UPmémoires

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Evaluation of hepatic iron concentration heterogeneities using MRI R2* mapping method

Purpose: The aim of the study was to measure hepatic iron concentration (HIC) heterogeneities using a magnetic resonance (MR) R2* mapping method.

Patients and methods: Ninety-four patients suspected of hepatic iron overload and ten volunteers were included prospectively. A multi-echo R2* sequence with different post-treatment fitting methods (a single exponential decay model with or without truncation, SED and SEDt, and a constant offset model, COS) was compared to a signal intensity ratio method (SIR), considered as reference, from a single region of interest (ROI) placed in the upper right liver. HIC heterogeneity was evaluated from R2* mapping after placing a ROI on each liver segment. To limit impact of fatty liver deposit, fat saturation was used.

Results: A strong linear correlation between SIR and R2* methods using SEDt and COS models was observed (respectively r = 0.973 and 0.955) contrasting with a lower correlation with SED (r = 0.657). Intra-liver volunteers and patient variabilities, quantified by mean intra-liver standard deviation and mean range, were respectively 1.58 µmol/g and 5.06 µmol/g, and 4.73 µmol/g and 19.08 µmol/g. For the patient group, the highest HIC was observed in the IVa segment. Heterogeneity increased for patients with HIC > 60 µmol/g (mean intra-liver SD = 13.90 µmol/g; mean range = 50.60 µmol/g). The same heterogeneity distribution was observed in cases of significant fat content (>5%).

Conclusion: This study is the first to demonstrate in-vivo HIC heterogeneities using whole liver mapping analysis. These preliminary results require confirmation through further studies and might have to be considered in cases of single ROI analysis.