Real time surgery simulation

		Anatomical structures that can be handled in real-time. Uterus with 5000 tetrahedra Volumetric collision detection of a deformable uterus model and a surgical instrument. Interactive simulation of blood flow in a surgical simulation environment. Finite elements coupled with particle system.

Physically plausible soft-tissue deformation in real-time

We have implemented various integration schemes which can handle complex deformable mass- spring models in real-time. All schemes work on tetrahedral models. Our approach to deformable modelling handles non-linear elastic and plastic deformation and preserves volume. Volumetric models have been provided by our project partners T. Frauenfelder, S. Wildermuth, R. Sierra, S. Weiss, and G. Szekely. A software library for physically-plausible deformable modelling has been accomplished which is provided to the Co-Me research network.

Real-time soft-tissue deformation based on linear finite elements

In addition to the mass-spring approach, a very efficient linear Finite Element method has been implemented. A corotated formulation is employed to eliminate artefacts in case of large deformations or rotations. Implicit numerical integration is used for very efficient and robust computation of the dynamic behaviour of the deformable model. The approach handles elastic and plastic deformation. Further, a fracture model based on internal stress tensors has been integrated.

Collision handling for deformable models

We have investigated a new efficient collision detection method, which is especially suitable for deformable models. In contrast to methods for rigid models, our approach does not require time- consuming pre-processing steps. The approach handles collisions of complex, dynamically deforming objects in real-time. The method does not only detect interfering surfaces, but can compute volumetric intersections. The method is based on Layered Depth Images and its implementation is accelerated by current graphics hardware.

Interactive modeling of fluids

Fluids, such as blood or water, are an important component in surgery simulation. Since we are interested in interactive simulators, our investigations in fluids are focused on performance aspects. Our model is based on a Lagrangian formulation, i. e. it is particle-based. Forces at particles are derived from the Navier-Stokes equation using Smoothed Particle Hydrodynamics. The fluid surface is generated as a iso-surface of a colour function via marching cubes. Interactive simulation speed can be achieved for up to 3000 particles. Currently, we are investigating the interaction of fluids with deformable objects.

Applications in computational surgery

In order to apply our simulation components to surgical simulation, we collaborate with several projects within Co-Me. At the moment, we focus on hysteroscopy simulation (project 8, G. Szekely, M. Harders, ETH Zurich), simulation of stent placement (project 12, S. Wildermuth, University Hospital Zurich), and cranio-maxillofacial surgery simulation (project 3, I. Pappas, ME Muller Institute, Bern).