Computational study of the effects of orthopedic plates on gradient-induced peripheral nerve stimulation under MRI using electromagnetic and neurophysiological modeling.

Purpose: This study investigates the impact of orthopedic plates on peripheral nerve stimulation (PNS) during MRI, focusing on how the presence of implants affects PNS thresholds.

Methods: A combination of anatomical electromagnetic and neurophysiological modeling was utilized. Electromagnetic fields in human body models were simulated, both with and without orthopedic plates. Simulations were performed under x-, y-, and z-axis gradient coils, with plates implanted at two clinically relevant locations. Nerve responses were modeled using an established neurophysiological model.

Results: The presence of orthopedic implants significantly influenced nerve stimulation, leading to reductions in stimulation thresholds of up to 80%. Some of the reduced thresholds were close to the PNS limits outlined in International Electrotechnical Commission (IEC) 60601-2-33, suggesting a considerably reduced safety margin compared to cases without implants.

Conclusion: Orthopedic implants can substantially lower the activation thresholds of nearby nerves, with some thresholds approaching the PNS limits defined in IEC 60601-2-33 for MRI gradient field. This finding indicates a reduced safety margin for patients with implants, highlighting the need for more comprehensive safety assessments.