Table 2.

Differences among region-of-interest placement methods and the total number of DECT variables measured

	Method 1a	Method 2	Method 3
No. of DECT ROIs used	Three ROIs in areas of the greatest tumor heterogeneity (variables averaged across all three)	One ROI corresponding to the highest CT attenuation	One ROI corresponding to area of the highest SUVmax
No. of image contrasts	22 Images: 1 effective Z image + 11 keV images (40–140 keV in 10-keV increments) + 10 material images: two images per basis pair × five basis pairs: (1) I-water, (2) Ca-I, (3) Ca-water, (4) HAP-I, and (5) HAP-Ca
No. of variables measured per image contrast	Six variables: mean, SD, mean–max, mean–min, max–max, min–min	Four variables: mean, SD, max, min
Total No. of DECT variables	133 Variables: (22 image contrasts × 6 variables per contrast) + mass	89 Variables: (22 image contrasts × 4 variables per contrast) + mass

Ca calcium, CT computed tomography, DECT dual-energy computed tomography, HAP hydroxyapatite, I iodine, max maximum, min minimum, ROI region of interest, SUV standardized uptake value

^aIn method 1, three ROIs were measured, resulting in three maxima and three minima. “Max–max” refers to the highest of the three maxima, “mean–max” to their arithmetic mean. Similarly, “min–min” is the lowest of the three minima, whereas “mean–min” is their arithmetic mean