Direct Labeling of Macroaggregated Albumin with Indium-111-Chloride Using Acetate Buffer

Indium-111-labeled macroaggregated albumin (MAA) would be suitable for combined pulmonary perfusion and ventilation scan using a 99mTc ventilation agent. MAA suspended in 0.1 M sodium acetate buffer, pH 5.8, was incubated with 111In-chloride for 30 min at room temperature. An in vitro study of the obtained 111In-MAA was performed for labeling efficiency and stability in human normal serum. The 111In-MAA was intravenously injected into normal mice, and the biodistribution was studied at 15 and 180 min postinjection. A gamma camera image was obtained at 15 min after injection. MAA was directly and stably labeled with 111In-chloride, and the labeling efficiency of the preparation was more than 96%. More than 90% of the administered 111In-MAA was caught in the murine lung. The scintigraphy with 111In-MAA showed a clearly visualized murine lung. Indium-111-MAA can be conveniently prepared by direct labeling at room temperature. It provides an alternative perfusion tracer for combined perfusion-ventilation imaging.