Comparison of four technetium-99m radiopharmaceuticals for detection and localization of gastrointestinal bleeding in a sheep model.

Four Tc-99 radiopharmaceuticals, Tc-99m sulphur colloid, Tc-99m red blood cells (RBCs), Tc-99m mercaptoacetyltriglycine (MAG3), and Tc-99m DTPA, were studied in an experimental animal model for detection and localization of gastrointestinal (GI) bleeding site in both the upper and lower abdomen. With Tc-99m sulphur colloid and Tc-99m RBCs, it was possible to detect and localize the GI bleeding site in the lower abdomen. With Tc-99m MAG3, it was possible to visualize the bleeding site in both the upper and lower abdomen. However, Tc-99m MAG3 is partially excreted by the liver into the bile, hence it will be difficult to use Tc-99m MAG3 to localize the GI bleeding site in the lower abdomen. With Tc-99m DTPA, it was possible to detect and localize the GI bleeding site simultaneously in both upper and lower abdomen. The overall background radioactivity was reduced considerably by diuresis with frusemide and catheterization of the urinary bladder.