Focused Ultrasound
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Focused ultrasound (FUS) is a non-invasive, image-guided surgical technology that uses multiple sources of ultrasound energy, arranged in a specially designed helmet, to target areas deep within the brain.

Ultrasound is acoustic energy at frequencies not audible to the human ear. At very high frequencies, ultrasound energy can be focused with precision to targets as small as one millimeter, and generate high temperatures creating lesions at a desired focal point. The ability to focus ultrasound energy non-invasively, through the human skull was largely pioneered by scientists at Sunnybrook Health Sciences Centre. This work created a spring-board for the development of new therapeutic applications, by enabling surgeons and scientists safe and precise access to deeper brain structures, without opening the skull. Sunnybrook has become a global leader in FUS research and clinical trials.

VIDEO: a patient with essential tremor sees dramatic improvement following focused ultrasound treatment:

» Read more: Scalpel-free surgery for essential tremor is effective and safe (Aug. 2016)

» What is involved in a FUS procedure?

FUS is a surgical procedure that eliminates skin incisions, drilling and removing the skull, or passage of probes through the brain. Patients are usually awake throughout the entire procedure and carefully monitored by the medical team.

On the morning of a FUS procedure, a stereotactic frame is attached to the patient’s head with local anaesthetic. This ensures the head remains completely still during the procedure. With the head frame on, the patient lies down in the MRI scanner and a FUS helmet is connected. The helmet contains transducer elements that remain selectively active to deliver ultrasound. Following the procedure, patients are transferred to the neurosurgical ward for recovery and are discharged home the next day, following an MRI scan. The surgical and medical teams closely monitor each patient’s post-treatment recovery and longer term outcome.

» For which conditions is FUS currently being used?

Approved Treatments: FUS is currently Health Canada approved for the treatment of severe Essential Tremor that is not responsive to medical treatment. A neurologist expert in the diagnosis and treatment of movement disorders works with the neurosurgery team to identify potentially eligible patients. Individuals who are eligible for FUS would be eligible for other surgical treatments for their tremor, including radiofrequency ablation and deep brain stimulation. The decision to proceed with FUS or another surgical treatment is made by the patient, after thorough discussion with their medical team.

Clinical Investigations: For many indications, including tremors caused by Parkinson’s Disease or dystonia, and brain tumors, FUS is an experimental procedure, done in the context of a clinical trial.

Currently at Sunnybrook, we have the following trials actively enrolling patients:

1) Blood Brain Barrier Opening for Chemotherapy Delivery

2) Brain Tumor Ablation

3) Essential Tremor

4) Movement Disorders

5) Pallidotomy

» How else can FUS be used?

FUS can currently be used in two ways:

1) High frequency FUS can be used to heat brain tissue, and kill the neurons that are responsible for generating troublesome symptoms. The treatment of severe tremor is frequently treated by ablating, or destroying, the neurons in the thalamus that generate the tremor. This is an irreversible procedure.

2) Low frequency FUS can be used to temporarily open the blood brain barrier, to help transport medications and other agents that may be too large to ordinarily pass through the barrier. This opening of this barrier is reversible.

As described above, several clinical trials are active at Sunnybrook investigating both high and low frequency FUS for a wide range of disorders, from brain tumours, to tremor, to Alzheimer’s Disease.

» Who is eligible to receive focused ultrasound treatment for tremor related movement disorders?

Eligible patients must be:

  • Between 18 and 85 years of age
  • Canadian citizens
  • Have a tremor dominant movement disorder, that has failed medical treatment with a neurologist

» What are the advantages to FUS treatments?

  • For Research Patients: The clinical expertise of neurosurgeon can be applied without an invasive surgical procedure or general anesthetic. Combined with the guidance of 3D MRI, precise, real-time feedback from the ultrasound treatment can be garnered before the patient has left the treatment bed.
  • For the Health Care Delivery:
    • Potential for reducing the burden of limited and costly operating room time
    • Non-invasive approaches lessen the risks of infections or complications inherent with open-surgical procedures
    • Shorter hospital stays and recovery are associated with less invasive procedures

» Information for patients interested in this treatment for essential tremor

Thank you for your interest. Many people have essential tremor, but in many, the disability is relatively mild, and in others, medication is effective. MRI guided focused ultrasound treatment is suitable for people with severe tremor that interferes with activities of daily living like writing, eating and drinking from a cup, that does not respond to medication. If you have already seen your doctor for this problem, or better still, a neurologist, you can send your referral to 416-480-6085.
- Michael Schwartz MD, FRCSC

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