Human serum albumin macroaggregates (MAA)

Human serum albumin macroaggregates (MAA) are denatured protein particles used as a diagnostic carrier in nuclear medicine. When labeled with Gallium-68 (Ga-68), the coordination sites on the albumin surface bind the radioisotope to form a PET imaging agent (Jain et al., 2015, Nuclear Medicine and Biology). These particles typically range from 10 to 90 micrometers in diameter, allowing them to be physically trapped in the pulmonary precapillary sphincters upon intravenous injection (StatPearls, 2023). This process, known as microembolization, provides a map of regional lung perfusion, which is essential for diagnosing pulmonary embolism and evaluating lung function (Zhu et al., 2020, Journal of Nuclear Medicine). While MAA interacts with the pulmonary vasculature, it is not a biological target like a receptor or enzyme; instead, it acts as a mechanical tracer. Safety considerations include avoiding use in patients with severe pulmonary hypertension or right-to-left shunts to prevent systemic embolization (NIH, 2022).

Other names

Ga-68 MAAGallium-68 MAA68Ga-macroaggregated albuminHuman serum albumin macroaggregatesAlbumin macroaggregates

Physical entrapment in pulmonary precapillary sphincters (microembolization) proportional to regional blood flow.