CN102034272B - Generating method of individualized maxillofacial soft tissue hexahedral mesh - Google Patents

Abstract

The invention discloses a generating method of an individualized maxillofacial soft tissue hexahedral mesh based on quasi-conformal body area mapping, comprising the following steps: first, constructing a standard hexahedral mesh of a standard maxillofacial model; then, respectively creating body area parameterized mapping phi on the standard maxillofacial model and an individualized maxillofacial model of a patient; and finally, mapping the standard hexahedral mesh to the individualized maxillofacial soft tissue model of the patient through the body area mapping to generate a high-quality hexahedral mesh on the special maxillofacial model. The hexahedral mesh generated by using the method can automatically adapt to the configuration of the special maxillofacial soft tissue and can be effectively applied to the mechanical analysis of the maxillofacial soft tissue because the arrangement structure of the mesh units is consistent with the anatomical characteristics of the maxillofacial soft tissue.

Description

The generation method of the facial soft tissue hexahedral mesh of personalized jaw

Technical field

The present invention relates to a kind of method that generates the facial soft tissue hexahedral mesh of personalized jaw.

Background technology

The facial soft tissue anatomical structure of jaw is complicated, mainly is made up of meat fiber, fat, body of gland and mucous membrane.Epidermis, corium and hypodermis constitute facial skin major part.The thick about 0.1mm of its mesocuticle mainly is made up of keratinocyte.The thick about 0.5～4mm of corium of below mainly is made up of snapback fibre, and has determined the elastic behavior of skin texture.Hypodermic layer mainly is made up of fat, fiber and mucous membrane, can the slight slip on the cranio-maxillofacial surface.The musculature that connects skin histology is very complicated, domination facial expression and linguistic function.In recent years; Medical 3 D image viewing technology develops rapidly; The particularly appearance of tomoscan such as CT, MRI image technology; Create necessary condition for three-dimensional reconstruction simulation truth, be applied to the research of facial shape architecture basics, craniofacial deformity diagnostic analysis and operation designing more and more.Three dimensional CT resolution is high, clear picture, and aspect is continuous; Can correctly show bone tissue image on every side; The reestablishment imaging stereoscopic sensation is strong, can fully show the three-dimensional anatomical structure of the facial soft tissue of human body jaw, has remedied the deficiency of two dimensional image; Can concern by facial three-dimensional anatomic image and the surrounding structure thereof of a jaw clear, show complex intuitively, directly disclosed the structure of soft tissue wherein.Through CT scan and resurfacing, can obtain to have the geometric model of good similarity with the facial entity of a jaw.

The most frequently used method of describing the biomechanics behavior of the facial soft tissue of jaw is a Finite Element Method.Finite Element Method can be carried out stress analysis to structure, form, load and the material mechanical performance of complicacy relatively, is the important means in the tissue biomechanics Research.In recent years, finite element analysis has been acknowledged as the effective method of simulation soft tissue deformation.The key of finite element analysis is the foundation of model, and the division of its geometric similarity, dynamic similarity, grid directly influences result calculated.Finite element modeling adopts tetrahedron, hexahedron or the two mixed cell usually.Hexahedral mesh is in computational accuracy, division numbers, anti-distortion degree and heavily divide aspects such as number of times and have clear superiority than tetrahedral grid.The division methods of tetrahedral grid is gradually ripe with relevant commercial software at present; And hexahedral mesh because its complicated topological relation and with the restriction of the aspects such as consistance on body surface border, this directly becomes the bottleneck of analyzing large complicated three-dimensional scientific and engineering problem.

Summary of the invention

Technical matters to be solved by this invention provides a kind of facial soft tissue hexahedral mesh of personalized jaw generation method based on certainly angle body territory mapping.For this reason, the present invention adopts following technical scheme:

It may further comprise the steps:

(1), according to the inside and outside surface of the facial soft tissue model of the standard jaw of importing, interactive configurations standard hexahedral mesh;

(2), the body field parameter mapping phi on the facial soft tissue model of the said standard jaw of establishment;

(3), to the facial soft tissue model tetrahedral grid of the said personalized jaw of input, create the body field parameter mapping on the facial soft tissue model of personalized jaw

(4), use body territory mapping

that the standard hexahedral mesh is mapped on the facial soft tissue model of personalized jaw, generate the hexahedral mesh of the facial soft tissue of personalized jaw.

