Soft Tissue Deformation Simulation Based On The Element-Free Galerkin Method

Virtual surgery simulation system(VSSS)based on virtual reality(VR)has become a research hotspot and development trend among the social transition and the renovation of medical training methods.The VSSS presenting a virtual surgery scene through computer simulation,provides the operators for interacting with the virtual tissue and organ,which is implemented by a haptic device that can perform surgical operations such as palpating,cutting,tearing and sucking.With high efficiency,low cost,high utilization rate,and no moral and ethical constraints,the VSSS has opened up a brand-new application field for surgical navigation,doctor training and telemedicine.As one of basal and universal operation in actual surgery,realistic simulation of tissue cutting is an essential part of virtual surgery simulation.However,it is very difficult to establish an accurate and efficient model for soft tissue deformation and cutting because human tissue is a special elastomeric material with nonlinear,viscoelastic,anisotropic and incompressible properties.At present,two main problems remaining in the virtual surgery simulation system are that the simulation system is not realistic enough and the real-time performance is not enough.This paper has carried out research on the above two issues:Firstly,the platform composition of the virtual surgery simulation system is introduced including each hardware and software module.Then,the existing soft tissue modeling methods are reviewed from two major modeling systems based on physical and non-physical models.In order to improve the accuracy of the model and to more fully describe the material properties of the soft tissue,Kelvin viscoelasticity was introduced into the soft tissue deformation model based on the meshless method.Finally,the human liver model was used to carry out the deformation simulation experiment.The experimental results show that the model not only shows the deformation process of soft tissue,but also presents the viscoelasticity of soft tissue better than the traditional method.The mesh-based soft tissue cutting model needs to reorganize complex topologies when cutting,and the soft tissue cutting model based on the meshless framework is computationally intensive,the essential boundary conditions are difficult to apply,and the incision drawing is difficult.This paper proposes a cutting model based on meshless method.The model uses a Bezier curve to draw a smooth surface incision that is consistent with the actual surgical incision,while using the surface mesh method to render the outside of the model,which further enhances the effect of visual feedback.The whole point cloud model of the soft tissue is divided into the cutting affected area and the non-affected area,while the level set method is used to judge whether the nodes in the cutting affected area need to be re-calculated,which effectively improves the calculation speed of the model.The accuracy and effectiveness of the proposed model are proved by the cutting test of the two-dimensional model.Finally,the cutting simulation was performed on the soft tissue of human abdomen.The experimental results show that the model not only shows better visual effect,but also improves the calculation efficiency.The soft tissue deformation and cutting models established in this paper belong to the meshless method,which has a lot of advantages in accuracy and computational efficiency because of it does not need to establish a complex mesh topology and saves storage space.It provides an effective method for real-time interaction of virtual surgical systems and lays a solid foundation for the widespread use of virtual surgical systems.