A method for constructing a refined Chinese human head digital model

Abstract

The present application belongs to the technical field of human simulation model, and particularly relates to a refined Chinese human head digital model construction method, which comprises medical image acquisition, three-dimensional reconstruction, unit discretization of detailed cranium and brain structure and partition, material attribute assignment, connection relationship definition and processing of fluid-structure coupling interface between cranium and brain, and can solve the problem of poor existing Chinese human head digital model.

Description

Technical Field

[0001] This invention belongs to the field of human body simulation model technology, and in particular relates to a method for constructing a refined digital model of the Chinese human head. Background Technology

[0002] Data from Chinese road traffic accidents shows that the head is the part of the human body with the highest risk of injury, and head injuries are also the most fatal form of injury. Currently, new vehicle testing procedures and regulations in various countries use physical dummies to evaluate head injuries. However, simple mechanical structures and dynamic damage indicators cannot predict complex head injuries. With the rapid development of computer simulation technology, more refined digital head models are beginning to be widely used in the study of head injury mechanisms, using virtual assessment methods to ensure road traffic safety.

[0003] Currently, most digital head models are developed based on the characteristics of European and American anatomy. Related research indicates that there are differences in the geometric dimensions and material properties between the heads of Europeans and Americans and those of Chinese people, leading to a mismatch between the calculation results of European and American head models and the actual head injury responses of Chinese individuals. Furthermore, existing methods for constructing digital head models generally suffer from low geometric data accuracy, high head structural complexity, and difficulty in simulating brain tissue responses. Therefore, it is necessary to establish a highly biorealistic digital head model with detailed anatomical structure based on Chinese human head data. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a method for constructing a refined digital model of the Chinese human head, so as to solve the problem of the poor quality of existing digital models of the Chinese human head.

[0005] The basic solution provided by this invention is a method for constructing a refined digital model of the Chinese human head, comprising:

[0006] S1: Acquire computed tomography (CT) and magnetic resonance imaging (MRI) images of the human skull and preprocess them to generate a geometric model of the head;

[0007] S2: Based on the head geometry model, a solid mesh of brain tissue is created using the Block-control method, and solid meshes of bones and cerebrospinal fluid are also created to generate the head solid mesh;

[0008] S3: Assign corresponding material properties to each structure in the head solid mesh, and connect them to common nodes;

[0009] S4: Define the cerebrospinal fluid and the area enclosed by the cerebrospinal fluid as the fluid domain and the blank domain. Use state equations to define the state of the fluid domain and the blank domain. Use a preset contact algorithm to define the coupling mechanism for the cerebrospinal fluid, skull and brain tissue. Simulate the fluid-structure interaction between the cerebrospinal fluid, skull and brain tissue. Combine with skin solid mesh and facial bone solid mesh to generate a finite element digital model of the human head.

[0010] Furthermore, S1 includes:

[0011] S1-1: Select computed tomography and magnetic resonance imaging images of the skull of a human body that meets the physical characteristics of 50% of Chinese individuals.

[0012] S1-2: Point cloud data of the scalp skin and bones are segmented from the computed tomography images based on threshold segmentation and stored in their respective layers; the bones include the skull and facial bones.

[0013] S1-3: Obtain point cloud data of detailed regions of brain tissue from MRI images based on threshold segmentation and save them to different layers;

[0014] S1-4: Repair the acquired head skin layer, bone layer and brain tissue layer. After the repair is completed, slice and stack the slices to reconstruct the geometric contours of each anatomical structure of the head.

[0015] S1-5: Preprocess the geometric contours of the scalp skin, bones, and brain tissue to obtain the geometric models of the scalp skin, bones, and brain tissue, and combine them to generate the head geometric model.

[0016] Furthermore, S2 includes:

[0017] S2-1: Create a Block and cut its edges to fit the geometry of the brain tissue.

[0018] S2-2: Based on the geometric model of brain tissue, nodes are created on the surface and inside of brain tissue. The nodes of the Block are mapped to the nodes on the surface and inside of the brain tissue to establish a hexahedral brain tissue solid mesh that matches the geometric surface of the brain tissue.

