Instrument guide for MRI-guided percutaneous interventions

Abstract

As MRI guided interventions are becoming more widely practiced, the goal of this thesis was to design an instrument guidance device for MRI-guided percutaneous interventions in closed bore systems, namely cryoablation procedures where multiple probes need to be placed to treat a tumor. Multiple meetings with researchers and clinicians the Brigham and Women's Hospital were conducted to understand the challenges currently faced by interventionists, to set functional requirements for the design of a system to overcome them, and to help select a clinically viable strategy. The strategy selected involved making a device that had two degrees of angular freedom about a remote center of motion located at the probe entry point on the skin. This device is designed to be incorporated with a custom built MR coil. Structural and finite element analysis was conducted for a number of different mechanism concepts to examine their stiffness and the effect of structural displacements on the end-point probe placement accuracy. The selected concept was a curved arm piece that travels around the pivot point on a circular base, and an additional needle holder that travels along the curved arm. The sliding parts were designed with five points of constraint so that only sliding motion was possible. Thumb screws were used for preload and locking so that the probe guide could be locked along a specific trajectory. The device was prototyped via stereolithography as a proof of concept. It was found that sanding was required to fit the parts together because of overbuild in the stereolithography process. The parts functioned as designed and demonstrated that a probe could be angled about a remote pivot point. However, wear of the plastic parts eventually caused increased play between the plastic parts. Further testing and optimization of the device is planned.