Improved method for generating curved surface tomographic image through CBCT circular scanning track

Abstract

An improved method for generating a curved surface sectional image through a CBCT circular scanning track comprises the steps that head model projection data are collected, and a corresponding CBCT head model three-dimensional image is reconstructed according to the head model projection data; extracting a dental arch curve according to the CBCT head model three-dimensional image, and determining a simulated panoramic scanning track according to the dental arch curve; calculating a corresponding CBCT scanning track according to the simulated panoramic scanning track, and extracting panoramic projection data; and reconstructing a panoramic image according to the panoramic projection data. Compared with a physical panoramic image, the method disclosed by the invention does not need extra radiation dose, and can directly reconstruct the panoramic image from CBCT projection data; compared with other methods for synthesizing the panoramic image from the CBCT image, the method provided by the invention can effectively reduce the problem of panoramic image quality caused by CBCT image quality and metal artifacts.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging technology, and in particular to a method for generating curved surface tomographic images using an improved CBCT circular scanning trajectory. Background Art

[0002] CBCT, or Cone Beam Computed Tomography, refers to cone beam computer tomography. CBCT uses cone beam X-rays for projection and three-dimensional reconstruction by computer to obtain a three-dimensional image of the examined part. Dental CBCT and curved tomography are important imaging methods used in dental diagnosis and treatment plans. Generally, dental CBCT uses a circular scanning trajectory to collect three-dimensional data, and curved tomography uses an arc motion based on a specific focal plane to synthesize a two-dimensional image. The two use different motion systems.

[0003] At present, there are two methods for obtaining curved tomographic images: physical panoramic images and simulated panoramic images. Physical panoramic images collect data and synthesize two-dimensional panoramic images through specific panoramic scanning trajectories, but additional radiation doses are required to generate panoramic images. Simulated panoramic images extract necessary data from CBCT three-dimensional images to obtain two-dimensional panoramic images. Simulated panoramic images are usually divided into two steps: the first step is to extract the dental arch from the CBCT image, and the second step is to generate a panoramic image based on the extracted dental arch. This method is greatly affected by the quality of CBCT images and the accuracy of the dental arch, especially when the metal artifacts are severe. Even if an ideal dental arch is set, the metal artifacts of CBCT will remain in the panoramic image, thereby reducing the quality of the panoramic image. Summary of the invention

[0004] In view of the above problems, the present invention is proposed to provide an improved method for generating curved tomographic images using a CBCT circular scanning trajectory, which overcomes the above problems or at least partially solves the above problems.

[0005] In order to solve the above technical problems, the embodiments of the present application disclose the following technical solutions:

[0006] The embodiment of the present invention discloses a method for generating curved surface tomographic images using an improved CBCT circular scanning trajectory, comprising:

[0007] S100. Collecting head model projection data, and reconstructing a corresponding CBCT head model three-dimensional image according to the head model projection data;

[0008] S200. Extracting a dental arch curve according to the 3D image of the CBCT head model, and determining a simulated panoramic scanning trajectory according to the dental arch curve;

[0009] S300. Calculating the corresponding CBCT scanning trajectory according to the simulated panoramic scanning trajectory, and extracting panoramic projection data;

[0010] S400. Reconstruct a panoramic image according to the panoramic projection data.

[0011] Furthermore, in S200, a dental arch curve is extracted according to the three-dimensional image of the CBCT head model, and a simulated panoramic scanning trajectory is determined according to the dental arch curve. The specific method includes: obtaining a MIP image of the CBCT coronal plane and segmenting the tooth area using a threshold method, using a histogram to determine the upper and lower boundary indexes of the teeth and obtaining a MIP image of the axial plane, using a threshold method to generate binary images of the teeth and jaws respectively and realign the head position, fitting a parabola and generating a dental arch curve, and determining a simulated panoramic scanning trajectory according to the dental arch curve.

