Focused ultrasound (FUS) is a treatment option for some people with essential tremor.

What is focused ultrasound?

Focused ultrasound, also called high-intensity focused ultrasound (HIFU), is a procedure that uses high-intensity sound waves to heat up and burn (ablate) small areas of tissue. The targeted tissue is typically an abnormal growth or an area responsible for transmitting abnormal neurological signals.

In the past decade, its use has been expanded to treat essential tremor by targeting specific areas within the brain.

Focused Ultrasound in the Brain: How It Works

Focused ultrasound uses an acoustic lens technology to converge multiple high-intensity sound waves coming from different directions into a specific location in the brain. Think of it as beams of light being concentrated through a magnifying glass. Where the waves cross paths, the temperature slowly rises, reaching a point at which the target cells are destroyed. The entire procedure is guided by magnetic resonance imaging (MRI) to monitor brain temperature and make sure the targeting is precise. The procedure is permanent, meaning it cannot be reversed.

How Focused Ultrasound Thalamotomy Treats Essential Tremor

Focused ultrasound is approved by the U.S. Food and Drug Administration (FDA) for people who have essential tremor that is not well-controlled by medications.

To treat essential tremor, focused ultrasound is used to target the thalamus, a brain structure that acts as a relay center for sensory and movement information. Research suggests that destroying a small part of the thalamus, the ventralis intermedius nucleus, can help stop or reduce the brain activity that contributes to essential tremor.

The procedure to destroy or remove a part of the thalamus is called thalamotomy. In the past, it has been performed surgically by making an opening in the skull. Focused ultrasound is a way to perform thalamotomy without making incisions to access the brain. This procedure is called focused ultrasound thalamotomy.

The FUS essential tremor treatment usually results in a reduction of hand tremor on one side of the body almost right away. Focused ultrasound thalamotomy can be performed on both sides of the brain, which means essential tremor can improve on both sides of the body. However, the procedures for each side are spaced several months apart.

Results vary from patient to patient, and tremor can worsen in some people after FUS.

Preparing for Focused Ultrasound Treatment in the Brain

Shortly before the FUS procedure, your care team may perform tests to establish a baseline for your symptoms. The tests may include writing, drawing or performing other tasks that are typically affected by the essential tremor. This will help evaluate how the symptoms improve after the treatment.

What happens during focused ultrasound treatment of the brain?

Focused ultrasound in the brain is performed while the patient is awake, although mild sedation may be used. This helps the doctors monitor the effects of the procedure in real time. Most patients can go home the day of the procedure, and the effects are felt immediately.

The focused ultrasound procedure in the brain takes about two to four hours. Before the FUS procedure:

• Medications may be given via IV or by mouth to help with nausea, pain or keeping calm.
• Hair is shaved off the entire head, close to the skin, because hair may interfere with ultrasound delivery.
• A metal frame is attached to the patient’s head to keep it still during the procedure.
• A silicone cap is placed over the frame to create a sealed area where cold water will be circulated against the scalp to keep it cool and help conduct the sound waves.

During the FUS procedure:

• The patient lies in an MRI scanner while the head is placed in a special helmet that will focus ultrasound waves.
• The doctor may take several MRI images to make sure all equipment is properly aligned.
• The treatment starts with a few low-intensity ultrasound doses to check that the correct location is being targeted. Then, the doctor switches to high-intensity ultrasound.
• MRI images offer a real-time temperature map of the treatment area. Doctors make sure the right temperature is reached to destroy the tissues in the target area through a process called thermal ablation.
• Each ultrasound dose is delivered for about a minute, and the process is repeated until the target tissue is destroyed. Between the doses, the care team talks to the patient and may ask them to perform simple tasks, such as drawing, to see how the treatment is affecting the symptoms.

Once the treatment is finished, the head frame is removed, and patients are monitored for side effects in the recovery room for a short period of time. Patients should arrange for a ride home after the procedure as they should not drive. The doctor will prescribe steroids to help reduce any brain inflammation.

Recovery, Risks and Side Effects

Because focused ultrasound treatment is performed without making incisions, infection and brain bleed are less likely than with surgery.

Recovery after FUS in the brain is typically quick. Most patients can return to work and regular activities after a few days of rest. Patients may experience the following after the procedure:

• Headache
• Dizziness and nausea
• Numbness and tingling
• Imbalance or gait changes
• Slurred speech
• Changes in taste

For most people, these symptoms go away in days to weeks after FUS. However, certain side effects such as speech abnormalities, facial tingling and balance issues may last up to a year or become permanent. It is important to discuss the pros and cons of the procedure with your neurosurgeon to understand your unique risks and prognosis.

Focused Ultrasound vs. Deep Brain Stimulation (DBS)

Focused ultrasound has similar goals to DBS: to disrupt abnormal brain activity. The way each procedure achieves this is different. Focused ultrasound is less invasive than DBS, which involves incisions, implants and an adjustment period. On the other hand, the effect of DBS can be adjusted over time with reprogramming of the system, while FUS is a one-time procedure with permanent effects. However, the relationship between these two procedures is more complex than choosing one over the other:

• Focused ultrasound does not prevent a person from having DBS surgery in the future.
• Focused ultrasound may be an alternative to DBS for people who are not candidates for DBS.
• Focused ultrasound can be performed on people who had their DBS electrodes taken out without a possibility to reimplant them.

Working closely with your neurosurgeon and the extended multispecialty care team can help you evaluate each option and determine the best care plan for your situation.

The Future of Focused Ultrasound for Movement Disorders

Research is underway to explore other uses of focused ultrasound for treatment of movement disorders, as well as how to make the approved uses safer and better. Research topics include:

• Opening the blood-brain barrier. The blood-brain barrier is a membrane in the brain that separates the blood vessels from the brain tissue. Researchers are studying how focused ultrasound can be used to open this barrier. This may allow for desired substances, such as immunotherapy medicines, to reach the right parts of the brain, while allowing unwanted substances to leave the brain.
• Different areas of the brain related to movement disorders. Researchers are testing focused ultrasound on various targets within the brain to see what other movement symptoms it can help treat.