Safely Detecting Device Coupling using Reversed RF Polarization and Pre-Spoiled EPI

Purpose: Patients with many types of common implants, including pacemakers and neurostimulators, are ineligible for MR scans due to the potential for tissue heating arising from RF coupling between the excitation field and their device. The severity of this coupling can be detected by reversing the RF polarization in the birdcage RF receiver. Ideally, this results in MR signal only around coupled structures within the excitation volume. To exploit this effect for implant safety assessment, total RF power must be kept under a safe limit even in the case of maximum coupling. Here, we show that a four-shot projection EPI image of the region containing the implant can be used safely given some reasonable assumptions. Furthermore, robustness can be improved by adding a pre-spoiler gradient that effectively suppresses signal imperfections due to electrodynamic effects while minimally affecting the desired signal.