[0012] Furthermore, the MIP image of the CBCT coronal plane is obtained and the tooth region is segmented by a threshold method. The specific method includes: obtaining the MIP image of the CBCT coronal plane and segmenting the tooth region by a threshold method, calculating the maximum value of the corresponding pixel position of each layer of the coronal plane by a MIP algorithm according to the CBCT three-dimensional image, generating the MIP image of the coronal plane, and segmenting the tooth region in the MIP image of the coronal plane by a threshold method; using a histogram to determine the upper and lower boundary indexes of the teeth and obtaining the MIP image of the axial plane, the specific method includes: calculating a histogram in the y direction according to the tooth binary image to determine the distribution of the teeth, thresholding the number of pixels in each row of the teeth, determining the upper and lower boundary indexes of the tooth region, and the edge of the tooth region by a threshold method. The slice range of the tooth axial plane is expanded by adding 20 slice indexes to fully extract the area of ​​the teeth on the axial plane, and the MIP algorithm is used to calculate the maximum value of the pixel position corresponding to the upper and lower boundaries of the tooth area on the axial plane to generate the MIP image of the axial plane; the threshold method is used to generate binary images of the teeth and jaws respectively and the head position is realigned. The specific method includes: according to the MIP image of the axial plane, different thresholds are used to extract the areas of the teeth and jaws respectively, the minimum circumscribed rectangle of the jaw binary image is extracted, and the inclination angle of the minimum circumscribed rectangle is calculated, and the binary image of the teeth and jaws is adjusted according to the rigid transformation matrix generated by the inclination angle to deal with the problem of left-right asymmetry of the panoramic image caused by incorrect head model positioning, and the aligned binary image of the teeth and jaws is generated.

[0013] Furthermore, a parabola is fitted and a dental arch curve is generated. The specific method includes: dividing the aligned tooth binary image uniformly at a preset angle with the center of the image, calculating the center point of the tooth segmentation area in each angle sector, fitting the tooth parabola using the RANSAC algorithm according to the center point of each angle sector, and recording the center coordinates of the molars on the left and right sides, calculating the coordinates of the jaw tip according to the aligned jaw binary image, combining the center coordinates of the molars on the left and right sides, fitting the jaw parabola using the least squares method, and fusing the two parabolas with the intersection of the two parabolas as the center using the cosine weighted function. line to generate a smooth dental arch curve; determine the simulated panoramic scanning trajectory according to the dental arch curve, the specific method includes: calculating the position of the incisor in the dental arch curve, and moving the center line of the simulated panoramic scanning trajectory to the incisor position, and uniformly sampling 2801 points of the dental arch curve by presetting the starting scanning angle and the ending scanning angle; calculating the tangent of each sampling point, and calculating the intersection of the perpendicular line of the tangent and the center line of the simulated panoramic scanning trajectory, recording the intersection position as the panoramic axis position of the current scanning angle, and detecting abnormal panoramic axis position points and correcting them according to the displacement to generate a simulated panoramic scanning trajectory.

[0014] Furthermore, in S300, a corresponding CBCT scanning trajectory is calculated according to the simulated panoramic scanning trajectory, and panoramic projection data is extracted. The specific method includes: converting the panoramic beam into a parallel beam, converting the parallel beam into a CBCT beam, verifying the CBCT beam projection data range, extracting the panoramic projection data, and calculating the panoramic stitching coefficient.

[0015] Furthermore, the panoramic beam is converted into a parallel beam, and the first conversion formula is:

[0016]

[0017] θ=γ p +β p

[0018]

[0019] Among them, u p represents the lateral position of the panoramic beam on the detector plane, S p represents the lateral position of the panoramic beam on the virtual detector plane, D represents the distance from the ray source to the rotation axis, R represents the distance from the rotation axis to the detector plane, and γ p represents the fan angle of the panoramic beam, β p represents the ray angle of the panoramic beam, θ represents the ray angle of the corresponding transformed parallel beam, and t p represents the lateral position of the corresponding transformed parallel beam on the virtual detector plane. The parameters of the panoramic beam (θ, t p) is converted into the parameters of a parallel beam (β p ,γ p ,S p ).

[0020] Furthermore, the parallel beam is converted into a CBCT beam, and the second conversion formula is:

[0021] t c =t p +x p ·cosθ+y p sinθ

[0022]

[0023] β c =θ-γ c

[0024] Among them, (x p ,y p ) represents the central coordinate of the panoramic rotation axis under the CBCT system, t c represents the lateral position of the CBCT beam on the virtual detector plane, S c represents the lateral position of the CBCT beam on the virtual detector plane, u c represents the lateral position of the CBCT beam on the detector plane, γ c represents the fan angle of the CBCT beam, β c The ray angle of the CBCT beam is represented by the second conversion formula, which can convert the parameter of the parallel beam (β p ,γ p ,S p ) is converted into the parameters of the CBCT beam (β c ,u c ).

