Impact of lateral movement of patients on radiofrequency-induced heating of active and passive implantable medical devices at 3T MRI.

Purpose: To investigate the implications of lateral patient position on radiofrequency (RF)-induced heating of active and passive implantable medical devices (AIMDs and PIMDs) in a wide-bore 3T MRI system.

Methods: In vitro simulations for two rod positions and three lateral phantom shifts were experimentally validated inside a wide-bore 3T MRI scanner. Three commercially available AIMDs (40-cm peripheral nerve stimulator [PNS], 45-cm restorative neurostimulator, and 50-cm cardiac rhythm management system) were analyzed. RF-induced heating for AIMDs was assessed using the transfer function method, which combines transfer functions with tangential electric fields along clinically relevant device pathways for the Duke, Ella, and Fats human body models. Thirty-minute temperature rises were numerically simulated near four orthopedic PIMDs (shoulder, hand-wrist plate, femoral plate, hip replacement) inside human body models.

Results: RF-induced heating of the titanium rod varied with lateral phantom shifts due to changes in electric-field distribution. Centrally positioned cardiac rhythm management and restorative neurostimulator devices exhibited less than 4°C and 1°C 95th percentile temperature rise variation, respectively. Meanwhile, some PNS devices, due to their peripheral placement in regions with varying electric-field exposure, showed up to 8.8°C variation in 95th percentile temperature rise. Similarly, 1-g mass-averaged specific absorption rate near PIMDs increased by up to 50 W/Kg, and a 19.7% increase in temperature rise is noted.

Conclusion: The increased flexibility in lateral patient position within wide-bore MRI can increase RF-induced heating with implications for MR conditional labeling, especially for PNS devices and PIMDs.