99mTc ovalbumin labelled eggs for gastric emptying scintigraphy: in-vitro comparison of solid food markers

BACKGROUNDThe reliability of solid phase gastric emptying measurements by scintigraphy requires a marker that remains within the solid component of the test meal, and which is not degraded by the gastric juice throughout the scintigraphic procedure. In Europe, foods are most often labelled with Tc rhenium sulfide macrocolloid (RSMC) but this solid phase marker was withdrawn from the market in January 2004. OBJECTIVETo test other potential solid phase markers and to compare them to the reference marker RSMC. These markers were rhenium sulfide nanocolloid (RSNC), tin fluoride colloid (TFC), phytates and two albumins (Alb and AlbC). All were radiolabelled with Tc. METHODSAfter quality control, each Tc marker was incorporated into the albumin of one egg. Then, egg white and yolk were mixed together, and a well-cooked omelette was prepared. Aliquots of the omelette were incubated with an acidic solution of pepsin at 37°C which mimicked gastric juice. Unbound radioactivity in the supernatant fraction was measured at various times up to 3 h. RESULTSThe radiochemical purity was > 95% for all radiopharmaceuticals. During the in-vitro incubation, the percentage of Tc labelled colloids released from the omelette increased continuouslyafter 3 h, 5% for TFC and RSMC, 8% for phytates, and > 9% for the two albumins and RSNC. CONCLUSIONConsidering quality controls and release of Tc during in-vitro incubation of the omelette, TFC showed the same behaviour as the reference marker RSMC. Thus, TFC seems to be the best candidate to replace RSMC for the radiolabelling of the solid phase of the gastric emptying test meal.