Comparison of whole liver and small region-of-interest measurements of MRI liver R2* in children with iron overload.

BACKGROUND: Measurement of liver MRI T2* and R2* is emerging as a reliable alternative to liver biopsy for the quantitation of liver iron content. A systematic investigation of the influence of the region-of-interest size and placement has not been conducted.
OBJECTIVE: To compare small and whole liver region-of-interest (ROI) MRI R2* values to each other and to biopsy liver iron content in patients with iron overload.
MATERIALS AND METHODS: Forty-one iron-overloaded patients, ages 7-35 years, underwent biopsy for liver iron content quantitation and MRI for liver R2* measurement within 30 days. Three reviewers independently used small and whole liver ROIs to measure R2*. Inter-reviewer agreement was assessed with the intra-class correlation coefficient (ICC). Associations between R2* and liver iron content were investigated using Spearman's rank-order correlation and Monte Carlo estimated exact P values.
RESULTS: Biopsy liver iron content and small and whole liver ROI R2* measurements were strongly associated for all reviewers (all P < 0.0001). Although inter-reviewer agreement was excellent for both ROI methods (ICC = 0.98-0.99), the small ROI technique more frequently led to inter-reviewer differences larger than 75 Hz, slightly higher R2* values, larger standard errors and greater range in values.
CONCLUSION: Small and whole liver ROI techniques are strongly associated with biopsy liver iron content. We found slightly greater inter-reviewer variability in R2* values using the small ROI technique. Because such variability could adversely impact patient management when R2* values are near a threshold of iron chelation therapy, we recommend using a whole liver ROI.