A New Approach to Ultra-Thin Needle Steering

Abstract

Flexible steerable needles can follow curved paths inside the human body, allowing to steer around objects, to adjust for mispunctures, and to reach multiple targets. However, the designs of existing ultra-thin (diameter < 1 mm) steerable needles require axial rotation of the needle to steer in 3D space causing needle twisting, which results in difficulties in needle trajectory control. Therefore, the goal of this paper is to design and experimentally evaluate an ultra-thin steerable needle, which can steer omnidirectional without the need of axial rotation.This study describes a new way of ultra-thin needle steering by a retractable steering mechanism inside a flexible cannula. The steering mechanism prototype consists of three Nitinol wires with a small custom-made curvature at the tip to increase the internal bending moment. Pulling one or multiple elements results in reorientation of the tip , thereby allowing to steer without axial rotation of the needle. An experimental prototype was made, which includes the needle together with a control unit. The final needle prototype has a total of three elements to steer in three-dimensional space and has an outer diameter of 0.5 mm.The prototype was tested in porcine gelatine phantoms (10 wt%) to evaluate the performance of the needle in terms of steering direction and curvature. The needle was able to steer towards the direction of the retracted element. Increasing the level of element retraction resulted in a higher steering curvature.The maximal median deflection was 62.76 mm for an insertion of 65 mm into the gelatine. The proposed needle showed good potential in omnidirectional steering with high curvature and it is able to follow multi-curved trajectories. Future improvements can be done to refine the design and make it user-friendly. Possibly, this will allow the proposed needle to compete with ultra-thin standard bevel-tip and pre-curved needles.