Individualized Tractography-Based Parcellation of the Globus PallidusPars Interna using 7T MRI in Movement Disorder Patients Prior to DBSSurgery

摘要

The success of deep brain stimulation (DBS) surgeries for the treatment of movement disorders relies on the accurate placement of an electrode within the motor portion of subcortical brain targets. However, the high number of electrodes requiring relocation indicates that today’s methods do not ensure sufficient accuracy for all patients. Here, with the goal of aiding DBS targeting, we use 7 Tesla (T) MRI data to identify the functional territories and parcellate the globus pallidus interna (GPi) into motor, associative and limbic regions in individual subjects.7T MRI scans were performed in seventeen patients (prior to DBS surgery) and one healthy control. Tractography-based parcellation of each patient’s GPi was performed. The cortex was divided into four masks representing motor, limbic, associative and “other” regions. Given that no direct connections between the GPi and the cortex have been shown to exist, the parcellation was carried out in two steps: 1) The thalamus was parcellated based on the cortical targets, 2) The GPi was parcellated using the thalamus parcels derived from step 1. Reproducibility, via repeated scans of a healthy subject, and validity of the findings, using different anatomical pathways for parcellation, were assessed. Lastly, post-operative imaging datawas used to validate and determine the clinical relevance of theparcellation.The organization of the functional territories of the GPi observed in ourindividual patient population agrees with that previously reported in theliterature: the motor territory was located posterolaterally, followedanteriorly by the associative region, and further anteroventrally by the limbicterritory. While this organizational pattern was observed across patients, therewas considerable variability among patients. The organization of the functionalterritories of the GPi was remarkably reproducible in intra-subject scans.Furthermore, the organizational pattern was observed consistently by performingthe parcellation of the GPi via the thalamus and via a different pathway, goingthrough the striatum. Finally, the active therapeutic contact of the DBSelectrode, identified with a combination of post-operative imaging andpost-surgery DBS programming, overlapped with the high-probability“motor” region of the GPi as defined by imaging-basedmethods.The consistency, validity, and clinical relevance of our findings havethe potential for improving DBS targeting, by increasing patient-specificknowledge of subregions of the GPi to be targeted or avoided, at the stage ofsurgical planning, and later, at the stage when stimulation is adjusted.