Transcranial MRI-guided high-intensity focused ultrasound for treatment of essential tremor: A pilot study on the correlation between lesion size, lesion location, thermal dose, and clinical outcome

Background: Transcranial MR-guided high-intensity focused ultrasound (tcMRgFUS) is a promising noninvasive method to treat medication-refractory essential tremor. Purpose/Hypothesis: To define the correlation between lesion size after ablation, thermal dose, and clinical outcome in tcMRgFUS treatment of essential tremor. Study Type: Retrospective. Population/Subjects/Phantom/Specimen/Animal Model: Eight patients with medication-refractory essential tremor were treated using a tcMRgFUS system at 3T. Field Strength/Sequence: T ₂ -weighted images were acquired immediately and at 1 year posttreatment at 3T. Assessment: An atlas of the thalamic nuclei and dose maps were warped to the posttreatment images. The thermal dose, the immediate posttreatment lesion volume and 1-year final lesion volume, and the volumes confined inside the ventral division of the ventral lateral posterior thalamic nucleus (VLpv) were correlated to clinical outcome at 1 month and 1 year using Pearson's coefficient. The spatial region of treatment correlating with maximal clinical outcome was derived in a normalized space from average maps of clinical tremor score improvement at 1 year. Statistical Tests: Statistical significance was assessed using the Wilcoxon two-tailed rank test. Results: The correlations between thermal dose, lesion volume posttreatment and at 1 year, and outcome at 1 year were good (r = 0.73, 0.65, 0.73, respectively), and were slightly better than at 1 month (r = 0.57, 0.49, 0.65). Reducing the measurement to include only the portion within the VLpv did not significantly modify the correlations (P = 0.09). The center of the spatial region of treatment was found in the anterior commissure – posterior commissure plane, 14.3 mm lateral from the midline, and 8.3 mm rostral to the posterior commissure. Data Conclusion: In this pilot study a good correlation was found between the size of the lesion, the thermal dose, and the clinical outcome in patients treated for essential tremor with ablation of the VLpv with tcMRgFUS. Level of Evidence: 1. Technical Efficacy: Stage 4. J. Magn. Reson. Imaging 2017.