203 Application Accuracy of a Second Generation Interventional MRI Stereotactic Platform

INTRODUCTION: Interventional MRI-guided stereotaxy has become an established alternative to frame-based surgery for a variety of neurosurgical procedures including deep brain stimulation, drug delivery, laser ablation and brain biopsy. ClearPoint is a commercially available, second-generation platform for performing iMRI-guided surgery using real-time MR imaging under general anesthesia with no physiological mapping. The performance of this system has been characterized in phantom testing, but not in real-world application accuracy. METHODS: 101 consecutively implanted electrodes were prospectively studied in 60 patients undergoing iMRI-guided DBS implantation at UCSF between August 2010 and March 2013. Radial error was defined as the vector difference between intended and actual stylet placement in the plane used for targeting (typically 4 mm below AC-PC plane for STN and at the AC-PC plane for GPi). Surgical time was defined as time from skin incision to closure. RESULTS: Twenty-eight STN (27 Parkinson's disease, 1 dystonia), 31 GPi (18 Parkinson's disease, 13 dystonia) and 1 medial thalamic (Tourette syndrome) implantations were performed. The average radial error was 0.6 mm (range 0 to 1.8 mm). 8 electrodes had errors > 1.0 mm, and 7 electrodes had errors 6 months clinical followup (range 6-25 months), and no electrodes have required repositioning due to lack of clinical response or stimulation induced adverse effects. CONCLUSION: The ClearPoint platform demonstrates application accuracy of 0.6 mm. This is a significant improvement over the first generation iMRI technique using the NexFrame (1.2 mm). Errors are consistently in the submillimetric range, with the overwhelming majority of electrodes placed with 1 pass. No patients to date have required electrode repositioning using this anatomically targeted, real-time image guided technique.