Objective: To characterize an optimized magnetic resonance imaging (MRI) sequence (high-resolution three-dimensional T2 star weighted angiography: HR 3-D SWAN) for direct STN targeting.
Methods: Sequence distortions were measured using the Leksell stereotactic phantom. Eight consecutive candidates for STN-DBS underwent HR 3-D SWAN MRI for direct identification of the STN (16). Two senior neurosurgeons independently determined the boundaries of STN on a semiquantitative scale (ranging from 1 (identification very easy) to 4 (identification very difficult)) and the anatomical target within the nucleus. The anatomical data were compared with electrophysiological recordings (48 micro-recordings). We examined the anatomical location of the active contacts on MRI.
Results: The mean distortion error over the phantom was 0.16 mm. For the 16 STNs, identification of the upper, internal, anterior and external edges was considered to be easy (scores of 1 or 2). The distinction between the substantia nigra and the STN was rated 1 or 2 for all but 6 nuclei. In the mediolateral axis, electrophysiological recordings covered perfectly anatomical data. In the craniocaudal axis, the mean differences between the electrophysiological data and the anatomical data were 0.8 mm and 0.19 mm for the “entry” and “exit” of the STN, respectively. All active contacts were located within the STN on MRI.
Conclusion: HR 3-D SWAN allows an easy visualization of the STN. Adapted to stereotactic requirement, the sequence simplifies direct targeting in STN-DBS surgery.
From: High-resolution Three-dimensional T2 Star Weighted Angiography (HR 3-D SWAN): An Optimized 3T MRI Sequence for Targeting the Subthalamic Nucleus by Lefranc et al.