[0019] S2-3: Project the outer surface nodes of the brain tissue onto the inner surface of the skull to establish a three-layer hexahedral mesh unit. From the inside to the outside, the three layers of hexahedral mesh units correspond to the cortical bone, the intermediate cancellous bone, and the outer cortical bone, respectively, to represent the solid mesh of the skull.

[0020] S2-4: Generate temporary shell units based on the mesh units of the skull and brain tissue, establish a cerebrospinal fluid solid mesh in the area surrounded by the shell units, delete the temporary shell units after the cerebrospinal fluid solid mesh is generated; and establish a facial bone solid mesh according to each structure of the facial bone based on the stretching method.

[0021] S2-5: Establish a solid mesh for the skin based on the outer surface nodes of the skull and facial bones;

[0022] S2-6: Based on the established surface of each entity mesh, shell elements are created to simulate the three layers of meninges, falx cerebri, tentorium cerebelli, and facial cortical bone.

[0023] Furthermore, S3 includes:

[0024] S3-1: Apply viscoelastic material to the solid mesh of brain tissue and solid mesh of cerebrospinal fluid, apply elastic material to the shell unit, apply elastoplastic material to the solid mesh of skull and solid mesh of facial bone, and apply fibrous material to the solid mesh of skin.

[0025] S3-2: Common nodes are used to connect the various detailed regions of the brain tissue, the skull and facial bones, and the skin, skull, and facial bones.

[0026] Furthermore, S3 also includes:

[0027] S3-3: Select the nodes on the inner surface of the skin in the transition region to establish a node set, and establish a biased binding contact between the node set and the shell unit on the surface of the skull to bind the nodes in the skin transition region to the skull.

[0028] Furthermore, S4 includes:

[0029] S4-1: Define the area enclosed by cerebrospinal fluid as a blank domain and the cerebrospinal fluid as a fluid domain. Simultaneously initialize the blank domain and the fluid domain and assign them a viscoelastic material.

[0030] S4-2: Use the Lagrange algorithm for the skull and brain tissue, and the ALE algorithm for the fluid domain and the blank domain. Define the state equations for the fluid domain and the blank domain.

[0031] S4-3: The coupling relationship between cerebrospinal fluid-skull and cerebrospinal fluid-brain tissue is defined using a fluid-structure interaction contact algorithm based on penalty function.

[0032] Furthermore, S4-2 specifically includes:

[0033] S4-2-1: Select the cell algorithm with ELFORM=12. The fluid domain and blank domain adopt the formulas for the conservation of mass, momentum, and energy as follows:

[0034]

[0035]

[0036]

[0037] in, Indicates density, Indicates time, Indicates fluid velocity. Represents the velocity in the reference coordinate system. Indicates Cauchy stress, denoted by force density, e represents internal energy per unit volume.

[0038] S4-2-2: The state equations for the fluid domain and the blank domain are defined using *EOS_GRUNEISEN, specifically as follows:

[0039]

[0040] in, Indicates the shock wave velocity. Represents the velocity of a particle. Indicates the speed of sound in the material. , , These are the three coefficients representing the polynomial fit between the shock wave velocity and the particle velocity;

[0041] S4-2-3: Using the *EOS_GRUNEISEN definition, establish the relationship between pressure and volume of a fluid under high pressure variable rate conditions, under compressible conditions:

[0042]

[0043] Under tension:

[0044]

[0045] in, , It's density. It is the initial density. It is the Grüneisen parameter of the material. Yes The first-order volume correction factor, It is the internal energy per unit volume.

