Simulation Study Of Soft Tissue Deformation Based On Finite Element Method And Mass Spring

As an emerging research direction, Virtual Surgery Simulation(VSS) is acrossing field integrated with material science, biomedical, computer vision,computer graphics and other disciplines. The main purpose of VSS is buildingvirtual human tissue models and human organ models, and gaining realisticsimulation of the deformation process under surgery operation in real medicalsurgery by visualizing the virtual models in computer. As the virtual human tissuemodels and organ models are the operation objects and research targets of VSS, theaccuracy of modeling will directly affects the overall performance of virtual surgerysystem. Therefore, building accurate soft tissue model has become a key topic ofVSS research.The main work of this paper are as follows:In the aspect of the choice of physical modeling method for soft tissue, make acomparison about the pros and cons of two widely used physical modeling methods,i.e., Finite Element Model(FEM) and Mass Spring Method(MSM). Based on themechanical analysis of Kelvin MSM and corresponding beam FEM, build thefunctional relationship between the parameters of Kelvin MSM and the materialparameters, geometrical features of the beam unit, thus offering theoretical basis forthe design of elastic coefficient of springs.As for the dynamic design of elastic parameter of springs, this paper make ananalysis of stress and strain of soft tissue. With the periodic change of stress-straincurve, a fractional analysis can be conducted, therefore obtaining the dynamicvariation rule of parameters of MSM, which means the relationship of stress andstrain is linear when deformation is quite small, and exponential when greatdeformation occurs.For the anisotropy of soft tissue, the paper conducts compression experimentsof pig kidney in axial direction and radial direction. Based on the collected data offorce and displacement, axial and radial stress-strain curve can be acquired, whichtestifies its sectional change. After linear fitting and exponential fitting of the curve,we get the responding characteristics of the two curves. Then according to therelationship of parameters of MSM and material parameters of soft tissue, afunctional relationship between spring force and spring direction has been set up,i.e., the relation between spring force and the angle which spring deviates from theaxial direction of soft tissue.At last, simulation experiments about drag and press have been conducted onmedical simulation platform SOFA, and the results shows that the UMSM developed in this paper has great accuracy, which can match operations.