R2* magnetic resonance imaging of the liver in patients with iron overload

Abstract

R2* magnetic resonance imaging (R2*-MRI) can quantify hepatic iron content (HIC) by noninvasive means but is not fully investigated. Patients with iron overload completed 1.5T R2*-MRI examination and liver biopsy within 30 days. Forty-three patients (sickle cell anemia, n = 32; beta-thalassemia major, n = 6; and bone marrow failure, n = 5) were analyzed: median age, 14 years, median transfusion duration, 15 months, average (+/-SD) serum ferritin 2718 plus or minus 1994 ng/mL, and average HIC 10.9 plus or minus 6.8 mg Fe/g dry weight liver. Regions of interest were drawn and analyzed by 3 independent reviewers with excellent agreement of their measurements (intraclass correlation coefficient = 0.98). Ferritin and R2*-MRI were weakly but significantly associated (range of correlation coefficients among the 3 reviewers, 0.41-0.48; all P < .01). R2*-MRI was strongly associated with HIC for all 3 reviewers (correlation coefficients, 0.96-0.98; all P < .001). This high correlation confirms prior reports, calibrates R2*-MRI measurements, and suggests its clinical utility for predicting HIC using R2*-MRI. This study was registered at www.clinicaltrials.gov as #NCT00675038.

Figure 1

R2*-MRI versus HIC. Agreement among the 3 reviewers was very high (ICC = 0.98); therefore, only data for reviewer 1 are illustrated. (A) Plot of R2*-MRI measurements versus HIC values obtained by liver biopsy with linear regression lines and 95% prediction limits. The intercept was −454.85 (P = .31), the slope was 28.02 (P < .001), and R² was 0.72. The correlation coefficient for R2*-MRI and HIC was 0.98 (P < .001). (B) Standard Bland-Altman plot^, shows the difference versus the average of HIC (R2*) and HIC (biopsy), that is, (HIC [R2*] − HIC [biopsy]) versus (HIC [R2*] + HIC [biopsy])/2. The solid line represents the mean difference between HIC (R2*) and HIC (biopsy); dashed lines, upper and lower 95% limits of agreement between the 2 measurements. (C) R2*-MRI versus HIC regression line overlaid with regression lines from 2 other published methods of R2*-MRI showing that the Wood et al regression line falls well within our 95% predicted interval across the entire range of values, but the regression line from Anderson et al (extrapolated from a published log-transformed plot) has a substantially lower slope, probably reflecting differences in instrumentation and biopsy iron quantification technique.