Cross‐Vendor Validation of Proton Density Fat Fraction and T1 Mapping Using a Combined Proton Density Fat Fraction—T1 Phantom

ABSTRACT Background In chronic liver disease, fat and fibroinflammatory changes often coexist. However, their biomarkers, proton density fat fraction (PDFF) and T1, are typically assessed separately. Their reproducibility under mutual confounding remains unclear. Purpose To assess multicenter, multi-vendor reproducibility of confounder-corrected chemical shift-encoded (CSE)-MRI-based PDFF mapping and MOLLI-based T1 mapping using a combined PDFF-T1 phantom. Study Type Prospective phantom study. Phantom Commercial PDFF-T1 Phantom (Model 725) with varying PDFF (0%–30%) and T1 (200–1400 ms) values. Field Strength/Sequence 1.5 T and 3 T multi-echo, three-dimensional spoiled-gradient-echo (SGRE) sequence for PDFF mapping, and MOLLI sequence (5(3)3 acquisition scheme) using two-dimensional SGRE readouts for T1 mapping across four centers and vendors. Assessment PDFF and T1 maps were acquired using standardized protocols. PDFF maps were reconstructed locally, while T1 maps were generated using a centralized algorithm. All maps were quantitatively analyzed by a single radiologist using standardized region-of-interest placement. Phantom temporal stability was assessed at one center across five sessions over 9 months (baseline, retest, 1 week, 6 and 9 months). Statistical Tests Intraclass correlation coefficients (ICC), reproducibility coefficients (RDC), and linear regression analysis were used. A p value < 0.05 was considered statistically significant. Results PDFF showed overall excellent reproducibility (ICC = 0.987, RDC = 3.7%), with increased variability at higher T1 values (RDC up to 7.9% at T1 = 1400 ms). T1 mapping showed good reproducibility in the absence of fat (RDC 16–161 ms at PDFF = 0%), but moderate to poor reproducibility in the presence of fat, with RDC increasing up to 1553 ms at PDFF 30%. Temporal stability was excellent ICC ≥ 0.998 for both PDFF and T1, and RDC of 1.1%–1.3% for PDFF and 52–57 ms for T1. Data Conclusion This phantom study demonstrated high reproducibility of PDFF, whereas T1 reproducibility deteriorated at higher fat and T1 levels, underscoring the need for fat-corrected T1 mapping for reliable assessment of fibroinflammatory changes. Evidence Level N/A. Technical Efficacy Stage 1.