| Part One: Radioimmunoimaging of experimental pulmonary embolism with 99mTc labeled monoclonal antibody-SZ51Background: 99mTc-SZ51 is a radiolabeled activated platelet monoclonal antibody that binds with high affinity and specificity to GMP140 receptors expressed on the activated platelet that are involved in acute embolism. The purpose of this study was to evaluate the value of 99mTc-SZ51 radioimmunoimaging in detecting experimental pulmonary embolism and distinguishing the fresh thrombosis from old thrombosis.Materials and Methods: Monoclonal antibody (McAb) SZ51 was modified with 2-iminotholane (2-IT) and labeled with 99mTc-GH. Radiochemical purity and immunoreactivity were determined by ITLC-SG, Sephadex G-25 chromatography and ELISA, respectively. Pulmonary embolisms were induced in 12 dogs by steel coils implantation in pulmonary arteries and endothelial injures formed. 99mTc-SZ51 pulmonary thrombosis scintigraphies were performed 1 day, 6 or 7 days, and 1 month after pulmonary embolisms formed. Images were obtained 1, 2, and 3 hours after 99mTc-SZ51 injection.Results: Positive images of fresh pulmonary embolism, formed 1 day, were apparent and clearly visualized as early as 1 hour after injection, then improved within 3 hours. The ratio of ratioactive uptake of thrombi to surrounding lungs reached 2.90 ± 0.49 at 3 hour postinjection by ROI measurements in vivo imaging. The ratio of per gram of tissue uptake of fresh thrombus to lung was 18.0 ± 3.5. Negative images of old thrombi were demonstrated 1 month after pulmonary thrombi formed. The ratio of thrombi to surrounding lungs in ROI measurements was 1.25± 0. 17, and the ratio of per gram of tissue uptake of old thrombus to lung reduced to 3.3 ± 0.5. Conclusion: 99mTc-SZ51 radioimmunoimaging for detecting acute pulmonary embolism seem to be a potential approach and may distinguish the fresh thrombosis from old thrombosis.
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