A North American pioneer in the field of cerebrovascular ultrasound, the Neuro-Doppler Laboratory at Sunnybrook is celebrating 25 years of advancing and innovating stroke care.Doppler ultrasound testing is being used to evaluate both the head (transcranial) and the neck (carotid) arteries as a proven safe, effective and reliable technology for identifying the risk of stroke.
“Most recently we have started using transcranial Doppler in the ER to provide us with real time monitoring of a patient’s artery during a stroke,” says Dr. Demetrios Sahlas, neurologist at Sunnybrook Health Sciences Centre and co-medical director of the Neuro-Doppler Lab. “During the critical window of a stroke’s acute phase, transcranial Doppler can give us important information about whether an artery reopens during treatment. We can monitor the artery while the patient is still in the ER, as the machine is portable and can be brought right to the patient’s bedside whereas CT or MRI requires moving the patient and is a snapshot in time. In addition, recent evidence indicates a blood clot is more likely to break up when transcranial ultrasound is applied.”
A Doppler probe is placed on the head or neck and uses ultrasound to measure the blood flow velocity of different arteries. “Doppler ultrasound can determine abnormalities in blood flow caused by atherosclerotic plaques or clot,” says Dianne Brodie, technical director of the Neuro-Doppler Lab and registered vascular technologist. “Traditional ultrasound shows the vessels and tissues; the Doppler component shows velocity waveforms used to calculate the narrowing of an artery. Before CT scans or MRI’s were being used, Doppler ultrasound was the only non-invasive way we were able to determine a dangerous narrowing of the carotid artery, and Sunnybrook was one of the first centres in Canada to do this.”
Doppler is used clinically in addition to MRI and CT scans to identify diseased arteries with the goal of preventing a stroke. The Family Practice Unit at Sunnybrook has an arrangement in which patients who have experienced a transient ischemic attack (TIA, or a “mini-stroke”) can be sent to the Neuro-Doppler Lab immediately for same day service as risk of stroke is very high within 24 hours of a TIA. “This practice should be the standard everywhere,” says Sahlas.
Sunnybrook researchers are in the process of collaborating to combine Doppler with another imaging technique called Magnetic Resonance Direct Thrombus Imaging (MRDTI) to better determine stroke risk in asymptomatic patients.
The Neuro-Doppler Laboratory at Sunnybrook was one of the first fully accredited cerebrovascular laboratories in Canada and one of the first ten centres in North America where transcranial Doppler was used. It is a great resource for training stroke and neurology experts from across North America and around the world.
Opened in 1981, the lab has seen giants in the field of stroke get their training here, including Dr. John Norris (the visionary who started the Neuro-Doppler Laboratory), Dr. Andrei Alexandrov (director of the University of Texas Ð Houston Medical School STAT neurosonology service) and Dr. Roberta Bondar (who learned the techniques here for application in space).