Modeling In vivo Soft Tissue Probing

A biomechanical model of in vivo soft tissue derived from experimental measurements is critical for developing a reality-based model for minimally invasive surgical training and simulation. In our research, we have been focusing on developing a biomechanical model of the liver with the ultimate goal of using this model for local tool-tissue interaction tasks and providing feedback to the surgeon through a haptic (sense of touch) display. In this paper, we present our approach for characterizing the nonlinear property of soft tissue in vivo under large deformation. We developed an experimental method for in vivo soft tissue test, and an axisymmetric finite element model to obtain the local effective elastic modulus (LEEM) of the tissue. A microcontroller-based portable probe was developed to measure the force and displacement in vivo of the pig liver tissue undergoing large deformation. The probe indented the liver up to 40% of its nominal thickness at a speed of 1.5 mm/sec. Based on the experimental force and displacement data, we obtained the LEEM by an inverse finite element method