Interventional procedure overview of MRI-guided focused ultrasound thalamotomy for treating moderate to severe tremor in Parkinson's

What the procedure involves

This outpatient procedure is done with the patient lying supine inside an MRI scanner for several hours. The person's head is shaved, and a stereotactic head frame is attached. The person is usually kept awake during the procedure so they can be regularly assessed by the treating physician to evaluate the clinical response (report any improvement of symptoms or adverse events). Some people may be offered light sedation.

Real time MRI guidance and thermal mapping are used to identify the target area of the brain (the thalamic nucleus) precisely, and monitor treatment. Low power ultrasound is delivered to confirm the chosen location. Then, several high-power focused ultrasound pulses are delivered to ablate target tissue in the thalamus. The energy released and the location of the ultrasound focus are monitored in real time during the procedure by MRI thermometry, and adjusted to reach above the definitive ablation temperature (of 55°C) according to clinical response. Chilled water is circulated around the head during the treatment to prevent thermal damage to the scalp caused by the increase in bone temperature. The procedure is considered finished when there is sufficient clinical improvement, and considering the total amount of energy delivered and the number of sonications. The procedure takes about 2 hours and symptom relief should be immediate.