Multi-probe robotic positioner for cryoablation in MRI

Abstract

This thesis describes the design of a guidance device for faster and more accurate targeting of multiple probes during cryoablation and other percutaneous interventions performed in closed bore magnetic resonance (MR) imaging systems. The device is intended to be mounted onto a Siemens 110 mm MR loop coil that rests on the patient and contains a cable driven two-degree-of- freedom spherical mechanism that orientates the intervention probes about a remote center of motion located 15 mm above the skin entry point. A carriage, pulled by strong and low stretch cables, can position up to three intervention probes as it travels on a rotating hoop. Its motion is constrained by a custom designed roller bearing to minimize friction. A thumbscrew fastened latch allows a probe to be engaged in a guide that constrains the probe along a specific trajectory. The probe can also be disengaged from its track, freeing it to move with respiration and enabling the guide to be repositioned for another probe to be inserted. Compact MR compatible piezoelectric motors are used to actuate the system. A prototype was built from 3D printed ABS plastic as a proof of concept. Bench level evaluation demonstrated that each component of the device performs according to the design specifications. The device performance was characterized by analyzing still images taken before and after movement, which yielded sub-degree accuracy, sub-degree repeatability near vertical position, and an incremental step resolution of at least 0.5 degree. Upon further developments of the registration and calibration modules in 3D slicer to interface the robot with image data, evaluation of the device in MRI will be performed.