Heba Elhamy R, Desai Ajinkya, Zand Kevin A, Hamilton Gavin, Wolfson Tanya, Schlein Alexandra N, Gamst Anthony, Loomba Rohit, Sirlin Claude B, Middleton Michael S
Liver Imaging Group, Department of Radiology, University of California, San Diego, San Diego, California, USA.
Computational and Applied Statistics Laboratory (CASL), San Diego Supercomputing Center (SDSC), University of California, San Diego, San Diego, California, USA.
J Magn Reson Imaging. 2016 Feb;43(2):398-406. doi: 10.1002/jmri.25006. Epub 2015 Jul 22.
To determine the accuracy and the effect of possible subject-based confounders of magnitude-based magnetic resonance imaging (MRI) for estimating hepatic proton density fat fraction (PDFF) for different numbers of echoes in adults with known or suspected nonalcoholic fatty liver disease, using MR spectroscopy (MRS) as a reference.
In this retrospective analysis of 506 adults, hepatic PDFF was estimated by unenhanced 3.0T MRI, using right-lobe MRS as reference. Regions of interest placed on source images and on six-echo parametric PDFF maps were colocalized to MRS voxel location. Accuracy using different numbers of echoes was assessed by regression and Bland-Altman analysis; slope, intercept, average bias, and R2 were calculated. The effect of age, sex, and body mass index (BMI) on hepatic PDFF accuracy was investigated using multivariate linear regression analyses.
MRI closely agreed with MRS for all tested methods. For three- to six-echo methods, slope, regression intercept, average bias, and R2 were 1.01-0.99, 0.11-0.62%, 0.24-0.56%, and 0.981-0.982, respectively. Slope was closest to unity for the five-echo method. The two-echo method was least accurate, underestimating PDFF by an average of 2.93%, compared to an average of 0.23-0.69% for the other methods. Statistically significant but clinically nonmeaningful effects on PDFF error were found for subject BMI (P range: 0.0016 to 0.0783), male sex (P range: 0.015 to 0.037), and no statistically significant effect was found for subject age (P range: 0.18-0.24).
Hepatic magnitude-based MRI PDFF estimates using three, four, five, and six echoes, and six-echo parametric maps are accurate compared to reference MRS values, and that accuracy is not meaningfully confounded by age, sex, or BMI.
以磁共振波谱（MRS）为参考，确定基于幅值的磁共振成像（MRI）在估计已知或疑似非酒精性脂肪性肝病成人不同回波数下肝脏质子密度脂肪分数（PDFF）时的准确性以及可能的基于受试者的混杂因素的影响。
在对506名成年人的回顾性分析中，以右叶MRS为参考，通过未增强的3.0T MRI估计肝脏PDFF。放置在源图像和六回波参数PDFF图上的感兴趣区域与MRS体素位置共定位。通过回归分析和布兰德-奥特曼分析评估使用不同回波数时MRI的准确性；计算斜率、截距、平均偏差和R²。使用多元线性回归分析研究年龄、性别和体重指数（BMI）对肝脏PDFF准确性的影响。
对于所有测试方法，MRI与MRS的结果高度一致。对于三到六回波方法，斜率、回归截距、平均偏差和R²分别为1.01 - 0.99、0.11% - 0.62%、0.24% - 0.56%和0.981 - 0.982。五回波方法的斜率最接近1。两回波方法最不准确，与其他方法平均低估0.23% - 0.69%相比，平均低估PDFF 2.93%。发现受试者BMI（P范围：0.0016至0.0783）和男性性别（P范围：0.015至0.037）对PDFF误差有统计学上显著但临床上无意义的影响，而受试者年龄对PDFF误差无统计学显著影响（P范围：0.18 - 0.24）。
与参考MRS值相比，使用三、四、五和六回波以及六回波参数图的基于幅值的肝脏MRI PDFF估计是准确的，且准确性不会受到年龄、性别或BMI的显著干扰。
