overlap during the entire spiral scan. It should be further explained that the arrangement method demonstrated in this embodiment is a general arrangement method that partially sacrifices efficiency, but it does not limit the arrangement of markers in this application. Therefore, those skilled in the art may also use special rules, such as spiral lines, single inclined lines, etc., to ensure that projections do not cross, thereby accelerating the marker arrangement design process of the spiral CBCT geometric phantom device, 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, including:

[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 marker;

[0066] S3: Decode and identify the position of the marker and map its coordinates according to the projection size of the marker;

[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 ray generator and the flat-panel detector perform synchronous rotation scanning around the center of the slip ring, and during the scanning process, the imaging bed is controlled to move uniformly along the axial direction at a preset speed to form a spiral trajectory;

[0070] While forming the spiral trajectory, the flat panel detector is used to continuously acquire X-ray projection images passing through the spiral CB CT geometric phantom device to form an X-ray projection image sequence. Specifically, Figure 3 As shown, 30 is a spiral CBCT acquisition system, 301 is a ray emitting device, 302 is a flat panel detector, 302 is an imaging bed, 304 is a slip ring, and 10 is a spiral CBCT geometric phantom device; the spiral CBCT acquisition system includes: a ray generating device, a flat panel detector, an imaging bed and a slip ring, wherein the distance between the ray generating device and the flat panel detector is 1050 mm, and the distance between the ray generating device and the center of the slip ring is 640 mm. The ray generating device and the flat panel detector are connected to the slip ring, and the two rotate together around the center point of the slip ring; since the slip ring does not have the problem of winding, the ray generating device The ray generator and the flat panel detector rotate continuously until the beam emission stops. Synchronously, as the two rotate, the imaging bed carries the imaging object and moves forward in a straight line at a uniform speed of 25 mm / s. For each rotation of the ray generator and the flat panel detector, the imaging bed moves forward 100 mm. The rotational motion of the ray generator and the flat panel detector and the uniform linear motion of the imaging bed form a spiral scanning motion. During the motion, the X-rays excited by the ray generator pass through the spiral CBCT geometric phantom device and the imaging bed and are partially attenuated. They are finally captured by the flat panel detector and converted into image signals to form projection data, which is recorded as I n , where n = 1, 2, 3, ..., N, n is the current image frame, N is the total number of collected projection images, and by default N = 720; Figure 4 One of the projection data images 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 projection image to extract the mask image of the marker;

[0073] Based on the pixel distribution of the marker area in the mask image, the coordinate point of the marker projection center is determined and the projection center coordinate is extracted. n Perform image segmentation and extract the actual projection center coordinates of the marker The present invention does not limit the image segmentation algorithm. The image segmentation algorithm used can be the classic threshold segmentation algorithm, the maximum entropy adaptive threshold segmentation algorithm, the random walk segmentation algorithm and the neural network segmentation algorithm. After the image segmentation algorithm is processed, the mask image of the marker can be obtained, which is denoted as M n In the mask image M n In the example, the area of ​​the marker is recorded as Ω, then the coordinate calculation logic of the projection center point of the marker is: in, is the actual projection center coordinate, i, j are the pixel coordinates in the area Ω, r(i, j) is I n The projection pixel value in the area Ω. According to the above formula, the actual projection center coordinates of the marker in all projection data can be calculated

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

[0075] Decode and identify markers of different sizes based on the area differences of the marker regions in the mask image and construct a decoding sequence;

[0076] Based on the decoding sequence, the mapping relationship between the actual coordinates of the marker in the three-dimensional space and its two-dimensional coordinates in the projected image is established by comparing the known sequences in the decoding library. Specifically, in the mask image, the sizes of the areas formed by markers of different sizes are also different. The area formed by the area of ​​the larger marker is significantly larger than the area formed by the smaller marker. 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 the known sequences in the decoding library, the serial number of each marker and the position of the marker in the three-dimensional space can be queried, thereby establishing a mapping relationship between the three-dimensional space coordinates and the 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, and the loss function is used to optimize the geometric projection matrix with the goal of minimizing the difference between the estimated projection center coordinates of the marker and the actual extracted projection center coordinates;

[0079] The key geometric parameters in the geometric projection matrix are fitted and optimized through the covariance matrix adaptive evolution strategy to obtain the optimized geometric parameter set;

[0080] The optimized geometric parameters include: the distance from the ray source to the detector, the distance from the ray source to the system's rotation center, the pitch corresponding to each rotation, the detector's lateral and longitudinal offsets, and the system's deflection angles in the three coordinate axes.

[0081] Based on the optimized geometric parameter set, the geometric parameters are applied to the reconstruction process of the spiral CBCT image to obtain the corrected spiral CBCT image. Specifically, the loss function calculation logic is: Where E is the loss function, which is used to measure the sum of squared deviations between the “estimated projection position” and the “actual extracted position”; is the geometric projection matrix; u, v are the coordinates of the estimated projection center point; The actual projection center coordinates calculated in step S3. The optimized geometric projection matrix can be obtained by minimizing the loss function E. Solve to obtain the geometric parameters of the spiral scan. The relationship between the estimated projection center point coordinates and the geometric projection matrix can be described by the following formula:

[0082] Among them, x, y, z are the three-dimensional spatial coordinates occupied by the marker; w is the normalization factor, which is essentially the perspective depth scaling generated when the spatial coordinates are projected onto the detector plane. It is calculated by the distance from the source point to the rotation center, the spatial position of the marker, the rotation posture, etc., and is used to normalize the homogeneous coordinates 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 rotation; u0 and v0 are the lateral and longitudinal offsets of the detector center, respectively, which are introduced by mechanical assembly errors and range from -10 to +10. The default initial value is 0; θ x′ θ y′ θ z The rotation angle of the spiral CBCT system along the x, y, and z axes is 0 by default. It should be noted that the three-dimensional space coordinates x, y, and z are different from the actual projection center coordinates. There is a mapping relationship. This mapping relationship has been given in step S3. For example, according to the three-dimensional coordinates x, y, z of the first marker, the estimated projection center coordinates u, v of the corresponding first marker can be calculated according to the above formula. The actual projection center coordinates subtracted from the estimated projection center coordinates u, v are 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 calculation formula of the estimated projection coordinates of the spiral CBCT geometric phantom device in the first embodiment.

