Technique to assess the compatibility of medical implants to the RF field in MRI

Abstract

The standard technique for determining the compatibility of medical implants to the magnetic and RF fields present in Magnetic Resonance Imaging (MRI), requires access to an MRI machine. For implants comprising metals of mostly the non-ferrous kind, it is only the RF field of an MRI machine that is of concern. Implant electrodes can concentrate the RF field in the surrounding tissue and give rise to joule heating. The inherent design of Spinal Cord Stimulators (SCS) and Deep Brain Stimulators (DBS) makes these implants particularly susceptible to hazardous levels of RF heating. We propose a technique that offers a quick and indicative assessment of the compatibility of implant leads to the RF field in 3-Tesla MRI, without needing access to an MRI machine. A dipole antenna, driven by a power amplifier and Continuous Wave (CW), injects RF energy into a gelled saline phantom. The heating in the gel near a test implant electrode is monitored with a fiber optic thermometer. The results are calibrated against measurements made in a 3-Tesla MRI machine.