Research On Soft Tissue Deformation Model In Virtual Surgery Simulation System

With the improvement of clinical medicine and the development of computer science,virtual surgery simulation system plays an important role in the training of interns,telemedicine,surgery scheme planning,intraoperative navigation and postoperative evaluation.It can overcome the restrictions of traditional surgical training method,develop optimal surgical scheme and improve the success rate of surgery.Therefore,the research on virtual surgery has broad application prospects and is becoming a research hotspot and cutting-edge topic in medical field.Soft tissue deformation model is the most critical module in virtual surgery simulation system.It needs to meet the requirements of visual reality,deformation accuracy and real-time performance at the same time,which is a difficult problem to be solved urgently in the research.Therefore,the thesis focuses on how to guarantee the deformation accuracy and enhance the calculation efficiency simultaneously,and conducts an in-depth study on soft tissue deformation models in virtual surgery and optimizes these models accordingly.The main work is as follows:(1)To solve the problem that mass-spring model has poor model stability and low deformation accuracy,this thesis proposes an optimized mass-spring model with shape restoration ability based on volume conservation to simulate soft tissue deformation.The proposed method adopts a new flexion spring in the mass-spring model,so as to improve the shape restoration ability when large deformation occurs.Then,the particle swarm optimization algorithm is employed to achieve the optimal solution of the model parameters,so that the deformation accuracy is enhanced.Besides,the volume conservation constraint is introduced for the interior structure of soft tissue in order to ensure the incompressibility,i.e.,maintain the volume of the soft tissue.(2)To solve the problem that low calculation efficiency in the finite element model,this thesis proposes a real-time finite element cutting model based on model order reduction method.Firstly,the proposed model uses the finite element model to simulate the soft tissue deformation,and during the simulation process,a model order reduction method combining proper orthogonal decomposition and Galerkin projection is added to reduce the amount of deformation calculation.Then,the cutting path is formed according to the position of collision intersection between the surgical instrument and the soft tissue.Finally,the Bezier curve is utilized to draw the surface incision after the cutting.(3)To solve the problem of unbalance between deformation accuracy and real-time performance in the meshless model,this thesis proposes a fast and accurate simulation model based on improved point primitive method.The proposed model control the motion of the nodes inside the soft tissue by adopting the point primitive method.Besides,the stretching constraint and elastic potential energy constraint are added to correct the node motion and so as to characterize the elasticity of soft tissue.Furthermore,a mapping function from the interior to surface of the soft tissue is constructed to render the deformation effect based on moving least squares algorithm.By building a virtual simulation platform,the human-computer interaction between users and simulation system is realized.With the help of PHANTOM OMNI force feedback device,three models mentioned above are simulated in multiple groups of soft tissue deformation experiments and performance analysis.The experimental results show that three soft tissue deformation models proposed in this thesis have a real visual rendering effect,and the real-time performance is enhanced without losing the calculation accuracy.And in addition,some virtual surgical operations,such as stretching,compression and cutting,can be implemented well in three models,which provide strong supports for virtual surgery.