Fig. 2

Examples of PET and CT images of axial slices acquired from a scanner of vendor A (a, b; obtained from scanner number 5) and vendor B (c, d; obtained from scanner number 15) to emphasize the differences between the two scanner vendors. Both scanners were calibrated shortly after each other, so decay of the reference activities was negligible. At the time of calibration, the top vials contained a reference activity A _r of 2.49 MBq. Clockwise, the other vials contained 2.6, 127, 514, 13, and 26 kBq, respectively. a, c CTAC images, with circular regions of interest matching with the VOIs (in red). b, d corresponding CT images