BASIC SCIENCES Evaluation of Indium-111-LabeledAnti-Fibrin Antibody for Imaging VascularThrombi

Monoclonal antibody 59D8 developed by Hui et al., binds to fibrin but not fibrinogen. An 111ln labeled Fab fragment of 59D8 was studied in vitro and in animal models to evaluate its potential for imaging thrombi and emboli in man. Rabbits and dogs were used as models for studying thrombus uptake in vivo.Thrombiand emboli up to 4 days old were successfully visualized at 4—24hr postinjection in five of eight rabbits. Indogs, 0.5-hr-old and 24-hr-old thrombi were successfully imaged at 24 hr in six of eight animals, and 3/6 of these were positive at 3—4hr postinjection. Thrombus-to-blood ratios in the dogs averaged 7.1 ±1.3. The findings suggest this antibody may be useful for imaging thrombi in man. J Nuci Med 29:494—502,1988 dioisotopic methods for detecting deep venous thrombosis (DVT) still suffer from many limitations despite the continued search for a scintigraphic method for locating thrombi (1). Radiolabeled antibodies have been tested as specific probes for thrombi in the past. Initial studies used polyclonal antibodies which reacted with fibrinogen as well as fibrin (2-5). These antibodies rapidly became bound to circulating fibrinogen, and thus traced the incorporation of fibrinogen into forming thrombi. Pro longed antibody residence time in the blood resulted in a delay of at least 48 hr before thrombi could be visualized. More recent studies have used both poly clonal (6) and monoclonal (7) radioiodinated anti bodies which react with fibrin monomer but not with fibnnogen. Although fibrin-specific antibodies may have increased affinity for aged thrombi, they still suffer froma longresidencetimein theblood.Thislimitsthe rapidity with which thrombi can be detected in the presence of the blood background. Previous studies with radiolabeled antibody for thrombus detection used iodine-l3