Localization of clinically effective stimulating electrodes in the human subthalamic nucleus on magnetic resonance imaging

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Abstract
Object. The authors sought to determine the location of deep brain stimulation (DBS) electrodes that were most effective in treating Parkinson disease (PD). Methods. Fifty-four DBS electrodes were localized in and adjacent to the subthalamic nucleus (STN) postoperatively by using magnetic resonance (MR) imaging in a series of 29 patients in whom electrodes were implanted for the treatment of medically refractory PD, and for whom quantitative clinical assessments were available both pre- and postoperatively. A novel MR imaging sequence was developed that optimized visualization of the STN. The coordinates of the tips of these electrodes were calculated three dimensionally and the results were normalized and corrected for individual differences by using intraoperative neurophysiological data (mean 5.13 mm caudal to the midcommissural point [MCP], 8.46 mm inferior to the anterior commissure—posterior commissure [AC—PC], and 10.2 mm lateral to the midline). Despite reported concerns about distortion on the MR image, reconstructions provided consistent data for the localization of electrodes. The neurosurgical procedures used, which were guided by combined neuroimaging and neurophysiological methods, resulted in the consistent placement of DBS electrodes in the subthalamus and mesencephalon such that the electrode contacts passed through the STN and dorsally adjacent fields of Forel (FF) and zona incerta (ZI). The mean location of the clinically effective contacts was in the anterodorsal STN (mean 1.62 mm posterior to the MCP, 2.47 mm inferior to the AC—PC, and 11.72 mm lateral to the midline). Clinically effective stimulation was most commonly directed at the anterodorsal STN, with the current spreading into the dorsally adjacent FF and ZI. Conclusions. The anatomical localization of clinically effective electrode contacts provided in this study yields useful information for the postoperative programming of DBS electrodes.