New Approaches in MRI at 3T Dedicated to Targeting Subthalamic Nucleus on Parkinsonian Patients (Optimise_3T)

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a validated procedure, used in many French and international centers for the treatment of severe forms of Parkinson's disease (PD). The improvement of parkinsonian motor symptoms by stimulation of the STN is 50 to 80% on average. The main advantage of DBS is that the surgery has low morbidity and mortality, it is adaptable to the patient's symptoms and that its effect is reversible. This treatment is now a routine and more than 85,000 patients worldwide have benefited from the installation of this system. Since 1997, this treatment is available to patients followed in the Pitié Salpêtrière (GHPS).

The quality of the implantation of stimulating electrodes into deep brain structures to achieve, particularly in the NST for PD patients, is crucial to obtain an excellent result. Accurate identification of these deep nuclei and especially the NST on MRI of each patient to be operated is an essential step and directly affects the smooth running of the surgery and the final clinical outcome.

The visualization of the NST on MRI remains difficult, variable between patients, requiring specific sequences or even sequences dedicated to this activity. In GHPS the investigators opted for the realization of an efficient particular sequence for viewing the NST but the latter has several disadvantages the first being its duration. Indeed, the patient needs to keep still, head fixed for 40 minutes, and this major constraint is sometimes impossible due to the importance of abnormal movements. The second is the variability between patients with visualization being sometimes inconspicuous. The third is the susceptibility of this sequence to flow artifacts at the level of the third ventricle that significantly disrupt viewing NST.

The new MRI techniques available for some years, especially at 3 Tesla should allow better visualization of the deep nuclei of the brain and NST in particular. Indeed, the high-field MRI has become an indispensable tool for both define the morphological and structural features but also functional and metabolic deep nuclei of the brain, particularly the NST.

The accuracy of preoperative anatomic targeting in stereotactic neurosurgery will improve with the use of high-field MRI. However, several new issues and inherent in that high-field MRI should be evaluated before the images can be used directly.

The chosen sequence must be short to be feasible, minimizing patient discomfort, and evaluated several patients to ensure the low interindividual variability. In addition, the quality of the display on all of the sections should provide a reliable three-dimensional information. Finally, the quality of targeting and its possible improvement should be checked.