Imaging of atherosclerosis

Atherosclerosis is a chronic disease potentially involving the whole arterial system that causes a spectrum of clinical manifestations ranging from acute myocardial infarction to stable angina or stroke. The continuous accumulation of lipids, fibrous and inflammatory elements in the arterial wall leads to progressive lumen narrowing with subsequent ischemia. Acute coronary syndromes (unstable angina, acute myocardial infarction) have a more complex and dynamic pathogenesis with coronary plaque rupture and thrombosis as the final common pathway. As only some plaques lead to clinical events whereas many others remain asymptomatic life-long, different imaging modalities have been applied to define the atherosclerotic burden and/or the anatomical characteristics of unstable or vulnerable lesions. Carotid ultrasound, multislice computed tomography (MSCT) or nuclear magnetic resonance (NMR) have been applied to assess the atherosclerotic burden in asymptomatic subjects, while coronary angiography has been mainly used to assess unstable plaques at the time of coronary events. Today intravascular ultrasound (IVUS) offers qualitative details on plaque composition, like hard and soft components, that are helpful to assess unstable lesions, but other important details (lipid pool areas or fibrous cap thickness, ulcerations, thrombotic apposition or erosion) are either below the resolution of IVUS or not easily visualized. In the last years novel techniques have been developed to overcome these limitations. Optical coherence tomography and the combination of anatomical and biological imaging using hybrid techniques (like virtual histology or the combination of positron emission tomography and MSCT or NMR) appear to be particularly attractive. These approaches will likely provide new insights into the pathophysiology of acute coronary events and into the effects of aggressive preventive therapies.