单纯性肥胖症学龄儿童肝脏脂肪含量的MRI研究

目的分析学龄儿童单纯性肥胖症的MRI表现及MRS特点,确定其肝脏脂肪的MRI定量评估方法。方法将2015年1月—2016年12月期间临床诊断单纯性肥胖症的学龄儿童52例(男31例,女21例)作为病例组,平均年龄(10.1±1.1)岁。同年龄组[平均年龄(9.8±0.9)岁]的正常健康儿童40例(男22例,女18例)作为对照组。采用SIEMENS 1.5 T Avanto MR设备行MRI和~1H-MRS检查。观察肝实质于同相位、反相位影像上的信号变化;通过~1H-MRS获得肝脏兴趣区的水峰峰值(P_w)、水峰下面积(A_w)、脂峰峰值(P_l)及脂峰下面积(A_l)并计算出脂肪分数(FF)。采用独立样本t检验比较正常儿童和肥胖症患儿间P_w、A_w、P_l、A_l、FF差异;采用单因素方差分析比较轻、中、重度肥胖症患儿间各项指标的差异。并利用受试者操作特征(ROC)曲线评估MRS诊断脂肪肝的敏感度、特异度及准确度。结果肥胖症患儿组于T_1WI反相位影像上信号不同程度减低,而正常组T_1WI同反相位影像信号一致。MRS结果如下:(1)正常组和肥胖症组的P_w、A_w差异无统计学意义(P>0.05)。(2)肥胖症患儿P_l、A_l、FF明显高于正常组(均P<0.05);其中FF的诊断效能最高,敏感度为100%,特异度为82%,准确度为85%。(3)随着肥胖分级的增加,肥胖患儿的P_l、A_l均增高。结论 T_1WI双回波同反相位技术和MRS是目前定量测量肝脏脂肪含量的有效方法,在前者对脂肪肝做出初步诊断的基础上, MRS可进一步对脂肪肝进行量化分级。

MRI study of liver fat content in school-age children with simple obesity

Objective To analyze the MRI features and MRS characteristics of simple obesity in school-age children, and to determine the method for quantitative evaluation of liver lipid by MRI. Methods Fifty-two school-age children (31 males and 21 females, average age 10.1±1.1 years) with clinically diagnosed simple obesity during January 2015 to December 2016 were selected as patient group. Forty age-matched (22 males, 18 females, average age 9.8±0.9 years) healthy children were selected as control group. MRI and 1H-MRS examination were performed using SIEMENS 1.5 T Avanto MR. The signal changes of liver parenchyma on the in-phase and opposed-phase images were observed. Water peak (Pw), area under water peak (Aw), lipid peak (Pl) and area under lipid peak (Al) on 1H-MRS were measured from regional of interest, and fat fraction (FF) was calculated. The differences in Pw, Aw, Pl, Al and FF between normal and patient froup were compared with independent sample t test. One-way ANOVA was used to compare the differences in indexes among children with mild, moderate, and severe obesity. The ROC curve was used to evaluate the diagnostic sensitivity, specificity, and accuracy of MRS in the diagnosis of fatty liver. Results The T1WI signal on the opposed-phase imaging decreased to varied degrees in the patient group, while in the normal group the signal intensities were consistent on the opposed-phase imaging. MRS results were as follows: ①Pw and Aw did not statistically differ between the normal and patient groups (P>0.05); ②Pl, Al, and FF in the patient group were significantly higher than those in the normal group (all P<0.05). FF achieved the highest diagnostic efficacy, with 100% sensitivity, 82% specificity, and 85% accuracy. ③With increase of obesity classification, Pl and Al increased in the patient group. Conclusion Combination of T1WI with double echo opposed-phase technique and MRS technology is an effective method for quantitatively measuring the liver fat content on MRI, the T1WI can be used to make a preliminary diagnosis of fatty liver, and the MRS can be used to quantitatively grade fatty liver.