Evaluate the safety and efficacy of unilateral focused ultrasound pallidotomy using the ExAblate 4000 System in the management of dyskinesia symptoms or motor fluctuations for medication refractory, advanced idiopathic Parkinson's disease.

The goal of this prospective, two-arm, sham-controlled, randomized, multi-center pivotal study is to evaluate the safety and efficacy of unilateral focused ultrasound pallidotomy using the ExAblate 4000 System in the management of dyskinesia symptoms or motor fluctuations for medication refractory, advanced idiopathic Parkinson's disease.

Inclusion Criteria:

1. Men and women, age 30 years and older.
2. Subjects who are able and willing to give informed consent and able to attend all study visits through 12 Months.
3. Subjects with a diagnosis of idiopathic PD by UK Brain Bank Criteria as confirmed by a movement disorder neurologist at the site.
4. Levodopa responsive as defined by at least a 30% reduction in MDS-UPDRS motor subscale in the ON vs OFF medication state.
5. MDS-UPDRS score of ≥ 20 in the meds OFF condition OR Motor complications of PD on optimum medical treatment .
6. Subjects should be on a stable dose of all PD medications for 30 days prior to study entry as determined by medical records.
7. Subject is able to communicate sensations during the ExAblate procedure.
8. Subjects on stable antidepressant medications for at least 3 months

Exclusion Criteria:

1. Hoehn and Yahr stage in the ON medication state of 3 or greater.
2. 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.
3. Any suspicion that Parkinsonian symptoms are a side effect from neuroleptic medications.
4. Subjects who have had deep brain stimulation or a prior stereotactic ablation of the basal ganglia.
5. Presence of significant cognitive impairment using MMSE ≤ 24.
6. Unstable psychiatric disease, defined as active uncontrolled depressive symptoms, psychosis, delusions, hallucinations, or suicidal ideation.
7. Subjects with an active alcohol or drug dependency or history of drug/alcohol abuse within the past year
8. Subjects with unstable cardiac status
9. Severe hypertension (diastolic BP > 100 on medication).
10. Current medical condition resulting in abnormal bleeding and/or coagulopathy.
11. 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.
12. 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
13. Patient with kidney disease or on dialysis.
14. Subjects with standard contraindications for MR imaging
15. Significant claustrophobia that cannot be managed with mild medication.
16. Subjects who weigh more than the upper weight limit of the MR scanner table and who cannot fit into the MR scanner.
17. Subjects who are not able or willing to tolerate the required prolonged stationary supine position during treatment.
18. History of intracranial hemorrhage, multiple strokes, or a stroke within past 6 months.
19. Subjects with a history of seizures within the past year.
20. Subjects with brain tumors.
21. Subjects with intracranial aneurysms requiring treatment or arterial venous malformations (AVMs) requiring treatment.
22. Are participating or have participated in another clinical trial in the last 30 days.