Online Hypermodel-based Path Planning for Feedback Control of Tissue Denaturation in Electrosurgical Cutting

The first closed-loop control of electrosurgical power satisfying a specified tissue damage bound along the desired tissue dissection path is presented. The damage is represented by the 82 °C isotherm corresponding to the admissible tissue denaturation front position in relation to that of the cutting probe tip. The front location is assessed in real time through the infrared temperature readings of the 40 °C isotherm tightly related to the emerging denaturing patch size around the moving probe tip. A control-oriented denaturing hypermodel and its recasting into a form amenable for use in a moving-horizon locally linear model predictive control law are presented. The optimal control action is determined by solving a compound model predictive control problem that targets a number of active one-dimensional domains. This model is obtained from an offline trained nonlinear autoregressive model with exogenous input. To enforce the safety constraints, a supervisor system precedes the path planning control law. This system prevents excessive denaturation by excluding certain system moves, and determines system termination conditions. We experimentally demonstrate the system's performance in two different line-cutting tasks on ex vivo porcine tissue with a desired denaturation front.