A Study to Evaluate the Safety and Efficacy of ExAblate Subthalomotomy for the Treatment of Parkinson's Disease Motor Features

1. Men and women age 30 years or older
2. Subjects who are able and willing to give consent and able to attend all study visits.
3. Subjects with a diagnosis of PD by UK Brain Bank Criteria as confirmed by a movement disorder neurologist at the site.
4. Predominant motor features/disability from one side of the body (i.e asymmetry index > 1.5) as determined by a movement disorders neurologist.
5. Motor clinical features non-optimally controlled by an adequate medical treatment prescription. An adequate medication prescription is defined as a therapeutic dose of each medication or the development of side effects as the medication dose is titrated.
6. No major changes in pharmacological regime for PD should be done for the 30 days prior to procedure.
7. Topographic coordinates of the subthalamic nucleus are localizable on MRI so that it can be targeted by the ExAblate device.
8. Able to communicate sensations during the ExAblate MRgFUS treatment Inclusion and exclusion criteria have been agreed upon by two members of the medical team

Exclusion Criteria:

1. Hoehn and Yahr stage in the ON medication state of 2.5 or greater
2. Presence of severe dyskinesia as noted by a score of 3 or 4 on questions 4.1 and 4.2 of the MDS-UPDRS.
3. Presence of other central neurodegenerative disease suspected on neurological examination. These include: multisystem atrophy, progressive supranuclear palsy, corticobasal syndrome, dementia with Lewy bodies, and Alzheimer's disease.
4. Any suspicion that Parkinsonian symptoms are a side effect from neuroleptic medications.
5. Subjects who have had deep brain stimulation or a prior stereotactic ablation of the basal ganglia
6. Presence of significant cognitive impairment defined as score ≤ 21 on the Montreal Cognitive Assessment (MoCA) or Mattis Dementia Rating Scale of 120 or lower.
7. Unstable psychiatric disease, defined as active uncontrolled depressive symptoms, psychosis, delusions, hallucinations, or suicidal ideation. Subjects with stable, chronic anxiety or depressive disorders may be included provided their medications have been stable for at least 60 days prior to study entry and if deemed appropriately managed by the site neuropsychologist
8. Subjects with significant depression as determined following a comprehensive assessment by a neuropsychologist. Significant depression is being defined quantitatively as a score of greater than 14 on the Beck Depression Inventory.
9. Legal incapacity or limited legal capacity as determined by the neuropsychologist
10. Subjects exhibiting any behavior(s) consistent with ethanol or substance abuse as defined by the criteria outlined in the DSM-IV as manifested by one
11. Subjects with unstable cardiac status including
12. Severe hypertension (diastolic BP > 100 on medication).
13. History of or current medical condition resulting in abnormal bleeding and/or coagulopathy.
14. Receiving anticoagulant (e.g. warfarin) or antiplatelet (e.g. aspirin) therapy within one week of focused ultrasound procedure or drugs known to increase risk or hemorrhage (e.g. Avastin) within one month of focused ultrasound procedure
15. Subjects with risk factors for intraoperative or postoperative bleeding as indicated by: platelet count less than 100,000 per cubic millimeter, a documented clinical coagulopathy, or INR coagulation studies exceeding the institution's laboratory standard
16. Patient with severely impaired renal function with estimated glomerular filtration rate \<30mL/min/1.73m2 (or per local standards should that be more restrictive) and/or who is on dialysis;
17. Subjects with standard contraindications for MR imaging such as non-MRI compatible implanted metallic devices including cardiac pacemakers, size limitations, etc.
18. Significant claustrophobia that cannot be managed with mild medication.
19. Subject who weight more than the upper weight limit of the MR table and who cannot fit into the MR scanner
20. Subjects who are not able or willing to tolerate the required prolonged stationary supine position during treatment.
21. History of intracranial hemorrhage
22. History of multiple strokes, or a stroke within past 6 months
23. Subjects with a history of seizures within the past year
24. Subjects with malignant brain tumors
25. Subjects with intracranial aneurysms requiring treatment or arterial venous malformations (AVMs) requiring treatment.
26. Any illness that in the investigator's opinion preclude participation in this study.
27. Subjects unable to communicate with the investigator and staff.
28. Pregnancy or lactation.
29. Subjects who have an Overall Skull Density Ratio lower than 0.35 as calculated from the screening CT.