Canadian researchers are testing an advanced form of MRI to see if it could prevent stroke by detecting a specific type of dangerous plaque in the major arteries that send blood to the brain.

Using high-resolution magnetic resonance images, researchers at Toronto's Sunnybrook Health Sciences Centre have been able to identify plaque in the carotid artery that is in danger of rupturing and causing a stroke.

Principal investigator Dr. Alan Moody, radiologist-in-chief at the Toronto hospital, said the MRI technique produces three-dimensional images of the artery and shows "bright signals" in areas of the vessel where hemorrhaging of plaque deposits is occurring.

"The vessel itself is a complex thing, it's not just a tube that transports blood from A to B," said Moody, noting that tiny blood vessels develop within plaque deposits attached to the artery wall, which are abnormally fragile and prone to bleeding.

Over time, these microbleeds can cause the chunk of plaque to rupture, spewing a "rather messy core of debris that it's been accumulating for years" into the bloodstream and causing clots to form as the body attempts to repair the damage, he said.

"If one of those small clots flies off, then it will lodge in the next smallest vessel, which in around the carotid is one of the brain vessels," Moody explained. The blocked vessel cuts off blood flow to part of the brain, causing a stroke.

How dangerous is the plaque?

Traditionally, doctors have used ultrasound, CT and basic MRI scanning to determine whether a patient's carotid artery in the neck have become narrowed by plaque build-up, and to what degree. When a carotid artery has a large amount of blockage, doctors often opt for surgery known as an endarterectomy to clean out the deposits.

Moody said the 3-D MRI, which he helped develop in England before coming to Canada, can detect disease within the blood vessel wall itself, often before any significant narrowing occurs.

"It tells us how dangerous the plaque is and if it is likely to rupture," he said of the MRI technique.

"If we now look at trying to identify these patients who are at higher risk than other patients, it then gives us the opportunity maybe not to do an operation," he said. "Maybe we could get away with just stenting the vessel — putting a mesh across the vessel to stop it rupturing — or if we catch it even earlier than that, we may be able to find drugs that particularly turn off this type of disease."

Predictive potential

In the Sunnybrook study, published in the October issue of the journal Radiology, researchers found that areas pinpointed by the 3-D MRI in the carotid arteries of 11 patients did in fact correlate with the spots where dangerous plaque had built up when surgeons performed endarterectomies.

The Toronto team is collaborating with other scientists and clinicians in the Canadian Atherosclerosis Imaging Network to undertake multicentre patient trials using the MRI technique to see if they can "prove categorically that these areas of bright signals are actually going to predict stroke," Moody said.

"We want to then take this and then say we can look at patients and hopefully predict to a certain degree which of those are at higher risk of having a stroke."

Commenting on the research, Dr. David Spence of the University of Western Ontario said the MRI technique is a promising approach for identifying those with vulnerable plaques.

That would include patients with moderate carotid artery blockage who had experienced small warning strokes — called transient ischemic attacks, or TIAs — but who were not yet recommended for surgery.

"This might identify among that group someone at higher risk who might benefit from surgery, and it might be useful in patients with narrowing but no symptoms to identify higher-risk people," Spence, director of UWO's Stroke Prevention and Atherosclerosis Research Centre, said from London, Ont.