TY - JOUR T1 - <strong>TAGGING EFFICIENCY OF RADIOLABELED EGGS WITH TECHNETIUM 99M MACROAGGREGATED ALBUMIN COMPARED TO TECHNETIUM 99M SULFUR COLLOID FOR GASTRIC EMPTYING STUDIES</strong> JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 4078 LP - 4078 VL - 63 IS - supplement 2 AU - Hayley Bergner AU - Jonathan Baldwin AU - Wendy Galbraith Y1 - 2022/06/01 UR - http://jnm.snmjournals.org/content/63/supplement_2/4078.abstract N2 - 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&lt;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&lt;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. ER -