Direct stereotactic targeting of the ventrointermediate nucleus of the thalamus based on anatomic 1.5-T MRI mapping with a white matter attenuated inversion recovery (WAIR) sequence

Abstract

BackgroundThe ventrointermediate nucleus (Vim) of the thalamus is still considered “invisible” on current magnetic resonance imaging (MRI), requiring indirect methods based on stereotactic atlases for estimation of its location. Direct visualization of Vim is desirable to improve targeting. ObjectiveTo evaluate the ability of Inversion-Recovery 1.5-T MR images to produce high-resolution, anatomical depiction of the thalamus suitable for direct Vim targeting. MethodsTwenty patients with essential tremor or tremor associated with Parkinson’s disease received Vim deep brain stimulation (DBS). Fahn-Tolosa-Marin and Unified Parkinson’s Disease Rating Scale (UPDRS) tremor scores were assessed pre- and postoperatively. Preoperative stereotactic 1.5-T MR images of the thalamus were acquired using a White Matter Attenuated Inversion Recovery (WAIR) sequence. Thalamic nuclei were manually contoured on the basis of spontaneous MRI contrasts; labeling relied on 3D identification from stereotactic books and in-house ex vivo 4.7-T microscopic MRI atlas. Vim was then directly probed for electrophysiological confirmation and determination of the optimal site for electrode placement. ResultsThe shape, spatial orientation, and signal contrast of Vim as depicted on our WAIR images were similar to those observed on the Schaltenbrand and Bailey atlas, as well as in our high-field MRI atlas. These images were successfully used for pure direct Vim targeting: at the last follow-up (median = 46.3 months), the average tremor score improved from 3.80 preoperatively to 0.50 postoperatively (on stimulation; P < 0.01). Conclusion1.5-T MRI with WAIR sequence provides high-quality images of Vim suitable in DBS surgery, for accurate preoperative planning, direct targeting and anatomic analysis.