[0025] Further, the CBCT beam projection data range is verified, the panoramic projection data is extracted, and the panoramic stitching coefficient is calculated. The specific method includes: by moving the position of the panoramic axis to approach the data beyond the CBCT projection range, so that the adjusted panoramic beam is closer to the rotation axis of the CBCT scanning system, and the panoramic projection data is extracted from the CBCT projection data according to the verified CBCT beam parameters, and the ray angle β of the CBCT beam c Determine the index of the CBCT projection data, the lateral position u of the CBCT beam on the detector plane c Determine the position in the current projection data; calculate the stitching coefficient corresponding to each sampling point according to the dental arch sampling points and the panoramic scanning trajectory in S200, and the calculation formula is as follows:

[0026]

[0027] Among them, f i represents the splicing coefficient of the i-th sampling point, d i Represents the vertical distance from the i-1th sampling point to the panoramic beam where the i-th sampling point is located, r i Represents the distance from the i-th sampling point to the current panoramic axis, i=1,...,2800.

[0028] Furthermore, the panoramic image is reconstructed according to the panoramic projection data, and the specific method includes:

[0029] First, adjust the uniformity of the panoramic projection data and calculate the average pixel value m of all projection data. total And the average pixel value m of each projection data proj ; Then calculate the weight w of each projection data proj , the calculation formula is as follows:

[0030]

[0031] Finally, the calculated weights are multiplied by the respective projection data to obtain uniform panoramic projection data.

[0032] Furthermore, the panoramic image post-processing improves the resolution of the panoramic image by an edge enhancement algorithm, and the calculation formula of the edge enhancement algorithm is as follows:

[0033] I=α0·I0+α1·(I0-G1)+α2·(I0-G2)+α3·(I0-G3),

[0034] Among them, I represents the enhanced panoramic image, I0 represents the original panoramic image, G n represents the panoramic image after Gaussian filtering, α n Represents the weighting coefficient, which is used to weigh different levels of image detail, n = 0, 1, 2, 3.

[0035] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0036] The present invention discloses a method for generating curved tomographic images from an improved CBCT circular scanning trajectory, comprising: collecting head model projection data, reconstructing a corresponding CBCT head model three-dimensional image according to the head model projection data; extracting a dental arch curve according to the CBCT head model three-dimensional image, and determining a simulated panoramic scanning trajectory according to the dental arch curve; calculating a corresponding CBCT scanning trajectory according to the simulated panoramic scanning trajectory, and extracting panoramic projection data; and reconstructing a panoramic image according to the panoramic projection data. Compared with physical panoramic images, the method disclosed by the present invention does not require additional radiation doses, and can directly reconstruct panoramic images from CBCT projection data; compared with other methods for synthesizing panoramic images from CBCT images, it can effectively reduce CBCT image quality and panoramic image quality problems caused by metal artifacts.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0039] Figure 1 This is a flow chart of a method for generating curved tomographic images using an improved CBCT circular scanning trajectory in Embodiment 1 of the present invention;

[0040] Figure 2 This is a flow chart of extracting a dental arch curve according to a 3D image of a CBCT head model and determining a simulated panoramic scanning trajectory according to the dental arch curve in Example 1 of the present invention;

[0041] Figure 3 This is a flow chart of calculating the corresponding CBCT scanning trajectory according to the simulated panoramic scanning trajectory and extracting the panoramic projection data in Example 1 of the present invention;

[0042] Figure 4 A geometric diagram of converting a panoramic light beam into a parallel light beam in Embodiment 1 of the present invention;

[0043] Figure 5 FIG. 1 is a geometric diagram of converting a parallel light beam into a CBCT light beam in Example 1 of the present invention. DETAILED DESCRIPTION

[0044] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0045] In order to solve the problems existing in the prior art, an embodiment of the present invention provides a method for generating curved tomographic images using an improved CBCT circular scanning trajectory.

