Registering Surgical Tool to a Soft Body using Mechanical Palpation

Registering a surgical tool to an a priori model of the environment is an important first step in computer-aided robotic surgery. Registration of the surgical tool to a flexible environment such as an organ is difficult due to organ shifting and deformation. Palpating an organ reveals stiffness information that can serve as anatomic fiducials and facilitate the registration. In this work, locally stiff features such as arteries and tumors are used to preregister the tool to the organ model. Following that, we use a Kalman filtering framework to register the surgical tool to the surface of the organ. The tissue is palpated with regulated forces and a palpation depth dependent stiffness model is used to capture the interaction between the tool and the tissue. We believe this is the first presentation of a method to preregister and register a surgical tool to a flexible environment using only mechanical palpation. The algorithm is experimentally evaluated using a 3-DOF Cartesian slave robot that interacts with a phantom tissue model. The effectiveness of the preregistration step and the registration algorithm are validated and the results demonstrate that the proposed method improves registration accuracy and the preregistration step leads to faster convergence