Soft tissue deformation using a nonlinear hierarchical finite element model with real-time online refinement.

Simulating soft tissue deformation in real-time is a requirement for realistically rendering the VR interaction between human organs and surgical tools. Finite Element Model (FEM) describes complex mechanical and physiological behaviour but it is computationally too demanding especially when a nonlinear model is to be implemented. For this reason, we introduce a multiresolution approach to FEM that only employs the region of the object under deformation to find the solution of the differential equations of motion. In order to increase the quality of the deformation, refinement of the original mesh is performed with the insertion of new surface nodes in real-time in the region of interaction. To guarantee the stability of the nonlinear model, the presence of flat tetrahedra (slivers) has to be avoided; therefore a sliver elimination technique has been implemented resulting in a more stable simulation.