Effects on absolute TRT of various quantitative PET measures. Box plots illustrating the effects of (local) rigid and non-rigid registration strategies on the absolute test-retest variability (TRT) of SUVmax (a), SUVmean (b), metabolic volume (c) or total lesion glycolysis (TLG, d). These TRT values were obtained using PET, CT or both (CTPET). Reference shows those TRT values that were obtained by delineating VOIs on both scans separately. Lower values are better than higher values. The mean is illustrated by a square, outliers by dots, and minimum and maximum values by crosses.