| Biomechanical model of soft tissue derived from experimental measurements is critical to develop a reality-based model for minimally invasive surgical training and simulation. In our research, we have focused 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. Our method is to measure the tissue's biomechanical properties both ex vivo and in vivo . The Local Effective Elastic Modulus (LEEM) values are derived by the inverse finite element method. LEEM describes the tissues' stiffness and is the critical model parameter to develop a reality-based haptic display.; Liver tissue is nonlinear, non-isotropic, non-homogeneous and inelastic material. It has an extremely nonlinear stress-strain relationship. Our initial research proposed a hybrid liver model derived from a series of indentation experiments, which is valid in both low strain and large strain regions. However, this model does not provide an accurate displacement field of the area surrounding the probe, though it can provide an accurate force-displacement behavior at the point of probing. To develop the model for soft-tissue response to probing, we developed a large probe model, whereby the probe is larger than the tissue sample being probed. An experimental apparatus was developed to perform large-probe compression tests for pig liver specimens with cylindrical geometry.; In vivo tissue has drastically different properties from the ex vivo tissue because of the changing factors in temperature, hydration, break-down of protein, and loss of blood. In surgery, the surgeons contact with in vivo tissues rather than ex vivo tissues. It is critical to obtain the mechanical properties of in vivo tissues for a surgical simulator. As a result, after completing large probe modeling work on ex vivo tissue, we proceeded to develop an in vivo model. 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 in vivo soft tissue. (Abstract shortened by UMI.)... |
