Methods for Improving the Curvature of Steerable Needles in Biological Tissue

Objective: Robotic needle steering systems have the potential to improve percutaneous interventions such as radiofrequency ablation of liver tumors, but steering techniques described to date have not achieved sufficiently small radius of curvature in biological tissue to be relevant to this application. In this study, the impact of tip geometry on steerable needle curvature was examined. Methods: Finite-element simulations and experiments with bent-tip needles in ex vivo liver tissue were performed. Motivated by the results of this analysis, a new articulated-tip steerable needle was designed, in which a distal section is actively switched by a robotic system between a straight tip (resulting in a straight path) and a bent tip (resulting in a curved path). Results: Selection of tip length and angle can greatly improve curvature, with radius of curvature below 5 cm in liver tissue possible through judicious selection of these parameters. An articulated-tip mechanism allows the tip length and angle to be increased, while the straight configuration allows the needle tip to still pass through an introducer sheath and rotate inside the body. Conclusion: Validation testing in liver tissue shows that the new articulated-tip steerable needle achieves smaller radius of curvature compared to bent-tip needles described in previous work. Significance: Steerable needles with optimized tip parameters, which can generate tight curves in liver tissue, increase the clinical relevance of needle steering to percutaneous interventions.