[0046] Example 1

[0047] The present invention discloses a method for generating curved tomographic images using an improved CBCT circular scanning trajectory. Figure 1 ,include:

[0048] S100. Collect head model projection data, and reconstruct the corresponding CBCT head model three-dimensional image according to the head model projection data; specifically, in this embodiment, head model data collection and image effect verification are performed on the oral CBCT product Bojue 1040. Specifically, parameters such as field of view size, voxel and scanning mode can be selected to collect a circle of head model projection data. According to the collected head model projection data, the FDK algorithm is used to reconstruct the corresponding CBCT head model three-dimensional image. Among them, the FDK algorithm (Feldkamp-Davis-Kress algorithm) is one of the most widely used classic algorithms in CBCT reconstruction. It is an algorithm based on filtered back projection (Filtered Back Projection, FBP), which is used to reconstruct a three-dimensional image from the projection data of the head model. Through the above steps, the head model projection data can be successfully collected and the corresponding CBCT head model three-dimensional image can be reconstructed. This process is of great significance for medical research and clinical practice.

[0049] S200. Extracting a dental arch curve according to the 3D image of the CBCT head model, and determining a simulated panoramic scanning trajectory according to the dental arch curve;

[0050] In S200 of this embodiment, a dental arch curve is extracted according to the 3D image of the CBCT head model, and a simulated panoramic scanning trajectory is determined according to the dental arch curve, such as Figure 2 The specific method includes: obtaining the MIP image of the CBCT coronal plane and segmenting the tooth area using the threshold method, using the histogram to determine the upper and lower boundary indexes of the tooth and obtaining the MIP image of the axial plane, using the threshold method to generate the binary images of the teeth and jaws respectively and realign the head position, fitting the parabola and generating the dental arch curve, and determining the simulated panoramic scanning trajectory according to the dental arch curve.

[0051] In some preferred embodiments, the MIP image of the CBCT coronal plane is obtained and the tooth region is segmented using a threshold method. The maximum value of the corresponding pixel position of each layer of the coronal plane can be calculated using the MIP algorithm based on the CBCT three-dimensional image to generate the MIP image of the coronal plane. Further, the threshold method can be used to segment the tooth region in the MIP image of the coronal plane.

[0052] In some preferred embodiments, a histogram is used to determine the upper and lower boundary indexes of the teeth and to obtain the MIP image of the axial plane. The histogram in the y direction can be calculated based on the above-mentioned tooth binary image to determine the distribution of the teeth. Preferably, the number of pixels in each row of teeth can be thresholded to determine the upper and lower boundary indexes of the tooth area. Preferably, the edge of the tooth area is expanded by adding 20 slice indexes to expand the slice range of the tooth axial plane to fully extract the area of ​​the teeth on the axial plane. Furthermore, the MIP algorithm can be used to calculate the maximum value of the pixel position corresponding to the upper and lower boundaries of the tooth area on the axial plane to generate a MIP image of the axial plane.

[0053] In some preferred embodiments, the threshold method is used to generate the binary images of teeth and jaws respectively and the head position is realigned. The areas of teeth and jaws can be extracted respectively using different thresholds according to the MIP image of the axial plane. Preferably, the minimum circumscribed rectangle of the binary image of the jaw can be extracted, and the inclination angle of the minimum circumscribed rectangle can be calculated. Preferably, the binary images of teeth and jaws are adjusted according to the rigid transformation matrix generated according to the inclination angle to deal with the problem of left-right asymmetry of the panoramic image caused by the incorrect positioning of the head model. Further, the aligned binary images of teeth and jaws are generated.

[0054] In some preferred embodiments, to fit a parabola and generate a dental arch curve, the aligned binary image of the teeth can be evenly divided by angle with the center of the image. In this embodiment, the angle is preferably set to 5 degrees; then the center point of the tooth segmentation area in each angle sector is calculated; finally, the RANSAC (RANdom Sample Consensus) algorithm is used to fit the dental parabola according to the center point of each angle sector, and the center coordinates of the molars on the left and right sides are recorded. Among them, the process of fitting the dental parabola using the RANSAC (Random Sample Consensus) algorithm is actually to apply the RANSAC algorithm to a specific problem - estimating the parameters of the dental parabola from the point cloud data of the teeth. Preferably, the coordinates of the tip of the jaw can be calculated based on the aligned binary image of the jaw, and the center coordinates of the molars on the left and right sides are combined to fit the jaw parabola using the least squares method. Furthermore, the cosine weighted function is used to fuse the two parabolas with the intersection of the two parabolas as the center to generate a smooth dental arch curve.

