Surgical modification of deep brain stimulation lead trajectories substantially reduces RF heating during MRI at 3 T: From phantom experiments to clinical applications

Introduction: Radiofrequency (RF) induced tissue heating around deep brain stimulation leads is a well-known safety risk during magnetic resonance imaging (MRI), resulting in strict imaging guidelines and limited allowable protocols. The implanted lead's trajectory and its orientation with respect to the MRI electric fields contribute to variations in the magnitude of RF heating across patients. Currently, there are no consistent requirements for surgically implanting the extracranial portion of the DBS lead. This produces substantial variations in clinical DBS lead trajectories and hinders RF heating predictions. Recent studies showed that incorporating concentric loops in the extracranial trajectory of the lead can reduce RF heating, but the optimal positioning of the loop remains unknown. In this study, we systematically evaluated the RF heating of 244 unique lead trajectories to elucidate the characteristics of the trajectory that minimize RF heating during MRI at 3 T. We also presented the first surgical implementation of these trajectory specifications and compared their RF heating to the RF heating of unmodified trajectories. Methods: We performed phantom experiments to assess the maximum temperature increase, {Delta}Tmax , of 244 unique lead trajectories. We systematically interrogated the effect of three characteristics related to the extracranial portion of the lead trajectory including the number of concentric loops, the size of the loops, and the position of the loops on the skull. Experiments were performed with a full DBS system from Abbott, and RF exposure was generated from a T1-weighted turbo spin echo dark fluid pulse sequence (B1+rms = 2.7 T). Additional experiments were conducted to assess the reliability of our measurements and to determine the effect of imaging landmarks and perturbations to the DBS device configuration on low-heating lead trajectories. Following the phantom experiments, recommended trajectory specifications were provided to two neurosurgeons and implemented in new patients. Results: Our search protocol elicited lead trajectories with {Delta}Tmax from 0.09 - 7.34 oC. Interestingly, increasing the number of loops and positioning them near the surgical burr hole, especially for the contralateral lead, substantially reduced RF heating. Trajectory specifications based on the results from the phantom experiments were easily adopted during the surgical procedure and generated nearly a 4-fold reduction in RF heating. Discussion/Conclusion: Surgically modifying the extracranial portion of the DBS lead trajectory can substantially mitigate RF heating during MRI at 3 T. Simple adjustments to the lead's configuration can be readily adopted during DBS lead implantation by implementing small concentric loops near the surgical burr hole.