Hepatic lipid composition analysis using 3.0-T MR spectroscopy in a steatotic rat model

Abstract

Purpose To investigate the feasibility of in vivo assessment of hepatic lipid composition using 3.0-T proton magnetic resonance spectroscopy ( 1H-MRS) in a steatotic rat model and compare it to histopathological and biochemical assessment. Materials and Methods Hepatic steatosis was induced by feeding rats with a methionine/choline-deficient (MCD) diet for 1, 2, 3, 5 or 7 weeks ( n=5 per group). At the end of the diet period, 1H-MRS of the liver was performed, and rats were sacrificed for histopathological and biochemical assessment of the liver. Spectra were acquired in a single voxel (1.2 cc) using a point-resolved spectroscopic sequence with TE/TR=35/2000 ms and 64 signal acquisitions. From the MR spectra, peak area ratios were calculated to estimate hepatic lipid composition. Results During MCD diet periods, hepatic steatosis significantly increased on histopathology ( P<.001). The 1H-MRS measurements of total hepatic fat content [1.3/(1.3+4.65) ppm] correlated strongly with histological macrovesicular hepatic steatosis ( r=0.93, P<.001) and with the biochemical total hepatic fatty acids ( r=0.94, P<.001). Total unsaturated fatty acids [TUFA, 5.4/(1.3+4.65) ppm] estimated with 1H-MRS strongly correlated with the biochemical unsaturated fatty acids ( r=0.90, P<.001). Polyunsaturated fatty acids [PUFA, 2.8/(1.3+4.65) ppm] estimated with 1H-MRS strongly correlated with biochemical PUFA ( r=0.91, P<.001). The proportion of total unsaturated fatty acids relative to the amount of total fatty acids (rTUFA, 5.4/1.3ppm) measured with 1H-MRS strongly correlated with the biochemical amount of unsaturated relative to total hepatic fatty acids ( r=0.81, P<.001). The proportion of PUFA relative to the amount of total fatty acids (rPUFA, 2.8/1.3 ppm) measured with 1H-MRS correlated with the biochemical amount of PUFA relative to total fatty acids ( r=0.59, P=0.005,) and with the biochemical amount of omega-6 PUFA relative to total fatty acids ( r=0.73, P<.001). PUFA at 1H-MRS correlated with the histopathologically assessed degree of lobular inflammation in the liver ( r=0.57, P=.001). Conclusion 3.0T 1H-MRS is able to measure poly- and unsaturated hepatic fatty acids and this strongly correlates with biochemical assessment. This study provides evidence that 3.0-T 1H-MRS is a noninvasive technique to assess hepatic lipid composition.