Evaluation of 0.55T MRI for Simultaneous R2* and Fat Fraction Quantification in the Presence of Hepatic Iron Overload...

To create virtual liver models simulating the concurrent presence of hepatic iron overload and steatosis based on human liver histology and to assess the accuracy and precision of R2* and fat fraction (FF) estimation at 0.55T compared to 1.5T.

Virtual liver models simulating the coexistence of iron overload and steatosis were created, encompassing clinical liver iron concentration (LIC) (0-20 mg/g) and FF (0%-30%) ranges, using morphological characteristics derived from human liver histology. MRI signals were synthesized via Monte Carlo simulations under varying SNR conditions (SNR original (SNR_orig) and SNR enhanced (SNR_enh)) at 0.55T (SNR_orig,0.55T = 20; SNR_enh,0.55T = 50) and 1.5T (SNR_orig,1.5T = 50). Simulation results were validated using iron-fat phantoms (FF: 0%-40%; iron concentration: 0-8 μg/mL) scanned across varying SNRs using different signal averages (SNR_orig,0.55T, SNR_orig,1.5T = 1; SNR_enh,0.55T = 4). Accuracy and precision of 0.55T for estimating R2* and FF compared to 1.5T were assessed using boxplots, heatmaps, and Kruskal-Wallis statistical tests.

SNR_orig,0.55T demonstrated reduced or comparable FF estimation bias relative to SNR_orig,1.5T, with significantly lower bias for SNR_enh,0.55T, especially for severe iron overload and FF ≤ 20%. LIC estimation for SNR_orig,0.55T and SNR_enh,0.55T demonstrated higher accuracy compared to SNR_orig,1.5T with significant differences (p < 0.028) for all combinations of LIC and FF except for severe iron overload with FF > 10% (p > 0.183). Further, SNR_enh,0.55T showed improved precision for FF and LIC estimation compared to SNR_orig,1.5T. Phantom experiments showed reduced bias for both FF and LIC estimation for SNR_enh,0.55T compared to SNR_orig,1.5T.

0.55T shows promising results for concurrent R2* and FF estimation, enhancing accuracy and precision compared to 1.5T, especially with enhanced SNR.