[0046] The principles and advantages of this invention are as follows: The technical solution process in this application includes medical image acquisition, three-dimensional reconstruction, unit discretization of detailed cranial structure and regions, material property assignment, connection relationship definition, and fluid-structure interaction interface processing between the cranium and brain. Specifically, firstly, volunteers meeting the 50th percentile physical characteristics of China are selected, and computed tomography (CT) and magnetic resonance imaging (MRI) images are acquired. Pixel segmentation, geometric extraction, smoothing, and symmetry processing are performed using medical image processing software to establish a geometric model of the head with detailed anatomical structure. Then, based on the Block-control method, solid units of brain tissue are rapidly established, and structures such as the skull, facial bones, skin, and cerebrospinal fluid are established through projection, stretching, and filling, ensuring that nodes in different structural regions correspond to each other during unit discretization. Next, material properties are assigned to each structure of the head. The skin, bones, and brain tissue are basically connected using shared nodes. A rotational hinge is established between the mandible and zygomatic bone in the facial bones to simulate the movement of the mandible. Automatic face-to-face contact and biased binding contact are established between the skin and skull to ensure smooth connection in transition areas. Finally, the cerebrospinal fluid and the area enclosed by the cerebrospinal fluid are defined as the fluid domain and the blank domain, respectively. The ALE element algorithm is applied and the state equation is defined. The coupling mechanism between the cerebrospinal fluid and the skull / brain tissue is then defined. The fluid-structure interaction relationship between the skull, cerebrospinal fluid and brain tissue is simulated using the ALE method. Finally, the model is coupled and assembled with the overall solid model to form a finite element digital model of the Chinese human head.

[0047] Therefore, the advantages of this application are:

[0048] 1. This solution designs a complete development process for the Chinese human head model, which can realize the fine modeling of the Chinese human head. The completed digital head model has high mesh quality and detailed cranial structure partitioning. It can be used for simulation in the fields of collision safety, medical health, sports and other fields to reflect the real kinematic and mechanical response of the internal structure of the head and accurately describe the head injury of the Chinese human body.

[0049] 2. This scheme employs a realistic modeling method for the skull sandwich structure, consisting of inner cortical bone, intermediate cancellous bone, and outer cortical bone. First, a two-dimensional mesh is created on the inner surface of the skull. Then, three layers of solid elements are established through extrusion. Since the skull is a heterogeneous model, it is divided into cortical bone and cancellous bone based on porosity. The porosity of cortical bone is 5-10%, while that of cancellous bone is 50-95%. Therefore, the three layers of elements from the inside out simulate the inner cortical bone, intermediate cancellous bone, and outer cortical bone, and are given different material properties to characterize the sandwich structure of the skull.

[0050] 3. This solution features a reasonable connection method for various head structures. Most of the head's skin, bones, and brain tissue structures utilize shared-node connections. Automatic face-to-face contact is defined between the skin and skull to prevent penetration of non-shared-node connection areas during simulation. Offset binding contacts are established between the skin's inner surface node set in transition regions and the skull entity to ensure a smooth transition between shared-node and non-shared-node areas of the skin and skull.

[0051] 4. This scheme possesses an advanced skull-cerebrospinal fluid (CSF)-brain tissue coupling mechanism. CSF is defined as a fluid domain, and the area enclosed by CSF is defined as a blank domain. The ALE element algorithm is employed, and a state equation is defined. Mesh nodes within both the fluid and blank domains can flow, ensuring automatic mesh redrawing to avoid distortion during large deformation calculations. A fluid-structure interaction (FSI) contact algorithm based on penalty functions is used to define the coupling relationship between CSF and skull / brain tissue, allowing CSF to slide freely tangentially on the inner surface of the skull and the outer surface of the brain tissue, but without separation. This allows for the transmission of radial tensile and compressive forces, ensuring that no gaps appear on the opposite side of the impact when the head is subjected to impact, thus more reasonably simulating the movement of CSF at the contact interface. Attached Figure Description

[0052] Figure 1 This is a flowchart of an embodiment of the present invention;

[0053] Figure 2 This is an exploded isometric view of the head model according to an embodiment of the present invention;

[0054] Figure 3 This is a side view of the head skeleton according to an embodiment of the present invention;

[0055] Figure 4 This is a side view of the head brain tissue structure according to an embodiment of the present invention;

[0056] Figure 5 This is a flowchart illustrating the construction process of fluid-structure interaction between cerebrospinal fluid, skull, and brain tissue in an embodiment of the present invention. Detailed Implementation

[0057] The following detailed description illustrates the specific implementation method:

[0058] The markings in the accompanying drawings of the instruction manual include: 1. Scalp skin, 201. External cortical bone, 202. Intermediate cancellous bone, 203. Internal cortical bone, 3. Mastoid process, 4. Zygomatic bone, 5. Ethmoid bone, 6. Nasal bone, 7. Maxilla, 8. Teeth, 9. Mandible, 10. Cerebrospinal fluid, 11. Superior sagittal sinus, 1201. Cerebral white matter, 1202. Cerebral gray matter, 13. Corpus callosum, 14. Lateral ventricle, 15. Thalamus, 16. Third ventricle, 17. Cerebellum, 18. Brainstem, 19. Tentorial region of cerebellum, 20. Falx cerebri.

