FAT1-weighted MRI-guided focused ultrasound thalamotomy for essential tremor.

Background and objective: Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy of the ventral intermediate nucleus (Vim) is an effective therapy for medication-refractory essential tremor (ET). The Vim is not readily visualised on conventional MRI and targeting is routinely performed indirectly, with atlas co-ordinates. Inaccurate targeting due to interindividual anatomical variability can result in side effects and reduced efficacy. FAT1-weighted MRI is a high-resolution, high-fidelity modality that combines fractional anisotropy mapping and anatomical T1 sequences and allows direct visualisation of the Vim. Here, we assessed the outcomes of ET patients treated with a novel FAT1-weighted MRgFUS thalamotomy technique. Methods: Targeting was performed through direct visualisation of the Vim on FAT1-weighted MRI sequence. Clinical, technical and imaging data were collected prospectively at baseline, 6 and 12 months follow-up. Results: The first 14 consecutive ET patients undergoing MRgFUS at our centre were assessed. Their mean age was 73.6 years and disease duration was 31.8 years. There were significant improvements in treated hand tremor score (60%), disability score (71%) and quality of life (72%) and no clinically relevant side effects at 12 months. A mean of 6.9 sonications was performed and the mean time from first to last sonication was 34.6 min. Greater tremor improvement was observed with lesions in the inferior and lateral part of the Vim. Conclusion: This is the first case series assessing FAT1-guided Vim targeting in MRgFUS thalamotomy. These results demonstrate that this method is safe and clinically effective, with added technical advantages including low sonication numbers and short procedural time.