Current status of radionuclide tracer imaging of thrombi and atheroma

The imaging of thrombi and atherosclerotic plaques has great potential for decision making in the management of patients with all types of disease wit hin the circulatory system. This importance is owing to the developments sh owing that areas of moderate stenosis with underlying atheroma are physiolo gically reactive and capable of causing reversible clinical symptoms that c an progress to irreversible end-organ damage if not effectively treated, Id entifying and quantifying areas of smaller vulnerable plaque and areas of a cute thrombosis will assist in identification of patients at risk and help determine when and how to treat these patients. Initial efforts in this are a used nonspecific constituents of thrombi and atheroma that were radiolabe led using long-lived isotopes, which had high background activity that requ ired imaging over 48 to 72 hours. Newer approaches have focused on the use of small antibody fragments or small peptides, so-called molecular recognit ion units, that specifically target antigens present only in areas of throm bosis or active atherogenesis. These compounds are labeled Technetium-99 m (Tc-99m) and provide excellent images. Efforts to image thrombi have been d irected at the IIB/IIIA receptor, which is present in low concentration on the cell membrane of circulating quiescent platelets, but on stimulation an d active thrombosis, more than 80,000 potential binding sites per platelet appear. One such peptide has been clinically approved for imaging of deep v ein thrombophlebitis, Parallel efforts are being made for imaging areas of active atherogenesis by targeting smooth muscle cells and other constituent s unique for vulnerable plaques, Efforts in developing these modalities are important to expand the applications to new areas in nuclear cardiology. C opyright (C) 1999 by W.B. Saunders Company.