[0059] The basic implementation examples are as follows: Figure 1As shown: A method for constructing a refined digital model of the Chinese human head, including:

[0060] S1: Acquire computed tomography (CT) and magnetic resonance imaging (MRI) images of the human skull, and preprocess them to generate a geometric model of the head; wherein, S1 includes:

[0061] S1-1: Select computed tomography and magnetic resonance imaging images of the skull of a human body that meets the physical characteristics of 50% of Chinese individuals.

[0062] S1-2: Point cloud data of the head skin 1 and bones are segmented from the computed tomography image based on threshold segmentation and stored in their respective layers; the bones include the skull and facial bones;

[0063] S1-3: Obtain point cloud data of detailed regions of brain tissue from MRI images based on threshold segmentation and save them to different layers;

[0064] S1-4: Repair the acquired head skin layer 1, bone layer and brain tissue layer. After the repair is completed, slice and stack the slices to reconstruct the geometric contours of each anatomical structure of the head.

[0065] S1-5: Preprocess the geometric contours of the scalp skin, bones, and brain tissue to obtain the geometric models of the scalp skin, bones, and brain tissue, and combine them to generate the head geometric model.

[0066] In this embodiment, users meeting 50% of the physical characteristics of Chinese individuals first undergo computed tomography (CT) and magnetic resonance imaging (MRI). The scan interval for CT and MRI scans does not exceed 0.7 mm, and the image resolution is not less than 512. 512, to obtain CT and MRI images, namely computed tomography (CT) images and magnetic resonance imaging (MRI) images.

[0067] The acquired CT and MRI images were imported into the medical image processing software Mimics. The threshold ranges for different tissues were set using the Threshold function under SEGMENT. In this application, the extraction threshold ranges were adjusted as follows: and Point cloud data of the head skin 1 and bones are segmented from CT images and stored in their respective layers. In this application, the human head skeleton includes the skull and facial bones, which are composed of multiple bone structures, such as the mastoid process 3, zygomatic bone 4, ethmoid bone 5, nasal bone 6, maxilla 7, teeth 8, mandible 9, etc. In this application, they are uniformly considered as the skull and facial bones. Similarly, point cloud data of detailed brain tissue partitions are obtained from MRI images based on threshold segmentation and stored in different layers. For example, detailed brain tissue partitions include the cerebrum 17, cerebellum 18, brainstem 18, corpus callosum 13, thalamus 15, third ventricle 16, lateral ventricle 14, etc.

[0068] To describe the various structures of the human head in more detail, such as Figure 2 , Figure 3 and Figure 4 As shown, an exploded axonometric view, a side view, and a schematic diagram of brain tissue of the human head are given respectively. Figure 2 In the diagram, it can be accurately identified that the human head, from the outside to the inside, consists of scalp skin 1, skull, cerebrospinal fluid 10, superior sagittal sinus 11, cerebrum, tentorium cerebelli 19, falx cerebri 20, the skull includes external cortical bone 201, intermediate cancellous bone 202, and internal cortical bone 203, and the cerebrum includes cerebral white matter 1201 and cerebral gray matter 1202. Figure 3 The composition of the facial bones can be accurately identified as follows: 3. mastoid process; 4. zygomatic bone; 5. ethmoid bone; 6. nasal bone; 7. maxilla; 8. teeth; 9. mandible. Figure 4 The brain tissues of the head include the corpus callosum 13, lateral ventricles 14, thalamus 15, third ventricle 16, cerebellum 17, and brainstem 18.