Adopting on the basis of technique scheme, the present invention also can adopt or combined with following further technical scheme:

The step of said interactive configurations standard hexahedral mesh further comprises following steps:

1-1, the outside surface grid of the thin-skinned organize models of standard jaw carried out quadrilateral divide, use the plane from the left side to the right side with from the top on earth extreme direction cut outside surface, connect the outline line that cutting obtains and generate preliminary quadrilateral mesh;

1-2, revise preliminary quadrilateral mesh on the outside surface,, introduce triangle and improve mesh quality, make the outside surface grid have anatomical features simultaneously for the grid cell structure in mouth, nose and eye zone with user interactions;

1-3, outside surface grid vertex normal direction is set, passes quadrilateral mesh that step 1-2 obtains to the inside surface place, generate the standard hexahedral mesh on the facial soft tissue model of standard jaw along normal direction.

Said step 2 and 3 is created body field parameter mapping steps and is further comprised following steps:

On the surperficial triangle gridding of the facial soft tissue model of jaw, respectively from the left side to the right side (U direction), from the top to the bottom the first end boundaries condition of mutual establishment on (V direction) and (W direction) three directions from the inner surface to outer surface;

Piecewise linearity constraint condition on the facial soft tissue model of jaw is set alternately;

Calculating is under first end boundaries condition and piecewise linearity constraint condition, and corresponding three are in harmonious proportion scalar field: U, V and W on the facial soft tissue model of jaw;

Said three orthogonalities that are in harmonious proportion between scalar field are improved, and the body field parameter mapping on the facial soft tissue model of the jaw that makes U, V and W form has accurate conformality.

The said piecewise linearity constraint condition that is provided with alternately on the facial soft tissue model of jaw is: the axis line of symmetry of U direction and the glabella line of W direction, muffle separatrix, lip center line.

The step of the first end boundaries condition of said mutual establishment further comprises following steps:

Submit mutual election at the surface mesh of the facial soft tissue of jaw and select occluding contour to constitute a simply connected region;

For the point of simply connected region is provided with corresponding binding occurrence as first end boundaries condition, wherein the binding occurrence of head end point set is 0, and the binding occurrence of terminal point set is 1.

In the step of three mediation scalar fields of said calculating under first end boundaries condition and piecewise linearity constraint condition, the discretization method of Laplace's equation on the tetrahedral grid is adopted the Laplace operator of the long-pending weights of belt body:

$\mathrm{\Δ}{f}_i=\frac{1}{\left|{\mathrm{\Ω}}_i\right|}\underset{j\∈N\left(i\right)}{\mathrm{\Σ}}\left(\frac{1}{6}\underset{k=1}{\overset{n}{\mathrm{\Σ}}}{l}_k\cot \left({\mathrm{\θ}}_k\right)\right)(f_i-f_j).$

Wherein, | Ω _i| be the volume of the Voronoi antithesis unit of summit i, N (i) is the adjacent point set of summit i, f _iBe the functional value at i place, summit, l _k=l _PqBe limit (i, opposite side j) (p, length q), angle θ _k=θ _PqBe limit (i, j) dihedral angle at place.Make

to be defined as following matrix for the Laplace operator on the whole tetrahedral grid:

$L_{\mathrm{ij}}=\left\{\begin{array}{cc}{\mathrm{\Σ}}_{v_k\∈N\left(i\right)}{w}_{\mathrm{ik}},& \mathrm{ifi}=j\\ -w_{\mathrm{ij}},& \mathrm{ifj}\∈N\left(i\right)\\ 0,& \mathrm{otherwise}\end{array}\right.$

Find the solution following linear system and obtain the mediation scalar field on the tetrahedral grid,

Lu＝0.

U=(u wherein ₀, u ₁... u _N-1) be the mediation scalar value to be found the solution at tetrahedral grid summit place.

The method of employing SuperLU is found the solution linear system and is obtained the mediation scalar field on the tetrahedral grid.

