RT Journal Article SR Electronic T1 TAGGING EFFICIENCY OF RADIOLABELED EGGS WITH TECHNETIUM 99M MACROAGGREGATED ALBUMIN COMPARED TO TECHNETIUM 99M SULFUR COLLOID FOR GASTRIC EMPTYING STUDIES JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 4078 OP 4078 VO 63 IS supplement 2 A1 Bergner, Hayley A1 Baldwin, Jonathan A1 Galbraith, Wendy YR 2022 UL http://jnm.snmjournals.org/content/63/supplement_2/4078.abstract AB 4078 Introduction: A gastric emptying study is a nuclear medicine procedure used to assess gastric motility using radioactive count data. Thisprocedure is noninvasive and is performed by ingesting a meal containing a radiopharmaceutical, which is then imaged over a period of two to four hours. According to Society of Nuclear Medicine and Molecular Imaging (SNMMI) the meal should contain 99mTc-Sulfur Colloid (SC) cooked in 4 oz of liquid egg whites. Recently, SC has been in short supply, so the question raised is whether or not 99mTc-Macroaggregated Albumin (MAA) could be used as a substitute for gastric emptying studies. SC is made up of particles which determine how the dose is incorporated during the cooking process. MAA is also a particulate radiopharmaceutical, however it is not the same chemical structure as SC. Our objective was to test the radiolabeling efficiency ofegg whites using MAA and SC after 2- and 4-hours incubation in simulated gastric fluid without pepsin (SGF) and with pepsin (SGF-P).Methods: 16 test tubes were filled with 0.5 mL liquid egg whites (Great Value 100% Liquid Egg Whites). SC (0.1 mL, ~4 µCi) was added to 8 tubes and MAA (0.1 mL, ~4 µCi) to the remaining 8 tubes. The radioactive egg whites were microwaved for 45 seconds perSNMMI protocol. After microwaving, the cooked egg whites were chopped up to simulate chewing. SGF-P was added to 80 total samples, while SGF was added to 64 total samples. The base of the SGF was 0.16% NaCl with 0.56% HCl, while the SGF-P included 0.32% pepsin. Tubes were placed on a heat source of 37 degrees Celsius and magnetic stirring rods placed in each tube. At 2-hours, half of the tubes were removed and at 4-hours the other half were removed from the heat source. Tubes werecentrifuged for 15-minutes and supernate was removed using a filtered needle. Tubes of supernate and solid phases (with 0.45 micron filter needles) were counted in a scintillation well counter (Packard Cobra II Auto-Gamma Counter) and corrected for radioactive decay. Percent radioactivity remaining in the solid phase at 2-hours and 4- hours were recorded as solid tagging efficiency. This process was completed over approximately 9 days yielding 144 total samples. Percent tagging efficiency at 2-hours and 4-hours were compared between MAA and SC in both SGF and SGF-P. An ANOVA test was used to detect differences in tagging efficiency at the 2-hour period, 4-hour period and among SGF and SGF-P conditions. All statistical tests assumed a 5 % chance of a type one error.Results: At both time points, SC and MAA showed lower tagging efficiency in the SGF-P compared to SGF (p<0.01 for all iterations). At the 2-hour mark, SC showed a 7.3% (95%CI: 1.2, 13.5) higher tagging efficiency compared to MAA when incubated in SGF-P(p=0.0213). Likewise, at the 4-hour mark, SC showed an 8.8% (95%CI: 2.8, 14.7) higher tagging efficiency compared to MAA in SGF-P. However, in SGF MAA showed a slightly higher (2.0% 2hr and 1.1% 4hr) tagging efficiency when compared to sulfur colloid. (p<0.0001 for both time points)Conclusions: The results of this study demonstrated that SC and MAA both tag to eggs whites. SC has a higher tagging efficiency at the 2- and4-hour mark compared to MAA in simulated gastric juice with pepsin. Pepsin is a gastric enzyme that breaks down protein. MAAis a protein, and we showed that in the presence of pepsin, MAA showed lower solid tagging efficiency compared to SC. These results show that MAA could be used as a possible alternative to SC, however study normal values will need to be considered since MAA’s tagging efficiency is lower than SC in the presence of pepsin.