[0069] After acquiring the point cloud data of each structure, the EditMark function is used to perform operations such as filling and erasing to repair the surface masks of the head skin, bones, and brain tissue frame by frame, so that the edges of the skin, bones, and brain tissue in each frame are closed and smooth. Then, the Caculate function is used to select the processed layers and stack them to lay the foundation for reconstructing the geometric contours of each anatomical structure. The stacked images are then exported as STL files and imported into the 3D scanning and analysis software Geomagic. The smoothness of the model is improved by quick smoothing, and then smoothing is performed by removing features and sanding to remove noise and burrs from local geometric surfaces. The hole filling function is used to repair geometric gaps to obtain continuous closed surfaces and perform symmetry processing to obtain the geometric models of the head skin, bones, and brain tissue. These are then combined to generate the head geometric model.

[0070] S2: Based on the head geometry model, a solid mesh of brain tissue is created using the Block-control method, along with solid meshes of bones and cerebrospinal fluid, to generate the head solid mesh; S2 includes:

[0071] S2-1: Create a Block and cut its edges to fit the geometry of the brain tissue.

[0072] S2-2: Based on the geometric model of brain tissue, nodes are created on the surface and inside of brain tissue. The nodes of the Block are mapped to the nodes on the surface and inside of the brain tissue to establish a hexahedral brain tissue solid mesh that matches the geometric surface of the brain tissue.

[0073] S2-3: Project the outer surface nodes of the brain tissue onto the inner surface of the skull to establish a three-layer hexahedral mesh unit. From the inside to the outside, the three layers of hexahedral mesh units correspond to the cortical bone, the intermediate cancellous bone, and the outer cortical bone, respectively, to represent the solid mesh of the skull.

[0074] S2-4: Generate temporary shell units based on the mesh units of the skull and brain tissue, establish a cerebrospinal fluid solid mesh in the area surrounded by the shell units, delete the temporary shell units after the cerebrospinal fluid solid mesh is generated; and establish a facial bone solid mesh according to each structure of the facial bone based on the stretching method.

[0075] S2-5: Establish a solid mesh for the skin based on the outer surface nodes of the skull and facial bones;

[0076] S2-6: Based on the established surface of each entity mesh, shell elements are created to simulate the three layers of meninges, falx cerebri, tentorium cerebelli, and facial cortical bone.

[0077] In this step of the embodiment, the purpose is to create the physical mesh structure of various tissues of the Chinese human head. First, the relevant model files of the generated brain tissue geometric model are imported into Ansys ICEM CFD software. In this software, a block is created and divided along different edges to fit the geometric surface of the brain tissue. Nodes are created on the surface and inside of the brain tissue. The nodes of the block are mapped to the nodes on the surface and inside of the brain tissue, thereby establishing a regular hexahedral block that matches the geometric surface of the cerebrum, cerebellum 17, and brainstem 18 in the brain tissue. The number of mesh nodes on each side of the block is adjusted according to each brain tissue to establish the physical mesh of the brain tissue.

[0078] After the solid mesh of the brain tissue was established, HyperMesh software was used to divide the brain regions into corresponding areas such as gray matter 1202, white matter 1201, corpus callosum 13, thalamus 15, third ventricle 16, and lateral ventricle 14, based on detailed brain tissue partitioning extracted from MRI images. The nodes on the outer surface of the brain tissue were projected onto the inner surface of the skull, establishing a three-layer hexahedral unit. From the inside out, these three layers correspond to the inner cortical bone 203, intermediate cancellous bone 202, and outer cortical bone 201, thus characterizing the sandwich structure of the skull. Solid mesh units of the skull are established. After the solid mesh of the skull is established, temporary shell units are generated from the mesh units of the skull and brain tissue. Solid mesh units of cerebrospinal fluid 10 are established in the area surrounded by the shell units. After the solid mesh of cerebrospinal fluid 10 is generated, the temporary shell units mentioned above are deleted. Solid mesh units of the facial bones are established based on hexahedral mesh units according to the various structures of the facial bones. Solid mesh units of the skin are then established based on the outer surface nodes of the skull and facial bones. Finally, shell units are created based on the surfaces of the established solid meshes to simulate the three layers of meninges, falx cerebri 20, tentorium cerebelli 19, and the cortical bone of the facial bones.

