Importance of gated CT acquisition for the quantitative improvement of the gated PET/CT in moving phantom

Objective The aim of this study was to investigate the utility of gated PET/CT and CT attenuation correction (AC) for the quantitation of radioactivity. Methods An ellipse phantom containing six spheres, ranging from 10 to 37 mm in diameter, was filled with 36.7 kBq/mL of F-18. The respiratory motion was simulated by a motor-driven plastic platform to move the phantom with a displacement of 2 cm in the craniocaudal direction at a frequency of 15/min. With the phantom at rest, PET/CT data were acquired and used as a standard (nonmotion). With the phantom in motion, PET data were acquired in both the static and gated modes (sPET and gPET, respectively). Helical CT (HCT), slow CT (SCT), average CT (ACT), and four-dimensional CT (4DCT) were acquired and used to correct attenuation. On both PET and CT images, the maximum radioactivity, dimensions, and CT numbers were measured on the central slices. Results In nonmotion, recovery coefficients whose spheres were 22 mm or smaller gradually decreased. Regarding motion, the PET counts of the spheres in the static acquisition were lower than those acquired in nonmotion with either type of CTAC (sPET–HCT: −43.8%, sPET–SCT: −51.4%, sPET–ACT: −49.5%). Gated acquisition of PET significantly improved the PET counts (gPET–HCT: −30.1%) ( p