Binding Affinity of Sulfur Colloid to Egg Whites in Nuclear Medicine Gastric Emptying Study

Introduction: The purpose of a nuclear medicine gastric emptying study is to evaluate the function of the stomach to determine specific pathologies related to the rate of emptying. Radiolabeled egg whites with Tc99m Sulfur Colloid, toast, and jam are the preferred standardized meal. For the purpose of this research study, we evaluated egg whites alone (not the entire standardized meal) to gather information about the loss of radioactivity during the cooking process of egg whites which is the crucial part of the standardized meal.

Methods: This research was carried out without the use of human subjects. 1mCi Tc-99m Sulfur Colloid was measured in a dose calibrator and then injected into 4 ounces of liquid egg whites. The syringes were measured again to account for any residual radioactivity. The eggs whites were cooked to the FDA recommended temperature of 165 degrees Fahrenheit in a hot plate sprayed with canola oil to prevent sticking. The cooking pan and spatula were measured under the gamma camera before and after cooking. The cooked egg whites were measured on the plate before simulation of eating. The disposable plate, utensils, and chux, were measured under the gamma camera for detection of residual radioactivity and the process was repeated 10 times. Unit counts were estimated for each cooking stage using generalized linear mixed models assuming negative binomial distribution, where observations were tested by replicate.

Results: The total count possible was 167,607 (95% CI [154885, 181374], but the total count of the meal was 142,479 (95% CI [131663, 154184]) — an overall average loss count of 25,128 or a reduction of 15% (Figure 1). This discrepancy was accounted for (in part) by the residual count in the syringe (18,576 or 11%) and the residual count on the pan (2241.14-1592.78=648.36 or .4%); after measuring residual count after eating (2,065.98 or 1.2%), the total residual count was 21,290.34 (or 13%). Geiger counter reading in the pan before (0.024, 95% CI [0.01568, 0.03674]) vs. after (0.723, 95% CI [0.325, 1.6085) was significantly higher, p<.001. Dose calibration before (0.9598, 95% CI [0.9136, 1.0083] vs. after (0.09159, 95% CI [ 0.07885, 0.1064] was also significantly lower, p<.001.

Conclusions: In conclusion, the largest amount of activity lost was noted in the syringe post injection. The least amount of residual activity was shown in the pan measurement after cooking, indicating that most of the activity remains in the eggs throughout the cooking process. There was a 2.4% discrepancy in the total number of counts lost, which could have been contributed to not measuring the cup in which the eggs were injected. Overall, it appears that the Tc99m Sulfur Colloid binds well to the egg whites due to the small number of counts measured in the pan after cooking. The large amount of residual activity in the syringe could perhaps be reduced further with exploring a different injection technique.

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