Real-Time Finite Element Models for an Immersive Surgical Simulation Environment

Alex Lindblad, University of Washington

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The need for a realistic interactive suturing simulation arises from the inherent difficulties of teaching medical students suturing techniques and assessing the ability of these students. A realistic suturing simulation must be based on the physical properties of skin, tissue and bone, which can be incorporated in a finite element model.

The model presented uses quadratic triangular membrane elements to represent skin, quadratic triangular prismatic elements to model the underlying tissue, and fixed internal boundaries to represent the interface between bone and tissue. The skin is attached to the underlying tissue through use of nodal displacement constraints, allowing for undermining and repositioning of skin tissue throughout the simulation. Sutures are modeled as displacement constraints, thus allowing for dynamic modification of the system. Taking advantage of matrix preprocessing, condensing out subsurface nodes, using linear material properties and only solving for what is minimally needed allows this application to run in real-time.

The suturing simulation utilizes two haptic devices for force feedback, the left hand a forceps and the right hand a needle driver, and stereoscopic glasses for depth-of-field. To enable real-time graphic updates, the displacements in the finite element model must be updated at a rate of 30 Hz; while the haptic devices need force updates at a rate around 1000 Hz. To accommodate the necessary high haptic rates, the forces for each haptic device are interpolated from the previous force values.

A simulation of this caliber not only allows medical students to practice realistic suturing, it can give immediate feedback on the quality of each suture through visual displays of skin tension and deformation, and suture spacing. The use of real-time finite element models coupled with haptic force feedback and stereoscopic vision in this simulation push the state-of-the-art in surgical simulations closer to a point of medical integration.

Abstract Author(s): Lindblad, A., Turkiyyah, G., Weghorst, S., Berg, D., Sankaranarayanan, G.