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.