Focused ultrasound is a medical technology that uses sound waves to precisely target specific tissues deep within the body without incisions. This non-invasive approach treats medical disorders by concentrating ultrasonic energy at a focal point. It integrates with imaging modalities, such as magnetic resonance imaging (MRI) or ultrasound, for real-time monitoring.
The Science Behind Focused Ultrasound
Focused ultrasound operates on a principle similar to using a magnifying glass to concentrate sunlight onto a small area. Multiple individual ultrasound beams are generated and directed to converge at a specific point within the body. Each individual beam passes through the tissue with no significant effect, but at their convergence point, their combined energy creates a localized biological effect. The size of this target area can be precisely controlled, ranging from as small as 1×1.5 mm to 10×16 mm in diameter, depending on the system and parameters.
The interaction of focused ultrasound with tissue can induce various biological effects, primarily through thermal and mechanical mechanisms. When high-intensity ultrasound energy is continuously applied, it causes a localized temperature rise at the focal point, exceeding 55°C, leading to thermal ablation or destruction of targeted cells. This thermal effect can be precisely monitored using MRI thermometry to ensure accurate treatment.
Alternatively, pulsed focused ultrasound can generate mechanical effects with minimal heating. This involves the rapid oscillation of sound waves, which can lead to cavitation—the formation and collapse of microscopic bubbles within the tissue. These mechanical forces can disrupt cell membranes, a process known as histotripsy, or temporarily increase the permeability of barriers like the blood-brain barrier.
Therapeutic Applications
Focused ultrasound is applied across a range of medical fields for various conditions.
Neurology
In neurology, it has received approval for treating essential tremor and symptoms of Parkinson’s disease. For these conditions, sound waves are precisely aimed at specific brain regions, like the thalamus or pallidum, to disrupt abnormal electrical activity. Many patients experience immediate and lasting relief from tremors.
Oncology
In oncology, focused ultrasound is used to ablate tumors in areas like uterine fibroids, prostate, breast, and liver. Beyond direct tumor destruction, research explores its role in enhancing drug delivery to tumors by opening the blood-brain barrier, which normally restricts many therapies from reaching brain tumors. It is also being studied for its potential to stimulate immune responses against cancer cells.
Pain Management
Focused ultrasound also treats pain associated with bone metastases, a common complication of advanced cancer. It works by ablating nerves that serve the painful region, leading to significant and sustained pain reduction. It is also being investigated for chronic neuropathic pain and other pain conditions.
Benefits and Patient Considerations
A significant advantage of focused ultrasound is its non-invasive nature. This translates to a faster recovery and reduced risk of complications, such as infection or bleeding, compared to traditional surgical procedures. Patients can typically return to their regular activities soon after treatment, sometimes even the same day.
During a focused ultrasound procedure, patients generally remain awake and communicate with the medical team. They lie on a treatment table, often with their head secured in a helmet-like device, positioned within an MRI scanner. The MRI guides the ultrasound beams and monitors the treatment’s progress and temperature changes.
Patient eligibility for focused ultrasound depends on various factors, including the specific condition being treated and individual medical history. For instance, for tremor treatment, patients are typically at least 22 years old and have symptoms that have not responded to medication. Some temporary post-procedure effects can occur, such as dizziness, headache, nausea, or a temporary feeling of numbness or tingling in the lips or fingers. These effects are generally mild and resolve within days or weeks, though some sensory changes may persist in a small percentage of cases.