BACKGROUND: Tremor in essential tremor and in tremor-dominant Parkinson's disease is assessed by subjective observations in patients undergoing focused ultrasound thalamotomy, a minimally invasive procedure intended to alleviate tremor in these patients. OBJECTIVE: To develop an objective tool for tremor analysis to be used before and after focused ultrasound thalamotomy treatment in the treated hand (contralateral to ablation) and non-treated (ipsilateral to ablation). METHODS: Using image processing and signal processing that utilized images of a Archimedes spiral drawing, we created a tool to analyze tremor. First, we showed that the proposed tool reproduces known clinical dynamics on the treated hand, and then we used it to evaluate the clinical dynamics on the non-treated hand. RESULTS: Using the tool we developed, we were able to demonstrate a significant reduction in tremor following focused ultrasound thalamotomy among 132 essential tremor and 26 tremor-dominant Parkinson's disease patients in the treated hand using drawings of Archimedes spirals up to 1 year following the procedure. Thus, we reproduced known clinical data and therefore validated the proposed tool. In addition, we were able to demonstrate a significant improvement in the non-treated hand as well as a significant deterioration in the efficacy of focused ultrasound thalamotomy over time. CONCLUSION: Our objective method, which incorporated image processing and signal processing, provided a quantitative measure of tremor reduction following focused ultrasound thalamotomy. It demonstrated significant improvement in tremors in the treated and non-treated hands following focused ultrasound thalamotomy as well as deterioration in the efficacy of treatment over time. If replicated in other studies, this method may complement current subjective assessments.