Methods of assessment of thrombosis in vivo

The contributions of platelets and clotting factors in thrombosis on injured vessel and cardiovascular prostheses have been quantified with several tracers. Thrombus formation in vivo could be measured semiquantitatively in animal models and humans with 111In-labeled platelets, 123I- and 131I-labeled fibrinogen, 111In-labeled antibody to the fibrinogen receptor on the platelet membrane and to fibrin. Thrombus localization by imaging was possible for large thrombus in vessel with deep injury of thrombogenic surface in the acute phase. A single layer of adherent platelet could not be imaged, due to the high background radioactivity present in blood. Thrombogenicity of graft was compared with that of contralateral vessel. The dynamic process of platelet deposition could be followed accurately using the in vivo imaging technique. In addition, in vitro quantification permits determination of platelet and fibrin density and of the number of fibrin monomers per platelet in thrombus. The roles of prostacyclin, thromboxane inhibitors, and nonsteroidal antiinflammatory drugs have also been evaluated in animals models and humans. The tracer techniques thus provide invaluable information about platelet-fibrin deposition, its organization and dissolution, and for development of less thrombogenic surfaces for use in cardiovascular prostheses.