Less is more: comparison of automated spiral-drawing metrics with clinician-rated tremor scores after MRgFUS thalamotomy

Objective measures of tremor could improve assessment of response to magnetic resonance-guided focused ultrasound (MRgFUS) for essential tremor in practice, but it is unclear whether image-derived metrics from spiral drawings reflect clinician judgment. In this study, we analyzed 410 spiral-drawing observations from 106 patients with essential tremor undergoing MRgFUS thalamotomy and compared two recent computer-vision measures with a simple geometric metric (total line length) against an ordinal clinical rating scale for tremor spiral scores using ordered logistic mixed-effects models. Only line length independently tracked worse clinician-rated severity (odds ratio_{(per 1 mm)} 1.017, p < 0.01), whereas the two image-based scores showed no significant association. The model captured the expected treatment signature, with marked post-procedural improvement confined to the treated hand. These findings suggest that low-complexity interpretable features may better approximate clinically meaningful tremor severity than more elaborate image-processing metrics and support further validation against functional outcomes.