Accelerating multi-echo water-fat MRI with a joint locally low-rank and spatial sparsity-promoting reconstruction

Our aim was to demonstrate the benefits of using locally low-rank (LLR) regularization for the compressed sensing reconstruction of highly-accelerated quantitative water-fat MRI, and to validate fat fraction (FF) and relaxation against reference parallel imaging in the abdomen. Reconstructions using spatial sparsity regularization (SSR) were compared to reconstructions with LLR and the combination of both (LLR+SSR) for up to seven fold accelerated 3-D bipolar multi-echo GRE imaging. For ten volunteers, the agreement with the reference was assessed in FF and maps. LLR regularization showed superior noise and artifact suppression compared to reconstructions using SSR. Remaining residual artifacts were further reduced in combination with SSR. Correlation with the reference was excellent for FF with = 0.99 (all methods) and good for with = [0.93, 0.96, 0.95] for SSR, LLR and LLR+SSR. The linear regression gave slope and bias (%) of (0.99, 0.50), (1.01, 0.19) and (1.01, 0.10), and the hepatic FF/ standard deviation was 3.5%/12.1 s, 1.9%/6.4 s and 1.8%/6.3 s for SSR, LLR and LLR+SSR, indicating the least bias and highest SNR for LLR+SSR. A novel reconstruction using both spatial and spectral regularization allows obtaining accurate FF and maps for prospectively highly accelerated acquisitions.