Technical Factors in Labeling Test Meals to Determine Gastric Emptying Rate

Objective: This study investigates the behavior of two different radionuclide labels for liquid test meals and the stability of radionuclide labeling of solid meals. Methods: Technetium-99m DTPA and mTc colloid were compared as labels for liquid test meals in an in vivo investigation of gastric emptying rate. Half emptying time and retention percentages were used as parameters. Stability of solid test meals labeling using mTc colloid on liver pate was determined in vitro. After incubation in gastric acid, samples of the labeled solid meals were incubated in bile with pancreatic juice. After separation, activity of mTc is determined in the solid phase and in the supernatant. Technetium-99m activity was also measured in plasma during gastric emptying measurements for solids in healthy volunteers. Results: Liquid gastric emptying was faster if DTPA was used. Colloid remained in the stomach longer. There was little dissociation of mTc from the solid test meal into gastric acid and into bile with pancreatic juice. Activity levels of mTc in plasma remained low throughout the emptying study. Conclusion: We prefer DTPA as the label for gastric emptying study of liquid meals. We suspect that colloid adheres to the gastric wall and falsifies the results. The current labeling of solid test meals is stable in gastric and duodenal environments. Adsorption of mTc into plasma remains very limited. Subsequent resecretion of mrc in whatever form into gastric juice is excluded.