Experimental evaluation of Tc-99m sulfur colloid as a potential imaging agent in thromboembolic disease: concise communication.

Based on literature reports suggesting the possible incorporation of Tc-99m sulfur colloid (Tc-SC) into fibrin deposits, this study was undertaken to evaluate the potential of this radiopharmaceutical as an imaging agent in thromboembolic disease. Animal models of deep-vein thrombosis and pulmonary embolism were used. The mean thrombus-to-blood (T/B) uptake ratios were comparable for fresh and older thrombi (up to 72 hr). Thrombus uptake was significantly lower in a group of five control dogs that received pertechnetate instead of Tc-SC. Intravenous heparin administration (5,000 IU) 2 hr before injection of Tc-SC caused a depression in T/B ratios but did not totally block Tc-SC uptake. Gamma imaging with Tc-SC allowed demonstration of deep-vein thrombi, but imaging of pulmonary emboli as areas of increased activity was not satisfactory. This study supports the concept of thrombus detection with radiolabeled particles but not the extension of this principle to the imaging of pulmonary emboli.