[0055] In some preferred embodiments, the simulated panoramic scanning trajectory is determined according to the dental arch curve. First, the position of the incisor in the dental arch curve is calculated, and the center line of the simulated panoramic scanning trajectory is moved to the incisor position; then the dental arch curve is uniformly sampled at 2801 points through a specific starting scanning angle and an end scanning angle; finally, the tangent of each sampling point is calculated, and the intersection of the perpendicular line of the tangent and the center line of the simulated panoramic scanning trajectory is calculated, and the intersection position is recorded as the panoramic axis position of the current scanning angle. In order to ensure the continuity of the panoramic axis position, the present invention generates a simulated panoramic scanning trajectory by detecting abnormal panoramic axis position points and correcting them according to the displacement.

[0056] Extracting the dental arch curve from the 3D image of the CBCT head model and determining the simulated panoramic scanning trajectory based on it is a complex but important process. Through precise extraction and planning, it can provide strong support for subsequent panoramic scanning, thereby ensuring the accuracy and reliability of the scanning results.

[0057] S300. Calculate the corresponding CBCT scanning trajectory according to the simulated panoramic scanning trajectory, and extract panoramic projection data; In S300 of this embodiment, calculate the corresponding CBCT scanning trajectory according to the simulated panoramic scanning trajectory, and extract panoramic projection data, such as Figure 3 ,The specific method includes converting the panoramic beam into a parallel beam, converting the parallel beam into a CBCT beam, verifying the CBCT beam projection data range, extracting the panoramic projection data, and calculating the panoramic ,stitching coefficient.

[0058] In some preferred embodiments, since the positions of the ray sources along the panoramic scanning trajectory and along the CBCT scanning trajectory do not completely overlap, the present invention first converts the panoramic beam into a parallel beam. The geometric diagram of the conversion is as follows: Figure 4 As shown, the calculation formula is as follows:

[0059]

[0060] θ=γ p +β p

[0061]

[0062] Among them, So p Indicates the ray source position of the panoramic scan, D p represents the panoramic detector plane, O p represents the center position of the panoramic rotation axis; D represents the distance from the ray source to the rotation axis, R represents the distance from the rotation axis to the detector plane, and u p represents the lateral position of the panoramic beam on the detector plane, S p represents the lateral position of the panoramic beam on the virtual detector plane, γ prepresents the fan angle of the panoramic beam, β p represents the ray angle of the panoramic beam, θ represents the ray angle of the corresponding transformed parallel beam, and t p The above formula can be used to calculate the parameters of the panoramic beam (θ, t p ) is converted into the parameters of a parallel beam (β p ,γ p ,S p ).

[0063] In some preferred embodiments, after the panoramic beam is converted into a parallel beam, the parallel beam is converted into a CBCT beam. The geometric diagram of the conversion is as follows: Figure 5 As shown, the calculation formula is as follows:

[0064] t c =t p +x p ·cosθ+y p sinθ

[0065]

[0066] β c =θ-γ c

[0067] Among them, So c represents the radiation source position of CBCT scanning, D c represents the CBCT detector plane, O c Indicates the center position of the CBCT rotation axis; (x p ,y p ) represents the central coordinate of the panoramic rotation axis under the CBCT system, t c represents the lateral position of the CBCT beam on the virtual detector plane, S c represents the lateral position of the CBCT beam on the virtual detector plane, u c represents the lateral position of the CBCT beam on the detector plane, γ c represents the fan angle of the CBCT beam, β c The ray angle of the CBCT beam is represented by the above formula. p ,γ p ,S p ) is converted into the parameters of the CBCT beam (β c ,u c ).

[0068] In some preferred embodiments, due to the movement of the rotation axis in the panoramic scanning system and the asymmetry of the detector fan angle in the dental CBCT system, some projection data of the panoramic scanning trajectory cannot be obtained in the dental CBCT projection data. Therefore, the present invention moves the position of the panoramic axis to approach the data beyond the CBCT projection range, thereby making the adjusted panoramic light beam closer to the rotation axis of the CBCT scanning system.

