Structured hexahedral mesh generation method for individualized blood vessel wall

Abstract

The invention belongs to the technical field of medical image processing, and relates to a method for generating a structured hexahedral mesh of an individualized vascular wall, which comprises the following steps of: s1, when a target aortic blood vessel has no branch, entering an entity construction step of the aortic blood vessel wall, otherwise, performing the entity construction step of the aortic blood vessel wall and the entity construction step of each branch blood vessel wall; s2, grid seeds are given to all boundaries of the blood vessel wall entity, and a structured hexahedral grid of the blood vessel wall is generated through lofting or scanning; and s3, performing grid inspection by calculating the included angle, the length-width ratio coefficient and the geometric deviation coefficient so as to ensure that the grid quality meets the calculation requirement. According to the method, the layered structured hexahedral mesh can be generated for the blood vessel wall without branches, the regular hexahedral mesh can be generated for complex three-dimensional entities such as the blood vessel wall with holes and branches, and the method is low in shape requirement, high in generalization and low in calculation cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical image processing, and in particular relates to a method for generating a structured hexahedral grid of an individualized blood vessel wall. Background Art

[0002] In the field of biomechanics, imaging methods (such as X-rays, CTA, OCT, and ultrasound) are often used to capture the in vivo morphology of organisms. Once this morphology is captured, numerical simulation methods (such as finite element methods) can be used to simulate and study the organism. The core of the finite element method is to divide the continuous solution domain into several smaller subregions, called "cells." Therefore, to perform mechanical finite element analysis, the image must be modeled in three dimensions and the model divided into cells. This process is called mesh generation.

[0003] Meshing three-dimensional entities can be categorized into tetrahedral and hexahedral meshes based on their shape. Tetrahedral meshes offer flexibility and can accommodate complex geometries, but they offer lower finite element accuracy. Hexahedral meshes offer higher finite element accuracy and numerical stability, but are only suitable for geometries that can be divided into regular meshes. Mesh structure also categorizes them into unstructured and structured meshes. Unstructured meshes have irregular node and element arrangements, but can be flexibly divided based on geometry. Structured meshes have regular node and element arrangements, resulting in high mesh quality and finite element accuracy, but they have poor adaptability to geometries and can only be used for structures with regular geometries. Therefore, if high finite element accuracy and regular node and element arrangements are required, structured hexahedral meshes are a relatively superior choice.

[0004] Currently, some existing methods exist for generating three-dimensional solid models of blood vessel walls from CTA images. CTA, or CT angiography, involves intravenous injection of contrast agents, using CT equipment to image blood vessels throughout the body. The image shows the blood flow area (blood flow domain). Assuming the thickness of the blood vessel wall (1-2 mm), expanding the blood flow domain outward by 1-2 mm can produce a three-dimensional solid model of the vessel wall. After obtaining the three-dimensional solid model, a mesh must be generated before finite element analysis can be performed. Existing mesh generation techniques applied to blood vessel walls all generate tetrahedral meshes (structured or unstructured), resulting in poor accuracy in subsequent finite element calculations. Furthermore, because the blood vessel wall is a layered structure with different mechanical properties for the intima, media, and adventitia, unstructured meshes make it difficult to distinguish between different layers using node and element numbers during calculations, making accurate mechanical modeling difficult. Currently commonly used finite element simulation techniques such as the cohesive force model and extended finite element method all need to accurately describe the layered structure of the vascular wall. Unstructured grids cannot obtain the boundary information between layers and cannot regularly describe the layered structure in proportion to the thickness. Structured grid units must be generated for subsequent analysis.

[0005] The Chinese patent application "Finite element unstructured hexahedral mesh generation method" with application number CN202210884754.2 uses a traversal method to generate an unstructured hexahedral mesh from a full tetrahedral mesh model. This application can only generate unstructured meshes, not structured meshes. The Chinese patent application "Actual stratum full hexahedral mesh generation method and device" with application number CN201811241872.1 is a hexahedral mesh generated for the stratum, a solid structure without holes. This application generates a hexahedral mesh according to the rules after regularly resampling the actual stratum layers and generating the grid node coordinates. It can only be used for stacked entities, with strong targeting, weak generalization, and high computational cost.

