Local SAR near deep brain stimulation (DBS) electrodes at 64 and 127 MHz: A simulation study of the effect of extracranial loops.

PURPOSE: MRI may cause brain tissue around deep brain stimulation (DBS) electrodes to become excessively hot, causing lesions. The presence of extracranial loops in the DBS lead trajectory has been shown to affect the specific absorption rate (SAR) of the radiofrequency energy at the electrode tip, but experimental studies have reported controversial results. The goal of this study was to perform a systematic numerical study to provide a better understanding of the effects of extracranial loops in DBS leads on the local SAR during MRI at 64 and 127 MHz.

METHODS: A total of 160 numerical simulations were performed on patient-derived data, in which relevant factors including lead length and trajectory, loop location and topology, and frequency of MRI radiofrequency (RF) transmitter were assessed.

RESULTS: Overall, the presence of extracranial loops reduced the local SAR in the tissue around the DBS tip compared with straight trajectories with the same length. SAR reduction was significantly larger at 127 MHz compared with 64 MHz. SAR reduction was significantly more sensitive to variable loop parameters (eg, topology and location) at 127 MHz compared with 64 MHz.

CONCLUSION: Lead management strategies could exist that significantly reduce the risks of 3 Tesla (T) MRI for DBS patients. Magn Reson Med 78:1558-1565, 2017. © 2016 International Society for Magnetic Resonance in Medicine.