What is the usefulness of CT in imaging atherosclerosis?
Atherosclerosis is the leading cause of death in the United States. Cardiac CT plays an important role in evaluating atherosclerotic disease. Nonenhanced coronary CT for calcium scoring can assess overall atherosclerotic plaque burden, and coronary CTA can directly visualize the plaque itself in addition to evaluating the degree of luminal stenosis. There are two particularly important concepts for plaque imaging with coronary CTA: the Glagov phenomenon and plaque components.
The Glagov phenomenon (positive remodeling) is outward remodeling of the coronary arteries in the earlier stages of atherosclerosis. Although there is significant atherosclerotic plaque present in the vessel wall, the lumen remains patent without significant narrowing due to this phenomenon.
Coronary CTA can detect different atherosclerotic plaque components: noncalcified plaque = plaque with lower attenuation compared with the contrast-enhanced vessel lumen without any calcification; calcified plaque = plaque that is predominantly calcified; or mixed plaque = plaque with both calcified and noncalcified portions.
Recent studies have demonstrated the utility of coronary CTA in assessing vulnerable plaque which can be seen in some noncalcified plaques; features thought to demonstrate vulnerability of the plaque include positive remodeling, low attenuation plaque, and the so-called “napkin-ring” sign where a low attenuation lipid-rich necrotic plaque core is surrounded by a peripheral area of higher attenuation fibrous plaque tissue.