Validation of tremor measurements using quantified drawing analysis in patients with essential tremor or Parkinson’s disease treated with MR-guided focused ultrasound thalamotomy

Background During MR–guided focused ultrasound (MRgFUS) thalamotomy, patients’ tremors are qualitatively assessed with drawing tests to provide near-real-time feedback on the treatment effect. The objective of this study was to validate an automated measure of kinetic tremor in patients with essential tremor (ET) or Parkinson’s disease (PD) by computerized analysis of standardized drawings. Methods Drawings were performed in three settings: (1) patients supine in the MR scanner during the procedure, (2) patients seated immediately before and after treatment, and (3) months after discharge. Drawings comprised of a signature, the Archimedes spiral, and a straight line. Once the drawings were digitized, the automated analysis was used to calculate quantitative metrics. For validation, the composite scores were compared with wrist angle simultaneously measured using accelerometers during the patients’ drawings. Results Quantitative drawing scores for the spiral and line showed significant improvement immediately after thalamotomy in patients with ET (spiral: p = 0.0002; line: p = 0.017) and PD (spiral: p = 0.12; line: p = 0.016); no significant change occurred in the months after treatment. In addition, quantitative drawing scores for spirals and lines were correlated with accelerometer-measured wrist angle in ET (spiral: R2 = 0.51, p = 0.029; line: R2 = 0.63, p = 0.004) and PD (spiral: R2 = 0.85, p = 0.0008; line: R2 = 0.69, p = 0.017) groups. Conclusions Quantitative drawing scores for patients with ET or PD accurately reflect the degree of tremor and can be used for objective assessment of tremor improvement during and after treatment.