Study Of Bleeding Simulation In Virtual Surgery

Virtual surgery is an interdiscipline composed of modern medical and computer technology, and it involves in model medical, computer graphics, digital image processing, biomechanics, force feedback technology and so on. The virtual surgery simulation system is an important tool for medical education and preoperative planning, which provides a real and correct virtual environment for doctors using computer modeling and simulation technology according to the existing patient data. In order to make it easy for researchers to research and develop in virtual surgery field, domestic and foreign scholars provide some general framework of virtual surgery based on their research results, such as Spring, SOFA, GiPSi and so on. The framework contains the basic algorithm and modules needed for virtual surgery simulating system’s constructing, such as human-computer interaction, collision detection, organization modeling, deformation and cutting simulation, fluid engine, graphics engine, sound engine, force feedback and so on. With the framework, developers can set up a simulation system for specific operation process.Visual feedback is an important interaction of virtual surgery simulation system. The system providing realistic and real-time visual feedback can enhance the user’s experience and improve training effect. Blood is an important component of a human body, and organs or skin bleeding is a common phenomenon during the operation, therefore, bleeding simulating is an important part of virtual surgery simulation system.Based on the Navier-Stokes equation, the paper adds the temperature transmission equation as the blood’s controlling equation. We use the smooth particle hydrodynamic method to research the bleeding simulation after cut, the blood flowing in the organs and interaction between them. The paper also describes the changers of human body by constructing body bleeding model. The simulating process is dispersed into many discrete time points, and in each time points, blood is described as discrete particles, we can get the accelerated speed of particles by solving the blood flow’s controlling equations, then use the Leap-Frog numerical calculation method to update the position of particle. During the computation we only need to save the particle state of last moment using intermediate variables.The whole bleeding simulation consists of two parts including system’s initialization and cyclically calculation. In system’s initialization part, we read the data from model file or the wound, set the related parameters of blood and the human bleeding model, init the state of the blood particles, complete the GPU’s memory’s allocation and transform the data. In cyclically calculation phase, we need to solve the blood flow’s controlling equation to get the position, temperature of particles and the force acting on the particles, and compute the interact force between the particle and organs. When the temperature of the particle reach the low threshold value, we modify the attribute of particle to simulate the blood’s coagulation effect and use the OpenGL graphics interface to make a feedback for the user when the calculation is completed.There is a contradiction between a sense of reality and real-time required in bleeding simulation of virtual surgery. Thus, this paper uses GPU to deal with the time-consuming calculations of solving the Navier-Stokes equation, for the reason that the computing power of GPU is better than CPU. In the simulation, GPU is used to extract the surface of blood stored in the memory and uses the OpenGL to draw the data in the memory directly based on the characteristics of CUDA to reduce the transmission of data between the CPU and GPU end. In addition, we design a parallel algorithm of collision detection based on the idea treating the model as the particle to reduce the computational scale and improve the computational efficiency.