Plaque burden measurement becomes research priority

The recognition that it is better to study a forest than its individual trees is leading to major changes in atherosclerosis imaging research.

During a plenary lecture at the SCMR meeting in February, Dr. Valentin Fuster, director of the cardiovascular institute at Mount Sinai Hospital in New York City, asked colleagues to forgive him for promoting apparently misguided assumptions about the nature of atherosclerosis. After devoting years to MR methods that evaluate individual plaques, he has concluded that overall plaque burden is more important.

"There is no such thing as a single plaque that is vulnerable," he said. "All the studies now show there is a lot of plaque everywhere, and there is no clue where the plaque is going to rupture."

The term vulnerable plaque itself is misleading, according to Fuster. It should be called high-risk plaque to reflect the varied structure and physiology of dangerous plaque residing in the various arteries.

The emphasis on plaque burden has earned broad support since its proposal about four years ago. Many cardiac imagers now believe that patient burden measures will have more influence on clinical decision making related to atherosclerosis than will imaging of individual high-risk plaque, Fuster said.

The direction of MR research has changed radically, said Zahi A. Fayad, Ph.D., an associate professor of radiology at Mount Sinai. Fayad is credited with several innovations associated with MR imaging of vulnerable coronary plaque. While that work required nearly microscopic resolution, MR measurement of plaque burden places a premium on speed and anatomic coverage.

"You need imaging that can cover a lot of territory with the ability to capture 3D views of the plaque to calculate its volume," he said.

CT angiography is extremely fast, but it can't find plaques that are not calcified or stenotic, Fayad said.

He favors black-blood MR techniques capable of extending the measurement of plaque volume to disease that is embedded in vessel walls.

Although the emphasis of research is shifting away from the study of individual plaques, work on better MR methods to evaluate the risk of coronary artery plaque rupture will continue, he said.

"The coronary arteries are still a challenge because of motion and problems with imaging the whole heart, but in the future, this is something that we will probably do," Fayad said.