Macro-aggregates (MAA) of albumin for lung imaging. Studies on better tissue to background ratio, on MAA stability and reuse after its first preparation.

The present study was designed to develop stable and economically competitive radioactive technetium-99m macro-aggregates of albumin ((99m)Tc-MAA) which could be used for imaging of lungs. Macro-aggregates were freshly prepared and labeled with (99m)Tc pertechnetate by following the standard protocol which included incubation of formulation at 80(o) C for 10 min. We studied 7 rats in every experiment. The rats were injected intravenously with (99m)Tc MAA and were sacrificed after 10 min to study its distribution in the lungs and other non target tissues using gamma ray spectrometer. This standard protocol was further experimented upon in order to achieve high target to non target ratio. Different formulations were prepared by incubating them at 80 degrees for different incubation times of 5, 10, 15, 20, 25 and 30 min. Formulation of MAA prepared by incubating at 80 degrees for 20 min labeled with (99m)Tc showed the highest target to non target ratio. Another group of rats that received the above formulation were sacrificed after two additional time intervals of 5 and 15 min. The target to non target ratio was high in animals sacrificed after 5 min of injecting them with (99m)Tc the MAA formulation prepared by heating at 80 degrees for 20 min as compared to animals sacrificed after 10 and 15 min. Formulations of MAA following storage at room temperatures which varied from 5(o)C to 18(o)C, for different time durations 1, 2 and 9 days were also evaluated for their ability to be reused after reheating and labeling with (99m)Tc. The formulation of MAA kept for 9 days showed the best target to non-target ratio. The present study suggests that MAA once prepared can be reused following labeling with (99m)Tc even after 9 days of storage with better target to non target ratio as compared to storage timer period of 1 and 2 days.