Impact of Lower Limb Amputation on Implant Heating During 1.5 T MRI: Assessment of Active and Passive Device

This study investigates the impact of lower limb amputation on radiofrequency (RF)-induced heating of active and passive implantable medical devices (AIMDs and PIMDs) in a 1.5 T MRI environment.

High-resolution anatomical models representing various body types and levels of amputation (below-knee and above-knee) were explored in the study. Full-wave electromagnetic simulations were used to assess specific absorption rate (SAR) near modular hip prostheses. The RF-induced lead-tip heating for a clinically relevant peripheral nerve stimulation (PNS) device was evaluated following ISO 10974. Results were normalized using whole-body SAR and averaged B1_+rms. Experimental validation was performed using an anatomically inspired leg phantom with embedded metallic implants.

SAR near passive implants increased with implant length and was influenced by the level of amputation. In general, more extensive amputations resulted in reduced SAR due to alterations in tissue geometry. For active implantable medical devices (AIMDs), temperature rise also decreased with greater amputation extent; however, localized heating effects were intensified near the amputation site. Phantom simulation results were in strong agreement with experimental measurements, supporting the accuracy of the modeling approach.

Limb amputation significantly alters RF field distribution, affecting RF-induced heating near both active and passive implants. These results highlight the need for amputation-specific safety assessments during MRI to ensure accurate evaluation of heating risks and implant compatibility in amputee patients.