The Research Of The Deformation And Tearing Of The Soft Tissue In Brain Surgery Simulation

With the rapid development of computer technology in recent years,at the end of the twentieth Century,virtual reality which is a new information technology has emerged.Virtual reality technology has been widely applied to many fields,such as industry,medicine,entertainment and education etc..Virtual surgery is one of the important applications of virtual reality technology.It can help doctors make the operation scheme,intraoperative navigation,can also be used to train interns to reduce failure rates.At present,many types of surgery have been simulated.However,the brain surgery simulation system is very few,because the brain surgery is one of the most complex and the most delicate operation,the training of brain surgeon is very necessary.Aiming at this requirement,this paper developed a brain virtual surgery simulation system.The most important problem of this brain surgery simulation system is how to let users have realistic visual and tactile perception and interaction in virtual scenes.Realistic vision and real-time computation has been the goal of virtual surgery simulation system.In order to achieve this goal,the following several problems are researched in this paper:Firstly,because the brain involves rich tissues and organs,deformation simulation of all organs will be very consumption.In order to obtain high quality simulation effect with low time and space complexity,a novel improved algorithm for shape mathcing based on Splat graphic element is presented.In the algorithm,a new Splat graphic element is adopted instead of the classical point graphic element,the surface of object is seamlessly covered with the least number of Splats to ensure rendering quality,which can be achieved by controlling the sampling density and automatically adjusting the radius of circular Splats.The deformation of Splats is calculated with shape matching algorithm.The algorithm has good stability and meets the real-time computation in simulation system.Secondly,the doctor will determine what will carry on in next operation according to the deformation of each organ tissue in brain surgery.Therefore,it is not enough to just considering the system operating speed,the accuracy of the soft tissue deformation in brain surgery is very important.In order to reflect the real effect of the soft tissue deformation,the viscoelastic properties are integrated into the meshless physical and mechanical model of the soft tissue.According to the biomechanical test of the vivo soft tissue,the physical and mechanical parameters of the soft tissue are determined,and the accurate calculation results of the deformation are obtained.Thirdly,doctors need to timely see the accurate change of the soft tissue,otherwise wrong operation may be led to in brain surgery.In order to obtain high authenticity of soft tissue deformation and movement simulation in real time,a multi-resolution soft tissue deformation model based on point primitive is proposed.After the geometric model of soft tissue being sampled and sample points being given physical attributes,the new position of sample points is calculated with the mechanical model based on point primitive.For getting high resolution display,the new displacement of the nearest neighbors of sample points is computed with affine transfomation in local deformation zone.The experimental results show that this algorithm meets the requirements of users in the visual effect and greatly improve computational efficiency.Fourthly,a suction device can be used to suck the brain tumor in brain surgery.To achieve realistic virtual effect of soft tissue tearing,the meshless physical model was used to compute tearing.In the meanwhile,the height-field technology combining with purposely-used noise interference is employed to render surface fracture of soft tissue.To meet the requirement of real time computation,a fast data-updating strategy based onthe hierarchical bounding ball of octree is adopted.A prototype was developed to show the feasibility of the developed modeling method,operation simulation and computation strategy.Fifthly,a variety of new surface of the object can be produced when interaction happens,which increases the collision detection in the brain surgery simulation.In order to ensure a high-level of accuracy and to meet the real-time requirement,a fast collision detection algorithm between soft bodies is proposed.The developed algorithm is a combination of stochastic methods and particle swarm optimization with adaptive Cauchy mutation.The hierarchical bounding box method is used for a rough detection in order to filter out obvious disjoint space,and the problem is converted to a nonlinear optimization problem based on the distance of points characteristics according to stochastic collision detection,then particle swarm optimization with adaptive Cauchy mutation is used to find the optimal solution.When group iterative update,keeping some particles experience value and variation of other particles avoids particles trapped in local optimum and further accelerates the speed of collision detection.This algorithm has a higher speed and optimization efficiency and it can meet the requirements of real-time and accurate collision detection in virtual environments.