| Background and purposeThe proportion of people who were stucked in obesity and fatty liver is increasing, with the improvement of living standards. Non-alcoholic fatty liver disease(NAFLD) has become a serious problemof society. Fatty liver disease is reversible and, therefore, it is essential for early diagnosis and treatment of fatty liver to prevent further development of hepatic steatosis. Even though pathological diagnosis of liver biopsy is the golden standard for the assessment for fatty liver, not all patients accepte can it, because pathological biopsy is invasive. It means that puncture pathology can not be used in examing and monitoring in long term. Therefore, researchers are investigating a non-invasive to measure the fat content. Chinese Medical Association in 2006 to developed fatty liver Classification: F0(normal liver): fatty degeneration of the liver cells is less than 5%; F1: fatty degeneration of the liver cells of 5%-30%, F2(mild fatty liver): steatosis hepatocytes 31%-50%, F3(moderate fatty liver): fatty change hepatocytes 51%-75%, F4(severe fatty liver): hepatocyte steatosis greater than 75%.Currently, the methods of measuring the fat content without invasiveness include: ultrasound(US), computed tomography(CT) and magnetic resonance imaging(MRI). As for mild steatosis, US method is not very sensitive, which shows highly subjective and low objective. CT can not be used as a method of screening and monitoring illness in long term. MRI is considered to be an excellent imaging method for liver fat owing to its non-invasive detection and quantification. At present, MRI sequences include positive and negative phase, MRS, IDEAL and IDEAL-IQ. Materials and methods1. Sixty 5.5-week-old Sprague-Dawley male rats which were supplied by the Experimental Animal Center of Zhengzhou University were randomly divided into two groups(weighed 94.6±8.9g): experimental group(46) and control group(14). The experimental group and control group were fed with high fat diet and normal diet, respectively, for 8 and 12 weeks. And then, the rats can be divided into low-dose group, the conventional dose group and high dose group.2. Magnetic Resonance Imaging: All MRI experiments were performed on a 3.0TMRI scanner(Discovery MR 750; GE Medical Systems, Milwaukee, WI, USA). Scanning coil is knee coil. Besides, every group was scanning at 8 weeks and 12 weeks, respectively. MRI sequences included T1-weighted imaging(T1WI), T2-weighted imaging(T2WI), diffusion-weighted imaging(DWI), magnetic resonance spectroscopy(MRS) and IDEAL-IQ. After a three-plane localizer sequence, the IDEAL-IQ sequence of two groups was scanned after injection of contrast agent 1 min, 3 min, respectively. After scanning, the liver tissue was dissected, embedded with paraffin, sliced and stained by HE.3. Postprocessing was conducted through GE processing workstation. : 1 The fat content was calculated through obtaining area under the peaks MRS aliphatic in SAGE 7.0 software; 2 We got fat ratio and R2* in value in the corresponding voxel MRS scanning location through postprocessing for IDEAL-IQ. 3 We got fat ratio and R2* in value in the corresponding voxel MRS scanning location through postprocessing for IDEAL-IQ. Then, IDEAI fat content-IQ and R2* value were calculated at corresponding time before and after injection of contrast agent conducted in special software. 4 The pathology was graded as the proportion of fatty infiltration in the total number of hepatocytes through the light microscope.4. The experimental data were analysised in SPSS17.0 softwareand then they were expressed as mean ± standard deviation. The degree of correlation among MRS(under the peak area ratio), IDEAL-IQ(fat ratio) and the degree of fatty liver was analyzed in simple linear regression. The ROC was analysised and evaluated the cut-off point at which MRS and IDEAL-IQ could diagnosis excellently non-alcoholic fatty liver. The difference of fat ratio ratio and the R2* value before and after injection of the contrast at varying time was investaged through L-SD. P <0.05 shows that difference was valuable. Results1. Pathology results: F0(the proportion of fatty degeneration of the liver cells was less than 5% and the number of the rats was 9) was LevelⅠ;(the proportion of fatty degeneration of the liver cells belongs to 5%-30% and the number of the rats was 11) was LevelⅡ; F2(the proportion of fatty degeneration of the liver cells belongs to 31%-50% and the number of the rats was 21) was Level Ⅲ; F3(he proportion of fatty degeneration of the liver cells belongs to 51%-75% and the number of the rats was 13) was Level Ⅳ; F4(the proportion of fatty degeneration of the liver cells was bigger than 75% and the number of the rats was 6) was Level Ⅳ.2. FF-IDEAL-IQ: Level Ⅰ: 4.63 ± 0.6%; Level Ⅱ: 6.48 ± 0.61%; level Ⅲ: 9.10 ± 1.89%; level Ⅳ: 18.9 ± 6.24%. Level Ⅴ: 37.67 ± 6.17%. There was a positive correlation(R = 0.825, p <0.01), and the threshold(7.31%) of fatty liver for rats was obtained by IDIQ value. FF-MRS results: Level Ⅰ: 4.24±1.69; % Level Ⅱ: 7.90±1.90%; Level Ⅲ : 13.18+3.83%; Level Ⅳ :20.71+10.15%. Level Ⅴ : 39.10±9.09%. There was a positive correlation(R= 0.796, p <0.01), and the threshold(10.56%) of fatty liver for rats was obtained by MRS. IDEAL-IQ showed higher pathological correlation with the fatty liver of rats than that of MRS.3. The fat fraction(IDEAL-IQ):(1). Low-dose group: before and after injection of the contrast at 1 min, 3 min, respectively, was not statistically significant(F = 2.28, P = 0.116).(2). The conventional dose group: he fat fraction before and after injection of the contrast at 1 min, 3 min, respectively, was not statistically significant(F=2.28, P = 0.181).(3). High dose group: the fat fraction before and after injection of the contrast at 1 min, 3 min, respectively, was not statistically significant(F = 2.554, P = 0.091).(4). The fat fraction was not statistically significant(F = 0.108,P = 0.898) before injection of the contrast in the table 1.(5). The fat fraction was not statistically significant(F = 0.337, P = 0.72) after 1 min for injection of the contrast.(6). The fat fraction was not statistically significant(F = 0.209, P = 0.812) after 3 min for injection of the contrast.4. R2* value(IDEAL-IQ):(1). Low-dose group: the fat fraction(FF) before and after injection of the contrast at 1 min, 3 min, respectively, was statistically significant(F = 163.30, P = 0.00).(2). The conventional dose group: the fat fraction(FF) before and after injection of the contrast at 1 min, 3 min, respectively, was statistically significant(F=347.457, P = 0.00).(3). High dose group: the fat fraction(FF) before and after injection of the contrast at 1min, 3 min, respectively, was statistically significant(F=380.586, P = 0.091).(4). The R2* value was not statistically significant(F = 1.912, P = 0.157) before injection of the contrast in the table 1.(5). The R2* value was statistically significant(F =5.236, P = 0.008) after 1 min for injection of the contrast.(6). The R2* value was statistically significant(F = 0.209, P = 0.812) after 3 min for injection of the contrast. Conclusions1. Fat fratio of MRS(area ratio under the peak) was positively correlated with NAFL fat content.2. Fat fratio of IDEAL-IQ was positively correlated with NAFL fat content, and the threshold of MRS which diagnoses of fatty liver was 6.945%.3. IDEAL-IQ showed higher pathological correlation with the fatty liver of rats than that of MRS.4. Low-dose, conventional dose and high dose of contrast agent had no effect on IDEAL-IQ value of rat fatty liver model.5. It was stable to measure fat content through IDEAL-IQ. |
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