Figure 2.

(A) Global calibration factor for a clinical PET/CT scanner during an 18-month period. Indicated is an erroneous calibration factor that was used for approximately one month before detection. Values are indicated for both the standard ¹⁸F-FDG calibration method and using long-lived ⁶⁸Ge sources showing significant variability. (B) FDG PET images using the median (left image) and the outlier (right image) global calibration factors. The images are identical except for an overall scale difference in all SUVs of approximately 25%. This type of periodically vulnerable calibration error has clear consequences for longitudinal studies.