Torsional dynamics compensation enhances robotic control of tip-steerable needles

Needle insertions serve a critical role in a wide variety of medical interventions. Steerable needles provide a means by which to enhance existing percutaneous procedures and afford the development of entirely new ones. Here, we present a new time-varying model for the torsional dynamics of a steerable needle, along with a new controller that takes advantage of the model. The torsional model incorporates time-varying mode shapes to capture the changing boundary conditions caused during insertion of the needle into the tissue. Extensive simulations demonstrate the improvement over a model that neglects torsional dynamics and illustrates the possible effect of torsional model order on efficacy. Pilot feedback control experiments, conducted in artificial tissue (plastisol) under stereo image guidance, validate the overall approach: our results substantially out-perform previously reported experimental results on controlling tip-steerable needles.