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

Abstract

AbstractIntroductionRadiofrequency (RF) induced tissue heating around deep brain stimulation (DBS) 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 modified trajectories and compared their RF heating to the RF heating of unmodified trajectories.MethodsWe performed phantom experiments to assess the maximum temperature increase, ΔTmax, of 244 unique lead trajectories. We systematically interrogated the effect of three characteristics related to the extracranial portion of the lead trajectory, namely, the number of concentric loops, the size of the loops, and the position of the loops on the skull. Experiments were performed in an anthropomorphic phantom implanted with a commercial DBS system, and RF exposure was generated by applying a high-SAR sequence (T1-weighted turbo spin echo dark fluid pulse sequence, B1+rms= 2.7 μT). Test-retest experiments were conducted to assess the reliability of measurements. Additionally, we determined the effect of imaging landmark and perturbations to the DBS device configuration on the efficacy of low-heating lead trajectories. Finally, recommended modified trajectories were implanted in patients by two neurosurgeons and their RF heating was characterized in comparison with non-modified trajectories.ResultsOur search protocol elicited lead trajectories with ΔTmaxfrom 0.09 – 7.34 °C. 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/ConclusionSurgically 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.