A Cascaded Heterogeneous Equivalent Network for Evaluating RF-Induced Hazards on Active Implantable Medical Devices

This article presents a cascaded heterogeneous equivalent network for the evaluation of radiofrequency (RF) induced safety hazards on electrically long active implantable medical devices (AIMDs) exposed to magnetic resonance imaging systems. AIMDs in a highly heterogeneous human body are represented by cascaded transmission line models consisting of segments with different values of effective wavenumbers and characteristic impedances. Two terminations, implantable pulse generator (IPG), and lead-tip are modeled as lumped elements. Methods to extract values for lead-tip impedance, IPG impedance, wavenumber, and characteristic impedance of the AIMDs are proposed and validated through numerical simulations and experimental investigations. Based on these values, one can build up a unique AIMD model along each implanted trajectory inside human body models. The developed models can be used to accurately evaluate the RF-induced voltage and heating for each implantation scenario.