[0079] S3: Assign corresponding material properties to each microstructure in the head solid mesh, and perform common node connections; wherein, S3 includes:

[0080] S3-1: Apply viscoelastic material to the solid mesh of brain tissue and solid mesh of cerebrospinal fluid, apply elastic material to the shell unit, apply elastoplastic material to the solid mesh of skull and solid mesh of facial bone, and apply fibrous material to the solid mesh of skin.

[0081] S3-2: Common nodes are used to connect the various detailed regions of the brain tissue, the skull and facial bones, and the skin, skull, and facial bones.

[0082] In this embodiment, the solid mesh of brain tissue and cerebrospinal fluid in HyperMesh software is given a viscoelastic material *MAT_KELVIN-MAXWELL-VISCOELASTIC, and the shell elements that make up the meninges, falx cerebri 20, tentorium cerebelli 19, etc. are given an elastic material *MAT_ELASTIC. The detailed partitions of the brain tissue are connected to each other by common nodes. For the solid mesh elements of the skull and facial bones, the elastic-plastic material *MAT_PIECEWISE_LINEAR_PLASTICITY is given, and the skull and facial bones are connected by common nodes. At the same time, the mandible 9 and zygomatic bone 4 of the facial bones are locally stiffened near the edge of the skull, and hinge connections are defined to simulate the normal rotation relationship of the mandible 9.

[0083] The skin solid mesh is assigned the fiber material *MAT_FABRIC. The connection areas between the skin and the skull and facial bones adopt a common node approach. A shell element is automatically generated on the skull surface and assigned the material *MAT_NULL. Then, the automatic surface contact between the skin solid mesh and the skull surface shell element is defined by the keyword *CONTACT_AUTOMATIC_SURFACE_TO_SUFACE to prevent penetration of non-common node connection areas during simulation calculations.

[0084] In addition, to ensure a smooth transition between the shared and non-shared node regions of the skin and skull, a node set is established by selecting nodes on the inner surface of the skin in the transition region. An offset binding contact is established between the node set and the shell unit on the skull surface using the keyword *CONTACT_TIED_NODE_TO_SURFACE_OFFSET, so that the nodes in the skin transition region are bound to the skull, thus realizing the transition between the shared and non-shared node regions.

[0085] S4: Define the cerebrospinal fluid 10 and the region enclosed by the cerebrospinal fluid 10 as a fluid domain and a blank domain, define the states of the fluid domain and blank domain using state equations, define the coupling mechanism for the cerebrospinal fluid 10, skull, and brain tissue using a preset contact algorithm, and simulate the fluid-structure interaction between the cerebrospinal fluid 10, skull, and brain tissue. Combine this with skin and facial bone solid meshes to generate a finite element digital model of the human head; S4 includes:

[0086] S4-1: Define the area enclosed by cerebrospinal fluid 10 as a blank domain and define cerebrospinal fluid 10 as a fluid domain. At the same time, initialize the blank domain and the fluid domain and assign them a viscoelastic material.

[0087] S4-2: Use the Lagrange algorithm for the skull and brain tissue, and the ALE algorithm for the fluid domain and the blank domain. Define the state equations for the fluid domain and the blank domain.

[0088] S4-3: The coupling relationship between cerebrospinal fluid 10-skull and cerebrospinal fluid 10-brain tissue is defined using a fluid-structure interaction contact algorithm based on penalty function.

[0089] like Figure 5 As shown, in this embodiment, the Lagrange-Euler method (ALE) is used to simulate the fluid-structure interaction between the skull, cerebrospinal fluid 10, and brain tissue. Specifically, the area enclosed by the cerebrospinal fluid 10 is first defined as the blank domain, and the cerebrospinal fluid 10 is defined as the fluid domain. After initializing the blank domain and the fluid domain, the viscoelastic material *MAT_KELVIN-MAXWELL-VISCOELASTIC is assigned.

[0090] Then, the Lagrange algorithm was used for the skull and brain tissue, while the ALE algorithm was selected for the fluid and blank domains. Specifically:

[0091] The cell algorithm with ELFORM=12 is selected. The formulas for the conservation of mass, momentum, and energy are used in the fluid domain and the blank domain as follows:

[0092]

[0093]

[0094]

[0095] in, Indicates density, Indicates time, Indicates fluid velocity. Represents the velocity in the reference coordinate system. Indicates Cauchy stress, denoted by force density, e represents internal energy per unit volume.