The said step of improving orthogonality between scalar field further comprises following steps:

Calculate three mediation scalar field U; V; The gradient vector of W in each tetrahedron element:

and

To three gradient vector in each tetrahedron element; By the good and bad ordering of its orthogonality; Select the best gradient vector of orthogonality vector as a reference; It is on the plane of normal direction that second gradient vector projected to the reference vector, and reference vector and second gradient vector are done the apposition computing obtains the 3rd gradient vector;

Use revised gradient vector field, recover the mediation scalar field in conjunction with the constraint condition that has been provided with.

Said body territory mapping

is synthetic by the mapping of body field parameter; And adopt following method that the standard hexahedral mesh is mapped on the facial soft tissue model of personalized jaw: to each summit on the standard hexahedral mesh, interpolation is obtained its geometric position that on the facial soft tissue model of personalized jaw, has identical parameter value point; The hexahedral mesh that the topological structure of standard hexahedral mesh is combined the facial soft tissue of the personalized jaw of generation with the summit geological information on being mapped to the facial soft tissue model of personalized jaw.

Owing to adopt technical scheme of the present invention, the present invention can be with high-quality on the facial soft tissue model of standard jaw, have the standard hexahedral mesh of facial anatomical features, is mapped on the facial soft tissue model of personalized jaw.For the personalized jaw mask tetrahedral grid of input, body territory, the certainly angle mapping on this method can generate from the facial soft tissue model of standard jaw to the facial soft tissue model of personalized jaw automatically.Because certainly the mapping of angle body territory has kept the dihedral angle angle of grid cell to greatest extent; So this method can generate, and transition is even, the high-quality hexahedral mesh of the specific facial shape of self-adaptation patient; Can be effectively applied in the mechanical analysis of the facial soft tissue of jaw, can set up the discrete platform of three-dimensional model for the problem analysis of biomedical engineering field.

Description of drawings

Fig. 1 is the process flow diagram of method used herein.

Fig. 2 is the outside surface tetrahedral grid and the normal vector figure thereof of the facial soft tissue model of standard jaw.

Fig. 3 is the standard hexahedral mesh figure of interactive configurations.

Fig. 4 is the tetrahedral grid figure of the facial soft tissue model of personalized jaw of input.

Fig. 5 is at the lip-deep boundary constraint point marking tool of the facial soft tissue model of jaw figure.

Fig. 6 is the constraint condition distribution plan of the facial soft tissue model of jaw on the U direction.

Fig. 7 is the constraint condition distribution plan of the facial soft tissue model of jaw on the V direction.

Fig. 8 is the constraint condition distribution plan of the facial soft tissue model of jaw on the W direction.

Fig. 9 is the mediation scalar field U distribution plan on the facial soft tissue model of jaw.

Figure 10 is the mediation scalar field V distribution plan on the facial soft tissue model of jaw.

Figure 11 is the mediation scalar field W distribution plan on the facial soft tissue model of jaw.

Figure 12 is in harmonious proportion the orthogonality figure in the preceding tetrahedron element of orthogonality improvement between the field.

Figure 13 is in harmonious proportion the orthogonality figure in the tetrahedron element of orthogonality improvement back between the field.

Figure 14 is the mediation scalar field U distribution plan on the standard hexahedral mesh.

Figure 15 is the mediation scalar field V distribution plan on the standard hexahedral mesh.

Figure 16 is the mediation scalar field W distribution plan on the standard hexahedral mesh.

Figure 17 is the hexahedral mesh figure that the facial soft tissue model of personalized jaw is generated.

