Comparison of hepatic iron quantification by MRI between 1.5 and 3 T, using different methods and conversion formulas.

Objectives: This study aimed to compare liver iron concentration (LIC) estimates obtained from 1.5-T and 3-T MRI systems, using multiple quantification methods.

Materials and methods: Seventy-eight participants from two centers were prospectively included and underwent liver MRI scans at both 1.5 T and 3 T. Two multi-echo gradient recalled echo (ME-GRE) sequences-one vendor-specific and one non-specific-were used to quantify liver fat and iron. Proton density fat fraction (PDFF) and R2* were obtained from vendor sequences via map reconstruction, and from non-specific sequences using MRQuantif software. LIC was derived from R2* using European or American calibrations, but also from signal intensity ratio (SIR) method at 1.5 T. Statistical analysis included linear correlation regression and Bland-Altman plots to evaluate agreement between LIC values across field strengths and methods.

Results: For LIC calculated from R2*, both sequences demonstrated a strong correlation between 1.5-T and 3-T results, with R = 0.84 and 0.99 for the vendor and MRQuantif methods, respectively. The LIC bias between field strengths remained low (± 7% maximum) when using the same calibration group or when comparing, at 1.5 T, the SIR method and European calibrations. However, this bias increased to 26% when comparing LIC values obtained from American and European calibrations.

Conclusion: LIC values are highly comparable when similar calibration methods are applied, but notable bias arises when comparing results from different calibration groups. For clinical convenience, a rapid and intermediate LIC (in µmol/g) can be estimated by dividing R2*values by 2 at 1.5 T or by 4 at 3 T.

Key points: Question There are differences in the estimation of liver iron concentration depending on the magnetic field, method and calibration used. Findings Liver iron concentration (LIC) reproducibility is high across methods or between 1.5-T and 3-T devices-only when identical calibration groups are used. Clinical relevance LIC determination from R2 is highly reproducible, but the conversion formula must align with the referring physicians' standard references.