Real-Time Ultrasound Simulator Us- Ing Deformable Mesh Models

Percutaneous puncture is a branch of minimally invasive surgery, and is widely used in many treatment occasions, such as biopsy, thrombus removal, tumor ablation et al. However, tradition-al ways of needle puncture training has many disadvantages and needle puncture virtual training system has the potential to solve the related problems. In this paper, real-time property of the training system is studied, and a virtual training system based on tissue deformation is built. The virtual training system is consist of three modules, respectively is the finite element analysis mod-ule, display module, and haptic module, this thesis research on real-time property around these respects.Firstly, the grid size function is used to control the size of the finite elements so as to reduce the total element number, and accelerate the process of finite analysis calculation. In needle puncture cases, we care deformation near the trajectory more than that far away, so element size near the trajectory could be smaller and the rest larger. On the other hand, elements with small angles should be avoided, thus need to limit gradient of the grid size function.Secondly, fast point location method is used to replace the original point location, optimize the ultrasound image generation algorithm, which makes the process of generating an ultrasound picture faster. Fast point location make full use of the intersection of the tetrahedron elements with ultrasound scanning plane, by means of an intermediate data structure to store the serial number of the intersected elements. To generate such a data structure, mainly refers to Bresenham line drawing algorithm to locate pixels unit between two pixel points.Finally, this thesis developed a real-time virtual training system with tissue deformation simu-lated, which is composed by three modules mentioned above. Display module can display both the three-dimensional virtual scene and two-dimensional ultrasound image. Finite element analysis module provides deformation information according to the interaction between tissue and needle. Force feedback module simulates the puncture force and renders it back to the manipulator.