Radioembolization is used to treat hepatocellular carcinoma, a type of liver cancer, by introducing radioactive yttrium 90 (90Y) directly into the hepatic vasculature. This method allows for a high dose of radiation to be delivered to the cancer cells while sparing the surrounding healthy liver tissue. Radioembolization requires careful pretreatment planning to determine if administration of 90Y is a suitable and safe treatment option. Planning includes mapping angiograms to assess vascular structures and conjoint technetium Tc 99m macroaggregated albumin hepatic perfusion imaging to study blood flow to surrounding healthy tissue.