Cardiac and vascular imaging with labeled platelets and leukocytes

The contribution of platelets in atherosclerosis and thrombosis in animal models and in clinical studies has been quantified with 111 In-platelet scintigraphy. New in vitro quantitative techniques have been developed using 111 In-labeled platelets to determine the number of adherent platelets on deendothelialized surfaces of damaged vessel walls and synthetic vascular grafts. In vivo imaging techniques are semiquantitative in nature; in these studies 111 In radioactivity on thrombotic vessels or graft surfaces of iliac, femoral, or popliteal arteries is compared with contralateral vessels. Background 111 In radioactivity in the circulating blood pool of venous and capillary networks and radioactivity in marrow decreases the sensitivity of these techniques. Despite these limitations, the dynamic process of platelet deposition in most of the denuded, atherosclerotic vessels and prostheses in the circulatory system can be recorded. This ongoing thrombosis and embolization has been observed in 5–10-year-old vascular grafts of Teflon and Dacron biomaterials. Currently used platelet function inhibitor drugs, eg, aspirin, Persantine, sulfinpyrazone, and Motrin, have a demonstrable effect on platelet deposition. Slight changes in reduction of platelet deposition on these surfaces due to medical intervention have been observed by noninvasive imaging with 111 In-platelets. Subtraction of blood pool radioactivity with 99m Tc-labeled autologous red cells and calculation of 111 In radioactivity associated with platelet thrombus on vessel walls also have been performed for coronary, carotid, and femoral arteries. Although platelet concentrates are used frequently after open heart surgery fone to six per patient), consumption of platelets in the artificial lung or oxygenator, lysis of platelets during pumping, and suction of blood only recently have been quantified with the use of 111 In-labeled platelets. These studies also demonstrated far less trauma to platelets with the use of a membrane rather than a bubble oxygenator. Further reduction in platelet consumption and trauma was observed with the use of prostacyclin, a short-acting drug with significant beneficial effect on platelet thrombus reduction and disaggregation of aggregated platelets. The role of polymorphonuclear leukocytes in inflammation, infection and myocardial infarction, and in vivo evaluation with 111 In-leukocyte scintigraphy in animals and humans has been described. Fortunately, due to the abundance of platelets in blood and their smaller size and density, quantitative studies of platelet thrombosis are possible with a pure preparation of 111 In-labeled viable platelets. Studies of platelet survival, lysis, platelet consumption and platelet thrombus formation, and subsequent embolization are possible in one study with 111 In-labeled platelets. Only survival and lysis can be measured with 51 Cr-labeled platelets. In most of the 111 In-leukocyte studies, more than 70% of 111 In radioactivity was bound to platelets and red cells; less than 30% of 111 In was with PMN leukocytes. The separation of pure polymorphonuclear leukocytes by Ficoll-Hypaque separation or elutriator, labeling in plasma media with 111 In-tropolone permits pure and viable preparation of 111 In-PMN leukocytes, which will enhance our understanding of the role of PMN-leukocytes in health and disease.