Medically intractable tremors are a common difficult clinical situation. Deep brain stimulation decreases Parkinson's disease tremor and essential tremor, but not all patients are candidates from a diagnostic, medical, or social standpoint, prompting the need for alternative surgical strategies. Less invasive lesional brain surgery (thalamotomy) procedures by radio-surgery or MRI-guided focused ultrasound have emerged and have proven to be effective in these third-line indications. Recently, a new technology has emerged allowing the performance of minimally invasive lesion surgeries by MRI-Guided Laser Interstitial Thermal Therapy (MRIg-LITT). MRIg-LITT has been shown to be effective and safe in management of epilepsies and brain tumors. However, no study has evaluated MRIg-LITT for performing thalamotomy in medically intractable tremor.In a pilot study, the investigators propose to evaluate the effect and safety of unilateral thalamotomy by MRIg-LITT in the management of medically intractable tremor of parkinsonian or essential origin.