SU‐F‐I‐63: Relaxation Times of Lipid Resonances in NAFLD Animal Model Using Enhanced Curve Fitting

Abstract

Purpose:The objective of this study is to evaluate the relaxation time of methylene resonance in comparison with other lipid resonances.Methods:The examinations were performed on a 3.0T MRI scanner using a four‐channel animal coil. Eight more Sprague‐Dawley rats in the same baseline weight range were housed with ad libitum access to water and a high‐fat (HF) diet (60% fat, 20% protein, and 20% carbohydrate). In order to avoid large blood vessels, a voxel (0.8×0.8×0.8 cm3) was placed in a homogeneous area of the liver parenchyma during free breathing. Lipid relaxations in NC and HF diet rats were estimated at a fixed repetition time (TR) of 6000 msec, and multi echo time (TEs) of 40–220 msec. All spectra for data measurement were processed using the Advanced Method for Accurate, Robust, and Efficient Spectral (AMARES) fitting algorithm of the Java‐based Magnetic Resonance User Interface (jMRUI) package.Results:The mean T2 relaxation time of the methylene resonance in normal‐chow diet was 37.1 msec (M0, 2.9±0.5), with a standard deviation of 4.3 msec. The mean T2 relaxation time of the methylene resonance was 31.4 msec (M0, 3.7±0.3), with a standard deviation of 1.8 msec. The T2 relaxation times of methylene protons were higher in normal‐chow diet rats than in HF rats (p<0.05), and the extrapolated M0 values were higher in HF rats than in NC rats (p<0.005). The excellent linear fit with R2>0.9971 and R2>0.9987 indicates T2 relaxation decay curves with mono‐exponential function.Conclusion:In in vivo, a sufficient spectral resolution and a sufficiently high signal‐to‐noise ratio (SNR) can be achieved, so that the data measured over short TE values can be extrapolated back to TE = 0 to produce better estimates of the relative weights of the spectral components. In the short term, treating the effective decay rate as exponential is an adequate approximation.