Embodiment

With reference to accompanying drawing.The present invention relates to a kind of generation method of the facial soft tissue hexahedral mesh of personalized jaw based on the mapping of angle body territory certainly.The facial soft tissue model of handled jaw is the facial soft tissue area of jaw below the forehead, before the ear among the present invention, mainly is made up of meat fiber, fat, body of gland and mucous membrane.For the facial soft tissue model of the specific jaw of patient; At first obtain its three-dimensional volumetric image through CT scan; Use the MarchingCube method to carry out iso-surface extracting then and obtain surface model; Obtain the tetrahedral grid on patient's the facial soft tissue model of personalized jaw through Delaunay tetrahedralization method at last, as the facial soft tissue model data of the personalized jaw of the present invention's input.The present invention adopt have the standard facial characteristics, the facial soft tissue model of flawless jaw is as the facial soft tissue model of standard jaw, through the standard hexahedral mesh of interactive configurations on it.Certainly the mapping of angle body field parameter is three directions mediation scalar field U, V and W that are defined on the said tetrahedral grid.In order to make the mapping of body field parameter as far as possible near conformality, this method is improved the orthogonality of UVW between the mediation scalar field.Through synthetic body territory, certainly angle mapping, the present invention maps to the hexahedral mesh on the facial soft tissue model of standard jaw on the facial soft tissue model of personalized jaw, generates the hexahedral mesh that adapts to the facial soft tissue form of the specific jaw of patient.

Following foundation process flow diagram of the present invention is elaborated to various piece:

1. interactive configurations standard hexahedral mesh

The facial soft tissue of jaw is the structure of a complicacy, comprises important zones with anatomical features such as mouth, nose and eye.Adopt the hexahedral mesh division methods of regularization that parameter field is carried out the anatomical features that grid dividing can not be looked after model.Therefore, letting user interactions with professional medical knowledge divide hexahedral mesh is better choice.Consider the distinctive geometric shape structure of complicacy and the thin-skinned organize models of jaw of carrying out three-dimension interaction; The present invention has designed an automanual interactive tool, makes things convenient for the professional user the facial soft tissue model of standard jaw to be carried out hexahedral mesh fastly and divides.The present invention regards hexahedral mesh as result that the outside surface quadrilateral mesh is passed inside surface along normal direction, and three-dimension interaction structure hexahedral mesh problem is converted into surperficial quadrilateral mesh division and two problems of normal direction adjustment.Mainly contain and comprise following four steps:

1). the present invention adopts the method for plane cutting, from the top to the bottom and from the left side to the right side, cuts the outside surface grid respectively, connects cutting and obtains horizontal wheels profile and vertical outline line, the preliminary quadrilateral mesh of automatic formation rule;

2). with the modification of user interactions to local unit structure on the preliminary quadrilateral mesh; Improve ropy quadrilateral; Make that simultaneously the arrangement of grid cell is consistent with the anatomical structure of the facial soft tissue of jaw as far as possible, like the similar ellipse of grid arrangement in mouth, eye zone, this step need be accomplished with user interactions; At first delete the grid cell of of poor quality or unreasonable structure, select the unit vertex position of the new interpolation of institute then through the some interactive tool among the VTK;

3). the normal direction of duplicating former outside surface and is improved the direction of normal direction alternately to the quadrilateral mesh summit of structure;

4). the outside surface quadrilateral mesh is passed to the inside surface place along normal direction, on the passing line segment, inserted two-layer node, connect the quadrilateral mesh that shows in the passing process, generate the standard hexahedral mesh on the facial soft tissue of standard jaw.

Fig. 2 has shown the outside surface quadrilateral mesh of structure, and the normal direction at place, summit is revised.The interaction mechanism that this method adopts VTK to provide carries out point selection, operations such as direction modification.Therefore it should be noted that method has been introduced some necessary triangles for tetragonal quality on the outside surface quadrilateral mesh that guarantees to construct, but when passing and the triangular prism that produces bring obstruction can not for follow-up finite element analysis.Fig. 3 has shown the standard hexahedral mesh to the facial soft tissue model structure of standard jaw.

