Detection of preformed venous thrombi in dogs by means of I-131-labeled antibodies to dog fibrinogen.

• Diagnostic measures to determine the existence and exact location of established or propagating thrombi would be of obvious clinical significance. The use of a gammaemitting isotope attached to a compound which would concentrate in such lesions could provide a diagnostic technique with the advantages of rapidity, portability, safety, and simplicity. Several investigators have studied the fate of I''-labeled fibrinogen or plasminogen in animals in which thrombi were actively propagating or later induced." It seemed possible that antibody to fibrinogen, labeled with V", could also localize and concentrate in preformed thrombi. Previous studies have indicated that such antibody preparations combined with circulating fibrinogen are carried along with the fibrinogen as it is converted into fibrin.' Since early sequelae to blood vessel damage include inflammation and fibrin deposition, such isotopically labeled antibodies should accumulate along with the fibrin. These preparations are also amenable to removal from circulation by immunological techniques.