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目的探讨频率饱和反转恢复序列(spectral saturation inversion recovery,SPIR)、梯度回波化学位移MRI及磁共振氢谱(proton magnetic resonance spectroscopy,1H-MRS)在定量分析肝脏脂肪含量中的价值。方法对31例健康自愿者及22例可获得肝脏标本的病例行常规T1加权和T2加权(不压脂+压脂)、梯度回波T1加权同相位/反相位(in-phase/opposed-phase,IP/OP)成像及肝脏1H-MRS检查。测得T1WI和T2WI压脂前、后及IP/OP的信号强度值(SInonfat1、SIfat1、SInonfat2、SIfat2、SIin及SIout),计算相对信号强度(relative signal intensity,RSI1及RSI2)和脂变指数(fat index,FI);测得1H-MRS的峰值及峰下面积,计算肝细胞相对脂肪含量(relative lipid con-tent,RLC)。病例组22例患者于MRI扫描后接受肝脏外科手术切除,切下的肝脏进行病理组织学检查,并用图像分析软件测量肝细胞中脂变细胞百分比(proportion of fatty degenerative cells,PFDC)。结果①脂肪肝组RSI1、FI及RLC的平均值均高于非脂肪肝组(P<0.05),但RSI2的平均值2组间差异无统计学意义(P>0.05)。②脂肪肝不同病理分级间RLC的差异具有统计学意义,且随脂肪肝病理级别的增加而增高(P<0.05);随着病理级别的增加,RSI1及FI逐渐增高,但差异无统计学意义(P>0.05);RSI2在脂肪肝不同病理分级间的差异亦无统计学意义(P>0.05)。③FI及RLC与PFDC之间存在线性正相关关系(r=0.468,P=0.027;r=0.771,P<0.000 1);RSI1及RSI2与PFDC之间无相关性(r=0.411,P=0.057;r=0.191,P=0.392)。结论 SPIR、梯度回波化学位移MRI及1H-MRS三种方法可在一定程度上区分有无脂肪肝;1H-MRS有助于脂肪肝的分级;在肝脏脂肪含量定量分析方面,1H-MRS较梯度回波化学位移MRI更具优越性,有助与肝脏脂肪的量化分析;而SPIR价值有限。
Objective To investigate the value of spectral saturation inversion recovery (SPIR), gradient echo chemical shift MRI (1H-MRS) and proton magnetic resonance spectroscopy (1H-MRS) in the quantitative analysis of liver fat content. Methods Thirty-one healthy volunteers and 22 cases of available liver specimens underwent routine T1-weighted and T2-weighted (non-fat and fat-suppressed), gradient echo T1-weighted in-phase / opposed- phase, IP / OP imaging and liver 1H-MRS examination. The signal intensity values (SInonfat1, SIfat1, SInonfat2, SIfat2, SIin and SIout) before and after IPT and T1 / T2WI were measured and the relative signal intensity (RSI1 and RSI2) fat index, FI). The peak area and the area under the peak of 1H-MRS were measured to calculate the relative lipid con-tent (RLC). Twenty-two patients in the case group underwent surgical resection of the liver after the MRI scan. The excised liver was examined histopathologically and the proportion of fatty degenerative cells (PFDC) in hepatocytes was measured using image analysis software. Results ① The mean values of RSI1, FI and RLC in fatty liver group were higher than those in non-fatty liver group (P <0.05), but there was no significant difference between the two groups in mean RSI2 (P> 0.05). ② The difference of RLC between different pathological grades of fatty liver was statistically significant, and increased with the increase of pathological grade of fatty liver (P <0.05). With the increase of pathological grade, RSI1 and FI increased gradually, but the difference was not statistically significant (P> 0.05). The difference of RSI2 in different pathological grades of fatty liver was not statistically significant (P> 0.05). There was a linear positive correlation between FI and RLC and PFDC (r = 0.468, P = 0.027; r = 0.771, P <0.0001); there was no correlation between RSI1 and RSI2 and PFDC (r = 0.411, P = r = 0.191, P = 0.392). Conclusions SPIR, gradient-echo chemical shift MRI and 1H-MRS can distinguish the presence of fatty liver to some extent; 1H-MRS contributes to the classification of fatty liver; 1H-MRS in the quantitative analysis of liver fat content Gradient-echo chemical shift MRI is more advantageous and helps quantify liver fat; SPIR is of limited value.