Novel Indentation Depth Measuring System for Stiffness Characterization in Soft Tissue Palpation

This paper presents a novel approach to measuring the indentation depth of a stiffness sensor in real time during a soft tissue palpation activity. The proposed system is integrated into a stiffness probe and is designed to intra-operatively aid the surgeon to rapidly identify the tissue abnormalities with minimum measurement inaccuracies due to tissue surface profile variations. Stiffness probe and the associated surface profile sensors are pneumatic and the newly designed system can concurrently measure the indentation depth and surface profile variations while sliding over the soft tissues in any direction in a near frictionless manner. With the pneumatic pressure maintained constant, the displacement of the sensing element is a direct function of the stiffness of the tissue under investigation. The sensor has a tunable force range and the indentation force can be adjusted externally to match tissue limitations. The prototype of the new design of stiffness probe was calibrated and tested on silicone blocks simulating soft tissue. The results show that this sensor can measure indentation depth more accurately than air cushion probe alone. The structure, working principle, and a mathematical model for this new design are described.