2. create the facial soft tissue model upper body field parameter mapping of jaw

Parametric maps on the body territory can be regarded as a mapping one by one from the body territory to its parameter field, and parameter field also is a domain of individuals usually.Be similar to and adopt the coordinate amount of three directions to describe a parameter body territory, method uses three orthogonal mediation scalar fields to constitute parametric maps.The theoretical demonstration, for the mediation field that constitutes the curved surface parameter maps, if its gradient vector field (1-form) mutually orthogonal, corresponding curved surface parameter maps has conformality.Therefore; For the body field parameter mapping in this method; Though on 3D solid, do not have strict theory to guarantee which kind of character is the body field parameterization of its conformal have, improve the conformality that its orthogonality between being in harmonious proportion can effectively be improved whole body field parameterization.To the class thin plate cylindrical structure of the thin-skinned tissue of jaw, the present invention defines three and is in harmonious proportion the scalar field directions and is: from facial left side to right direction (being labeled as the U direction), direction (V direction) and from the bottom to the top orientation (W direction) from the inner surface to outer surface.More than three directions be in harmonious proportion and confirm by the boundary condition constraint that is labeled as maximum, minimum scalar value.For the tetrahedral grid of the facial soft tissue of the jaw of input, Fig. 4 has shown the tetrahedral grid of the facial soft tissue of personalized jaw, and it is following to construct its body field parameter mapping key step:

1). first end boundaries obligatory point and piecewise linearity obligatory point are set alternately

The tetrahedral grid of the facial soft tissue model of jaw is made up of several ten thousand summits usually; Also have thousands of and need be set to the boundary condition obligatory point, this just causes the point on the manual preference pattern one by one to become the parameterized bottleneck of quick generation model body as the boundary condition obligatory point.For alternative condition obligatory point fast in enormous quantities, method utilizes constraint point all to be in the characteristics on the model surface, has designed the quick selection scheme of putting on the tetrahedral grid surface of the facial soft tissue of a kind of jaw: the surface model that at first obtains tetrahedral grid; On its surface mesh, pass through the profile of a simply connected region of Dijkstra critical path method (CPM) structure then; At last, obtain the interior have a few of simply connected region as point to be marked.Each gauge point all has its corresponding constraint scalar value, and for the first terminal boundary condition constraint of mediation field, the constraint scalar value of head end gauge point is 0, and the constraint scalar value of end mark point is 1.Fig. 5 has shown the selection and the mark of the constraint point that in this method ocular is carried out, and darker regions is the simply connected region that is surrounded by boundary profile, and its inner gauge point is the point that is constrained to maximum scalar value (1.0).For the piecewise linearity obligatory point that is used to guarantee that feature structure is corresponding, method adopts the mutual instrument of hand-deliver of VTK to confirm the plane at piecewise linearity obligatory point place, then the tetrahedral grid of plane and the facial soft tissue model of jaw is asked to hand over to obtain the piecewise linearity obligatory point.

2). the mediation scalar field under the calculation constraint condition

The scalar field that is in harmonious proportion is a Laplace's equation

Δf(x，y)＝0， (1)

Separating under the Dirichlet boundary condition.The key that generates the mediation scalar field is can the Precise Discrete Laplace operator.For the Laplace's equation on the tetrahedron territory, the Laplace operator of the long-pending weights of this method definition i place, summit belt body is following:

$\mathrm{\Δ}{f}_i=\frac{1}{\left|{\mathrm{\Ω}}_i\right|}\underset{j\∈N\left(i\right)}{\mathrm{\Σ}}\left(\frac{1}{6}\underset{k=1}{\overset{n}{\mathrm{\Σ}}}{l}_k\cot \left({\mathrm{\θ}}_k\right)\right)(f_i-f_j).---\left(2\right)$

Wherein, | Ω _i| be the volume of the Voronoi antithesis unit of summit i, l _k=l _PqBe limit (i, opposite side j) (p, length q), angle θ _k=θ _PqBe limit (i, j) dihedral angle at place.Suppose that tetrahedral grid has N summit, then concerning whole tetrahedral grid, its Laplace operator can be defined as a following matrix L:

$L_{\mathrm{ij}}=\left\{\begin{array}{cc}{\mathrm{\Σ}}_{v_k\∈N\left(i\right)}{w}_{\mathrm{ik}},& \mathrm{ifi}=j\\ -w_{\mathrm{ij}},& \mathrm{ifj}\∈N\left(i\right)\\ 0,& \mathrm{otherwise}\end{array}\right.---\left(3\right)$

Then the Laplace's equation on the tetrahedron model is equivalent to following linear system,

Lu＝0. (4)

U=(u wherein ₀, u ₁..., u _N-1) be the position mediation scalar value that tetrahedron top goes out.In order to find the solution said system, we need provide restrained boundary constraint condition, have also confirmed the direction of mediation field simultaneously.For the constraint point that is constrained to given value, the Laplace's equation of its corresponding position is reduced to u _i=c _iNoticeable thing, because only there is syntople on the summit with a spot of summit, so formula (4) formation is a sparse linear systems, this method adopts the SuperLU method that formula (4) is found the solution.According to first end boundaries constraint condition of three directions of user's mark and piecewise linearity constraint condition, the scalar field that calculates the tetrahedron model of the facial soft tissue of jaw distributes.