[0069] In some preferred embodiments, the panoramic projection data can be extracted from the CBCT projection data according to the verified CBCT beam parameters. c Determine the index of the CBCT projection data, the lateral position u of the CBCT beam on the detector plane c Determine the position in the current projection data. In a preferred embodiment of the present invention, the size of the extracted panoramic projection data is (60, 768, 2800).

[0070] In some preferred embodiments, the panoramic stitching coefficient is calculated by calculating the stitching coefficient corresponding to each sampling point according to the dental arch sampling points and the panoramic scanning trajectory in step S200, and the calculation formula is as follows:

[0071]

[0072] Among them, f i represents the splicing coefficient of the i-th sampling point, d i Represents the vertical distance from the i-1th sampling point to the panoramic beam where the i-th sampling point is located, r i Represents the distance from the i-th sampling point to the current panoramic axis, i=1,...,2800.

[0073] S400. Reconstructing a panoramic image according to the panoramic projection data. In S400 of this embodiment, the panoramic image is reconstructed according to the panoramic projection data, and the specific method includes:

[0074] First, adjust the uniformity of the panoramic projection data and calculate the average pixel value m of all projection data. total and the average pixel value m of each projection data proj ; Then calculate the weight w of each projection data proj , the calculation formula is as follows:

[0075]

[0076] Finally, the calculated weights are multiplied by the respective projection data to obtain uniform panoramic projection data.

[0077] In some preferred embodiments, the panoramic image reconstruction can be performed using the Bondent panoramic stitching algorithm based on the uniform panoramic projection data and the panoramic stitching coefficients calculated in step S300. The panoramic image post-processing improves the resolution of the panoramic image by an edge enhancement algorithm, and the calculation formula of the edge enhancement algorithm is as follows:

[0078] I=α0·I0+α1·(I0-G1)+α2·(I0-G2)+α3·(I0-G3),

[0079] Among them, I represents the enhanced panoramic image, I0 represents the original panoramic image, G n represents the panoramic image after Gaussian filtering, α n represents a weighting coefficient used to weigh different levels of image detail, n = 0, 1, 2, 3. In a preferred embodiment of the present invention, α0 = 1.0, α1 = 1.0, α2 = 1.5, α3 = 1.5, and the values ​​of σ for Gaussian filtering are σ G1 =2.4,σ G2 =4.8,σ G3 =19.2.

[0080] The present embodiment discloses a method for generating curved tomographic images from an improved CBCT circular scanning trajectory, including: collecting head model projection data, reconstructing a corresponding CBCT head model three-dimensional image based on the head model projection data; extracting a dental arch curve based on the CBCT head model three-dimensional image, and determining a simulated panoramic scanning trajectory based on the dental arch curve; calculating a corresponding CBCT scanning trajectory based on the simulated panoramic scanning trajectory, and extracting panoramic projection data; and reconstructing a panoramic image based on the panoramic projection data. Compared with physical panoramic images, the method disclosed in the present embodiment does not require additional radiation doses, and can directly reconstruct panoramic images from CBCT projection data; compared with other methods for synthesizing panoramic images from CBCT images, it can effectively reduce CBCT image quality and panoramic image quality problems caused by metal artifacts.

[0081] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0082] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0083] Those skilled in the art will also appreciate that the various illustrative logic blocks, modules, circuits, and algorithmic steps described in conjunction with the embodiments herein can all be implemented as electronic hardware, computer software, or a combination thereof. In order to clearly illustrate the interchangeability between hardware and software, various illustrative components, blocks, modules, circuits, and steps are generally described above around their functions. Whether such functions are implemented as hardware or software depends on specific applications and the design constraints imposed on the entire system. A skilled person can implement the described functions in an alternative manner for each specific application, but such implementation decisions should not be interpreted as departing from the scope of protection of the present disclosure.

[0084] The steps of the method or algorithm described in conjunction with the embodiments herein may be directly embodied as hardware, a software module executed by a processor, or a combination thereof. The software module may be located in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a mobile disk, a CD-ROM, or any other form of storage medium well known in the art. An exemplary storage medium is connected to the processor so that the processor can read information from the storage medium and can write information to the storage medium. Of course, the storage medium may also be an integral part of the processor. The processor and the storage medium may be located in an ASIC. The ASIC may be located in a user terminal. Of course, the processor and the storage medium may also be present in a user terminal as discrete components.

