MRI-Based Quantitative R2* Mapping at 3 Tesla Reflects Hepatic Iron Overload and Pathogenesis in Nonalcoholic Fatty Liver Disease Patients

Abstract

Background: The role of hepatic iron overload (HIO) in nonalcoholic fatty liver disease (NAFLD) pathogenesis has not been fully elucidated.

Purpose: This study aimed to investigate the effect of HIO and examine the diagnostic usefulness of magnetic resonance imaging (MRI)-based R2^* quantification in evaluating hepatic iron content (HIC) and pathological findings in NAFLD.

Study type: Prospective and retrospective.

Population: A prospective study of 168 patients (age, 57.2 ± 15.0; male/female, 80/88) and a retrospective validation study of 202 patients (age, 57.0 ± 14.4; male/female, 113/89) with liver-biopsy-confirmed NAFLD were performed.

Field strength/sequence: 3 T; chemical-shift encoded multi-echo gradient echo.

Assessment: Using liver tissues obtained by liver biopsy, HIC was prospectively evaluated in 168 patients by atomic absorption spectrometry. Diagnostic accuracies of HIC and R2^* for grading hepatic inflammation plus ballooning (HIB) as an indicator of NAFLD activity were assessed.

Statistical tests: Student's t-test and analysis of variance (ANOVA) with Scheffe's multiple testing correction for univariate comparisons; multivariate logistic analysis. P-value less than 0.05 is statistically significant.

Results: HIC was significantly correlated with HIB grades (r = 0.407). R2^* was significantly correlated with HIC (r = 0.557) and HIB grades (r = 0.569). R2^* mapped an area under the receiver operating characteristic (AUROC; 0.774) for HIC ≥808 ng/mL (median value) with cutoff value of 62.5 s^-1 . In addition, R2^* mapped AUROC of HIB for grades ≥3 was 0.799 with cutoff value of 58.5 s^-1 . When R2^* was <62.5 s^-1 , R2^* correlated weakly with HIC (r = 0.372) as it was affected by fat deposition and did not correlate with HIB grades (P = 0.052). Conversely, when R2^* was ≥62.5 s^-1 , a significant correlation of R2^* with HIC (r = 0.556) and with HIB grades was observed (P < 0.0001) with being less affected by fat deposition.

Data conclusion: R2^* ≥ 62.5 s^-1 is a promising modality for non-invasive diagnosis of clinically important high grades (≥3) of HIB associated with increased HIC.

Level of evidence: 1 TECHNICAL EFFICACY STAGE: 2.

Keywords: NAFLD; ballooning; hepatic inflammation; hepatic iron content; proton density fat fraction.