Same day yttrium-90 radioembolization with single photon emission computed tomography/computed tomography: An opportunity to improve care during the COVID-19 pandemic and beyond

Figure 2 Spectral analysis of Technetium-99m macroaggregated albumin and yttrium-90 during the same-day session. A: Technetium-99m macroaggregated albumin (Tc-99m MAA) gamma-ray spectrum showing Compton scatter typical of Tc-99m MAA imaging of the liver. The 140 keV, 20% energy window is shown bracketing the 140 keV photopeak (red); B. Yttrium-90 (Y-90) bremsstrahlung exhibits a broad spectrum with no peaks other than the lead x-ray peak that originates in the collimator. Each point on the spectrum is a combination of original bremsstrahlung photons and Compton scatter from higher energy bremsstrahlung. If the only activity present is Y-90, the 108 keV, 32% energy window (blue) is used as it has a good combination of counts and contrast; C: If imaging of Y-90 bremsstrahlung is attempted with Tc-99m already present in the liver, the spectrum is a combination of both Tc-99m gamma-rays and Y-90 bremsstrahlung. A significant portion of the 108 keV, 32% energy window will be from scattered Tc-99m gamma-rays and will not accurately represent the distribution of Y-90 microspheres. A 22% energy window centered at 180 keV (green), however, can be used to demonstrate the activity of Y-90 microspheres without significant contribution from Tc-99m MAA delivered earlier in the day. Tc: Technetium.