Tissue property estimation and graphical display for teleoperated robot-assisted surgery

Manual palpation of tissue and organs during a surgical procedure provides clinicians with valuable information for diagnosis and surgical planning. In present-day robotassisted minimally invasive surgery systems, lack of perceptible haptic feedback makes it challenging to detect a tumor in an organ or a calcified artery in heart tissue. This study presents an automated tissue property estimation method and a real-time graphical overlay that allow an operator to discriminate hard and soft tissues. We first evaluate experimentally the properties of an artificial tissue and compare seven possible mathematical tissue models. Self-validation as well as cross-validation confirm that the Hunt-Crossley model best describes the experimentally observed phantom tissue properties and is suitable for our purpose. Second, we present the development of a system in which the phantom tissue is palpated using a teleoperated surgical robot, and the stiffness of the Hunt-Crossly model is estimated in real time by recursive least squares. A real-time visual overlay representing tissue stiffness is created using a hue-saturation-luminance representation on a semi-transparent disc at the tissue surface. Hue depicts the stiffness at a palpated point and saturation is calculated based on distance from the point. A simple interpolation technique creates a continuous stiffness color map. In an experiment, the graphical overlay successfully shows the location of an artificial calcified artery hidden in phantom tissue.