Thermal effects of radiofrequency fields in magnetic resonance imaging on implanted medical devices

Christopher Don Smith, Purdue University

Abstract

Magnetic resonance imaging (MRI) is a well established diagnostic technique, one which all patients should be able to benefit from, including those with implanted medical devices. This study focuses on determining the heating effects of the radiofrequency (RF) fields generated in MRI on a typical geometry that is representative of leads associated with implanted medical devices, such as cardiac pacemakers, nerve stimulators and spinal infusion stimulators. The principle bioeffect of RF fields generated during an MRI sequence is tissue heating. This study was conducted to develop an understanding of the heating which arises from the interaction of the RF field developed during MRI with medical implants, and develop a protocol which can be applied to any implanted medical device. Phantom experiments were performed to examine how heating in the presence of this RF field is affected by: phantom composition and electrical properties, wire insulation thickness, wire length, a partially submersed wire, and wire tip geometry. The knowledge gained from these experiments was used to measure and interpret the RF-induced heating for a commercial device. In the case of an elongated implant, the greatest RF-induced temperature rise occurs near the ends of the implant and the amount of temperature rise depends on implant geometry, implant location and other factors. For example, when magnet wires with thin insulation were in the phantom, a critical length was found such that RF-induced heating was greatest for a medium wire length, and less for the longer and shorter wires.

Degree

Ph.D.

Advisors

Bourland, Purdue University.

Subject Area

Electrical engineering|Biomedical engineering

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