This study investigates magnetic resonance-guided focused ultrasound thalamotomy (MRgFUSth) for people with Parkinson's disease (PD) and tremor not responding to conventional standard doses of dopamine replacement therapy. The aim is to identify clinical and imaging biomarkers predictive of sustained tremor control up to 24 months after MRgFUSth treatment. Participants will undergo a suprathreshold levodopa test and ¹⁸F-DOPA PET imaging to evaluate dopaminergic and serotonergic involvement in tremor. All participants will receive MRgFUSth and be followed for 24 months with standardized clinical, cognitive, and quality-of-life assessments. The study seeks to improve understanding the possible mechanisms of tremor relapse and inform patient selection for MRgFUSth in PD.