To the class thin plate cylindrical structure of the thin-skinned organize models of jaw, the present invention defines following three directions: from facial left side to right direction (being labeled as the U direction), direction (V direction) and from the bottom to the top orientation (W direction) from the inner surface to outer surface.For different directions, service condition obligatory point marking tool is selected the first end boundaries constraint condition on this direction.On the U direction, the summit binding occurrence that the left border place is set is 0, and the summit binding occurrence at right side boundary place is 1; On the W direction, the summit binding occurrence that is provided with on the inside surface is 0, and the summit binding occurrence on the outside surface is 1; On the W direction, the summit binding occurrence that the bottom boundary is set is 0, and the summit binding occurrence at top margin place is 1.According to the monotonicity of harmonic function, the mediation scalar field on the facial soft tissue model of jaw will transition glossily between first end boundaries.In addition, the anatomical features result can be corresponding excessively in the mapping process in order to make, and this method is provided with following four piecewise linearity constraint conditions: the axis of U direction, the glabella line of W direction, muffle separatrix and lip center line.This method adopts the mutual instrument of hand-deliver of VTK to confirm the plane at piecewise linearity obligatory point place, then the tetrahedral grid of plane and the facial soft tissue model of jaw is asked to hand over to obtain the piecewise linearity obligatory point.On corresponding feature constraint line, have identical binding occurrence through the facial soft tissue model of facial soft tissue model of the jaw that sets up standard and personalized jaw, the body territory mapping that this method generates can the specific facial shape of self-adaptation patient, the mapping of setting up anatomical features.Fig. 6-8 has shown that the first end boundaries obligatory point on facial each direction of soft tissue of jaw distributes; Wherein the constraint scalar value of head end obligatory point institute mark is 0.0; The constraint scalar value of end obligatory point institute mark is 1.0, and the constraint scalar value of piecewise linearity constraint condition point institute mark is then looked its position and decided.Fig. 9-11 has shown that the scalar field under the boundary condition point constraint of user's mark distributes, and is respectively the mediation scalar field of U direction, V direction and W direction.

3). improve orthogonality between the mediation scalar field

Utilize the resemblance of the facial soft tissue model of jaw, three directions mediations of the UVW that the constraint point that method is provided with from the user is constructed scalar field.But; Gradient vector field through calculating three mediation scalar fields is found; Can not guarantee orthogonal between vector field; Figure 12 has shown the local orthogonality of three vector fields in nasal area, and three continuous line segments are represented the gradient vector of three directions, irised out the poor unit of some typical orthogonalities simultaneously.Therefore, method need be carried out the orthogonality correction to the inner gradient vector of each tetrahedron element, and recovers new mediation scalar field from revised gradient vector field, and concrete steps are following:

(1). according to the scalar value at each place, tetrahedron element summit, calculate the inner gradient vector

of tetrahedron

(2). select the best gradient vector of orthogonality vector as a reference, it is in the plane of normal direction that second gradient vector projected to the reference vector, and reference vector and second gradient vector are done the apposition computing obtains the 3rd gradient vector;

(3). recover the corresponding scalar field that is in harmonious proportion from revised gradient vector field

, through finding the solution following system

${\mathrm{Lu}}^{\′}=G^{T}M{g}_u^{*},---\left(5\right)$

Obtain, wherein G is overall gradient operator matrix, and M is a diagonal matrix, and its diagonal entry is the volume of corresponding tetrahedron element.

