Rolling mechanical imaging: A novel approach for soft tissue modelling and identification during minimally invasive surgery

This paper proposes a novel approach for the identification of the internal structure and mechanical properties of biological soft tissue using a force sensitive wheeled probe to generate a ´mechanical image´ by rolling across the surface of a solid organ. Initially, a testing facility for validating the concept ex-vivo was developed. Preliminary validation tests were carried out on a silicone phantom with embedded abnormalities with the aim to link the derived ´mechanical image´ with the known internal structure. Ex-vivo validation tests were also conducted on excised porcine livers. The data were analyzed in four parts: 1) the dynamic analysis of wheel-tissue interaction to validate that the measured parameters are representative of underlying tissue stiffness; 2) the development of a ´mechanical image´ from the rolling data; 3) a comparison of standard 1-DOF indentation testing with 2-DOF rolling and 4) the characterization of the relationship between force and tissue deflection from the data contained within the mechanical image. The results show that the ´rolling mechanical image´ is capable of capturing information relating to the underlying tissue stiffness distribution and characterizing the force-tissue deflection profile for a tissue sample. Examples of scenarios, where this information could potentially be used, include providing a surgeon with the ability to probe solid organs in-vivo during robot-assisted MIS or providing prior information for the modeling of tool-tissue interactions, such as steerable needles.