Focused ultrasound is a non-invasive brain procedure that uses concentrated sound waves to destroy tiny, targeted areas of brain tissue responsible for Parkinson’s symptoms, primarily tremor. The procedure requires no incisions, no general anesthesia, and no implanted hardware. Instead, over 1,000 ultrasound beams pass through the intact skull and converge on a single point deep in the brain, generating enough heat to create a precise lesion while leaving surrounding tissue unharmed.
How the Procedure Works
The technology pairs two tools: high-intensity focused ultrasound (HIFU) and real-time MRI guidance. A helmet-like device fitted with a phased array of ultrasound elements is placed over the patient’s head. Each element can be independently controlled, allowing the surgical team to steer and focus the beam with sub-millimeter precision. MRI scans taken throughout the procedure show exactly where the energy is landing and how the tissue is responding.
Treatment happens in stages. First, low-energy pulses warm the target area to around 43°C (about 109°F), which is enough to temporarily disrupt the tissue without permanent damage. This lets the team confirm they’re hitting the right spot by checking whether tremor improves and whether any unwanted effects appear. If everything looks correct, the energy is gradually increased until the target reaches roughly 60°C (140°F), which permanently destroys the small cluster of cells causing the problem. The entire process, from preparation to leaving the table, takes about three to four hours. Patients are awake throughout, which allows doctors to assess tremor reduction and neurological function in real time.
Which Brain Targets Treat Which Symptoms
Parkinson’s disease produces several distinct motor problems, and no single brain target addresses all of them. The target your doctor recommends depends on which symptoms are most disabling.
- Thalamus (VIM nucleus): This is the most established target for focused ultrasound and is effective specifically against tremor. It has little to no effect on the stiffness and slowness that also characterize Parkinson’s.
- Subthalamic nucleus (STN): Ablation here can improve the full range of Parkinson’s motor symptoms and may allow a reduction in medication dosage. It is considered the best target for overall motor control.
- Globus pallidus (GPi): This target is most appropriate for people whose main problem is involuntary movements caused by long-term use of Parkinson’s medications. Early clinical experience shows it is highly effective against the full spectrum of these medication-induced dyskinesias.
In July 2025, the FDA approved the Exablate Neuro system for a procedure called pallidothalamic tractotomy in people with advanced Parkinson’s whose motor complications no longer respond adequately to medication. That approval also allows a staged bilateral approach, meaning the second side of the brain can be treated at least six months after the first.
How Well It Works for Tremor
Results vary significantly from person to person. In studies of thalamic-targeted focused ultrasound for tremor-dominant Parkinson’s, roughly half of patients qualified as strong responders, achieving at least a 50% improvement in hand tremor. Among those responders, the median tremor reduction was 91% at final follow-up, which represents a dramatic improvement. However, the other half of patients saw less than 50% improvement, with some experiencing no meaningful change at all.
Durability is a real concern. Researchers have consistently noted that tremor tends to recur more often in Parkinson’s patients than in people treated for essential tremor, a different condition where focused ultrasound has a longer track record. Some Parkinson’s patients who initially responded well have seen their tremor return over time, with disability scores climbing as follow-up continued. A portion of these patients ultimately pursued deep brain stimulation as a next step.
Side Effects and Risks
The best safety data comes from thalamotomy trials. The most common side effects are numbness or tingling (reported in 38% of patients) and gait disturbance (36%). These occur because the target sits near brain pathways that handle sensation and balance. The numbness typically affects the face, hand, or both, due to the proximity of a sensory relay nucleus next to the treatment zone.
The encouraging part is that most of these effects fade. At 12 months, numbness persisted in 14% of patients and gait problems in 9%. Ataxia, a specific type of coordination difficulty, was noted in 20% of patients immediately after the procedure but dropped to 4% by one year. A less common but notable finding from STN-targeted procedures: some patients developed involuntary movements on the treated side when off their medication, and in about one in five cases, the threshold for medication-induced dyskinesias decreased.
Focused Ultrasound Compared to Deep Brain Stimulation
Deep brain stimulation (DBS) remains the surgical standard for Parkinson’s. It involves implanting electrodes into the brain connected to a battery-powered stimulator in the chest. The two approaches differ in several important ways.
Focused ultrasound’s biggest advantage is that it requires no incision, no implanted device, and no general anesthesia. There is no risk of hardware infection, no battery to replace, and no need for ongoing programming visits. For people who cannot tolerate surgery, who take blood thinners, or who simply prefer a less invasive option, this matters.
DBS has its own strengths. Because it uses electrical stimulation rather than destroying tissue, it is adjustable and reversible. If side effects appear, settings can be changed. It also treats both sides of the brain in a single surgery, which is important because Parkinson’s typically affects both sides of the body. Focused ultrasound creates a permanent, irreversible lesion and has traditionally been limited to one side. The newer FDA-approved staged bilateral approach partially addresses this limitation, though it requires two separate procedures at least six months apart.
DBS can also target the STN or GPi bilaterally, giving it broader symptom coverage. Major neurosurgical organizations currently position focused ultrasound as an alternative for patients who are not good candidates for DBS rather than as a first-line replacement.
Who Qualifies for the Procedure
Not everyone with Parkinson’s is a candidate. The clearest indication is asymmetric parkinsonism, meaning symptoms are significantly worse on one side of the body, that is not adequately controlled with optimized medication.
A critical physical requirement involves skull density. Ultrasound beams must pass through the skull bone, and thicker or denser skulls transmit energy more efficiently. Doctors measure this using a skull density ratio (SDR) calculated from a CT scan. The FDA-approved cutoff is 0.40. Patients with an SDR below 0.4 can sometimes still be treated, but thermal efficiency drops and adequate lesioning becomes difficult. In practice, most centers rarely accept patients below this threshold.
Other factors that may affect eligibility include the presence of surgical clips or implants in the head, significant brain atrophy, or an inability to lie still in an MRI scanner for several hours.
Insurance and Cost
Coverage remains a significant barrier. As of 2025, both Medicare and most commercial insurers broadly do not cover focused ultrasound for Parkinson’s. The Centers for Medicare and Medicaid Services has acknowledged the procedure’s clinical rationale but notes that long-term effectiveness and safety data are still limited compared to DBS. Some Medicare contractors will cover it specifically for patients who are not candidates for DBS, following guidance from major neurosurgical organizations that endorse it in that context. For patients paying out of pocket, costs typically run into the tens of thousands of dollars, though exact figures vary by center.