Effects of similarity measures on absolute TRT of various quantitative measures. Box plots illustrating the effects of similarity measures derived using non-rigid PET registration on the absolute test-retest variability (TRT) of SUVmax (a), SUVmean (b), metabolic volume (c) or total lesion glycolysis (TLG, d). 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.