Focused Ultrasound (FUS) is an emerging non-invasive therapeutic technology that uses precisely focused acoustic energy to treat neurological disorders. Unlike traditional surgical approaches, FUS allows clinicians to target deep brain structures without craniotomy or radiation. The technology has evolved from a single application (essential tremor) to a versatile platform with nearly 30 identified mechanisms of action, making it one of the most promising frontiers in neurodegenerative disease treatment[@focused].
FUS offers several distinct therapeutic modalities that can be tailored to specific neurological conditions:
Focused ultrasound operates by concentrating multiple ultrasound waves onto a precise focal point within the brain. The intersection of these beams creates a region of focused acoustic energy while sparing surrounding tissue. This precision allows treatments to target structures as small as 1×1.5 mm or as large as 10×16 mm in diameter[@focused].
The biological effects of ultrasound are determined primarily by two key parameters:
Focused Ultrasound (FUS) is an emerging non-invasive therapeutic technology that uses precisely focused acoustic energy to treat neurological disorders. Unlike traditional surgical approaches, FUS allows clinicians to target deep brain structures without craniotomy or radiation. The technology has evolved from a single application (essential tremor) to a versatile platform with nearly 30 identified mechanisms of action, making it one of the most promising frontiers in neurodegenerative disease treatment[@focused].
FUS offers several distinct therapeutic modalities that can be tailored to specific neurological conditions:
Focused ultrasound operates by concentrating multiple ultrasound waves onto a precise focal point within the brain. The intersection of these beams creates a region of focused acoustic energy while sparing surrounding tissue. This precision allows treatments to target structures as small as 1×1.5 mm or as large as 10×16 mm in diameter[@focused].
The biological effects of ultrasound are determined primarily by two key parameters:
| Intensity Level | Primary Effect | Clinical Application |
|-----------------|----------------|-----------------------|
| Low (0.1-1 W/cm²) | Cavitation, BBB opening | Drug delivery |
| Medium (1-10 W/cm²) | Neuromodulation | Targeted stimulation |
| High (>10 W/cm²) | Thermal ablation | Tumor/volume ablation |
Modern FUS systems integrate with advanced imaging modalities:
The blood-brain barrier (BBB) presents a formidable obstacle to CNS drug delivery, preventing approximately 98% of small molecule drugs and virtually all large molecule therapeutics (proteins, antibodies, gene therapies) from reaching the brain[@pardridge2021]. Low-intensity FUS combined with circulating microbubbles can induce temporary, reversible opening of the BBB through mechanical effects.
When focused ultrasound is applied to the brain vasculature in the presence of circulating microbubbles, the acoustic pressure causes the bubbles to oscillate (stable cavitation) or collapse (inertial cavitation)[@hynynen2022]. These mechanical effects produce:
BBB opening is designed to be temporary and reversible:
LIFU-BBB opening enables delivery of:
HIFU delivers concentrated acoustic energy that is absorbed by tissue, generating localized heating. Temperatures of 55-80°C are achieved at the focal point, causing immediate and irreversible coagulation necrosis while the surrounding tissue remains unharmed.
The precision of HIFU ablation depends on:
In 2016, the FDA approved Insightec's Exablate Neuro device for treating essential tremor through thalamotomy—targeting the ventral intermediate nucleus (VIM) of the thalamus[@focused].
In December 2018, the FDA approved Exablate Neuro for tremor-dominant Parkinson's disease, specifically targeting the thalamus. This was expanded in 2021 to include patients with advanced PD suffering from mobility, rigidity, or dyskinesia symptoms[@focused].
| Target | Indication | Effect |
|--------|-----------|--------|
| Vim thalamus | Tremor | Tremor suppression |
| GPi | PD dyskinesias | Motor improvement |
| STN | PD motor symptoms | Reduced medication |
| Subthalamic nucleus | PD | Symptom control |
Sonodynamic therapy combines low-intensity ultrasound with systemically administered sonosensitizers—compounds that become cytotoxic when activated by acoustic energy. Unlike photodynamic therapy (which requires light), SDT can penetrate deep into brain tissue.
SDT is being investigated for:
FUS-enhanced delivery enables anti-amyloid therapeutics to reach the brain at therapeutic concentrations. Studies in AD mouse models have shown that FUS-enhanced delivery of anti-Aβ antibodies reduces amyloid plaque burden more effectively than systemic administration alone[@wu2024].
The first Alzheimer's trial using FUS to temporarily disrupt the BBB began in 2017 at Sunnybrook Research Institute in Toronto, Canada[@focused]. Multiple Phase I/II trials are now underway to assess:
FUS has shown particular promise in PD, with multiple FDA approvals for tremor treatment. The FDA expanded approval in 2021 to include treatment of patients with advanced PD suffering from mobility, rigidity, or dyskinesia symptoms[@focused].
In 2022, researchers in Spain used FUS to open the BBB in people with Parkinson's dementia, marking the first application for this specific indication[@focused].
FUS enables delivery of:
FUS applications in ALS focus on:
Research is exploring FUS-enhanced delivery of:
FUS may enable:
| Trial ID | Condition | Phase | Intervention | Status |
|----------|-----------|-------|--------------|--------|
| NCT02986932 | AD | Phase I | FUS + Donepezil | Completed |
| NCT04571632 | PD | Phase I/II | FUS Thalamotomy | Recruiting |
| NCT03344787 | Glioblastoma | Phase I | FUS + Pembrolizumab | Active |
| NCT04118764 | Breast Cancer Brain Mets | Phase I | FUS + Docetaxel | Recruiting |
Clinical trials have established a favorable safety profile:
Studies with up to 5-year follow-up show no increased risk of:
| Parameter | Typical Range | Notes |
|-----------|--------------|-------|
| Frequency | 0.2-2 MHz | Lower frequencies favor cavitation |
| Peak negative pressure | 0.3-1.5 MPa | Above threshold induces cavitation |
| Pulse duration | 1-10 ms | Shorter pulses reduce heating |
| Pulse repetition frequency | 1-10 Hz | Determines total exposure |
| Total treatment time | 30-120 seconds | Per target region |
Modern systems incorporate:
FUS can be combined with:
Recent advances in focused ultrasound for neurodegeneration: