Self-tuning control of Nd:YAG laser coagulation: principle

Abstract

Several medical and surgical fields are concerned by thermal actions of lasers. However, quantification of laser thermal action on biological tissue is not currently performed at the time of treatment. We propose to use a self-tuning control system, in order to improve the safety and efficiency of medical lasers. This study aims to develop a control strategy for real-time control of coagulation using a millisecond pulsed Nd:YAG laser. Temperature evolution was used as a relevant parameter since it is a key factor for thermal damage. A control law was stated using the dynamic programming algorithm which is an optimization technique based on the Bellman's optimization principle. Because the control law was depending on tissue parameters, a parametric adaptive algorithm, based on the least square method, was developed to estimate in real-time the tissue parameters altered by thermal action. Finally, the structure of the self-tuning algorithm was elaborated by linking the dynamic programming algorithm and the parametric adaptive algorithm. The self-tuning control was tested using computer simulation. The results shows that sequences of pulses are producing well-controlled thermal action and that unexpected perturbations are taken into account.