Efficiency of Radiolabeling Eggs Before and After Microwave Cooking for Gastric Emptying Scintigraphy Studies

The accuracy and reproducibility of nuclear medicine gastric emptying scintigraphy (GES) require strict adherence to the Society of Nuclear Medicine and Molecular Imaging standardized protocol, which contains precise instructions for meal ingredients and preparation. Previous research demonstrated that many laboratories were using whole eggs in the test meal as opposed to the guideline-recommended liquid egg whites and that some laboratories were attempting to radiolabel the egg by adding the radiotracer after cooking. This study aimed to document the labeling efficiency of ^99mTc-sulfur colloid (SC) added to whole eggs before and after microwave cooking. Methods: Whole eggs were mixed with ^99mTc-SC before and after microwave cooking. The radiolabeling stability of the eggs was tested after 2 and 4 h of incubation in gastric fluid simulated using just hydrochloric acid (HCl) and using HCl with pepsin. Results: The experiment showed that no matter what the testing condition, radiolabeling by adding ^99mTc-SC to whole eggs before cooking resulted in a significantly higher labeling efficiency than radiolabeling by squirting the ^99mTc-SC on eggs after cooking. This finding persisted over time, with the precooking method still showing significantly higher radiolabeling at 2 and 4 h after the egg was placed in the incubation medium for both gastric fluid mediums. For simulated gastric fluid with pepsin at 2 h, the labeling was significantly higher, at 73.3%, when the radiotracer was added before cooking than the 43.3% when added after cooking (P < 0.001). The results of this study further showed that when egg labeling efficiency was tested in HCl without pepsin, the labeling was less stable than when tested in HCl with pepsin. In the HCl-only medium, the labeling efficiency decreased significantly between 2 and 4 h for both radiolabeling methods. Conclusion: The results of this study demonstrated that the addition of ^99mTc-SC to whole eggs after cooking resulted in considerably inferior binding of the radiotracer to the eggs and that binding deteriorated significantly over time. The study further demonstrated that the results of radiolabeling efficiency varied depending on whether HCl or HCl with pepsin was used to simulate gastric fluid. Radiolabeling stability decreased over time when HCl without pepsin was used. The findings emphasize the criticality of adhering to the standardized meal and preparation, as alternate cooking methods have different radiolabeling efficiencies.