| In current medical diagnosis and treatment, medical assisted systems are receiving more and more attention. With their help, doctors can get their diagnosis much more easily, and give treatment much more quickly. Also, it can train the surgeons'operation skill, help them to find the conditions unusual to avoid accidents.In medical assisted systems, interative operations on soft tissues such as virtual cutting is always necessary, which contains cutting and deformation emulations. How to deal with so much data in real time is always a hard problem. In this paper we make researches on the problem mentioned before based on meshes built by surface reconstruction.To accelerate the data processing rate,an improved algorithm was proposed in this paper based on mass-spring algorithm to simulate mesh deformation. By processing only part of the entire data, the improved algorithm can get the deformation effect much more quickly within the range of given errors. By searching on the mesh, the algorithm generates a copy of part of the mesh, and then there is a refinement on the mesh copy. After refinement we give a second searching operation on the refined mesh to reduce the data further. At last the deformation happened . In the paper, the deformation parameters in mass-spring model are also improved ,which can avoid the result to be not convergence and make the result much better. We use the Breadth-first Traversal Algorithm to search data on the mesh. In mesh cutting we partition the triangles on the mesh collided by the cutting tool. To detect the collisions, we use the hierarchy tree based on OBB boxes, to simplify the updating operations of the tree, we get the collision triangles by the cutting directions and the topological structure of the mesh after the cutting operation is implemented. The results of the researches show that the algorithm proposed in this paper can simulate the cutting and deformation operations on soft tissues well, and they can also meet the real-time requirements.
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