[0096] Next, the state equations for the fluid domain and the blank domain are defined. In this application, *EOS_GRUNEISEN is used to define the state equations, specifically as follows:

[0097]

[0098] in, Indicates the shock wave velocity. Represents the velocity of a particle. Indicates the speed of sound in the material. , , These are the three coefficients representing the polynomial fit between the shock wave velocity and the particle velocity;

[0099] Then, the relationship between pressure and volume of the fluid under high pressure variable rate conditions is established using the *EOS_GRUNEISEN definition, under the compressible state ( ):

[0100]

[0101] Under tension ( ):

[0102]

[0103] in, , It's density. It is the initial density. It is the Grüneisen parameter of the material. Yes The first-order volume correction factor, It is the internal energy per unit volume.

[0104] Next, the mesh nodes within the fluid domain and the blank domain are ensured to be fluid-friendly, so that the mesh can be automatically redrawn to avoid distortion during large deformation calculations and analyses. Specifically:

[0105] The Arbitrary Lagrange-Euler method (ALE) is calculated in two stages within each time step. The first stage is the Lagrange stage, which satisfies the equations of conservation of momentum and energy.

[0106]

[0107]

[0108] in It is Cauchy stress. It is force density. It's acceleration.

[0109] Then comes the transport and convection phase, where the mesh is remapped to satisfy the following equation:

[0110]

[0111]

[0112] in It is the fluid velocity. It is the velocity in the reference coordinate system.

[0113] Finally, a fluid-structure interaction (FSI) contact algorithm based on penalty functions was used to define the coupling relationship between the cerebrospinal fluid (CSF) 10 and the skull / brain tissue using the *Constrained_Lagrange_in_Solid method. Contact parameters included CTYPE, NQUAD, DIREC, and NORM. CTYPE was set to 4 for shell and solid elements that do not erode; NQUAD was set to 3 for a denser fluid mesh; and DIREC was set to 1 to establish coupling under both normal stretching and compression, ensuring that the CSF 10 can slide freely tangentially on the inner surface of the skull / outer surface of the brain tissue, but cannot separate. Finally, the NORM parameter was adjusted based on the simulation results of the head model to ensure that the normal of the coupling interface points inwards towards the fluid.

[0114] Therefore, after simulating the fluid-structure interaction between cerebrospinal fluid 10, skull, and brain tissue, a finite element digital model of the human head is generated by combining the aforementioned skin solid mesh and facial bone solid mesh.

