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Free keywords:
Electromagnetics; Radio frequency (RF) safety; Heating; Active implantable medical devices
Abstract:
One of the major components of magnetic resonance imaging safety for patients with an active implantable medical device is the evaluation of in vivo radio frequency induced heating of tissue near a lead electrode, which can result in tissue damage. This numerical case study investigated a number of the recommendations, assumptions, and requirements of Clause 8 of the technical specification ISO/TS10974. For this, a lead electromagnetic model (LEM) of a generic coax lead at 128 MHz was evaluated with 3-D electromagnetic and thermal cosimulations of the entire lead. Two sets of 120 incident electric fields with different profiles were generated in a homogenous medium using the electrical properties of blood by an array of four antennas. Substantial dependence of power deposition and temperature profiles around lead electrodes on the incident electric field did not reduce the quotient of the variances of the fitted LEM values, observed values of power deposition, and the net temperature increase, above background, with the presence of the generic coax lead. Our results indicate that the power injection approach based only on the comparison of the temperature increase in the medium along the lead tip electrode axis can result in substantial underestimation or overestimation of power deposition around lead electrodes.