Combined accelerometry and writing analysis for quantifying tremor during focused ultrasound thalamotomy

MRI-guided focused ultrasound (MRgFUS) thalamotomy is used to treat tremors. Identifying the correct area to ablate relies on subjective physician assessment of tremor improvement during treatment. To address this limitation, objective quantification of tremor severity during MRgFUS is needed. The aim of this study was to develop and evaluate an objective method for quantifying tremor progression during MRgFUS using an MRI-compatible accelerometer and tablet.

Forty patients (30 male, mean age 74.5 years) who underwent MRgFUS thalamotomy to treat tremor were included in this analysis. All patients were evaluated during the procedure using analysis of drawn Archimedean spirals and a pen-mounted accelerometer. The severity of the tremor was determined by analysis of the rhythmic oscillatory patterns present in the drawings and accelerometer recordings after each sonication delivered. The patient's drawings were evaluated by two movement disorder neurologists using the drawing subsection of The Essential Tremor Rating Assessment Scale (TETRAS), and subsequently compared with the TETRAS score.

Using these methods, the mean ± standard error of the improvements in tremor after MRgFUS thalamotomy was 63.6% ± 7% by accelerometer analysis, 72.4% ± 9.9% by written spiral analysis, 68% ± 6.7% by combining the accelerometer and written spiral analyses, and 33.6% ± 3.1% by TETRAS analysis. When stratifying based on temperature, improvement was 22.8% ± 4.4% at < 50°C, 48.9% ± 5.5% at 50°C-53°C, and 70.8% ± 2.9% at > 53°C.

The measurements from the accelerometer and written spiral analysis were comparable with expert analysis of TETRAS scores, but the accelerometer had greater sensitivity for subtle improvement in tremor. This system of analysis provides an objective and instantaneous measure of tremor improvement during MRgFUS, potentially making the procedure safer and more efficient.