Iron overload: accuracy of in-phase and out-of-phase MRI as a quick method to evaluate liver iron load in haematological malignancies and chronic liver disease

Abstract

Objectives: The purpose of this prospective study was to evaluate the accuracy of in-phase and out-of-phase imaging to assess hepatic iron concentration in patients with haematological malignancies and chronic liver disease.

Methods: MRI-based hepatic iron concentration (M-HIC, μmol g(-1)) was used as a reference standard. 42 patients suspected of having iron overload and 12 control subjects underwent 1.5 T in- and out-of-phase and M-HIC liver imaging. Two methods, semi-quantitative visual grading made by two independent readers and quantitative relative signal intensity (rSI) grading from the signal intensity differences of in-phase and out-of-phase images, were used. Statistical analyses were performed using the Spearman and Kruskal-Wallis tests, receiver operator curves and κ coefficients.

Results: The correlations between M-HIC and visual gradings of Reader 1 (r = 0.9534, p < 0.0001) and Reader 2 (r = 0.9456, p < 0.0001) were higher than the correlations of the rSI method (r = 0.7719, p < 0.0001). There was excellent agreement between the readers (weighted κ = 0.9619). Both visual grading and rSI were similar in detecting liver iron overload: rSI had 84.85% sensitivity and 100% specificity; visual grading had 85% sensitivity and 100% specificity. The differences between the grades of visual grading were significant (p < 0.0001) and the method was able to distinguish different degrees of iron overload at the threshold of 151 μmol g(-1) with 100% positive predictive value and negative predictive value.

Conclusion: Detection and grading of liver iron can be performed reliably with in-phase and out-of-phase imaging. Liver fat is a potential pitfall, which limits the use of rSI.

Figure 1

T₁ weighted axial in-phase and out-of-phase images demonstrating the criteria of visual grading and measurements of relative signal intensity (rSI) difference method in four patients as examples of different grades of iron overload. Three regions of interests were obtained for the rSI analysis. Left, in-phase image; middle, out-of-phase image; right, subtracted image calculated as the signal intensity of the in-phase image minus the signal intensity of the out-of-phase image. (a) Normal iron concentration (Grade 0) with MRI-based hepatic iron concentration (M-HIC) of 33 μmol g^–1. (b) Minor iron overload (Grade 1) with M-HIC of 115 μmol g^–1. (c) Moderate iron overload (Grade 2) with M-HIC of 193 μmol g^–1. (d) Severe iron overload (Grade 3) with M-HIC of 271 μmol g^–1.