[0006] The Chinese patent application with application number CN202311124316.7, "Blood vessel modeling method, device, computer equipment and storage medium", is a method for modeling the vascular cavity and blood vessel wall, which generates an unstructured tetrahedral mesh rather than a hexahedral mesh. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of the prior art and propose a method for generating a structured hexahedral grid of an individualized blood vessel wall.

[0008] In view of this, the present invention proposes a method for generating a structured hexahedral mesh of an individualized blood vessel wall, the method comprising:

[0009] Step s1: When the target aorta has no branches, proceed to the step of constructing the entity of the aorta wall; otherwise, proceed to the step of constructing the entity of the aorta wall and the step of constructing the entity of each branch vessel wall;

[0010] Step s2: assigning mesh seeds to the boundaries of the vascular wall entity and generating a structured hexahedral mesh of the vascular wall by lofting;

[0011] Step s3: Perform mesh checking by calculating the angle, aspect ratio coefficient, and geometric deviation coefficient to ensure that the mesh quality meets the calculation requirements.

[0012] Preferably, the physical construction of the aortic vessel wall in step s1 includes:

[0013] Step 1: Obtain the target aortic blood flow area from the CT image;

[0014] Step 2: Expand the aortic blood flow area outward to generate the aortic vessel wall area;

[0015] Step 3: Divide the aorta wall region into cross sections and obtain the contour lines of each cross section;

[0016] Step 4: For each subdivided contour line, obtain at least one feature point in the same proportion and output the coordinates of each feature point;

[0017] Step 5: Draw the corresponding guide line through the spline curve according to each feature point obtained;

[0018] Step 6: Loft the entity according to the contour line and guide line of the aortic outer wall to complete the entity construction of the aortic outer wall; loft and cut according to the contour line and guide line of the aortic inner wall to complete the entity construction of the aortic wall.

[0019] Preferably, the step 1 comprises:

[0020] Starting from a set of seed points in the blood flow area, the algorithm gradually expands to adjacent pixels according to the similarity of grayscale until it grows to all target blood flow areas;

[0021] Remove the blood flow area in non-target areas and fill the gaps during generation;

[0022] Smooth the entire area.

[0023] Preferably, the step 2 comprises:

[0024] The outermost layer of the blood flow domain is expanded outward by a set distance in the thickness direction. The expanded area includes the blood flow domain. A Boolean subtraction operation is performed on the expanded area and the blood flow domain to obtain the blood vessel wall area.

[0025] Preferably, the step 3 comprises:

[0026] The aorta wall region is segmented according to a specified distance and a specified number, and the contour line of the aorta outer wall and the contour line of the aorta inner wall are generated respectively.

[0027] Preferably, the step of constructing the physical structure of each branch vessel wall in step s1 includes:

[0028] Step 1: Obtain the target aorta blood flow area with branch vessels from the CT image;

[0029] Step 2: Select the blood flow area of ​​the aorta and expand it outward to generate the aortic vessel wall area;

[0030] Step 3: Divide the aorta wall into cross sections and obtain the contour lines of each cross section;

[0031] Step 4: For each subdivided contour line, obtain at least one feature point in the same proportion and output the coordinates of each feature point;

[0032] Step 5: Select feature points from each contour line and draw the corresponding guide line through the spline curve;

[0033] Step 6: Loft the entity according to the contour line and guide line of the aortic outer wall to complete the entity construction of the outer wall of the aorta;

[0034] Step 7: Expand the blood flow area of ​​the aorta with branched vessels outward to generate the aorta vessel wall area with branched vessels;

