[Examination of bed overlaps in 18F-FDG PET/CT 3D data acquisition]

The purpose of this study was to determine the best bed overlaps in PET/CT 3D acquisition to reconstruct a transverse image with uniform quality not depending on axial slice position. First, the value of the image contrast ratio, non-uniformity (NU) value, and coefficient of variation (COV) were examined in the image of a cylindrical phantom at each slice position. The image-contrast ratio was almost constant in all slice images, and the NU value and COV were also constant in the slice images up to 13 and 19 slices from the center, respectively, but these values increased with closeness to the edge of the detector. Secondly, COV and image contrast ratios at different sizes of (18)F-FDG concentration (phi 19 mm, phi 16 mm, phi 13 mm, phi 10 mm) were examined in the case of overlapping the bed frame with 11, 15, and 21 slices in acquiring data in 3D mode. In 21 and 15 slices overlapping in acquisition, the image contrast ratios for all concentrations were greater than 0.13, which was the threshold image contrast ratio needed to identify FDG concentration from the background image with naked eye scanning under our conditions. However, in 11 slices with overlapping acquisition, the image-contrast ratio for a phi 10 mm concentration were close to or less than 0.13 in the all slice images. As a result, 15 overlapping slices was a reasonable minimum number of slices to identify a phi 10 mm (18)F-FDG concentration while maintaining the image quality in PET/CT 3D acquisition in our institution.