Continued experimental research with saline addition to a TC-99m Sulfur Colloid syringe used in Gastric Emptying studies to evaluate lost activity.

Introduction: Does the addition of saline to a syringe reduce the residual activity in the syringe for a gastric emptying study but add to the activity lost during the cooking and preparation process? The standard dose for a gastric study is 1mCi of Tc-99m Sulfur Colloid and is typically delivered as a unit dose varying in volume (less than 1mL). Research has been done in the past looking at the residual activity within the syringe with different volumes in the syringe to reduce residual activity (Parent). It has been shown that the addition of volume to the syringe can reduce residual activity in syringe after injection, thus reducing waste while preparing the meal, and maximizing the efficiency of administered activity. Another research study showed that most residual activity remaining was in the syringe after injection (Santos). The goal of this research is to evaluate if adding saline to the syringe will increase the activity lost during the cooking and preparation of the gastric emptying study meal and confirm a reliable dose is administered to the patient.

Methods: This research was conducted as a benchtop experiment and no human subjects were used. Unit doses of 1mCi of Tc-99m Sulfur Colloid in 2.5ml were ordered from the radiopharmacy. The dose was added to a foam cup containing 4oz of liquid egg whites, it was mixed, and then added to a hot plate that had been sprayed with canola oil spray to prevent sticking. After cooking the eggs and taking count measurements the act of eating was simulated by taking several spoonfuls of the eggs and moving it to another plate. The following count measurements were acquired using a dual-headed<s> </s>camera set consistently at 20cm distance: room background, the pan before and after cooking, the unit dose before and after injection, the eggs on the plate after cooking, and the plate and spoon after simulating the consumption of the meal. The experiment was run ten times.

Results: The largest amount of activity lost during preparation of the meal was seen within the residual activity in the syringe with 17% remaining in the syringe post injection into the pre-cooked egg . The amount of activity lost in the pan while cooking and the plate post-simulated meal consumption averaged to be 0.1% of the total counts. It was noted that if the egg whites cook longer before flipping them the GM-meter readings in the pan were lower than if the eggs were scrabbled earlier in the cooking process.

Conclusions: The most inefficient step in our study, i.e. the step with the largest percent loss of activity, was in residual activity retained within the syringe, which is consisted with previous research. The volume in the syringe did not change the binding affinity of the eggs and did not create more residual activity in the pan from cooking. One difference from previous research is that the syringe was not flushed with the egg whites which resulted in more residual in the syringe (17% compared to 10%) for this study. This suggests that added saline doesn’t necessary change the residual but flushing the syringe with the eggs might have more of an impact. More research with varying volumes may show that more volume reduces the residual in the absence of flushing the syringe with the egg whites.