BACKGROUND: Recent advances have enabled delivery of high-intensity focused 
ultrasound through the intact human cranium with magnetic resonance imaging 
(MRI) guidance. This preliminary study investigates the use of transcranial 
MRI-guided focused ultrasound thalamotomy for the treatment of essential tremor.
METHODS: From February 2011 through December 2011, in an open-label, 
uncontrolled study, we used transcranial MRI-guided focused ultrasound to target 
the unilateral ventral intermediate nucleus of the thalamus in 15 patients with 
severe, medication-refractory essential tremor. We recorded all safety data and 
measured the effectiveness of tremor suppression using the Clinical Rating Scale 
for Tremor to calculate the total score (ranging from 0 to 160), hand subscore 
(primary outcome, ranging from 0 to 32), and disability subscore (ranging from 0 
to 32), with higher scores indicating worse tremor. We assessed the patients' 
perceptions of treatment efficacy with the Quality of Life in Essential Tremor 
Questionnaire (ranging from 0 to 100%, with higher scores indicating greater 
perceived disability).
RESULTS: Thermal ablation of the thalamic target occurred in all patients. 
Adverse effects of the procedure included transient sensory, cerebellar, motor, 
and speech abnormalities, with persistent paresthesias in four patients. Scores 
for hand tremor improved from 20.4 at baseline to 5.2 at 12 months (P=0.001). 
Total tremor scores improved from 54.9 to 24.3 (P=0.001). Disability scores 
improved from 18.2 to 2.8 (P=0.001). Quality-of-life scores improved from 37% to 
11% (P=0.001).
CONCLUSIONS: In this pilot study, essential tremor improved in 15 patients 
treated with MRI-guided focused ultrasound thalamotomy. Large, randomized, 
controlled trials will be required to assess the procedure's efficacy and 
safety. (Funded by the Focused Ultrasound Surgery Foundation; ClinicalTrials.gov 
number, NCT01304758.).