Zhao Ruiyang, Zhang Yuxin, Wang Xiaoke, Colgan Timothy J, Rehm Jennifer L, Reeder Scott B, Johnson Kevin M, Hernando Diego
Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA.
Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, USA.
Magn Reson Med. 2020 Oct;84(4):2004-2017. doi: 10.1002/mrm.28263. Epub 2020 Apr 3.
Chemical shift encoded (CSE)-MRI enables quantification of proton-density fat fraction (PDFF) as a biomarker of liver fat content. However, conventional 3D Cartesian CSE-MRI methods require breath-holding. A motion-robust 2D Cartesian sequential method addresses this limitation but suffers from low SNR. In this work, a novel free breathing 2D Cartesian sequential CSE-MRI method using a variable flip angle approach with centric phase encoding (VFA-centric) is developed to achieve fat quantification with low bias, high SNR, and minimal blurring.
Numerical simulation was performed for variable flip angle schedule design and preliminary evaluation of VFA-centric method, along with several alternative flip angle designs. Phantom, adults (n = 8), and children (n = 27) were imaged at 3T. Multi-echo images were acquired and PDFF maps were estimated. PDFF standard deviation was used as a surrogate for SNR.
In both simulation and phantom experiments, the VFA-centric method enabled higher SNR imaging with minimal bias and blurring artifacts. High correlation (slope = 1.00, intercept = 0.04, = 0.998) was observed in vivo between the proposed VFA-centric method obtained PDFF and reference PDFF (free breathing low-flip angle 2D sequential acquisition). Further, the proposed VFA-centric method (PDFF standard deviation = 1.5%) had a better SNR performance than the reference acquisition (PDFF standard deviation = 3.3%) with P < .001.
The proposed free breathing 2D Cartesian sequential CSE-MRI method with variable flip angle approach and centric-ordered phase encoding achieved motion robustness, low bias, high SNR compared to previous 2D sequential methods, and low blurring in liver fat quantification.
化学位移编码（CSE）磁共振成像（MRI）能够定量检测质子密度脂肪分数（PDFF），作为肝脏脂肪含量的生物标志物。然而，传统的三维笛卡尔CSE-MRI方法需要屏气。一种运动稳健的二维笛卡尔序列方法解决了这一局限性，但信噪比（SNR）较低。在本研究中，开发了一种新颖的自由呼吸二维笛卡尔序列CSE-MRI方法，该方法采用可变翻转角方法和中心相位编码（VFA-中心），以实现低偏差、高SNR和最小模糊的脂肪定量。
进行数值模拟以设计可变翻转角方案，并对VFA-中心方法以及几种替代翻转角设计进行初步评估。对3T下的体模、成人（n = 8）和儿童（n = 27）进行成像。采集多回波图像并估计PDFF图。PDFF标准差用作SNR的替代指标。
在模拟和体模实验中，VFA-中心方法均能实现更高SNR的成像，偏差和模糊伪影最小。在所提出的VFA-中心方法获得的PDFF与参考PDFF（自由呼吸低翻转角二维序列采集）之间，在体内观察到高度相关性（斜率 = 1.00，截距 = 0.04， = 0.998）。此外，所提出的VFA-中心方法（PDFF标准差 = 1.5%）的SNR性能优于参考采集（PDFF标准差 = 3.3%），P <.001。
所提出的具有可变翻转角方法和中心有序相位编码的自由呼吸二维笛卡尔序列CSE-MRI方法，与先前的二维序列方法相比，在肝脏脂肪定量中实现了运动稳健性、低偏差、高SNR和低模糊。
