The Research And Application On Real-Time Deformation Simulation For Virtual Surgery System

Surgery is an important means of clinical treatment.With the development of technology and living standards,from open surgery to minimally invasive surgery,operation skills of surgeons needs to be more specialized which requires long-term training and accumulation.For a long time,surgeons lacked adequate training opportunities and methods which contradicted the society's huge demand for skilled surgeons.Due to the rapid development of virtual reality and graphic hardware,virtual surgery system has emerged.Through three-dimensional modeling and visualization of structures in vivo,also combining with the immersive human-computer interaction,the virtual surgery system can demonstrate the real surgical procedure and realize interactive operation.It provides targeted repetitive training for surgeons.Real-time deformation simulation is the most critical module in developing a virtual surgery system.It involves the realistic rendering of the human body,sush as the deformation of organs and tissues,trauma,bleeding and suturing.These effects make the virtual surgery system be closer to clinical manifestations.To meet the usability of real-time deformation simulation,there are three key problems needed to be resolved: First,accuracy.Deformability conforms to physical laws and is credible visually;Second,real-time.Deformation calculations can be completed in a very short time;Third,robustness.The model keeps numerical stability in long-term operation process and topology changes without loss of calculation accuracy.Further,to meet the demand of practical applicability,there are two key problems needed to be resolved: First,diversity.Second,usability.Focusing on these two needs,I begin this research work.Firstly,biological soft tissue is the most concern deformable body in virtual surgery system.Different to simple elastic body,as the organic polymers,biological soft tissue has mechanical properties of nonlinearity,viscoelasticity and incompressibility.In order to simulate biological soft tissue realistically,this dissertation proposes a method called SpringPBD.Through introducing the nonlinear-viscous spring into the position based dynamics and combining the volume-invariant constraint,it can simulate the typical mechanical characteristics of biological soft tissues.Compared with off-line finite element method of liver organs,the global error of the SpringPBD is lower than the exsiting mainstream real-time soft tissue deformation method.This method is real-time and highly accurate.Secondly,medical instruments,with the physical model of inextensible elastic rod,such as surgical thread,interventional guidewires and fiber endoscopes are widely used in surgery.The inextensible surgical thread can be used to puncture biological soft tissue,relational twist and tie knot.So its interactions are more complex than others.Therefore,this dissertation takes the inextensible surgical thread as the research target.Using discrete Cosserat rod model and direct distance constraint solver,we achieve a constant length of surgical thread during twisting and bending.The length change ratio is less than 3.2%.In addition,with the continuous collision detection and response,knotting,winding and biological soft tissue suturing are stable in large time step simulation.Furthermore,a complete virtual surgery scene includes biological soft tissue,surgical instruments and blood.According to the technical characteristics of 3D rendering,this dissertation builds a GPU-accelerated unified particle framework,named CSDynamic,by using compute shader.It simulates all types of dynamic objects in virtual surgery based on position based dynamics.Collision detection and constraint projection are the most time-consuming part in physical computing.Through improving parallelism in the algorithm,the acceleration ratio of collision detection goes up to 15 and the constraint projection goes up to 17 in the large number of primitive simulation scenarios.A clamping training scenario is built by CSDynamic.The average calculation time per frame is only 7.19 milliseconds.CSDynamic meets the practical requirements and has cross-platform technical features.Finally,in the application process,this dissertation proposes a rapid development process of virtual surgery system based on Visible Chinese Human,covering modeling methods of human organs and surgical instruments and real-time realistic rendering of surgical scenes.With the building of the Chinese reference man,it can be applied to Chinese of different ages and sizes.By using the process,we construct a virtual laparoscopic cholecystectomy surgery system.The system consists of a five-degree-freedom manipulator and a graphic rendering device.It can be used to train the basic skills and complete surgical procedure.In summary,this dissertation proposes two deformation simulation methods for biological tissue and inextensible surgical thread,a GPU-accelerated application framework and a rapid development process of virtual surgery system.We build a complete process to develop real-time deformation simulation method for virtual surgery system.This process provides reliable technical support for various types of surgical simulation.The method described in this dissertation also has broad prospects in other fields like interactive games,animations,movies and educations.