Biodistribution of 99mTc-MAA on SPECT/CT performed for 90Y-radioembolization therapy planning: a pictorial review

Purpose To evaluate the frequency of Tc-99m-MAA uptake in extrahepatic organs during Y-90-radioembolization therapy planning. Methods This retrospective case series of 70 subjects who underwent Tc-99m-MAA hepatic artery perfusion studies between January 2014 and July 2016 for Y-90-radioembolization therapy planning at our institution involved direct image review for all subjects, with endpoints recorded: lung shunt fraction, extrahepatic radiotracer uptake, time from MAA injection to imaging. Results Combined planar and SPECT/CT imaging findings in the 70 subjects demonstrated lung shunt fraction measurements of less than 10% in 53 (76%) subjects and greater than 10% in 17 (24%) subjects. All patients demonstrated renal cortical uptake, 23 (33%) demonstrated salivary gland uptake, 23 (33%) demonstrated thyroid uptake, and 32 (46%) demonstrated gastric mucosal uptake, with significant overlap between these groups. The range of elapsed times between MAA injection and initial imaging was 41-138 min, with a mean of 92 min. There was no correlation between time to imaging and the presence of extrahepatic radiotracer uptake at any site. Conclusions During hepatic artery perfusion scanning for Y-90-radioembolization therapy planning, extrahepatic uptake is common, particularly in the kidney, salivary gland, thyroid and gastric mucosa, and is hypothesized to result from breakdown of Tc-99m-MAA over time. Given the breakdown to smaller aggregates and ultimately pertechnetate, this should not be a contraindication to actual Y-90 microsphere therapy. Although we found no correlation between time to imaging and extrahepatic uptake, most of our injection-to-imaging times were relatively short.