[0115] The above are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for constructing a refined digital model of the Chinese human head, characterized in that: include: S1: Acquire computed tomography (CT) and magnetic resonance imaging (MRI) images of the human skull and preprocess them to generate a geometric model of the head; S2: Based on the head geometry model, a solid mesh of brain tissue is created using the Block-control method, and solid meshes of bones and cerebrospinal fluid are also created to generate the head solid mesh; S3: Assign corresponding material properties to each structure in the head solid mesh, and connect them to common nodes; S4: Define the cerebrospinal fluid and the area enclosed by the cerebrospinal fluid as the fluid domain and the blank domain, use the state equation to define the state of the fluid domain and the blank domain, use the preset contact algorithm to define the coupling mechanism for the cerebrospinal fluid, skull and brain tissue, and simulate the fluid-structure interaction between the cerebrospinal fluid, skull and brain tissue. Combine the skin solid mesh and facial bone solid mesh to generate a finite element digital model of the human head. S1 includes: S1-1: Select computed tomography and magnetic resonance imaging images of the skull of a human body that meets the physical characteristics of 50% of Chinese individuals. S1-2: Point cloud data of the scalp skin and bones are segmented from the computed tomography images based on threshold segmentation and stored in their respective layers; the bones include the skull and facial bones. S1-3: Obtain point cloud data of detailed regions of brain tissue from MRI images based on threshold segmentation and save them to different layers; S1-4: Repair the acquired head skin layer, bone layer and brain tissue layer. After the repair is completed, slice and stack the slices to reconstruct the geometric contours of each anatomical structure of the head. S1-5: Preprocess the geometric contours of the scalp skin, bones and brain tissue to obtain the geometric models of the scalp skin, bones and brain tissue, and combine them to generate the head geometric model. S2 includes: S2-1: Create a Block and cut its edges to fit the geometry of the brain tissue. S2-2: Based on the geometric model of brain tissue, nodes are created on the surface and inside of brain tissue. The nodes of the Block are mapped to the nodes on the surface and inside of the brain tissue to establish a hexahedral brain tissue solid mesh that matches the geometric surface of the brain tissue. S2-3: Project the outer surface nodes of the brain tissue onto the inner surface of the skull to establish a three-layer hexahedral mesh unit. From the inside to the outside, the three layers of hexahedral mesh units correspond to the cortical bone, the intermediate cancellous bone, and the outer cortical bone, respectively, to represent the solid mesh of the skull. S2-4: Generate temporary shell units based on the mesh units of the skull and brain tissue, establish a cerebrospinal fluid solid mesh in the area surrounded by the shell units, delete the temporary shell units after the cerebrospinal fluid solid mesh is generated; and establish a facial bone solid mesh according to each structure of the facial bone based on the stretching method. S2-5: Establish a solid mesh for the skin based on the outer surface nodes of the skull and facial bones; S2-6: Based on the established surface of each entity mesh, shell elements are created to simulate the three layers of meninges, falx cerebri, tentorium cerebelli, and facial cortical bone.

2. The method for constructing a refined digital model of the Chinese human head according to claim 1, characterized in that: S3 includes: S3-1: Apply viscoelastic material to the solid mesh of brain tissue and solid mesh of cerebrospinal fluid, apply elastic material to the shell unit, apply elastoplastic material to the solid mesh of skull and solid mesh of facial bone, and apply fibrous material to the solid mesh of skin. S3-2: Common nodes are used to connect the various detailed regions of the brain tissue, the skull and facial bones, and the skin, skull, and facial bones.

3. The method for constructing a refined digital model of the Chinese human head according to claim 2, characterized in that: S3 further includes: S3-3: Select the nodes on the inner surface of the skin in the transition region to establish a node set, and establish a biased binding contact between the node set and the shell unit on the surface of the skull to bind the nodes in the skin transition region to the skull.

4. The method for constructing a refined digital model of the Chinese human head according to claim 3, characterized in that: S4 includes: S4-1: Define the area enclosed by cerebrospinal fluid as a blank domain and the cerebrospinal fluid as a fluid domain. Simultaneously initialize the blank domain and the fluid domain and assign them a viscoelastic material. S4-2: Use the Lagrange algorithm for the skull and brain tissue, and the ALE algorithm for the fluid domain and the blank domain. Define the state equations for the fluid domain and the blank domain. S4-3: The coupling relationship between cerebrospinal fluid-skull and cerebrospinal fluid-brain tissue is defined using a fluid-structure interaction contact algorithm based on penalty function.

5. The method for constructing a refined digital model of the Chinese human head according to claim 4, characterized in that: Specifically, S4-2 is as follows: S4-2-1: Select the cell algorithm with ELFORM=12. The fluid domain and blank domain adopt the formulas for the conservation of mass, momentum, and energy as follows: in, Indicates density, Indicates time, Indicates fluid velocity. Represents the velocity in the reference coordinate system. Indicates Cauchy stress, represents force density, and e represents internal energy per unit volume; S4-2-2: The state equations for the fluid domain and the blank domain are defined using *EOS_GRUNEISEN, specifically as follows: in, Indicates the shock wave velocity. Represents the velocity of a particle. Indicates the speed of sound in the material. , , These are the three coefficients representing the polynomial fit between the shock wave velocity and the particle velocity; S4-2-3: Using the *EOS_GRUNEISEN definition, establish the relationship between pressure and volume of a fluid under high pressure variable rate conditions, under compressible conditions: Under tension: in, Indicates pressure, , It's density. It is the initial density. It is the Grüneisen parameter of the material. Yes The first-order volume correction factor, It is the internal energy per unit volume.

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