Water/fat separation for distortion‐free EPI with point spread function encoding

Purpose Effective removal of chemical‐shift artifacts in echo‐planar imaging (EPI) is a challenging problem especially with severe field inhomogeneity. This study aims to develop a reliable water/fat separation technique for point spread function (PSF) encoded EPI (PSF‐EPI) by using its intrinsic multiple echo‐shifted images. Theory and Methods EPI with PSF encoding can achieve distortion‐free imaging and can be highly accelerated using the tilted‐CAIPI technique. In this study, the chemical‐shift encoding existing in the intermediate images with different time shifts of PSF‐EPI is used for water/fat separation, which is conducted with latest water/fat separation algorithms. The method was tested in T1‐weighted, T2‐weighted, and diffusion weighted imaging in healthy volunteers. Results The ability of the proposed method to separate water/fat using intrinsic PSF‐EPI signals without extra scans was demonstrated through in vivo T1‐weighted, T2‐weighted, and diffusion weighted imaging experiments. By exploring different imaging contrasts and regions, the results show that this PSF‐EPI based method can separate water/fat and remove fat residues robustly. Conclusion By using the intrinsic signals of PSF‐EPI for water/fat separation, fat signals can be effectively suppressed in EPI even with severe field inhomogeneity. This water/fat separation method for EPI can be extended to multiple image contrasts. The distortion‐free PSF‐EPI technique, thus, has the potential to provide anatomical and functional images with high‐fidelity and practical acquisition efficiency.