1H MRS Analysis Using Ultrashort-TE Sequence of Hepatic Lipids in a 9.4T MRI Device
Authors:   Department of Research Equipment Operation Korea Basic Science Institute, Cheong-won, Ochang, Republic of Korea, Kim Jooyeon 
Published: March 2024

Non-alcoholic fatty liver disease is the most common cause of chronic liver diseases which is characterized by increased levels of obesity, and diabetes. Liver lipid content has been suggested to play an important pathogenic role in the development of liver fibrosis, and cirrhosis In particular, it is associated with the risk of hepatocellular carcinoma (HCC). Liver biopsy is still the gold standard for diagnosing and assessing the disease. However, the invasive and limited tissue sampling of the biopsy presents problems. Proton magnetic resonance spectroscopy (1H-MRS) enables the study of cellular biochemistry and metabolism and provides a non-invasive means to determine disease abnormalities and progression in vivo and longitudinally. With the increased availability of high-field magnetic resonance (MR) systems for clinical and preclinical studies, both signal-to-noise ratio (SNR) and spectral resolution of metabolites in the MR spectra can be improved significantly, allowing more accurate metabolite identification, quantification, and thus disease characterization. 1H-MRS permits longitudinal assessment of fat fraction, saturated and unsaturated. This study aims to characterize early hepatic lipid changes in the fatty liver mouse model by in vivo short-echo time (TE) 1H-MRS (Proton- Magnetic Resonance Spectroscopy). This study examined 17 male C57BL/6 mice, including 8 high-fat diet (45%) mice for 20 weeks and 9 normal mice for 17 weeks. C57BL/6 mice were fed with 60% high-fat diet containing 60% fat, 20% protein, and 20% carbohydrate. MR imaging with single-voxel 1H-MRS was performed using a PRESS sequence at 9.4T magnetic resonance imaging (MRI). The full width at half maximum (FWHM) ranged from 4 to 8 Hz. Water suppression was accomplished with "VAPOR" pulses. The examination (voxel size, 2×2×2 mm3) was performed from the liver parenchyma in mice at normal and high-fat diets, respectively. The spectral acquisition parameters were TR/TE = 2500/16 ms, and 256 acquisitions for averaging. LCModel fitting was conducted using an experimental basis sets. Less than 10% standard deviation (%SD) of metabolite quantification data was allowed. The areas under the peaks were measured as follows: signal integrals of lipid methyl protons (-CH3; 0.9 ppm), methylene proton ((-CH2-)n; 1.3 ppm), allylic protons (- CH2-C=C-CH2; 2.1 ppm), α-methylene protons (-CO-CH2- CH 2; 2.3 ppm), diallyl ic protons (=CCH-2C=; 2.8 ppm), glycerol protons (CH2-COO; 4.1 ppm), glycerol protons (CH2-COO; 4.3 ppm) and methene protons (CH=CH; 5.3 ppm). For relative quantification, total lipid (TL), total saturated fatty acid (TSFA), total unsaturated fatty acid (TUFA), total unsaturated bond (TUB), polyunsaturated bond (PB) and choline-containing compound (Cho) were normalized by separating each peak of (-CH2-)n, -CH2- C=C-CH2-, -CO-CH2-CH2=C-CH-2-C= and –CH=CH-.Significant increases in lipid signals of 0.9, 1.3, 2.1, 2.3, 2.8, 4.1, 4.3, and 5.3 ppm were found in animals at high-fat diet(p<0.01, p<0.001). TL, TSFA, TUFA, TUB, PUB and Cho was significantly increased at high-fat diet(p<0.01, p<0.05). Therefore, 1H-MRS is useful in detecting and characterizing various hepatic lipid alterations.