Study On The Modeling Of Deformation And Cutting Of The Soft Tissue Based On Meshless Method In Surgery Simulation

With the development of virtual technology and computer technology,people combine such technology with medical discipline to design a medical simulation system.The research and development of virtual surgery system has become a hot research topic at home and abroad,and the modeling of human soft tissues is also a major subject.This paper researched the modeling of human soft tissue deformations based on a meshless method.Such modeling approach can help obtain the deformation result quickly and in real time when an external force acts on the virtual soft tissue,and give full play to its advantage of good adaptability.In addition,simulation analysis was carried out on the cutting deformations of soft tissues.Soft tissues are considered as a problem domain in the meshless modeling method.A large number of discrete nodes are arranged in the problem domain and connected through shape functions to establish a stiffness matrix,and then build an approximate function model describing the mechanical properties of the soft tissue material.The total nodal displacement obtained by the function model can be used to represent soft tissue deformations.In order to better understand and apply the meshless method,we analyzed the typical modeling method---finite element modeling.Considering that the material properties of soft tissues would be involved in the modeling process,the method for measuring the material properties of soft tissues was researched.After that,several attempts were made in the 2D simplified modeling of soft tissue deformations by local meshless method,and satisfactory results were obtained.With these knowledge reserves,the application of global meshless method to the 3D modeling of soft tissues was researched,and the model function was obtained through modeling.Thus the soft tissue deformations represented by total nodal displacement could be obtained by solving the model function.However,the solving process of model functions is very time-consuming and cannot meet the need of real-time representation of virtual soft tissue deformations in virtual surgery.In order to solve this problem,it is proposed to introduce Levenberg-Marquardt algorithm to pre-fit the mathematical relationship between force and total nodal displacement obtained through the meshless soft tissue model in this paper.When soft tissues are under stress in virtual surgery,the soft tissue deformations can be represented by calling the fitted mathematical relationship immediately.An experiment was designed in this paper to prove the feasibility of this method.A 48 mm × 48 mm × 6mm geometric model with elastic modulus of the liver was used instead of soft tissues,and a number of space forces in the range of 0 to 1N were applied to the geometric model to calculate total nodal displacements corresponding to the applied space forces.The mathematical relationship between force and deformations fitted by Levenberg-Marquardt algorithm helps obtain the nodal displacement quickly,and obtain the curve fitted by the nodal displacement to visually represent the soft tissue deformations.The experimental result shows that it takes an average of 0.1509 seconds to calculate each deformation,with the maximum deformation error less than 0.5mm.In the last part of this paper,the global meshless method is used to analyze and calculate cutting deformations.The core idea is to consider the nodes on the cutting path as the superposition of two nodes,and substitute the extrusion on both sides of the cutting path from the cutting blade as a natural boundary condition into the global meshless calculation equation to obtain the deformation,finally represent the deformation of open incision and closed incision through MATLAB,and give a test program designed by Fortran for describing the dynamic cut.