Because coronary artery disease (CAD) is the most frequent cause of death in industrialized nations and its onset is currently unpredictable, there is a need for new methods of screening apparently healthy individuals to identify those at increased risk. Technical advances in the noninvasive imaging techniques of computed tomography (CT), magnetic resonance imaging (MRI), and nuclear imaging now make it possible to image the heart and perform a partial evaluation of the coronary arteries without the need for an invasive procedure such as cardiac catheterization. Despite these capabilities, prediction of heart attack is likely to require characterization of the amount and composition of atherosclerotic lesions (plaques) within the coronary arteries. At present, CT is the only noninvasive technique in widespread clinical use that can obtain information about the composition of coronary atherosclerotic plaque in living patients. Although the information is currently limited to determination of the presence and amount of calcium in the plaque, the test has already been documented to provide information about the presence of disease or its probability. Thus, many healthy individuals who could be considered at risk for CAD because of age, high cholesterol level, or other factors now wonder if they should undergo CT scanning to determine if their coronary arteries are calcified. The decision to undergo this test is more complicated than might be expected because of conflicting opinions about the significance of coronary artery calcification. Atherosclerosis is a diffuse disease that affects many arteries of the body, not just the coronary arteries. In the early stages, it causes changes in the walls of the arteries, with increases in cholesterol content and scar tissue. In later stages, it causes plaques that thicken the wall of the artery, and in some cases, narrow the center of the artery so that the flow of blood is …