Insulation, Lead-Length, and Sample-Size Affect the MRI-Safety of Implanted Leads

Ananda Kumar¹, Perry Karmarkar¹, William A. Edelstein¹, Paul A. Bottomley¹

Concerns about RF heating of implanted devices precludes MRI for many patients who could otherwise benefit. Implanted leads are insulated and vary in length, depending on function and patient size. We investigated experimentally and theoretically the local specific absorption rate (SAR) and heating of leads as a function of sample size, lead length, and insulation thickness in gel phantoms exposed to 4W/kg at 1.5T. Heating and SAR are maximum at the bare electrode, increasing with lead insulation thickness and sample size. SAR is highly nonuniform so sensor sampling volume is critical for matching local theoretical SAR with measured temperature changes.