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; β-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.

Purpose To determine the tracking factor by studying the relationship between kidney and diaphragm motions and to compare the efficiency of the gating‐and‐following and gating‐only algorithms in reducing motion artifacts in navigator‐gated scans. Materials and Methods Diaphragm and kidney motions were measured by using real‐time TrueFISP sequences from 10 healthy human volunteers to determine tracking factors at different acceptance windows. Mean tracking factors were used to calculate mean residual errors and improvement factors for the gating‐and‐following and gating‐only algorithms. Results Mean tracking factors for ±4, ±6, ±8 mm and full acceptance windows ranged from 0.6 to 0.7, with large interindividual variations. Acceptance rates increased as the size of the acceptance window increased (acceptance rate for a 4 mm window ∼50%). There was a greater reduction of motion errors by gating‐and‐following (maximum of 1.86 mm) than gating‐only (maximum of 7.05 mm). Conclusion Mean tracking factors obtained in this study can be used as a guideline for using the gating‐and‐following algorithm in navigator‐gated kidney scans. The gating‐and‐following and gating‐only algorithms were quantitatively compared, and it was found that the former is more effective in reducing motion errors. J. Magn. Reson. Imaging 2011;33:143–148.