Figure 2a:

Comparison of the measurements performed in the (a) small and (b) large phantoms on scanner 4 at 80 and 140 kVp with tin filtration. Note the lower standard deviation of the blank sample and the tighter distributions of the repetitions of the higher concentrations in the small phantom that lead to a calibration curve with a lower fitting error and, ultimately, a lower limit of detection. The limit of blank (LOB) was defined as the upper limit of the 95% confidence interval of the water sample. The limit of detection (LOD) was defined as the concentration with a 95% chance of having a signal above the LOB. The limit of quantification was defined as the lowest concentration where the coefficient of variation was below 20%.