From 256 segments (2×16×8), 170 segments were used for derivation and 70 for validation; one stress data (16 segments) was excluded due to beam-hardening artifacts. In the derivation group, segments with MBF_ref smaller than MBF_MU and MBF_dec were excluded from the analysis because they could not be corrected by the Renkin-Crone equation. As a result, 125 of 170 segments (74%) and 138 of 170 segments (81%) were used to derive the parameters for Renkin-Crone equations, respectively. the mean MBF_MU (0.92 ml/min/g ± 0.63) and MBF_dec (0.85 ml/min/g ± 0.62) were lower than MBF_ref (2.12 ml/min/g ± 1.83, both p <0.001) (Table 1).

 In the validation group, the mean MBF_MU (1.01 ml/min/g ± 0.66) and MBF_dec (0.87 ml/min/g ± 0.68) were lower than MBF_ref (2.14 ml/min/g ± 1.97, both p <0.001). Bland-Altman analysis showed that MBF_MU was underestimated before (mean difference (MD) = 1.11 ml/min/g, 95% confidence interval (CI): 0.80−1.42, p<0.001), which was not resolved after correction (MD = 0.66 ml/min/g, 95% CI: 0.40−0.92, p<0.001). MBF_dec was underestimated before (MD = 1.26ml/min/g, 95%CI: 0.94−1.60, p <0.001), but was resolved after correction (MD = -0.05 ml/min/g, 95%CI: -0.14−0.04, p = 0.30). (Table1, Figure 3-5).