The Model Of Soft Tissue Deformation Based On The Method Of Meshfree

With the development of virtual reality and computer technology, virtual surgery has played a more and more important role in the field of medical treatment and public health. It can be utilized in the training of operation skills, operation planning, rehearsal of operations, and navigation of operation etc. In a virtual surgery the key technique is the simulation of soft tissue deformation whose basic function is to stimulate the deformation which occurs when the operation instruments get to contact the soft tissues. Although the model of soft tissue deformation has evolved from non-physical model into deformation model in accordance with its physical characteristics, most existing deformation models are models based upon gridding, which easily lead to gridding distortions or reconstructing gridding and severely affect preciseness and efficiency of the deformation stimulation once changes of topological structure, like material distortion, cutting or suturing happen. Aiming at the lack of existing models, this dissertation carries out a deep research into the stimulation of soft tissue deformation in the virtual surgery. The main contributions of the paper are as follows: Build a compling of Galerkin-based Meshfree and Mass-Spring Models based Viscoelastic model, achieve deformation simulation of soft tissue.Based on limitations existing during the operation process, the soft tissues is described by the soft tissue coupling of Galerkin-based Meshfree Methods and Mass-Spring Models. The soft tissues to be operated on are divided into two parts: operation area and non-operation area. In the operation area, Galerkin-based Meshfree Methods are applied to obtain a precise stimulation, while in the non-operation area, Mass-Spring Models are employed to make stimulation more efficient. Since the definition of discrete model boundary in Galerkin-based Meshfree Methods are relatively vague, in this dissertation a search algorithm to determine the meshfree boundary is put forward. This kind of algorithm is very adaptable, and lays a sound foundation for the establishment of the approximate displacement function of following transitional unit.In order to establish a smooth transition between Meshfree domain and Mass-Spring domain effectively, the approximate displacement function between the two areas needs to be built. In this dissertation a transitional unit is proposed between Meshfree domain and Mass-Spring domain. Also transitional joint point is built in transitional unit. A search algorithm of transitional unit is devised, and the approximate displacement function of transitional unit is built according to the balance conditions about forces and displacements that should be satisfied by transitional joint point.The liver data are sampled to conduct the deformation model in order to prove the effectiveness of the deformation realized in this dissertation. The experiment shows the models based on Kelvin Viscoelastic model of coupling model which Galerkin-based Meshfree methods and Mass-Spring methods can present creep as well as looseness occurring in the deformation process of soft tissues effectively. Not only does it increase the calculation accuracy, but also reduces complication of calculation and improves operating efficiency.