Indentation test of soft tissue for investigating needle tissue machining

In biopsy operations, a sharp edged needle is used to cut and remove the desired tissue specimen to identify and diagnose cancer and other diseases. Accurate needle insertion into soft tissue is of practical importance in cancer diagnosis and therapies. When the needle is inserting into soft tissue, the nonlinear material behaviors result in large tissue deformation and the needle deflection, which will induce large insertion error. In this paper, the concept of needle tissue machining was introduced. Tissue is a new "work piece material" in cutting process, and its mechanical properties have crucial effects on the machining process. Indentation experiments of porcine livers are performed to measure the force response depending on various indentation depths and indentation velocities. The Kelvin model and Neo-Hookean model are selected to develop the nonlinear model of porcine liver. Matlab codes based on Nonlinear Least Square Method have been created to fit the indentation results. This methodology can be used to investigate needle bending, soft tissue deformation and cutting behaviors.