[0035] Step 8: Perform steps 9 to 12 on each branch vessel wall in sequence:

[0036] Step 9: Divide the branch vessel wall into cross sections and obtain the contour lines of each cross section;

[0037] Step 10: Output the coordinates of the feature points on the branch vessel wall contour line;

[0038] Step 11: Draw the scanning guide line based on the feature points of the branch blood vessel contour line;

[0039] Step 12: Scan according to the contour lines and guide lines of the branch vessel's outer wall, with the scanning starting point being the selected outer wall contour line and the scanning end point being the outer wall of the aorta, completing the physical construction of the branch vessel's outer wall; scan and cut according to the contour lines and guide lines of the branch vessel's inner wall, completing the physical construction of the branch vessel's wall;

[0040] Step 13: Loft the entity according to the contour line and guide line of the inner wall of the aorta to complete the entity construction of the aortic vessel wall.

[0041] Preferably, the step s2 includes:

[0042] A specified number of grid seeds are assigned to the boundaries of the vascular wall entity in the thickness direction, circumferential direction, and axial direction. When the target aorta has no branches, a layered structured hexahedral mesh is generated by lofting; when the target aorta has branches, aorta lofting generates a layered hexahedral mesh, and branch scanning generates a layered structured hexahedral mesh.

[0043] Preferably, the step s2 further comprises: dividing the blood vessel wall entity whose size and / or structural changes meet the set requirements into a plurality of sub-regions, and performing lofting or scanning according to the set lofting or scanning boundaries and sequence.

[0044] Preferably, step s3 includes:

[0045] Calculate the angle between each two faces of each tetrahedral element to ensure that the angle is not less than 10° and not greater than 160°;

[0046] Calculate the aspect ratio for each hexahedral element separately to ensure that the aspect ratio is not greater than 10;

[0047] Calculate the geometric deviation coefficient of each unit, that is, the ratio of the maximum gap between the unit edge and the geometric edge to the unit edge length, and ensure that the geometric deviation coefficient of no unit exceeds 0.2;

[0048] When the above three conditions are met at the same time, the mesh quality of the individualized blood vessel wall meets the calculation requirements.

[0049] Compared with the prior art, the advantages of the present invention are:

[0050] 1. The method of the present invention starts from medical imaging and integrates the complete process of generating individualized vascular wall finite element models.

[0051] 2. This method takes into account the hierarchical structural characteristics of the blood vessel wall, and the generated mesh is hierarchical.

[0052] 3. The method of the present invention can generate a layered structured hexahedral mesh for unbranched blood vessel walls, and a regularized hexahedral mesh for complex three-dimensional entities such as blood vessel walls with holes and branches. This method has weak shape requirements, strong generalization, and low computational cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG1(a) is a flow chart of a method for generating a structured hexahedral mesh for an aorta without branches according to the present invention; FIG1(b) is a flow chart of a method for generating a structured hexahedral mesh for an aorta with branches according to the present invention;

[0054] Figure 2 It is the area of ​​the aortic vessel wall;

[0055] Figure 3 It is the outline of the aorta wall and its cross section;

[0056] Figure 4 It is the guide wire for aortic layout;

[0057] Figure 5 It is the entity of the aortic vessel wall and aortic blood flow basin after lofting;

[0058] Figure 6 It is the entity of the aortic vessel wall after lofting and resection;

[0059] Figure 7 is the structured hexahedral mesh of the aorta vessel wall;

[0060] Figure 8 It is the area of ​​the aorta blood flow with branch vessels;

[0061] Figure 9 It is the outline of each cross section of the branch vessel wall;

[0062] Figure 10 It draws the guide line for scanning based on the outline of branch blood vessels;

[0063] Figure 11 It is the outer wall entity of the branch vessel wall after scanning;

[0064] Figure 12 It is a physical scan of the branch vessel wall after resection;

[0065] Figure 13 This is the final hexahedral mesh of the aorta with branched vessels. DETAILED DESCRIPTION

[0066] In finite element simulation, a mesh divides a continuum into a finite number of elements, which are interconnected through nodes. The physical behavior of each element is described using a mathematical model, thus approximately representing the physical characteristics of the entire continuum. Therefore, mesh generation is crucial in finite element simulation.

