DALLAS, – A simple imaging test identified people with dangerous clogging in their carotid (neck) arteries according to researchers who say the test may someday help identify individuals who need immediate surgery to prevent stroke. Their findings were reported in today’s Circulation: Journal of the American Heart Association.
The researchers caution that because the study was small the results need to be confirmed in a large prospective study. For that reason, they say it is too soon to recommend using MRI to guide clinical decisions.
“However, these early, promising results suggest that in the future it may be possible to use MRI to track the progress of atherosclerosis and to better select patients for surgical intervention,” says Chun Yuan, Ph.D., a professor of radiology at the University of Washington, Seattle.
Yuan says the new technique, which uses high resolution magnetic resonance imaging (MRI), helps identify unstable plaque in patients with atherosclerosis – a disease that narrows arteries and increases the risk for stroke.
Plaque is a hard fatty substance that accumulates in the blood vessels of people with atherosclerosis. This build-up can become unstable and break off. When the plaque breaks or ruptures, a blood clot can form around the broken tissue and block blood flow.
In the heart this process causes a heart attack. When it happens in the carotid arteries, which supply blood to the brain, it can cause a stroke. Yuan explains that the core of plaque in the carotid arteries has an outside covering of fibrous tissue. This fibrous cap can be thick, thin or ruptured. By studying the tissue, researchers discovered that the plaque becomes unstable and prone to rupture when the cap thins.
The researchers used high-resolution MRI to study the condition of fibrous caps in the carotid arteries of 53 patients (49 men, average age 71) who were scheduled for carotid endarterectomy, the surgical procedure in which plaque is removed from the carotid artery. They found subtle differences in the images of the fibrous cap that allowed researchers to identify “intact thick cap, intact thin cap and ruptured cap.”
People with atherosclerosis who had unstable plaque, as detected by MRI, were 23 times more likely to have a stroke than people with the same amount of artery narrowing, but no unstable plaque.
In addition to MRI scans, participants underwent a thorough neurological evaluation to determine if they had a history of stroke or “mini strokes,” which are called transient ischemic attacks, or TIAs, within the previous 90 days. Patients with a positive history were classified as symptomatic. He then compared the MRI results to the patient’s neurological symptoms.
“There was a clear and consistent association between the condition of the fibrous cap as seen by MRI, and the patient’s clinical status,” Yuan says. There was an association between history of recent stroke or TIA and cap status. Only 9 percent of those with intact caps had a positive stroke/TIA history, compared to 70 percent of those with ruptured caps. For those with intact, but thin caps, 50 percent had a history of recent stroke or TIA.
He adds that MRI is uniquely suited for serial, repeated examinations of plaque because it is non-invasive.
Stroke is the third leading cause of death in the United States, ranking behind disease of the heart and cancer. Each year about 600,000 people suffer a stroke, and every 3.1 minutes someone dies of stroke.
Yuan’s coauthors were Shao-xiong Zhang, M.D.; Nayak L. Polissar, Ph.D.; Denise Echelard, B.S.; Geraldo Ortiz, B.S.; Joseph W. Davis, B.S.; Elizabeth Ellington, B.S.; Marina S. Ferguson, B.S.; and Thomas S. Hatsukami, M.D. This research was funded in part by the National Institutes of Health.
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