Inter-method reproducibility of biexponential R 2 MR relaxometry for estimation of liver iron concentration.

Purpose: To assess the reproducibility of biexponential R ₂ -relaxometry MRI for estimation of liver iron concentration (LIC) between proprietary and nonproprietary analysis methods.
Methods: This single-center retrospective study, approved by investigational review board and compliant with the Health Insurance Portability and Accountability Act, included 40 liver MRI exams in 38 subjects with suspected or known iron overload. From spin-echo images of the liver, acquired at 5 different echo times (TE = 6-18 ms), biexponential R ₂ maps were calculated using 1 proprietary (FerriScan, Resonance Health Ltd., Claremont WA, Australia) and 3 nonproprietary (simulated annealing, nonlinear least squares, dictionary search) analysis methods. Each subject's average liver R ₂ value was converted to LIC using a previously validated calibration curve. Inter-method reproducibility for liver R ₂ and LIC were assessed for linearity using linear regression analysis and absolute agreement using intraclass correlation and Bland-Altman analysis. For point estimates, 95% confidence intervals were calculated; P values < 0.05 were considered statistically significant.
Results: Linearity between the proprietary and nonproprietary methods was excellent across the observed range for R ₂ (20-312 s ^-1 ) and LIC (0.4-52.2 mg/g), with all coefficients of determination (R ² ) ≥ 0.95. No statistically significant bias was found (slope estimates ∼ 1; intercept estimates ∼ 0; P values > 0.05). Agreement between the 4 methods was excellent for both liver R ₂ and LIC (intraclass correlations ≥ 0.97). Bland-Altman 95% limits of agreement in % difference between the proprietary and nonproprietary methods were ≤ 9% and ≤ 16% for R ₂ and LIC, respectively.
Conclusion: Biexponential R ₂ -relaxometry MRI for LIC estimation is reproducible between proprietary and nonproprietary analysis methods.
(© 2018 International Society for Magnetic Resonance in Medicine.)