Research On Soft Tissue Deformation Modeling And Cutting Simulation In Virtual Surgery

Virtual surgery system creates three-dimensional virtual surgery environment through computer technology,constructs human organ model based on medical image data,and simulates the operation objects with the aid of tactile interaction equipment,so that doctors can obtain realistic operation training senses.Compared with traditional operation training methods,virtual surgery system can make doctors perform repetitive operation training on specific tissues and organs without time and space constraints,which is of great significance to improve the efficiency of doctor training and reduce the cost of medical training.In addition,virtual surgery system also has important application value in preoperative operation planning and prediction,intraoperative assisted surgical navigation,postoperative rehabilitation training and evaluation,and medical education.This paper focuses on the key technologies of soft tissue modeling,collision detection and force feedback calculation in the virtual surgery system.A virtual surgery system with visual feedback and tactile interaction functions is built,and soft tissue deformation and cutting simulation are experimentally verified.The main work is as follows:Firstly,this paper constructs the framework of virtual surgery system reasonably and efficiently,and divides the system into three major modules,including surgical scene modeling and rendering module,virtual operation simulation and calculation module,and human-computer interaction module.The software and hardware structure of the system are introduced.Using the OpenGL graphics engine and Chai3D haptic engine,the interactive interface design of the virtual surgery system is completed in the Qt development framework.In order to improve the efficiency of system simulation,the parallel running mode of two threads is adopted.Then,the whole virtual surgery system simulation platform is built to realize the visual feedback and tactile interaction in the process of virtual surgery simulation.Secondly,the geometry model of soft tissue is constructed with 3D image software,and the data storage structure of the model is designed to provide important data source for the subsequent simulation calculation.The biomechanical properties and viscoelastic model of soft tissue are simply analyzed.Compared with the common soft tissue deformation modeling methods,a physical modeling method of filled sphere combined with spring dampers is proposed.The topological connection relationship is established for discrete filled spheres,and the Voigt spring damper is set up to realize the deformation process of the model under the stress.Then,the mapping relationship between the geometry model and the physical model is established to realize the deformation linkage of the soft tissue model.Then,the AABB hierarchical bounding box tree is constructed for the soft tissue geometric model to realize the collision detection between the virtual surgical instrument and the soft tissue geometric model,and a collision detection algorithm based on the soft tissue physical model is proposed.The spring damping force feedback model is constructed by the proxy method,and the force feedback model is improved by the collision detection algorithm of the filled sphere.The posture of the virtual surgical instrument was matched with the force feedback device,and the compression deformation simulation and clamping deformation simulation of the liver model were completed in the system simulation platform using the Omega7.0 device.The simulation results of model deformation are verified from three aspects of deformation displacement,force feedback and real-time performance,which prove the effectiveness of the proposed method.Finally,this paper studies the simulation of soft tissue cutting.Aiming at the collision detection between virtual scalpel and soft tissue model,an optimization method based on the time-space coherence is proposed,and the search method of adjacent triangle patch is used to improve the collision detection efficiency.In order to balance the accuracy of cutting simulation and the efficiency of system calculation,the progressive surface mesh cutting method is used.Through the nearest point movement,cutting point splitting,and notch groove construction,the cutting drawing is completed,and the cutting force feedback model was established,which enhances the realism of cutting simulation.Then,in the virtual surgery system,the cutting simulation of the liver model is completed,and the realistic cutting visual and tactile effects are achieved.