Maximum Local Tissue Temperature Increase by Implanted Medical Devices Due to Electromagnetic Field Exposure

摘要

High frequency currents induced on electrically conducting implants represent a con-siderable risk for exposed persons in uncontrolled environments. Electrical fields which arise due to current discontinuities, e.g., at the tips of the implant leads can cause strong localized heating of the tissue the leads are embedded in. Heating of up to 2 is gen-erally considered as safe by the U. S. Food and Drug Administration [1]. During MR imaging of patients with metallic implants, the RF fields of the scanner cause currents on the implants which expose the patient to serious risk of exceeding this limit. Whereas this has been described in the recent literature [2], a generalized analysis covering a large range of implant dimensions and frequencies has not been performed. The objective of this study therefore is to evaluate the maximum increase of the tissue temperature for implants at the exposure at the levels of the reference levels [3] fora large frequency range.