PET and PET-CT imaging in the diagnosis and characterization of atheroma

Activation of macrophages in coronary atheroma is associated with an increase in cellular metabolism. The energy required for this activation is primarily exogenous glucose. This inflammation can be imaged with the positron-emitting tracer, F-18-2-fluorodeoxyglucose. In addition to metabolism, apoptosis is also a recognized component of atheroma. The distribution of macrophage glucose utilization and apoptosis are related, but may differ in intensity in specific lesions. Histologically, lesions with apoptosis were AEA Stages IV-V, suggesting that imaging apoptosis may be the most specific approach to identify lesions at high risk of rupture. In addition to the association of apoptosis with cell death, the process is also associated with micro-calcifications in the organelles of dying tissue. The low concentration of calcium in these organelles is not detectable with conventional radiographic techniques until the micro-calcifications become confluent. Confluent lesions can be readily identified as coronary calcifications on computed tomography (CT). Cardiac CT imaging now plays a major role in screening patients at risk of coronary events. Combining PET-CT with FDG offers the opportunity to measure two parameters related to coronary atherosclerosis: (1) vascular inflammation, based on the focal localization of FDG in the coronary artery; and (2) the distribution of calcification in the vessel, based on the information recorded on the CT scan. Together, these two measurements may identify lesions and characterize their likelihood of producing an acute event. (C) 2004 Published by Elsevier B.V.