THE ROLE OF 3TESLA MRI FOR TARGETING THE HUMAN SUB-THALAMIC NUCLEUS IN DEEP BRAIN STIMULATION FOR PARKINSON’S DISEASE.

BACKGROUND: The subthalamic nucleus (STN) represents the optimal target for DBS in advanced Parkinson’s disease (PD). 3T MRI in pre-operative STN localization is rarely described. Objectives of the study are: define mean errors in targeting STN with 3T MRI fused with a 1Tesla stereotactic MRI, avoid magnetic field distortion and verify clinical impact of this methodology. Pre-operative targeting represents one of the most difficult stages of this technique. Two are methods nowadays accepted in literature for obtain targeting in Parkinsons disease DBS : 1) indirect targeting. It is based on the identification on MR, TC or ventriculographic images of the anterior commissure – posterior commissure line as fundamental landmark: sub-talamic nucleus is 12 mm lateral, 1-2 mm posterior and 2-4 mm inferior to the middle AC-PC point. 2) Direct targeting. It is based on the direct identification of STN on MR T2 weighted images. The nuleus is anterior and lateral to red nucleus anterior border on coronal images. As discussed during the II year relation, in this study it is used a third, new technique: a non-stereotactic 3T MRI fused with a 1T stereotactic MRI (routinely adopted for indirect targeting) in order to reduce 3T peripheral magnetic field distortion. MATHERIALS AND METHODS. 20 patients with advanced PD underwent STN-DBS at our center. (M:F=12:; mean age 56y; mean disease duration 11,6 yrs). According to the different targeting methods were divided into two groups: Group A (6 patients, 1T stereotactic MRI alone – indirect targeting) and Group B (14 patients, 3T non-stereotactic MRI fused with 1T stereotactic MRI- direct targeting). Intraoperative neurophysiology - microrecording exploration (3-5 tracks) and macrostimulation - were always performed. Intraoperative leads position was checked with direct fluoroscopy. RESULTS. All patients had an adequate follow-up patients have an adequate follow-up of minimum 6 months (mean 20 months). . Mean UPDRS III score reduction (med-off/stim.-on vs. preoperative med-off) was respectively 69% in Group A and 74% in Group B (p=0.01487, chi-square). Postoperatively, antiparkinsonian treatment was reduced by 66% in Group A and 75% in Group B (p=0.58). The preoperative “central” track (which corresponds to ideal STN targeting) proved to be the most clinically effective in 2/12 leads for Group A vs. 21/28 for Group B (p<0.001). In all patients ha been also calculated on post-op CT scan mean error in the three axis of space (x,y, and z) referring to the pre-operative “optimal” targeting coordinates: X: 0.8 mm +/- 1 SD Y: 0.95 mm +/- 2 SD Z*: 1-2 mm +/- 2 SD *influenced by neurophysiology CONCLUSIONS: 3T MRI is an useful tool in STN-DBS target localiziation, imporving its accuracy. Magnetic field distortion is reducede by fusion with a stereotactic 1T MRI. THE NEUROPHYSIOLOGICAL MONITORING REMAINS FUNDAMENTAL FOR “Z” (ELECTORDE DEPTH) COORDINATE DURING LEAD POSITION AND PREVENTING CLINAL SIDE EFFECTS