Quantification of liver fat in the presence of iron overload

Abstract

Purpose To evaluate the accuracy of R2* models (1/T2* = R2*) for chemical shift-encoded magnetic resonance imaging (CSE-MRI)-based proton density fat-fraction (PDFF) quantification in patients with fatty liver and iron overload, using MR spectroscopy (MRS) as the reference standard. Materials and Methods Two Monte Carlo simulations were implemented to compare the root-mean-squared-error (RMSE) performance of single-R2* and dual-R2* correction in a theoretical liver environment with high iron. Fatty liver was defined as hepatic PDFF >5.6% based on MRS; only subjects with fatty liver were considered for analyses involving fat. From a group of 40 patients with known/suspected iron overload, nine patients were identified at 1.5T, and 13 at 3.0T with fatty liver. MRS linewidth measurements were used to estimate R2* values for water and fat peaks. PDFF was measured from CSE-MRI data using single-R2* and dual-R2* correction with magnitude and complex fitting. Results Spectroscopy-based R2* analysis demonstrated that the R2* of water and fat remain close in value, both increasing as iron overload increases: linear regression between R2*W and R2*F resulted in slope = 0.95 [0.79–1.12] (95% limits of agreement) at 1.5T and slope = 0.76 [0.49–1.03] at 3.0T. MRI-PDFF using dual-R2* correction had severe artifacts. MRI-PDFF using single-R2* correction had good agreement with MRS-PDFF: Bland–Altman analysis resulted in −0.7% (bias) ± 2.9% (95% limits of agreement) for magnitude-fit and −1.3% ± 4.3% for complex-fit at 1.5T, and −1.5% ± 8.4% for magnitude-fit and −2.2% ± 9.6% for complex-fit at 3.0T. Conclusion Single-R2* modeling enables accurate PDFF quantification, even in patients with iron overload.

Autoregressive moving average modeling for hepatic iron quantification in the presence of fat

“…Likewise, the presence of iron increases R2*, which causes rapid signal decay and compromises fat quantification. Although signal modeling techniques that consider the multispectral nature of fat and water have been proposed to simultaneously quantify R2* and FF, proper extraction of quantitative results in situations of high iron content might be hampered because of the rapid signal decay . In this study we evaluated the performance of an ARMA model for R2* and FF quantification, and compared the results with those obtained using a monoexponential model and an NLSQ model available in the ISMRM Fat–Water Toolbox …”

“…Using pure iron doped phantoms as a reference might not be the best choice, as R2* values might change slightly with fat content . Nevertheless, these changes are considered quite small compared with the effect of iron particles on R2* and, hence, it was recently proposed to treat R2* values of both species as a combined value and therefore to apply a single R2* fitting approach for simultaneous fat–water modeling …”

“…Further, although water and fat might have different T 2 * decays, this model fits only a single R2* value for both water and fat peaks in order to reduce model complexity . Although this model has been well validated for quantifying the fat fraction (FF), limited information is available on how accurately it quantifies R2* in the presence of iron and fat …”

Assessment of MR‐based and quantitative susceptibility mapping for the quantification of liver iron concentration in a mouse model at 7T

“…Because of the strong paramagnetic nature of iron, f B is highly dependent on the presence of iron in the local area. A common for all chemical species was assumed in this work, because it has been shown that, even for cases of iron overload and high hepatic fat concentrations, accurate measurements can be obtained …”

Addressing metabolic heterogeneity in clear cell renal cell carcinoma with quantitative Dixon MRI

“…Additionally, a tROI was placed on representative locations on the FF map correlating to tissue samples obtained for ORO staining. Although magnetic susceptibility from hemorrhage is common in ccRCC, these Dixon methods are accurate for determination of FF even in the presence of iron overload (56). Visceral and subcutaneous fat with > 90% FF and the native kidneys with negligible FF (< 3%) served as the internal reference for adequate fitting.…”