Quantification of Hepatic Steatosis with T1-independent, T2*-corrected MR Imaging with Spectral Modeling of Fat: Blinded Comparison with MR Spectroscopy

Abstract

Purpose:To prospectively compare an investigational version of a complex-based chemical shift-based fat fraction magnetic resonance (MR) imaging method with MR spectroscopy for the quantifi cation of hepatic steatosis. Materials and Methods:This study was approved by the institutional review board and was HIPAA compliant. Written informed consent was obtained before all studies. Fifty-fi ve patients (31 women, 24 men; age range, 24-71 years) were prospectively imaged at 1.5 T with quantitative MR imaging and single-voxel MR spectroscopy, each within a single breath hold. The effects of T2* correction, spectral modeling of fat, and magnitude fi tting for eddy current correction on fat quantifi cation with MR imaging were investigated by reconstructing fat fraction images from the same source data with different combinations of error correction. Single-voxel T2-corrected MR spectroscopy was used to measure fat fraction and served as the reference standard. All MR spectroscopy data were postprocessed at a separate institution by an MR physicist who was blinded to MR imaging results. Fat fractions measured with MR imaging and MR spectroscopy were compared statistically to determine the correlation ( r 2 ), and the slope and intercept as measures of agreement between MR imaging and MR spectroscopy fat fraction measurements, to determine whether MR imaging can help quantify fat, and examine the importance of T2* correction, spectral modeling of fat, and eddy current correction. Two-sided t tests (signifi cance level, P = .05) were used to determine whether estimated slopes and intercepts were signifi cantly different from 1.0 and 0.0 , respectively. Sensitivity and specifi city for the classifi cation of clinically signifi cant steatosis were evaluated. Results:Overall, there was excellent correlation between MR imaging and MR spectroscopy for all reconstruction combinations. However, agreement was only achieved when T2* correction, spectral modeling of fat, and magnitude fi tting for eddy current correction were used ( r 2 = 0.99; slope 6 standard deviation = 1.00 6 0.01, P = .77; intercept 6 standard deviation = 0.2% 6 0.1, P = .19 ). Conclusion:T1-independent chemical shift-based water-fat separation MR imaging methods can accurately quantify fat over the entire liver, by using MR spectroscopy as the reference standard, when T2* correction, spectral modeling of fat, and eddy current correction methods are used.q RSNA, 2011

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