[0067] Because biological tissues such as blood vessels are located within the body, they are difficult to observe directly. Their geometric features are often obtained through imaging methods such as X-rays, CT scans, and ultrasound. Because biological tissues such as blood vessels need to meet the various functional requirements of the human body, their geometric shapes are very complex. For the aorta, its geometric shape has the following characteristics: (1) different diameters at different locations, (2) different degrees of curvature at different locations, and (3) the aorta is connected to many branching blood vessels. Therefore, for the aorta, an object with a complex geometric shape, mesh generation is difficult and complex.

[0068] Currently, when meshing blood vessel walls, most of the generated meshes are tetrahedral meshes. However, if tetrahedral meshes are used for finite element calculations, the calculation accuracy is low, while the accuracy of hexahedral meshes is higher. Therefore, it is necessary to generate hexahedral meshes for the blood vessel walls. In addition, since the blood vessel wall is a layered structure, not only does it have three layers of structure with different mechanical properties, namely the intima, media, and adventitia, but the interior of the media and adventitia is also a layered structure, with collagen fibers connecting the elastic fiber sheets. Therefore, modeling the aorta as a layered structure in finite element calculations not only helps to assign different material properties to different membranes and simulate real tissues, but also helps to construct a layered structure between layers, which plays an important role in simulating pathological processes such as the expansion and rupture of aortic dissection.

[0069] Currently, when meshes are generated for blood vessel walls, most of the generated meshes are unstructured. Unstructured meshes are highly flexible, but are prone to poor quality units and uneven size transitions, resulting in insufficient calculation accuracy. In addition, in unstructured meshes, the size of each unit is not controlled, and there is no unified relationship in the numbering between a node (or unit) and its adjacent nodes (or units), and the node numbers (or unit numbers) are all random in arrangement order. This makes it difficult to control the mechanical or motion behavior of a certain (or certain) node (or unit) through the node number (unit number) when writing a finite element subroutine, which is extremely unfavorable for the secondary development of the finite element. In the structured mesh generated by this patent, adjacent nodes (or units) have a sequential relationship. During secondary development, it is only necessary to specify the range of nodes (or units) to control the mechanical or motion behavior of a certain (or certain) node (or unit).

[0070] Currently, most of the mesh generation for vascular walls focuses only on the aorta and fails to consider the branch vessels. The blood flow in the aorta will flow into the branch vessels to supply blood downstream. The presence of branch vessels will also affect the configuration of the aorta. The branch vessels and the aorta directly interact with each other to maintain the mechanical stability of the vascular system. Therefore, in finite element simulation, the influence of branch vessels cannot be ignored. However, there is currently no method for generating hexahedral meshes for aortas with branch vessels, let alone layered hexahedral mesh generation. This application develops a method for generating layered hexahedral meshes for aortas with branches, and can specify the range of node (or unit) numbers for each layer of the branch module and the aorta module, making it possible to describe the layer-specific behavior in subsequent calculations. The aortic mesh generated using this method can be used to construct cohesion models based on individualized patient vascular configurations, extended finite elements, and other finite element simulation calculations, because these methods need to accurately describe the layered structure of the vascular wall. Unstructured meshes cannot obtain the boundary information between layers and cannot regularly describe the layered structure in proportion to the thickness. Structured mesh units need to be generated before subsequent analysis can be performed.

