Just Published: Motion-robust, high-SNR liver fat quantification using a 2D sequential VFA approach
Representative PDFF maps from two children, obtained with three different CSE‐MRI acquisitions (3D, LFA‐linear, and VFA‐centric). One child was able to sustain a 20‐s breath‐hold (“Good BH,” top row), whereas another child was unable to sustain such breath‐hold (“Poor BH,” bottom row). In the Good BH case, negligible motion artifacts are observed with the three acquisitions. In the Poor BH case, substantial motion artifact is observed in the BH 3D acquisition. In contrast, the free breathing 2D acquisitions (LFA‐linear and VFA‐centric) effectively freeze breathing motion. In both subjects, LFA‐linear acquisition leads to high noise levels in PDFF maps. The proposed VFA‐centric method is able to freeze breathing motion while maintaining high SNR. Yellow circles represent sample ROIs used for further analysis. [Figure from Zhao R, Zhang Y, et al. Magn Reson Med. 2020 Apr 3.]
Abstract
Purpose
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.
Methods
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.Results
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.
Conclusions
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.