Design and evaluation of duty-cycling steering algorithms for robotically-driven steerable needles

Asymmetric-tip, robotically controlled steerable needles have the potential to improve clinical outcomes for many needle-based procedures by allowing the needle to curve and change direction within biological tissue. Algorithms have previously been developed to change the curvature of the needle trajectory via duty-cycled spinning. However, these algorithms require continuous rotation of the steerable needle, preventing the use of instrumentation such as force-torque sensors and electromagnetic trackers, due cable wind-up issues. In this paper, we present two novel control methods for duty-cycling a steerable needle without the need for continuous rotation: bidirectional duty-cycled spinning and duty-cycled flipping. These algorithms can be implemented on existing robotic needle steering systems without hardware changes. We evaluate our algorithms using a custom hollow steerable needle, with an embedded EM tracker and a force-torque sensor. We compare the path tracking error, needle insertion forces, and needle axial rotation torques of our algorithms and found no significant differences between the two algorithms in terms of tracking error. Duty-cycled flipping has significantly lower mean insertion forces and torques than bidirectional duty-cycled spinning, and differences in insertion force and rotation torque variability were also found. These results may have interesting implications for tissue health.