The Preparation Parameters of Technetium-99m-Macroaggregated Albumin-Low Particle Number

Abstract

Objective: The preparation of technetium-99m-macroaggregated albumin-low particle number (^99mTc-MAA-LPN) for lung scans of right-to-left shunt in neonates and young children involves the reconstitution of the reagent kit with 0.9% sodium chloride, USP, to obtain the desired low particle number before radiolabeling.

Methods: Volume effects of normal saline and ^99mTc-pertechnetate were studied by using 2.5 to 10.0 ml of normal saline for reconstitution and 2.0 to 8.0 ml of ^99mTc-pertechnetate for radiolabeling. The effect of time lapse after reconstitution was also studied by incubating the reconstituted kits for 5–60 min at room temperature before radiolabeling. Labeling efficiencies of the prepared ^99mTc-MAA-LPN were evaluated using radiochromatography techniques at various time points up to 30 min after radiolabeling. The rate of ^99mTc-MAA-LPN formation was calculated as the association rate constant (ka) from the fitted curves of labeling efficiencies versus time.

Results: The MAA labeling reaction with ^99mTc proceeded at biphasic exponential rates. Both the reconstitution volume of normal saline and the ^99mTc-pertechnetate labeling volume significantly decreased the initial reaction rate (ka₁). These results indicate that the labeling efficiencies of ^99mTc-MAA-LPN preparations are highly dependent on the time of incubation after the addition of ^99mTc-pertechnetate and this dependency increases with larger volumes of prepared ^99mTc-MAA-LPN. In addition, the time between reconstitution and radiolabeling also has a significant impact on the reaction kinetics of radiolabeling.

Conclusions: This study suggests that the optimal labeling condition of ^99mTc-MAA-LPN is achieved by minimizing both the volumes of reconstitution and ^99mTc-pertechnetate radiolabeling immediately after reconstitution and a radiolabeling incubation time of 20–30 min.