Focused Ultrasound Therapy Explained Simply

1. What It Is About

In focused ultrasound therapy, sound waves are focused, much like light through a magnifying glass. The waves pass through skin and bone and only take effect at the precise point they are directed at. There, the tissue can be heated so strongly that a small area is selectively ablated, meaning permanently switched off. The surrounding tissue remains unaffected.

During treatment, an image is continuously generated via MRI. MRI stands for magnetic resonance imaging, a non-invasive imaging technique that does not use X-rays. This allows the treatment team to see exactly where the focal point is located and how hot it is. As a result, the focal point can be controlled with millimetre precision without incisions or implants.

Established The method dates back to the 1950s and was initially developed for tumours. Since the 2000s, it has been safely applied in the brain with MRI guidance. Today, it is primarily being studied for movement disorders, such as tremor and Parkinson’s disease. Applications outside the brain, for example on skin and mucous membranes, are also being explored.

2. What Studies Show

Plausible The treatment is used for movement disorders. Essential tremor is an involuntary shaking that occurs without an identifiable cause and typically affects the hands. In a 2018 study, 30 people were treated: 18 with essential tremor, 9 with Parkinson’s disease, and 3 with both. The thalamus, a deep brain structure, was targeted. Immediately after the procedure, the tremor in the treated hand stopped. One month later, it was significantly reduced compared to before, and after six months, the condition remained stable. Side effects such as temporary gait instability and tingling were mild and resolved 2.

A second study followed 76 people with essential tremor over two years. Nine participants discontinued early, while the remaining showed stable outcomes 3. Several controlled trials—comparisons with a control group—and a review support this finding in essential tremor 4.

Hypothesis In the first human trial for a brain tumour in 2014, a 63-year-old patient with recurrent glioblastoma—a malignant brain tumour—was treated. Using 25 sonication pulses, parts of the tumour were destroyed. The patient experienced no neurological deficits afterwards 1. Whether this approach works in more people and whether it changes the course of the disease remains unclear.

Hypothesis In four people with ALS, a disease affecting the nerve cells that control movement, the blood-brain barrier was temporarily opened. This barrier acts as a filter between the blood and the brain and closed again after 24 hours without severe side effects occurring 6. Whether this allows medications to be delivered more effectively to the brain is still under investigation.

3. What Remains Unclear

In most studies, follow-up lasts less than two years. Whether late effects occur later—such as changes in cognition or new movement disorders—remains an open question. Treatments targeting both hemispheres of the brain have scarcely been investigated. The skull also plays a role: its structure and density determine whether sufficient sound energy reaches the target, which means the procedure is not suitable for everyone. Direct comparisons with deep brain stimulation, where a device is implanted, are rare and based on small groups. Studies also use different target points in the brain, making results difficult to compare. For brain tumours and nerve-related pain, only small initial studies exist. The next steps are to clarify whether the effects persist over many years and how the procedure can be made more accessible to more people.

4. What This Means in Practice

For movement disorders such as essential tremor, the method is best studied. Here, studies show a clear and lasting reduction in tremor, and comparisons with control groups are available. For all other applications, the evidence is less certain.

When reading the studies, two questions stand out: How many people were treated, and how long were they followed up? Large groups over several years are rare. The procedure is performed in specialised centres with MRI and is not suitable for everyone due to individual skull anatomy. The next steps involve developing standardised protocols, observing more people over longer periods, and directly comparing the treatment with other procedures. Only then can its role alongside surgery and deep brain stimulation be determined.

All details with study numbers and sources: Detailed page on Focused Ultrasound Therapy. For children: Focused Ultrasound Therapy for Children.