Atherosclerosis: imaging techniques and the evolving role of nuclear medicine

Quantitative assessment of atherosclerotic or atherothrombotic disease during its natural history and following therapeutic interventions is important for understanding the progression and stabilization of the disease and for selecting appropriate medical or surgical interventions. A number of invasive and noninvasive imaging techniques are available to detect and display different characteristics of vascular lesions of clinical and/or research interest.

Angiography, the traditional "gold standard," detects advanced lesions and measures the degree of stenosis. Angioscopy clearly identifies thrombus. In carotid arteries and arteries in lower extremities, duplex ultrasonography is useful for providing the degree of stenosis, as well as plaque morphology, and assessing changes in wall thickness.

Magnetic resonance angiography, being noninvasive, may replace conventional angiography for anatomical imaging of the vasculature. Ultrafast electron beam CT measures the calcium content in the atherosclerotic lesions. Intravascular ultrasound is the only technique that appears to be clinically useful in imaging the unstable, vulnerable plaques in coronary arteries. Magnetic resonance imaging techniques may be able to image vulnerable plaques and characterize plaques in terms of lipid and fibrous content and identify the presence of thrombus associated with the plaques. In regard to the nuclear scientigraphic imaging techniques, radiolabeled lipoproteins, platelets and immunoglobulins have shown some clinical potential as imaging agents, but due to poor target-to-background and target-to-blood ratios these agents are not ideal for imaging coronary or even carotid lesions. Technetium-99m-labeled peptides and monoclonal antibody fragments that clear from circulation rapidly and bind specifically to different components of the atherosclerotic lesion showed significant potential in animal models and in limited clinical studies. FRE Peptides capable of binding to GPIIb/IIIA receptors on activated platelets appear to offer significant diagnostic potential for imaging intra-arterial thrombus. Positron emission tomography with metabolic tracers like [18F]-fluorodeoxyglucose (FDG) also appears to offer new opportunities for noninvasive imaging of atherosclerosis and atherothrombosis.