| Virtual surgery is a typical application of virtual reality technology in the medical field,which uses a computer to generate a virtual environment to simulate various phenomena that may occur during surgery.In virtual surgery,the soft tissue model is the basis of the interaction between human organs and surgical instruments,and it directly affects the success rate of virtual surgery.However,soft tissue is a special elastic material with complex properties,which makes it difficult to coordinate the accuracy and real-time performance of the soft tissue model.In order to solve the above challenges,the main research in this paper is as follows:(1)In order to truly reproduce the force deformation of soft tissue and improve the accuracy and real-time performance of virtual surgery,it is necessary to perform collision detection on soft tissue.This paper evaluates three commonly used hierarchical bounding box algorithms from five indicators,and comparatively analyzes the construction method of the bounding box tree.Finally,the construction algorithm of AABB top-down bounding box tree was used to implement collision detection between liver organs and surgical instruments.Aiming at the complex characteristics of soft tissue,this paper studies the force feedback algorithm by the proxy rendering manner.The spring-damping force feedback model is used to calculate the feedback force,which enhances the capability of the human-computer interaction.(2)This paper proposes a soft tissue deformation model of nonlinear mass spring based on Verlet algorithm.Aiming at the problem that the spring stiffness coefficient in the mass spring model is difficult to determine,this paper proposes a method of mapping soft tissue material parameters to spring stiffness coefficients,which effectively improves the simulation accuracy.With respect to solving dynamic equations,Velocity Verlet algorithm and Beeman algorithm are used to determine the particle positions according to the change of particle force,which shortens the calculation time and improves the accuracy of the solution.Finally,an experimental platform of virtual surgery simulation was built,and the liver organ was constructed using a mass spring model based on tetrahedral topology,and medical staff were invited to conduct training and evaluation.Experimental results show that the proposed model has high simulation accuracy and can meet the requirements of virtual surgery for real-time performance.Compared with the traditional mass spring models,the proposed model has been improved outstandingly in terms of overall performance and actual training effect,which can be applied to the virtual surgery with high precision requirements.(3)A soft tissue deformation model of unfixed mass spring based on Euler algorithm is proposed.In view of the problem of the spring layout,this paper optimizes the quadrilateral topology of the model and improves its stability.In order to make up for the shortcomings of the traditional method in handling force points,a local comparison algorithm is proposed to reduce the number of iterations,which effectively improves the processing efficiency.In solving the dynamic equations,a Euler algorithm combining the explicit and implicit patterns is used to determine the particle position,reducing the calculation time while ensuring the simulation accuracy.Finally,an experimental platform for virtual surgery was built,where an intestine organ was constructed using the mass spring model based on the quadrilateral topology,and physicians were invited to score the proposed model.The experimental results show that the proposed model has good real-time performance,and the simulation accuracy can also meet the requirements of virtual surgery.Additionally,the proposed model is also better than the traditional mass spring models in terms of the overall performance,with good actual training effect,which is suitable for the surgical scenarios with high real-time requirements. |
