MRI measurements of carotid wall thickness improve predictions of cardiovascular disease risk more than a commonly used ultrasound-based test, according to research published Oct. 9 in Radiology.
Lead author Bruce A. Wasserman, MD, noted in a press release that plaque progression in the carotid arteries often mirrors that in the coronary arteries. And because the carotids are easier to image, they represent a good opportunity to assess patients for CVD risk and related outcomes, including heart attacks and strokes.
"The carotid artery serves as window into the cardiovascular system," said Wasserman, with Johns Hopkins University School of Medicine in Baltimore. "Plaque developing in the carotid artery can contribute directly to a stroke, and its features—which determine its vulnerability to rupture—are closely related to those found in coronary artery plaque in the same patients."
Carotid intima-media thickness (IMT) measured via ultrasound is the most commonly used method to gauge early carotid atherosclerosis, but recent meta-analyses suggest it offers little incremental prognostic value to the Framingham risk score.
Wasserman et al. sought to compare the predictive value of IMT against MRI wall thickness measures in 698 participants from the Multi-Ethnic Study of Atherosclerosis. The patients, who were 63 years old on average with no known history of CVD at baseline, were imaged using carotid ultrasound between 2000 and 2002. They also underwent carotid MRI on another visit between September 2002 and February 2004, and were followed through the end of 2013 for assessment of CVD events.
After adjusting for patient characteristics including age and traditional risk factors, the researchers found for each standard deviation increase in IMT, patients carried an additional 10 percent risk of coronary heart disease (CHD), which included myocardial infarction, angina, cardiac arrest and CHD-related death. The adjusted hazard ratio for stroke was 1.08 with each standard deviation increase in IMT.
Increases in mean MRI wall thickness, however, showed even greater associations with CHD and stroke-related events. Standard deviation increases in gadolinium-enhanced MRI were linked to increased risks of 27 percent and 58 percent, respectively, for CHD and stroke. A noncontrast MRI measurement yielded hazard ratios of 32 percent and 48 percent, respectively—slightly more specific for CHD than the gadolinium-enhanced test but less predictive of stroke.
“Our study showed for the first time, to our knowledge, that MRI measures of wall thickness were more strongly associated with incident CVD events, particularly stroke, compared with (ultrasound) measures of IMT, suggesting that MRI may be clinically more relevant in the prediction of future CVD events,” Wasserman et al. wrote.
Wasserman said the observed advantage with MRI may be related to the modality’s more complete imaging of the entire carotid wall circumference, whereas ultrasound-based IMT usually only looks at the artery’s far wall.
"High-resolution MRI can tell us the stage of plaque in the wall and tell us about plaque features that could lead to stroke," he said in the release. "It can also see the adventitia, a vessel layer that may have an important role in cardiovascular risk because small vessels proliferate there, leading to thickening of the artery, which may be responsible for early disease development and progression."
The authors said the results indicate gadolinium may help identify atherosclerosis at even early stages, but noted safety issues associated with the contrast agent need to be studied and further considered.
They added that additional hurdles need to be addressed before carotid MRI replaces IMT in routine practice. Also, due to its higher cost, the authors suggested carotid MRI might be better used as a second-line tool in multimodality screening.
“The clinical applicability of carotid MRI must be considered in light of several potential limitations, including relatively high cost and somewhat more limited availability, longer imaging times, and potential safety concerns of exposure to the magnetic field,” Wasserman and colleagues wrote. “Our study suggests that MRI wall thickness measurements may be a better marker for predicting CVD events, but its implementation in clinical practice needs to be considered in the context of cost-effectiveness analyses and future clinical trials.”