Figure 3
Relationship of new T2*-LIC to R2-LIC (Ferriscan) measurements. (A) R2-LIC plotted against T2*-LIC (derived from Equation 1) for comparison cohort; range with lowest scatter circled. Mixed model regression on whole range log-transformed data ln(R2-LIC) = 1.04×ln(T2*-LIC)-0.08, with slope and intercept 95% CI of 0.96 to 1.11 (p < 0.001) and -0.26 to 0.11 (p = ns), is shown here exponentiated to R2-LIC = 0.83×T2*-LIC1.04 with 95% CI 0.96 to 1.11 and 0.55 to 1.29, r squared = 0.65. (B) Whole range Bland-Altman plot of percentage difference vs mean LIC with non-uniform scatter with linear regression correction. Corrected bias is -1.29*(mean LIC)+23.03; absolute residuals R were related to LIC: R = 0.47*(mean LIC)+17.44, p = 0.01, therefore, accounting for growth in variance, 95% LoA were from -0.14*(mean LIC)+65.9 to -2.44*(mean LIC)-19.8 or changing from ±45 to ±90% across the whole range. (C) Mixed model linear regression of R2-LIC on T2*-LIC for R2-LIC range 0–10 mg/g dw: R2-LIC = 0.87 × R2*LIC-0.55, slope 95% CI 0.74 to 0.99 (p < 0.001), intercept -0.01 to 1.19 (p = 0.089); r squared = 0.86. Insignificant intercept can be abandoned to give a proportionality with a slope of 0.96, 95% CI 0.89-1.02, p < 0.001, which being indistinguishable from 1, follows the line of identity. (D) Bland-Altman plot of the mean of the two methods (x-axis) plotted against their percentage difference (y-axis) for the range marked by circle in 3A, which for R2-LIC values <10 mg/g dw (here in 37 scans on 26 patients) shows non-uniform scatter corrected by linear regression. Corrected bias is -4.51*(mean LIC)+40.23, p = 0.007, SD of residuals 23.22%. Absolute residuals did not relate to LIC (p = 0.99), therefore 95%LoA were bias ± 1.96*23.22% or ±45.51%.