Comparison of clinical MRI liver iron content measurements using signal intensity ratios, R 2 and R 2

Abstract

Purpose: To compare three types of MRI liver iron content (LIC) measurement performed in daily clinical routine in a single center over a 6-year period.

Methods: Patients undergoing LIC MRI-scans (1.5T) at our center between January 1, 2008 and December 31, 2013 were retrospectively included. LIC was measured routinely with signal intensity ratio (SIR) and MR-relaxometry (R ₂ and R ₂*) methods. Three observers placed regions-of-interest. The success rate was the number of correctly acquired scans over the total number of scans. Interobserver agreement was assessed with intraclass correlation coefficients (ICC) and Bland-Altman analysis, correlations between LIC_SIR, R ₂, R ₂*, and serum values with Spearman's rank correlation coefficient. Diagnostic accuracies of LIC_SIR, R ₂ and serum transferrin, transferrin-saturation, and ferritin compared to increased R ₂* (≥44 Hz) as indicator of iron overload were assessed using ROC-analysis.

Results: LIC MRI-scans were performed in 114 subjects. SIR, R ₂, and R ₂* data were successfully acquired in 102/114 (89%), 71/114 (62%), and 112/114 (98%) measurements, with the lowest success rate for R ₂. The ICCs of SIR, R ₂, and R ₂* did not differ at 0.998, 0.997, and 0.999. R ₂ and serum ferritin had the highest diagnostic accuracies to detect elevated R ₂* as mark of iron overload.

Conclusions: SIR and R ₂* are preferable over R ₂ in terms of success rates. R ₂*'s shorter acquisition time and wide range of measurable LIC values favor R ₂* over SIR for MRI-based LIC measurement.

Keywords: Biomarker; Blood transfusion; Hemochromatosis; Iron overload; Magnetic resonance imaging; Relaxometry.

Fig. 1

Placement of ROIs. A–F The placement of ROIs on the data. A–C How the ROIs for the total liver parenchyma (A) and intrahepatic vasculature and/or gall bladder (B) are drawn and the result of subtraction in (C). D The ROI-placement on the paraspinal muscles for SIR calculations. E, F The placement of a ghosting artifact ROI (E) and the final liver parenchyma ROI (F) obtained by subtracting (E) from (C)

Fig. 2

LIC_SIR or LIC_BIOPSY against R ₂ and R ₂*. A, B Scatter plots of LIC_SIR against R ₂ (A, top) and R ₂* (B, bottom) for all successful baseline measurements. Data points are grouped by SIR LIC type: T1; PD; T2; T2+; and T2++. Regression results (equations given in the figures) are shown by solid lines, with dotted 95% CI bands indicating the goodness of the fit. Additional dotted regression lines are based on regression analyses reflecting LIC_BIOPSY [, , –21] or LIC_SIR [14]

Fig. 3

T1W liver-to-muscle SIR against R ₂ *. This shows a scatter plot of R ₂* values (x-axis) against the liver-to-muscle SIR (y-axis) of successful baseline T1W SIR measurements. Data are grouped into the following: LIC_SIR <350 and LIC_SIR >350 µmol/g

Fig. 4

R ₂, LIC_SIR, and ferritin against R ₂*. A–C Scatter plots between R ₂* (x-axes) and R ₂, LIC_SIR, and serum ferritin (y-axes). Dotted lines at x = 44 and at y = 18.3 (A), y = 36 (B), and y = 524 (C) indicate the thresholds for R ₂, LIC_SIR, and serum ferritin to identify increased R ₂* (Table 4). Data points are grouped by SIR LIC type: T1; PD; T2; T2+; T2++; >350; and no LIC_SIR available. Regression results are shown by the solid lines with dotted 95% CI bands indicating the goodness of the fit. Shaded areas indicate true positive (), true negative (), false positive (), and false negative (), respectively