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

Abstract

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 to 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. Conclusions 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.

R2* Relaxometry for the Quantification of Hepatic Iron Overload: Biopsy-Based Calibration and Comparison with the Literature

“…They concluded that the single ROI approach can be safely used in the clinical area when taking care to avoid susceptibility artifact effect. McCarville et al evaluated 41 patients with iron overload by R2* mapping and correlated the results with liver biopsy [16]. In their study they compared small ROI placement and a whole liver method.…”

Liver Enzyme Levels and Hepatic Iron Content in Fatty Liver

“…McCarville et al showed that whole-liver R2* map is less subject to interreviewer discordance compared to R2* analysis drawn by multiple ROIs in liver. They proposed using R2* maps for quantification of liver iron content instead of biopsy in patients with hepatic iron overload (34).…”

Can multi-slice or navigator-gated R2* MRI replace single-slice breath-hold acquisition for hepatic iron quantification?

“…Off-line image analysis was performed on a computer workstation using a graphical user interface (GUI) developed in MATLAB (The MathWorks Inc., Natick, MA) [30]. For the entire image, pixel-wise T2* values were calculated by fitting a monoexponential decay to the magnitude of the mGRE signal while accounting for Rician noise bias [31, 32].…”

“…in images that showed the main portal vein as described in [30]: (i) Small regions of interest (ROIs) were drawn on the T2*-weighted source images or T2* maps in a homogenous region of liver parenchyma excluding large biliary and vascular structures in the right lobe of the liver. This ROI position was selected as described in [30] to ensure that no bias was introduced in the HIC calculation. The average T2* was subsequently calculated across all pixels within the ROI and the resulting R2* (=1/T2*) was recorded.…”