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Background:
MR-guided high intensity focused ultrasound (MRgFUS) is a novel, noninvasive technique for the treatment of functional brain disorders through the intact human skull at millimeter precision. The ExAblate Neuro transcranial MRgFUS system (InSightec Ltd, Haifa, Israel) is CE certified for interventions in the thalamus, hypothalamus and pallidum. It uses a 1024-element phased array transducer operating at 650 kHz integrated into a clinical 3T-MRI scanner (GE Healthcare, Milwaukee, USA) and a standard stereotactic frame (Radionics, Burlington, UK) to immobilize the patient’s head (Pict.1, 2).

Case Report:
We report the case of a 44 years old male patient suffering from treatment-resistant tremor dominant Parkinson’s disease (PD, UPDRS III 23/108, Hoehn and Yahr stage 2). Medical history included i.v. drug abuse, HIV infection, hepatitis C and lung disease as contraindications to Deep Brain Stimulation (DBS).

Intervention:
The stereotactic target, i.e. the pallido-thalamic tract (fasciculus thalamicus) of the subthalamic area, contralateral to the dominant resting tremor (Pict.3), was identified on intra-interventional MRI. Correct target location was verified with low, non-ablative sonications and evaluation of neurological response was performed. Sonications of 15 to 25 seconds duration were delivered with stepwise increased acoustic energy up to 12500 J to create local tissue coagulation under real-time MR-thermometry control. The sonications resulted in heating to 60°C at the focal point producing a thermal lesion of approximately 3x3x3mm in size. Circulating degassed water between the helmet shaped transducer and the patient’s head provided acoustic coupling and head cooling (Pict.1,2). After each sonication the patient was interviewed and neurologically tested. The size of the lesion was closely monitored by MR-imaging during and directly after treatment, 48 hours, 1 and 6 month after intervention (Pict.4).
Clinically, MRgFUS intervention resulted in a prompt and complete suppression of the tremor, both at rest and under provocation (UPDRS III: 11/108) remaining to date (16 months follow up).

Conclusion:
MRgFUS is a novel, non-invasive technique for the treatment of Parkinson’s disease that does not use ionizing or radioactive radiation. The technique has been successfully applied for neuropathic pain and essential tremor treatment in over 150 patients worldwide. First experience with MRgFUS is indicative for the technique to be a safe and potentially effective alternative to standard DBS implantation for the treatment of tremor-dominant Parkinson’s patients.