In order to make three mediation fields of UVW quadrature as far as possible, we have carried out iteration six times to above orthogonality makeover process.Figure 13 has shown that the orthogonality between the scalar field after recovering has obtained effective improvement.To sum up; The present invention is for the tetrahedral grid of the facial soft tissue model of given any jaw; Adopt the certainly body field parameter mapping at angle of following method construct:, calculate the mediation scalar field of three directions of UVW at first according to the edge-restraint condition and the piecewise linearity constraint condition of user interactions selection; Calculate the gradient vector field of mediation scalar field then, and improve the orthogonality of inner three gradient vectors of each tetrahedron element; At last, utilize constraint condition, from revised gradient vector field, recover its corresponding mediation scalar field, and constitute the body field parameter mapping of the facial soft tissue model of jaw with these three mediation scalar fields.

4). the body field parameter mapping on the facial soft tissue model of facial soft tissue model of six jaws of creating a standard and personalized jaw

Standard hexahedral mesh for manual structure; The present invention generates its corresponding tetrahedral grid through the method for adding auxiliary point; Edge-restraint condition and segmentation constraint condition are set then calculate three mediation fields of UVW, and obtain the body field parameter mapping phi at the certainly angle on the standard hexahedral mesh through the orthogonality correction.Therefore only the tetrahedral grid that is generated comprises all summits on the former hexahedral mesh, needs the body field parameter mapping on the structure tetrahedral grid and the UVW value of corresponding point position is back to hexahedral mesh to get final product.Figure 14-16 has shown mediation scalar field and the constraint condition thereof on the standard hexahedral mesh.Personalized facial soft tissue model for input; We through be provided with the standard hexahedral mesh on consistent constraint point calculate three of UVW and be in harmonious proportion, and shown the mediation field UVW distribution on the personalized jaw face soft tissue model through body field parameter mapping

Fig. 9-11 that the orthogonality correction obtains the certainly angle on the personalized jaw face soft tissue model.

3. the hexahedral mesh of the facial soft tissue model of personalized jaw is shone upon and generates in the compound body territory

Because set edge-restraint condition is [0,1] in this method, according to being in harmonious proportion scalar field equally distributed character on the tetrahedral grid model of the facial soft tissue of jaw, all there is individual parameter coordinate (u on each summit on the tetrahedral grid model of the facial soft tissue of jaw; V, w) ∈ [0,1] * [0; 1] * [0,1], that is to say that the body field parameter mapping on the facial soft tissue model of jaw is mapped to one [0 with the facial soft tissue model of jaw; 1] unit cube territory * [0,1] * [0,1].Making the said three-dimensional body territory at the facial soft tissue model of standard jaw place is M _S, the body field parameterization on it is mapped as φ: [0,1] * [0,1] * [0,1] → M _SLikewise, the facial soft tissue model body of personalized jaw territory is M _P, the body field parameterization on it is mapped as Then the standard hexahedral mesh is mapped to the body territory mapping f:M on the personalized soft tissue model _S→ M _PCan use Replace.

The present invention adopts following method that the standard hexahedral mesh is mapped on the facial soft tissue model of personalized jaw: for each the summit i on the standard hexahedral mesh, at first calculate its parameter coordinate (u under the facial soft tissue model upper body field parameter mapping of standard jaw _i, v _i, w _i), on the tetrahedral grid of the facial soft tissue of personalized jaw, search then and comprise this parameter coordinate (u _i, v _i, w _i) tetrahedron element j, go out the identical with it some position (x of parameter coordinate figure in tetrahedron element j interpolate value at last _Pi, y _Pi, z _Pi) as the mapping point of some i at the facial soft tissue model of personalized jaw.The topology information of geometric position, summit information and standard hexahedral mesh on the facial soft tissue model of personalized jaw is combined, can obtain the hexahedral mesh of the facial soft tissue model of personalized jaw.Figure 17 has shown the hexahedral mesh result of the facial soft tissue of personalized jaw.Adopt grid that this method generated to avoid the grid cell of counter-rotating, degeneration, the hexahedral mesh that can maintain the standard is arranged characteristic and simultaneously at the grid cell in zones such as mouth, nose and eye.Owing to the certainly angle characteristic of body territory mapping, the average twist error to dihedral angle on the grid cell in the mapping process is 6.9 ° simultaneously, and 90% angle distortion is controlled in 10 °.The hexahedral mesh that the body territory mapping of adopting the present invention to construct is generated can be effectively applied in the biomechanics finite element analysis of the facial soft tissue of jaw.

