The registered error between PET and CT imaging system was confirmed by a water model simulating clinical cases.A barrel of 6750 mL was filled with 59.2 MBq [18F]-FDG and scanned after 80 min by 2 dimension model PET/CT.The CT images were used to attenuate the PET images.The CT/PET images were obtained by image morphological processing analyses without barrel wall.The relationship of the water image centroids of CT and PET images was established by linear regression analysis

and the registered error between PET and CT image could be computed one slice by one slice.The alignment program was done 4 times following the protocol given by GE Healthcare.Compared with centroids of water CT images

centroids of PET images were shifted to X-axis(0.011slice+0.63) mm

to Y-axis(0.022×slice+1.35) mm.To match CT images

PET images should be translated along X-axis(2.69±0.15) mm

Y-axis(0.43±0.11) mm

Z-axis(0.86±0.23) mm

and X-axis be rotated by(0.06±0.07)

Y-axis by(0.01±0.08)

and Z-axis by(0.11±0.07).So

the systematic registered error was not affected by load and its distribution.By finding the registered error between PET and CT images for coordinate rotation random error

the water model could confirm the registered results of PET-CT system corrected by Alignment parameters.