40 ■ APPLIED RADIOLOGY November 2001 P laque accumulation in coro- nary arteries eventually leads to the obstruction of blood flow and angiographic stenosis. Sev- eral angiographic studies have shown the prognostic value of stenosis sever- ity. 1 However, it has become clear that dynamic changes of coronary plaques residing in the vessel wall precede luminal stenosis and, therefore, better reflect the development of coronary artery disease. In fact, most plaques that eventually cause acute coronary syndromes (vulnerable plaques) are not severely stenotic before the acute event 2-4 because early plaque develop- ment leads to expansion of the vessel wall (positive remodeling), thereby delaying luminal stenosis despite plaque accumulation. 5 More recently, investigators have focused on the composition of coronary plaques as an important factor in the development of acute coronary events. The first evi- dence that morphologic characteristics of the vessel wall have prognostic value came from angiography, demon- strating that the extent of coronary cal- cification is correlated to plaque burden and predicts the likelihood of coronary events. The prognostic value of coronary calcifications has been fur- ther defined with electron-beam com- puted tomography (EBCT) and more recently with fast multidetector CT. Other methods, particularly intravas- cular ultrasound (IVUS) and magnetic resonance imaging (MRI), attempt to characterize the morphology of individ- ual lesions to assess plaque vulnerabil- ity. There is accumulating evidence that plaque characterization can be used in clinical practice. The overall plaque burden and morphology has prognostic value and can influence preventive treatment plans; serial observation of plaque burden allows recognition of disease progression or regression. In addition, the pre-interventional mor- phology of individual lesions affects outcome after coronary interventions and could be used to guide the interven- tional treatment. Coronary plaque development and plaque vulnerability Histologic and intravascular ultra- sound studies have shown that coro- nary lesion development starts relatively early in life. 6 Macrophages accumulate at future plaque sites and, by incorporating cholesterol, become “foam cells.” In advanced lesions, fur- ther cell accumulation leads to the for- mation of a lipid-rich core, which is separated from the lumen by a fibrous cap. 6-8 Atheroma size is not well reflected by luminal stenosis because outward-directed growth of the plaque initially maintains lumen size despite increasing plaque burden. This com- pensatory vessel enlargement in response to plaque growth is termed positive arterial remodeling and was first described by Glagov et al 5 in human coronary atherosclerosis. Coronary artery wall calcification is part of the development of atheroscle- Paul Schoenhagen, MD; Sandra S. Halliburton, PhD; Richard D. White, MD; D. Geoffrey Vince, PhD; Steven E. Nissen, MD; E. Murat Tuzcu, MD Characterization of coronary atherosclerotic plaques and the significance of vessel calcification Dr. Schoenhagen is a Fellow in Car- diovascular Medicine; Dr. Halliburton is an Imaging Scientist in the Section of Cardiovascular Imaging, Division of Radiology; Dr. White is a Professor of Radiology and Medicine and Director of the Cardiovascular Imaging Center in the Department of Radiology; Dr. Vince is Assistant Staff in the Depart- ment of Biomedical Engineering; Dr. Nissen is Vice-Chairman of Cardiol- ogy; and Dr. Tuzcu is a Professor of Medicine and the Director of the IVUS Core Laboratory at The Cleveland Clinic Foundation, Cleveland, OH.