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Radiology: A Clearer Picture of Plaque
Among radiologists, angiography has long been the go-to tool for analyzing atherosclerosis—the buildup of fatty, cholesterol-based plaque on the interior walls of blood vessels, which shows up on angiograms as luminal narrowing.
But while angiography is helpful, it has limitations, says Johns Hopkins radiologist Bruce Wasserman. “Blood vessels can experience plaque buildup long before there is narrowing. Furthermore, angiograms tell us the degree of narrowing but not a lot about the plaque’s rupture risk.”
So Wasserman has turned instead to MRI, developing new techniques that are, for the first time, offering an unparalleled view into the arteries and intricate vessels supplying the brain. Perhaps most importantly, his methods are illuminating the very composition of the plaque itself.
This is particularly helpful for stroke prevention, since strokes are often caused when plaque becomes unstable and ruptures, not simply by narrowing that cuts off blood flow. These vulnerable features of plaque, Wasserman says, are not detectable by traditional imaging. “Low-grade carotid plaque is often unrecognized as a cause for stroke,” he says, “but its risk is not trivial when considering its very high prevalence in the United States.”
The impact of Wasserman’s work has been felt most profoundly in decisions to treat plaques causing low-grade narrowing. Previously, vascular surgeons made a go/no-go call based on broad standards, such as a 70-percent narrowing cutoff for surgery of the carotid artery. Wasserman’s MRI techniques offer more precise guidance for managing plaque for stroke prevention, even for lesions not identified by angiography.
Of course, the carotid artery is large and relatively easy to image. With the intricate, twisted vessels deeper in the brain, the challenge is greater still. Wasserman has nonetheless found ways to peer into these areas, as well.
“We can acquire 3-D scans of intracranial vessels with very high resolution,” Wasserman says. “This has been enthusiastically received by clinicians, since it offers an unprecedented view to identify areas of concern and guide management. Inflammation of the brain’s blood vessels, known as vasculitis, for example, can sometimes look like atherosclerosis on angiography, but the treatments are very different.”
Wasserman’s MRI techniques are also being incorporated into large, population-based studies that are yielding important insights into the risk factors and racial distributions of vascular disease. His group has shown, for instance, that the prevalence of intracranial plaque is highest in black men, with approximately half over age 65 in the U.S. estimated to have the disease.