Technetium-99m macroaggregated albumin scan before yttrium-90 radioembolization: what to look for and why it matters

Yttrium-90 (90Y) radioembolization is an established locoregional therapy for primary and metastatic liver malignancies. Technetium-99m macroaggregated albumin (99mTc-MAA) remains the standard clinically established surrogate for vascular simulation, lung-shunt assessment, detection of extrahepatic deposition, evaluation of tumor and normal-liver perfusion, and predictive dosimetry. Interpretation is nevertheless affected by nonidentity between MAA and therapeutic microspheres and by method-specific technical biases. 99mTc-MAA particles and 90Y microspheres differ in size, shape, density, number of particles, embolic effect, and flow behavior. A systematic and clinically practical approach to 99mTc-MAA interpretation can improve patient selection, reduce the risk of nontarget irradiation, and support safer and more effective radioembolization treatment. This pictorial and narrative review summarizes the current evidence on the applications, interpretation, and limitations of the pretreatment 99mTc-MAA scan before 90Y radioembolization, with emphasis on lung shunt fraction, extrahepatic tracer uptake, intrahepatic distribution, and the evolving role of personalized dosimetry.