Characterization of a pre-curved needle for use in distal tip manipulation mechanism

Abstract

The knowledge and technical expertise required for the development of telerobotic systems capable of needle distal tip manipulation is the focus of this thesis. An extensive prior literature review was conducted to examine (1) the current medical devices available to pulmonary radiologists and (2) the current steerable mechanism state of the art. Interviews were also conducted with interventional radiology and cardiology physicians at the Massachusetts General Hospital to define the mechanism functional requirements for a telerobotic system and a first order analysis was undertaken to evaluate three strategies. The selected strategy was based on the concept of deploying a flexible pre-curved stylet from a concentric straight cannula. Analytical models were developed to (1) understand what material properties are required to recover from the imposed strains, (2) compare stylet stiffness relative to each other and the cannulas, and (3) calculate the deployment and retraction forces required for moving the stylet relative to the cannula. Sixteen Nitinol stylets were prototyped and experiments were performed with four different diameter cannulas and an experimental setup and methodology was developed to measure the deployment and retraction forces. The data collected for 48 permutations of stylet diameter, stylet bend radius, and cannula gauge were compared to the analytical model. Retraction forces were measured between .277 and 13.9N, and deployment forces were measured between .191 and 6.95N. For a given cannula it was found that force increases as stylet diameter increases and bend radius decreases. The analytical model better matched the experimental retraction and deployment measurements for the smaller stylet diameters (0.508 and 0.635 mm) with low friction, retraction and deployment forces. It was found that the retraction and deployment force does not necessarily increase or decrease with cannula diameter and it was found that the stylets drawn through the 16 gauge cannula consistently had the lowest deployment and retraction forces recorded across the four cannulas tested. Ultimately, the experimental and analytical tools developed in this thesis helped us select appropriate needle materials and mechanism components for use in a telerobotic system that is under development.