[0071] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0072] Example 1

[0073] An embodiment of the present invention provides a method for generating a structured hexahedral mesh of an individualized blood vessel wall. FIG1( a ) shows a flow chart of the method for generating a structured hexahedral mesh for an aorta without branches. The method includes the following specific steps:

[0074] Part 1:

[0075] 1. Acquire the aortic blood flow region from CT images. CT images distinguish different structures and tissues by grayscale. Starting with a set of seed points in the blood flow region, the process gradually expands to adjacent pixels based on grayscale similarity until all target blood flow regions are captured. The generated blood flow regions are then manually inspected, non-target blood flow regions are removed, gaps in the generated regions are filled, and finally the entire region is smoothed.

[0076] 2. Such as Figure 2 As shown, the aortic blood flow domain is expanded outward to generate the vessel wall region. The blood flow domain generated in the previous step is expanded outward by a distance in the thickness direction. This distance is typically 1-2 mm, and the thickness of the vessel wall varies at different locations. The expanded region contains both the blood flow domain and the vessel wall region. A Boolean subtraction operation is performed on the expanded region and the blood flow domain to obtain the vessel wall region.

[0077] 3. Such as Figure 3As shown, the aorta wall is segmented into cross sections to obtain the segmentation contour lines of each cross section. The target vessel wall is segmented according to a specified distance and a specified number to generate the contour lines of the outer and inner walls of the vessel.

[0078] 4. Output the coordinates of the feature points on the aortic wall contour. For each contour line, generate at least one feature point (in one embodiment, ≥4) in the same proportion and starting from the same starting point, and output the coordinates of these feature points. It should be noted that the more feature points selected, the better. The more feature points and guide lines, the more similar the constructed vessel wall will be to the CT image. However, selecting one feature point and constructing one guide line is sufficient to roughly reconstruct the actual curvature of the aorta.

[0079] 5. Such as Figure 4 As shown in the figure, according to the coordinates of the feature points, the guide lines for the lofting are drawn. A feature point is selected on each contour, and these feature points are used to draw guide lines through spline curves for subsequent lofting.

[0080] 6. Such as Figure 5 As shown, the entity is lofted according to the contour line and guide line of the outer wall of the aorta to complete the entity construction of the outer wall of the aorta.

[0081] 7. Such as Figure 6 As shown, lofting and cutting are performed according to the contour line and guide line of the inner wall of the aorta to complete the entity construction of the aortic vessel wall.

[0082] 8. Assigning mesh seeds to each boundary of the vascular wall entity. Assign a specified number of mesh seeds to each boundary in the thickness direction, circumferential direction, and axial direction of the vascular wall entity.

[0083] 9. Such as Figure 7 As shown, lofting generates a structured hexahedral mesh of the vessel wall. Using the mesh seed from the previous step, lofting generates a structured hexahedral mesh. When the vessel wall model is large and has many structural variations, it is not possible to generate the mesh all at once. Therefore, the model needs to be segmented into multiple subregions. Meshes are generated for each subregion one by one, following the specified scanning or lofting boundaries and sequence. For the aorta with branches, the branches and the aorta need to be split into two parts, and each part needs to be meshed separately.

[0084] 10. Perform mesh inspection to ensure that the mesh quality meets the calculation requirements. Specifically:

[0085] 1) Calculate the angle between each two faces of each tetrahedral unit to ensure that the angle is not less than 10° and not greater than 160°;

[0086] 2) Calculate the aspect ratio for each hexahedral unit to ensure that the aspect ratio is no greater than 10;

[0087] 3) Calculate the geometric deviation coefficient of each unit, that is, the ratio of the maximum gap between the unit edge and the geometric edge to the unit edge length, and ensure that the geometric deviation coefficient of no unit exceeds 0.2;

[0088] When the above three conditions are met at the same time, the mesh quality of all cells of the individualized vascular wall meets the calculation requirements.

[0089] The second part is to generate the mesh of the aorta with branched vessels, as shown in Figure 1(b). The method is as follows:

[0090] 1. Obtain the blood flow region of the aorta with branching vessels from the CT image. Starting from a set of seed points in the blood flow region, the region is gradually expanded to adjacent pixels based on grayscale similarity until all target blood flow regions are reached. The generated blood flow regions are then manually inspected, non-target blood flow regions are removed, gaps in the generated regions are filled, and finally the entire region is smoothed.

