Effect of the extracranial deep brain stimulation lead on radiofrequency heating at 9.4 Tesla (400.2 MHz)

Purpose: To study the effect of the extracranial portion of a deep brain stimulation (DBS) lead on radiofrequency (RF) heating with a transmit and receive 9.4 Tesla head coil. Materials and Methods: The RF heating was studied in four excised porcine heads (mean animal head weight = 5.46 ± 0.14 kg) for each of the following two extracranial DBS lead orientations: one, parallel to the coil axial direction; two, perpendicular to the coil axial direction (i.e., azimuthal). Temperatures were measured using fluoroptic probes at four locations: one, scalp; two, near the second DBS lead electrode-brain contact; three, near the distal tip of the DBS lead; and four, air surrounding the head. A continuous wave RF power was delivered to each head for 15 min using the coil. Net, delivered RF power was measured at the coil (mean whole head average specific absorption rate = 2.94 ± 0.08 W/kg). Results: RF heating was significantly reduced when the extracranial DBS lead was placed in the axial direction (temperature change = 0-5°C) compared with the azimuthal direction (temperature change = 1-27°C). Conclusion: Development of protocols seems feasible to keep RF heating near DBS electrodes clinically safe during ultra-high field head imaging.