Research On Soft Tissue Modeling And Collision Detection Using Position Based Dynamics

As a new assistant technology of surgery,virtual surgery plays an important role in the training of novice doctors,telemedicine,intraoperative navigation,and postoperative evaluation.It can greatly improve the success rate of surgery and reduce the cost of medical training.Therefore,the research of virtual surgery has broad application prospects and is becoming a research hotspot and cutting-edge topic.There are many functional modules in virtual surgery simulation system,among which real-time deformation simulation is the most critical module.It needs to meet the requirements of visual reality,model deformation reality and real-time interaction at the same time,which is a difficult problem to be solved urgently in the research.Therefore,the dissertation focuses on the soft tissue modeling method and real-time collision detection technology of virtual surgery,and builds a virtual surgery simulation system.The main research contents are as follows:(1)In the aspect of geometry modeling of soft tissue,the method of coupling surface model and volume model is used to build the geometry model.High precision triangular surface mesh is used for visual rendering to express more realistic texture details of organ model.Based on Delaunay mesh generation algorithm,the simplified surface model of soft tissue is divided into tetrahedral mesh,which is used for deformation calculation to reflect the physical characteristics of soft tissue,and the coupling method of surface model and body model is given.Finally,the physical properties of soft tissue are analyzed,the modeling methods are summarized and compared with each other to lay a foundation for physical modeling of soft tissue.(2)The physical model of soft tissue is studied by the algorithm of position dynamics.Firstly,the mathematical principle and specific algorithm of the positional dynamic model are analyzed,and the constraint conditions of the algorithm are derived.In order to express the elastic,non bending and non compressible properties of soft tissue,the extension constraint bending constraint and volume invariant constraint are given to the volume model.Finally,the deformation simulation experiment is carried out with the liver model as an example,and the model has good deformation effect and visual reality.(3)After analyzing and comparing the advantages and disadvantages of various collision detection algorithms,aiming at the real-time deformation characteristics of soft tissue in virtualsurgery,a top-down local hybrid hierarchical bounding box tree method is proposed to achieve the real-time and accuracy of detection calculation.Sphere bounding box is built in the front of virtual surgical instrument,and local Sphere-AABB hybrid bounding box tree is built in liver organ model.The detection process between virtual instrument and software is given and collision detection between them is completed(4)A virtual surgery simulation system based on tactile feedback technology is designed and built,which realizes the human-computer interaction between users and simulation system,and improves the immersion of virtual surgery.With the help of force feedback device,the liver and other models are simulated in multiple groups of deformation experiments and time efficiency analysis.The experimental results show that: the model in the virtual scene shows rich texture information and has a real visual rendering effect;the soft tissue model based on the position dynamics method is realistic in the physical deformation effect under the operation;at the same time,the frame rate of the operation system reaches 60 frames per second to meet the requirements of real-time interaction.