MRI for targeting in surgical treatment of movement disorders

Background Deep brain stimulation (DBS) is approved by the US Food and Drug Administration and has <italic>Conformité Européenne</italic> CE Mark approval in Europe for the treatment of Parkinson’s disease (PD), dystonia, and essential tremor, with additional indications currently under investigation. The success of this technique is critically dependent on the accurate placement of a DBS electrode into the appropriate target structure. Currently, DBS targets for the treatment of PD include the subthalamic nucleus (STN) or the globus pallidus internus (GPi) [1], for dystonia the target is GPi [2], and for essential tremor the target is the ventral intermediate nucleus (VIM) of the thalamus [3]. Each of these brain targets is relatively small, and the optimal location for a DBS electrode within each structure is even more restricted. The challenge is thus one of placing an electrode array many centimeters deep to the cortical surface, within the motor territory of the structure of interest, but not so close to boundaries with surrounding structures that current spread to these structures results in intolerable side effects. Compounding this challenge is the fact that the target structures can be difficult, if not impossible, to resolve and visualize on standard clinical magnetic resonance (MR) imaging. Various strategies have therefore arisen to improve the likelihood of placing the DBS electrode into the optimal location. Nonetheless, suboptimal electrode location remains a significant problem besetting DBS surgery – with an incidence of 40% in a study of etiologies underlying “failed DBS surgery” [4], in a population of patients referred to a DBS center for evaluation. There remains, therefore, room for further work on the optimization of stereotactic targeting for the DBS procedure.