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Nonalcoholic Fatty Liver Disease: Rapid Evaluation of Liver Fat Content with In-Phase and Out-of-Phase MR Imaging¹

¹ From the Medical Imaging Centre of Southwest Finland, Turku University Hospital, Kiinamyllynkatu 4-8, PO Box 52, 20521 Turku, Finland (R.J.H.B., S.S., K.D., M.K., R.P.); and Turku PET Centre (R.J.H.B., R.L., P.N., R.P.) and Department of Medicine (P.N.), University of Turku and Turku University Hospital, Turku, Finland. Received November 15, 2007; revision requested January 18, 2008; revision received April 10; accepted May 20; final version accepted August 7. Supported by grants from Turku University Hospital, Turku, Finland. R.B. supported by the Instrumentarium Foundation, Finnish Diabetes Foundation, and Ella and Georg Ehrnrooth Foundation. P.N. supported by GlaxoSmithKline. This work is part of the Hepatic and Adipose Tissue and Functions in the Metabolic Syndrome Project (http://hepadip.org/), which is supported by the European Commission as an integrated project under the Sixth Framework Programme (contract LSHMCT-2005-018734). Address correspondence to R.J.H.B. (e-mail: Ronald.Borra{at}tyks.fi).

Purpose: To evaluate in-phase and out-of-phase magnetic resonance (MR) imaging in the estimation of liver fat content (LFC) in patients with nonalcoholic fatty liver disease (NAFLD), with hydrogen (¹H) MR spectroscopy as the reference standard.

Materials and Methods: Written informed consent was obtained from all subjects, and the local ethics committee approved this prospective study protocol. A total of 33 patients with type 2 diabetes mellitus who were at high risk for NAFLD (23 men, 10 women; overall mean age, 62.8 years ± 8.3 [standard deviation]; age range, 48–77 years) underwent 1.5-T MR imaging with ¹H MR spectroscopy and in-phase and out-of-phase imaging of the liver. Three fat indexes were calculated from the signal intensity (SI) measured on the images. Two radiologists independently graded SI changes between in-phase and out-of-phase images by means of visual inspection. The Pearson correlation coefficient was used to study the relationship between the obtained parameters of SI change and LFC measured with ¹H MR spectroscopy.

Results: Fat indexes calculated from in-phase and out-of-phase images correlated linearly with LFC measured with ¹H MR spectroscopy (P < .001, r = 0.94–0.96) and were superior (P = .004) to visual estimates (P < .001, r = 0.88). The simple difference in SI between in-phase and out-of-phase images was used to calculate the fat index. An intercept of the regression line with the x-axis was observed at 5.1%, discriminating between normal and elevated LFC with high sensitivity (95%) and specificity (98%).

Conclusion: In-phase and out-of-phase imaging can be used to rapidly estimate the LFC in patients with NAFLD. The cutoff value of 5.1% enables objective rapid and reliable discrimination of normal LFC from elevated LFC.

© RSNA, 2008