Research On Collision Detection And Soft Tissue Simulation Techonology For Virtual Surgery

With the development of medical imaging technology and computer technology, the simulation of virtual surgery is applied in medical field extensivly. It provides an interactive virtual system for doctors with the functions of surgery planning, simulation, result forecast and surgery training. So far some progresses have been made in the field of study, but how to strike a balance between reality and real-time in virtual surgery is still a challenging issue.Focus on two aspects of virtual surgery, this thesis discusses several techniques in virtual surgery, including real-time collision detection, the construction of soft tissue model, the deformation computation and cutting simulation. The main work and the innovation of this thesis are summarized as follows:1. Presented a hierarchical bounding volumes collision detection method based on hybrid strategy in order to improve the velocity and accuracy of collision detection in virtual surgery. The method implements intersection test by establishing different hierarchical bounding volumes for different objects in virtual surgery according to their topology features aim to improve the detection accuracy. The experiment shows that the average detection time of this method surpasses the traditional OBB (Oriented bounding box) algorithm-RAPID, and increases the detection velocity on average by26%. In view of the hierarchy updating problem after deformation of soft tissue, proposed a bottom-up and local updating approach to speed up the process of hierarchy renewing.2. Most FEM (Finite Element Method) mesh construction approach in virtual surgery is Inefficient and the boundary element is incompatible with the internal mesh. A mesh generation algorithm combined octree with AFT (Advancing front method) is proposed. The approach generates the background mesh by octree method, and the advancing front is applied to generate tetrahedrons based on the background mesh. This method can guarantee quality of boundary elements and reduce the intersaction conputation of internal mesh. The experiment shows that the approach contributes to generate uniform mesh efficiently and possesses superior performance compared to other algorithm.3、Proposed a soft tissue deformation FEM model based on partitioning strategy to solve the problem about real-time deformation computation of soft tissue. According to the feature of surgery, the surgery object model can be divided into two parts:surgery area and non-surgery area. The method set up the linear elastic FEM model and introduces the precomputation and condensation technology to reduce the computation time. In surgical area, a viscoelastic FEM model is established on the basis of generalized Maxwell model. The construction of the hybrid model realizes the realtime deformation of soft tissue within a certain range.4、Aimed at the problem that complexity of models increased fastly and elements of mesh is inconsistent, proposed an improved unit subdivision approach in simulation of soft tissue cutting. This algorithm applies the classification strategy to redefine the type of cutting model, for the purpose to reduce the difficulty of implementation of virtual cutting. In the virtual cutting process, a vertex splitting method is used to limit the amount of new generating elements. The experiment shows that it is effective to control the quantity of new units and reduce the processing time. Compared to traditional method, the algorithm can decrease the quatity by14%and the processing time by58%。5、Proposed a craniofacial holes repairing algorithm in view of curvature based on the research of mesh generation in virtual surgery. The key step is to cover holes entirely through advancing front method, to obtain initial repairing mesh, then it is redefined the initial mesh according to feature of curvature and Delaunay rules. The approach is suitable for different type of holes repairing and forms a good transition with surrounding area. Results of the paper provide a basis theroy and technology innovation to solve properties between reality and realtime, simultaneously support the further research in the future.