Claims (5)

1. the generation method of the facial soft tissue hexahedral mesh of personalized jaw is characterized in that it may further comprise the steps:

(1), according to the inside and outside surface of the facial soft tissue model of the standard jaw of importing, interactive configurations standard hexahedral mesh;

(2), the body field parameter mapping

on the facial soft tissue model of the said standard jaw of establishment

(3), to the facial soft tissue model tetrahedral grid of the said personalized jaw of input, create the body field parameter mapping on the facial soft tissue model of personalized jaw

(4), use body territory mapping

that the standard hexahedral mesh is mapped on the facial soft tissue model of personalized jaw, generate the hexahedral mesh of the facial soft tissue of personalized jaw;

The step of said interactive configurations standard hexahedral mesh further comprises following steps:

1-1, the outside surface grid of the thin-skinned organize models of standard jaw carried out quadrilateral divide, use the plane from the left side to the right side with from the top on earth extreme direction cut outside surface, connect the outline line that cutting obtains and generate preliminary quadrilateral mesh;

1-2, revise preliminary quadrilateral mesh on the outside surface,, introduce triangle and improve mesh quality, make the outside surface grid have anatomical features simultaneously for the grid cell structure in mouth, nose and eye zone with user interactions;

1-3, outside surface grid vertex normal direction is set, passes quadrilateral mesh that step 1-2 obtains to the inside surface place, generate the standard hexahedral mesh on the facial soft tissue model of standard jaw along normal direction.

2. according to the generation method of the facial soft tissue hexahedral mesh of the desired personalized jaw of claim 1, it is characterized in that said step (2) and (3) establishment body field parameter mapping steps further comprises following steps:

On the surperficial triangle gridding of the facial soft tissue model of jaw, on U direction, V direction and three directions of W direction, create first end boundaries condition respectively alternately; Said U direction is the direction from the left side to the right side, and said V direction is the direction from the top to the bottom, and said W direction is a direction from the inner surface to outer surface;

Piecewise linearity constraint condition on the facial soft tissue model of jaw is set alternately;

Calculating is under first end boundaries condition and piecewise linearity constraint condition, and corresponding three are in harmonious proportion scalar field: U, V and W on the facial soft tissue model of jaw;

Said three orthogonalities that are in harmonious proportion between scalar field are improved, and the body field parameter mapping on the facial soft tissue model of the jaw that makes U, V and W form has accurate conformality.

3. according to the generation method of the facial soft tissue hexahedral mesh of the desired personalized jaw of claim 2, it is characterized in that the said piecewise linearity constraint condition that is provided with alternately on the facial soft tissue model of jaw is: the axis line of symmetry of U direction and the glabella line of W direction, muffle separatrix, lip center line.

4. according to the generation method of the facial soft tissue hexahedral mesh of the desired personalized jaw of claim 2, it is characterized in that the step of the first end boundaries condition of said mutual establishment further comprises following steps:

Submit mutual election at the surface mesh of the facial soft tissue of jaw and select occluding contour to constitute a simply connected region;

For the point of simply connected region is provided with corresponding binding occurrence as first end boundaries condition, wherein the binding occurrence of head end point set is 0, and the binding occurrence of terminal point set is 1.

5. according to the generation method of the facial soft tissue hexahedral mesh of the desired personalized jaw of claim 1; It is characterized in that said body territory mapping

is synthetic by the mapping of body field parameter; And adopt following method that the standard hexahedral mesh is mapped on the facial soft tissue model of personalized jaw: to each summit on the standard hexahedral mesh, interpolation is obtained its geometric position that on the facial soft tissue model of personalized jaw, has identical parameter value point; The hexahedral mesh that the topological structure of standard hexahedral mesh is combined the facial soft tissue of the personalized jaw of generation with the summit geological information on being mapped to the facial soft tissue model of personalized jaw.

Images