Implantable electrode structures and their RF effects in MRI machines

Abstract

Medical implants incorporating long insulated conductors can generate a serious heating hazard to a patient undergoing a Magnetic Resonance Imaging (MRI) scan. Under the high-power RF field from an MRI machine, the conductors can behave as antennas and concentrate energy into small regions of body tissue, leading to excessive joule heating. Neurostimulator implants that employ long electrode leads such as those for Deep Brain Stimulation (DBS) and Spinal Cord Stimulation (SCS), are highly susceptible to this RF hazard. Patients with these implants are generally contraindicated from MRI.

This thesis examines the heating phenomenon and identifies a variety of methods to mitigate the hazard and gain implant leads MRI safety. Techniques such as thin insulation, surface roughening, and auxiliary decoy filars are explored, with the latter shown to be especially effective at providing safety. Designs are first modelled with electromagnetic simulation software then experimentally proven inside of a gelled saline phantom within a 3T MRI machine. A lab-based measurement method is also established to enable rapid low-cost testing of prototype lead designs.