Distortion-free water-fat separated diffusion-weighted imaging using spatiotemporal joint reconstruction
We present a novel diffusion-weighted imaging (DWI) technique that addresses two common challenges in standard echo-planar imaging (EPI): geometric distortion and residual fat signals.
Our method employs an echo planar time-resolved imaging (EPTI) readout to acquire multiple time-shifted echoes, which we jointly reconstruct in the spatiospectral domain to effectively separate water and fat. A fast spin echo (FSE) phase navigator is used to correct shot-to-shot motion-induced phase variations in multi-shot DWI. Chemical-shift encoding-based water/fat separation achieves robust fat suppression even in anatomically challenging regions with significant B₀ inhomogeneities, such as the head/neck and breast. We further enhance reconstruction fidelity using locally low-rank regularization and wavelet-based sparsity constraints, enabling accurate, alias-free water-fat separation and improved SNR.
Phantom and in vivo studies demonstrate that our proposed DW-EPTI method substantially reduces distortion, eliminates water-fat swap artifacts, and produces accurate apparent diffusion coefficient (ADC) maps.
In head and neck imaging, our technique effectively mitigates the severe off-resonance effects caused by dental hardware. In breast imaging, it resolves chemical shift artifacts at higher b-values and provides clearer lesion depiction compared to standard multi-shot EPI sequences. While the scan time is modestly increased due to the additional calibration shots and navigator readout, the significant improvements in artifact suppression and diagnostic clarity underscore the potential of our approach for high-accuracy clinical DWI applications.
Zhou X, Daniel BL, Hargreaves BA, Lee PK. Distortion-free water-fat separated diffusion-weighted imaging using spatiotemporal joint reconstruction. Magn Reson Med. 2024;92(6):2343-2357. doi:10.1002/mrm.30221
DW-EPTI images water (A, D) and fat image (B, E) in breast cancer patients compared with water-only DW-EPI (C, F). Dynamic contrast-enhanced water and fat images are included for reference. In both cases, prominent unsuppressed fat signal can be observed in the DW-EPI images. The DW-EPTI images show successful water-fat separation and reduced geometric distortion. Lesions (red arrows) demonstrate hyperintense contrast to surrounding fibroglandular tissues and reduced ADC. Minor leakage artifact presents in b = 800 s∕mm2 fat images of Patient 1 (B) (white arrow).
