Design and Implementation of Loop Shaped Steering Mechanisms for Flexible Needles

Abstract

The aim of this study was to develop steerable needle variations based on a simple loop shaped steering mechanism and assess steering performances using a tissue mimicking phantom. Two steerable needle types were developed based on the proposed loop shaped flexible mechanism, called Active Sheath. Each needle consisted of a loop shaped stylet with a conical tip made of superelastic metal alloy Beta-titanium inserted into a fluororesin flexible cannula of a percutaneous transhepatic cholangiodrainage (PTCD) tube with 1.3 mm outer diameter. Push and pull inputs applied to one of the proximal stylet ends can bend the needle right or left. Stylet (A) was homogeneous whereas stylet (B) was thinned around the tip. A robotic steerable system was developed to ensure accurate and precise inputs. The designs were implemented in agar phantom using two input patterns: (1) push and (2) push and pull sequentially. Needle paths with input pattern (1) could be curved depending on input magnitude from 0–0.5 mm at 0.1 mm intervals. Lateral distance for stylet (B) curved path with 0.4 mm input was 35.9 mm from the standard straight path and 16.9% longer than that for stylet (A). Compared with stainless steel and flexible bevel tip needles, stylet (B) distances were 3.1 times longer and 8.5% shorter, respectively. The proposed steerable needles could follow S shaped paths using input (2), and stylet (B) lateral distances were 1.9 times those for stylet (A). Thus, the proposed needles will enable physicians to plan curved paths and extend the target range depending on path shape flexibility.