SPECT quantification of technetium-99m microspheres within the canine lung

Attenuation compensated single photon emission CT (SPECT) count rates of 99mTc microsphere activities from 151 selected small regions of interest (ROIs) in an intact canine thorax were compared with the count rates obtained from scintillation camera images of similar ROIs from frozen slices of the thorax. A first-order method was used to compensate the SPECT and scintillation camera images for the effect of Compton scattering. The SPECT and scintillation camera count rates correlated well: r = 0.95 (RMS error 4.8 counts/s) for 19 X 19 X 13 mm thick ROIs. We conclude that regional quantification of 99mTc microspheres within the dog thorax is possible using camera-based SPECT systems.