IMAGING ARTERIAL THROMBOSIS - COMPARISON OF TC-99M-LABELED MONOCLONALANTIFIBRIN ANTIBODIES AND INDIUM-112 PLATELETS

Imaging with the Tc-99m-T2G1s monoclonal antifibrin antibody fragment (Fab') has demonstrated promise in the noninvasive detection of venous thrombi in humans. The purpose of this study was to determine whether chronic arterial thrombi can also be detected by antifibrin antibody imaging. Methods: Eighteen subjects with chronic arterial thrombi were studied with planar and tomographic imaging at 0 to 24 hr postinjecti on of Tc-99m-labeled T2G1s monoclonal antifibrin antibody fragment. Im aging with In-111-labeled platelets was also performed. Images were vi sually graded by two observers as 0, 1, 2 or 3 (no, faint, moderate or marked) uptake, and quantitative analysis of tomographic images was d one in 13 subjects. Results: On visual analysis of planar images, 44%( 8 of 18) of antifibrin patient studies were 1.0 or more and 66% (10 of 18) were judged negative compared with 94% (15 of 16) of platelet pat ient studies judged 1.0 or more and 6% (1 of 16) judged as negative (p < 0.01). Visual analysis of tomographic images was similar, with 61% (11 of 18) of antifibrin studies graded 1.0 or more compared with 100% (17 of 17) of platelet studies (p < 0.01). The tomographic target-to- background ratio was higher with platelets than with antifibrin antibo dy (2.5 +/- 1.4 versus 1.8 +/- 1.0, p < 0.05). Conclusion: In the larg e-vessel chronic arterial thrombi studied, the results of Tc-99m-label ed monoclonal T2G1s antifibrin Fab' imaging were positive in only one- half of the patients studied, significantly less than the findings wit h platelet imaging, which were positive in all subjects. The higher ra te of positive images with labeled platelets than with labeled antifib rin antibodies may be largely due to thrombus age, with continued plat elet deposition but little active fibrin deposition.