Biological background subtraction improves immunoscintigraphy by subsequent injection of antigen

We have developed an 111In-labeled antibody for in vivo use directed against tissue plasminogen activator demonstrating focal fibrinolytic activity. However, a major problem in immunoscintigraphy is the low signal-to-noise ratio due to circulating antibody. The hepatic clearance of t-PA is very rapid. The effect of a subsequent injection of a small amount of t-PA shortly after the antibody administration to increase the blood clearance rate of the formed antigen-antibody complexes was examined in six rabbits. More than 99% of the circulating antigen-antibody complexes were eliminated by the liver within 10 min. This technique could make immunoscintigraphy a first line diagnostic tool in acute medicine including imaging of thromboembolic lesions in organs with high blood volumes such as the lungs, the heart, and the brain.