[0085] For software implementation, the techniques described in this application can be implemented with modules (e.g., procedures, functions, etc.) that perform the functions described in this application. These software codes can be stored in a memory unit and executed by a processor. The memory unit can be implemented within the processor or outside the processor. In the latter case, it is coupled to the processor in a communication manner via various means, which are well known in the art.

[0086] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," is explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

Claims

1. A method for generating curved tomographic images using an improved CBCT circular scanning trajectory, characterized in that: include: S100. Collecting head model projection data, and reconstructing a corresponding CBCT head model three-dimensional image according to the head model projection data; S200. Extracting a dental arch curve according to the 3D image of the CBCT head model, and determining a simulated panoramic scanning trajectory according to the dental arch curve; S300. Calculating the corresponding CBCT scanning trajectory according to the simulated panoramic scanning trajectory, and extracting panoramic projection data; S400. Reconstruct a panoramic image according to the panoramic projection data.

2. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory according to claim 1, characterized in that: In S200, a dental arch curve is extracted according to the three-dimensional image of the CBCT head model, and a simulated panoramic scanning trajectory is determined according to the dental arch curve. The specific method includes: obtaining a MIP image of the CBCT coronal plane and segmenting the tooth area using a threshold method, using a histogram to determine the upper and lower boundary indexes of the teeth and obtaining a MIP image of the axial plane, using a threshold method to generate binary images of the teeth and jaws respectively and realign the head position, fitting a parabola and generating a dental arch curve, and determining a simulated panoramic scanning trajectory according to the dental arch curve.

3. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory as claimed in claim 2, characterized in that: The MIP image of the CBCT coronal plane is obtained and the tooth region is segmented by a threshold method. The specific method includes: obtaining the MIP image of the CBCT coronal plane and segmenting the tooth region by a threshold method, calculating the maximum value of the corresponding pixel position of each layer of the coronal plane by a MIP algorithm according to the CBCT three-dimensional image, generating the MIP image of the coronal plane, and segmenting the tooth region in the MIP image of the coronal plane by a threshold method; using a histogram to determine the upper and lower boundary indexes of the teeth and obtaining the MIP image of the axial plane, the specific method includes: calculating the histogram in the y direction according to the tooth binary image to determine the distribution of the teeth, thresholding the number of pixels in each row of the teeth, determining the upper and lower boundary indexes of the tooth region, and increasing the edge of the tooth region by 20 slice indexes are used to expand the slice range of the tooth axial plane to fully extract the area of ​​the teeth on the axial plane, and the MIP algorithm is used to calculate the maximum value of the pixel position corresponding to the upper and lower boundaries of the tooth area on the axial plane to generate the MIP image of the axial plane; the threshold method is used to generate binary images of the teeth and jaws respectively and the head position is realigned. The specific method includes: according to the MIP image of the axial plane, different thresholds are used to extract the areas of the teeth and jaws respectively, the minimum circumscribed rectangle of the binary image of the jaws is extracted, and the inclination angle of the minimum circumscribed rectangle is calculated, and the binary images of the teeth and jaws are adjusted according to the rigid transformation matrix generated by the inclination angle to deal with the problem of left-right asymmetry of the panoramic image caused by incorrect head model positioning, and the aligned binary images of the teeth and jaws are generated.

4. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory as claimed in claim 3, characterized in that: Fitting a parabola and generating a dental arch curve, the specific method includes: dividing the aligned tooth binary image evenly at a preset angle with the center of the image, calculating the center point of the tooth segmentation area in each angle sector, fitting the tooth parabola using the RANSAC algorithm according to the center point of each angle sector, and recording the center coordinates of the molars on the left and right sides, calculating the coordinates of the jaw tip according to the aligned jaw binary image, and combining the center coordinates of the molars on the left and right sides, fitting the jaw parabola using the least squares method, and fusing the two parabolas with the intersection of the two parabolas as the center using the cosine weighted function, Generate a smooth dental arch curve; determine a simulated panoramic scanning trajectory based on the dental arch curve, the specific method includes: calculating the position of the incisor in the dental arch curve, and moving the center line of the simulated panoramic scanning trajectory to the incisor position, uniformly sampling 2801 points of the dental arch curve by presetting the starting scanning angle and the ending scanning angle; calculate the tangent of each sampling point, and calculate the intersection of the perpendicular line of the tangent and the center line of the simulated panoramic scanning trajectory, record the intersection position as the panoramic axis position of the current scanning angle, and generate a simulated panoramic scanning trajectory by detecting abnormal panoramic axis position points and correcting them according to the displacement.

5. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory as claimed in claim 1, characterized in that: In S300, a corresponding CBCT scanning trajectory is calculated according to the simulated panoramic scanning trajectory, and panoramic projection data is extracted. The specific method includes: converting the panoramic beam into a parallel beam, converting the parallel beam into a CBCT beam, verifying the CBCT beam projection data range, extracting the panoramic projection data, and calculating the panoramic stitching coefficient.

6. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory as claimed in claim 5, characterized in that: To convert the panoramic beam into a parallel beam, the first conversion formula is: θ=γ p +b p Among them, u p represents the lateral position of the panoramic beam on the detector plane, S p represents the lateral position of the panoramic beam on the virtual detector plane, D represents the distance from the ray source to the rotation axis, R represents the distance from the rotation axis to the detector plane, and γ p represents the fan angle of the panoramic beam, β p represents the ray angle of the panoramic beam, θ represents the ray angle of the corresponding transformed parallel beam, and t p represents the lateral position of the corresponding transformed parallel beam on the virtual detector plane. The parameters of the panoramic beam (θ, t p ) is converted into the parameters of the parallel beam (β p ,γ p ,S p ).

7. The improved method for generating curved tomographic images using a CBCT circular scanning trajectory as claimed in claim 6, characterized in that: The parallel beam is converted into a CBCT beam. The second conversion formula is: t c =t p +x p ·cosθ+y p ·sinθ b c =θ-γ c Among them, (x p ,y p ) represents the central coordinate of the panoramic rotation axis under the CBCT system, t c represents the lateral position of the CBCT beam on the virtual detector plane, S c represents the lateral position of the CBCT beam on the virtual detector plane, u c represents the lateral position of the CBCT beam on the detector plane, γ c represents the fan angle of the CBCT beam, β c The ray angle of the CBCT beam is represented by the second conversion formula, which can convert the parameter of the parallel beam (β p ,γ p ,S p ) is converted into the parameters of the CBCT beam (β c ,u c ).

8. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory as claimed in claim 5, characterized in that: Verify the CBCT beam projection data range, extract panoramic projection data, and calculate the panoramic stitching coefficient. The specific method includes: moving the position of the panoramic axis to approach the data beyond the CBCT projection range, so that the adjusted panoramic beam is closer to the rotation axis of the CBCT scanning system, extracting the panoramic projection data from the CBCT projection data according to the verified CBCT beam parameters, and calculating the ray angle β of the CBCT beam. c Determine the index of the CBCT projection data, the lateral position u of the CBCT beam on the detector plane c Determine the position in the current projection data; calculate the stitching coefficient corresponding to each sampling point according to the dental arch sampling points and the panoramic scanning trajectory in S200, and the calculation formula is as follows: Among them, f i represents the splicing coefficient of the i-th sampling point, d i Represents the vertical distance from the i-1th sampling point to the panoramic beam where the i-th sampling point is located, r i Represents the distance from the i-th sampling point to the current panoramic axis, i=1,...,2800.

9. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory as claimed in claim 1, characterized in that: The panoramic image is reconstructed according to the panoramic projection data, and the specific method includes: First, adjust the uniformity of the panoramic projection data and calculate the average pixel value m of all projection data. total and the average pixel value m of each projection data proj ; Then calculate the weight w of each projection data proj , the calculation formula is as follows: Finally, the calculated weights are multiplied by the respective projection data to obtain uniform panoramic projection data.

10. The method for generating curved tomographic images using an improved CBCT circular scanning trajectory as claimed in claim 9, characterized in that: The panoramic image post-processing improves the resolution of the panoramic image by an edge enhancement algorithm. The calculation formula of the edge enhancement algorithm is as follows: I=α0·I0+α1·(I0-G1)+α2·(I0-G2)+α3·(I0-G3), Among them, I represents the enhanced panoramic image, I0 represents the original panoramic image, G n represents the panoramic image after Gaussian filtering, α n Represents the weighting coefficient, which is used to weigh different levels of image detail, n = 0, 1, 2, 3.

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