[0091] 2. Such as Figure 8 As shown, the blood flow domain of the aorta with branched vessels is expanded outward to generate the aortic wall region with branched vessels. For the blood flow domain generated in the previous step, the outermost layer of the blood flow domain is expanded outward by a certain distance in the thickness direction. This distance is generally 1-2 mm, and the thickness of the vessel wall varies at different locations. The expanded region contains both the blood flow domain and the vessel wall region. A Boolean subtraction operation is performed on the expanded region and the blood flow domain to obtain the vessel wall region.

[0092] 3. Such as Figure 9 As shown, the branched blood vessel wall is segmented into cross sections to obtain the segmented contour lines of each cross section. The target branched blood vessel wall is segmented according to the specified distance and the specified number to generate the contour lines of the blood vessel outer wall and the blood vessel inner wall.

[0093] 4. Output the coordinates of the feature points on the branch vessel wall contours. For each contour, generate at least one feature point (in one embodiment, ≥ 4) in the same proportion and starting from the same starting point, and output the coordinates of the feature points. It should be noted that the more feature points selected, the better. The more feature points, the more guide lines, and the more similar the constructed vessel wall is to the CT image. However, even selecting a single feature point and subsequently constructing a single guide line will already be sufficient to reflect the curvature of the aorta.

[0094] 5. Such as Figure 10As shown, feature points are generated based on the contours of the branch vessels, and guide lines for scanning are drawn. For each contour line on the branch vessel, at least one feature point (in one embodiment, ≥ 4) is generated, using the same proportions and starting point. The coordinates of the feature points are then output. A feature point is selected from each contour, and these feature points are used to draw a guide line using a spline curve for subsequent scanning.

[0095] After completing the solid lofting of the aortic outer wall, proceed with:

[0096] 6. Such as Figure 11 As shown, the entity is scanned according to the contour line and guide line of the outer wall of the branch blood vessel to complete the construction of the outer wall entity of the branch blood vessel wall.

[0097] 7. Such as Figure 12 As shown, scanning and cutting are performed according to the contour lines and guide lines of the inner wall of the branch blood vessel to complete the construction of the branch blood vessel wall entity.

[0098] After the above two steps, the step of lofting and cutting the inner wall of the aorta is performed.

[0099] Finally, the structured hexahedral mesh generation of the aorta wall with branch vessels is completed. Figure 13 As shown in FIG, the branch part is structured, and the aorta part is layered and unstructured, that is, a regular hexahedral mesh is generated for complex three-dimensional entities such as blood vessel walls with holes and branches.

[0100] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for generating a structured hexahedral mesh of an individualized blood vessel wall, the method comprising: Step s1: When the target aorta has no branches, proceed to the step of constructing the entity of the aorta wall; otherwise, proceed to the step of constructing the entity of the aorta wall and the step of constructing the entity of each branch vessel wall; Step s2: assigning mesh seeds to the boundaries of the vascular wall entity, and generating a structured hexahedral mesh of the vascular wall by lofting or scanning; Step s3: Perform mesh checking by calculating the angle, aspect ratio coefficient, and geometric deviation coefficient to ensure that the mesh quality meets the calculation requirements.

2. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 1, characterized in that: The physical construction step of the aorta vessel wall in step s1 includes: Step 1: Obtain the target aortic blood flow area from the CT image; Step 2: Expand the aortic blood flow area outward to generate the aortic vessel wall area; Step 3: Divide the aorta wall region into cross sections and obtain the contour lines of each cross section; Step 4: For each subdivided contour line, obtain at least one feature point in the same proportion and output the coordinates of each feature point; Step 5: Draw the corresponding guide line through the spline curve according to each feature point obtained; Step 6: Loft the entity according to the contour line and guide line of the aortic outer wall to complete the entity construction of the aortic outer wall; loft and cut according to the contour line and guide line of the aortic inner wall to complete the entity construction of the aortic wall.

3. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 2, wherein: The step 1 comprises: Starting from a set of seed points in the blood flow area, the algorithm gradually expands to adjacent pixels according to the similarity of grayscale until it grows to all target blood flow areas; Remove the blood flow area in non-target areas and fill the gaps during generation; Smooth the entire area.

4. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 2, wherein: The step 2 includes: The outermost layer of the blood flow domain is expanded outward by a set distance in the thickness direction. The expanded area includes the blood flow domain. A Boolean subtraction operation is performed on the expanded area and the blood flow domain to obtain the blood vessel wall area.

5. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 2, wherein: The step 3 comprises: The aorta wall region is segmented according to a specified distance and a specified number, and the contour line of the aorta outer wall and the contour line of the aorta inner wall are generated respectively.

6. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 1, wherein: The step of constructing the entity of each branch blood vessel wall in step s1 includes: Step 1: Obtain the target aorta blood flow area with branch vessels from the CT image; Step 2: Select the blood flow area of ​​the aorta and expand it outward to generate the aortic vessel wall area; Step 3: Divide the aorta wall into cross sections and obtain the contour lines of each cross section; Step 4: For each subdivided contour line, obtain at least one feature point in the same proportion and output the coordinates of each feature point; Step 5: Select feature points from each contour line and draw the corresponding guide line through the spline curve; Step 6: Loft the entity according to the contour line and guide line of the aortic outer wall to complete the entity construction of the outer wall of the aorta; Step 7: Expand the blood flow area of ​​the aorta with branched vessels outward to generate the aorta vessel wall area with branched vessels; Step 8: Perform steps 9 to 12 on each branch vessel wall in sequence: Step 9: Divide the branch vessel wall into cross sections and obtain the contour lines of each cross section; Step 10: Output the coordinates of the feature points on the branch vessel wall contour line; Step 11: Draw the scanning guide line based on the feature points of the branch blood vessel contour line; Step 12: Scan according to the contour lines and guide lines of the branch vessel's outer wall, with the scanning starting point being the selected outer wall contour line and the scanning end point being the outer wall of the aorta, completing the physical construction of the branch vessel's outer wall; scan and cut according to the contour lines and guide lines of the branch vessel's inner wall, completing the physical construction of the branch vessel's wall; Step 13: Loft the entity according to the contour line and guide line of the inner wall of the aorta to complete the entity construction of the aortic vessel wall.

7. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 1, wherein: The step s2 comprises: A specified number of grid seeds are assigned to the boundaries of the vascular wall entity in the thickness direction, circumferential direction, and axial direction. When the target aorta has no branches, a layered structured hexahedral mesh is generated by lofting; when the target aorta has branches, aorta lofting generates a layered hexahedral mesh, and branch scanning generates a layered structured hexahedral mesh.

8. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 7, characterized in that: Said step s2 further comprises: dividing the blood vessel wall entity whose size and / or structural changes meet the set requirements into a plurality of sub-regions, and performing lofting and scanning according to the set lofting or scanning boundaries and sequence.

9. The method for generating a structured hexahedral mesh of an individualized blood vessel wall according to claim 7, wherein: The step s3 comprises: Calculate the angle between each two faces of each tetrahedral element to ensure that the angle is not less than 10° and not greater than 160°; Calculate the aspect ratio for each hexahedral element separately to ensure that the aspect ratio is no greater than 10; Calculate the geometric deviation coefficient of each unit, that is, the ratio of the maximum gap between the unit edge and the geometric edge to the unit edge length, and ensure that the geometric deviation coefficient of no unit exceeds 0.2; When the above three conditions are met at the same time, the mesh quality of the individualized blood vessel wall meets the calculation requirements.

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