[0083] It is worth noting that the covariance matrix adaptive evolution strategy used in the present invention is an efficient optimizer suitable for solving complex nonlinear optimization problems with multiple parameters in this embodiment. It is a state-of-the-art technology. After the optimization algorithm is optimized, the eight key geometric parameters of the spiral CBCT system can be obtained: D, S, P, u0, v0, θ x ,θ y ,θ z Based on the above key geometric parameters, an optimized geometric parameter set is constructed. The optimized geometric parameter set is used to form 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 used in the reconstruction of spiral CBCT.

[0084] It should be noted that the spiral CBCT geometric phantom device provided in the above embodiment and the spiral CBCT geometric correction method provided in the above embodiment are based on the same concept. The specific manner in which the various modules and units perform their operations has been described in detail in the method embodiments and will not be repeated here. In actual applications, the spiral CBCT geometric phantom device provided in the above embodiment can, as needed, allocate the above functions to different functional modules, i.e., divide the internal structure of the system into different functional modules to complete all or part of the functions described above. This is not a limitation herein.

[0085] The above embodiments can be implemented in whole or in part by software, hardware, firmware or any other combination. When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer program are loaded or executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. 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 computer-readable storage medium. 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 a wired (e.g., infrared, wireless, microwave, etc.) method. The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server or data center that contains one or more available media sets. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium. The 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 association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the previous and next associated objects are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the previous and next context for specific 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 refers to any combination of these items, including any combination of single or plural 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 plural.

[0088] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean 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 the present application.

[0089] Those skilled in the art will appreciate that the units and algorithm steps of each example 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 performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel 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 clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned 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 schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0092] The units described as separate components may or may not be physically separate, and 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 these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0093] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0094] If the functions are implemented in the form of 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 the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

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

Claims

1. A spiral CBCT geometric phantom device, characterized in that: include: marker and support cylinders; The markers are encoded and embedded in a specific manner on the surface of the supporting cylinder to form a 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. The spiral CBCT geometric phantom device according to claim 1, characterized in that: The markers are available in two sizes; The supporting cylinder is hollow inside and has two sizes of cylindrical holes on its surface. The diameters of the cylindrical holes are the same as the size of the markers. The cylindrical hole is perpendicular to the outer surface and is used to embed markers of two sizes; The intersection of the three central axis surfaces and the outer surface of the supporting cylinder has four axial laser grooves and one radial laser groove spaced 90 degrees apart; Coding of markers of different specifications; The markers are embedded in the surface of the supporting cylinder in a spiral arrangement according to the marker coding. After the markers are embedded in the supporting cylinder, they are flush with the outer surface of the supporting cylinder to form a spiral CBCT geometric phantom device.

3. A spiral CBCT geometric correction method, applied to the spiral CBCT geometric phantom device according to 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 marker; S3: Decode and identify the position of the marker and map its coordinates according to the projection size of the marker; S4: Calculate the geometric parameters of the spiral CBCT system according to the optimization formula and perform spiral CBCT reconstruction.

4. The spiral CBCT geometric correction method according to claim 3, characterized in that: Said S1 comprises: The ray generator and the flat-panel detector perform synchronous rotation scanning around the center of the slip ring, and during the scanning process, the imaging bed is controlled to move uniformly along the axial direction at a preset speed to form a spiral trajectory; 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 to form an X-ray projection image sequence.

5. The spiral CBCT geometric correction method according to claim 3, characterized in that: The S2 includes: Based on the X-ray projection image sequence, image segmentation processing is performed on each frame of projection image to extract the mask image of the marker; Based on the pixel distribution of the marker area in the mask image, the coordinate point of the marker projection center is determined and the projection center coordinates are extracted.

6. The spiral CBCT geometric correction method according to claim 3, characterized in that: The S3 includes: Markers of different sizes are decoded and identified based on the area differences of the marker regions in the mask image, and a decoding sequence is constructed.

7. The spiral CBCT geometric correction method according to claim 6, characterized in that: Based on the decoded sequence, the known sequence of the decoding library is compared to establish a mapping relationship between the actual coordinates of the marker in the three-dimensional space and its two-dimensional coordinates in the projection image.

8. The spiral CBCT geometric correction method according to claim 3, characterized in that: The S4 includes: A loss function is constructed based on the mapping relationship, and the loss function is used 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.

9. The spiral CBCT geometric correction method according to claim 8, characterized in that: The key geometric parameters in the geometric projection matrix are fitted and optimized through the covariance matrix adaptive evolution strategy to obtain the optimized geometric parameter set; The optimized geometric parameters include: the distance from the ray source to the detector, the distance from the ray source to the system rotation center, the pitch corresponding to each rotation, the horizontal and vertical offset of the detector, and the deflection angle of the system in the three coordinate axes.

10. The spiral CBCT geometric correction method according to claim 9, characterized in that: According to the optimized geometric parameter set, the geometric parameters are applied to the reconstruction process of the spiral CBCT image to obtain a corrected spiral CBCT image.

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