Water/Fat Separated Echo Planar Time‐Resolved Imaging ( WFS ‐ EPTI ) for Distortion‐Free Multi‐Contrast MRI

ABSTRACT Purpose Echo‐planar time‐resolved imaging (EPTI) provides distortion‐ and T2/T2* blurring‐free multi‐echo/multi‐contrast imaging with fast speed, making it an efficient acquisition method for various MRI applications. Here, we aim to achieve water–fat separation for EPTI to improve fat signal removal for brain/body imaging applications. Theory and Methods A water/fat separated EPTI (WFS‐EPTI) technique is developed, which leverages the intrinsic multi‐echo data provided by EPTI readout and introduces a novel strategy for highly‐accelerated spatiotemporal encoding and reconstruction to separate water and fat signals. Specifically, DIXON encoding is integrated into the spatiotemporal acquisition by acquiring the echo train at scheduled TEs and echo‐spacing, therefore modulating the rapidly changing fat phase evolution across EPTI readout into a more uniform, coherent manner (e.g., in‐phase and out‐of‐phase conditions for odd and even image series). This enables robust subspace representations even in the presence of fat signals. A joint subspace reconstruction is then proposed, which separately performs data consistency for each echo group to ensure fidelity, while jointly leveraging shared information to improve conditioning. Furthermore, an auto‐calibrated WFS‐EPTI is developed to improve motion robustness for abdominal imaging, and a data‐driven basis extraction is employed to address imperfect in‐phase/out‐of‐phase conditions. Results Both phantom experiments and in vivo human imaging across multiple body regions—including brain, head–neck, and abdomen—demonstrated the feasibility of the proposed method. Conclusion The proposed WFS‐EPTI can provide water/fat separation in rapid acquisition and obtain high resolution, distortion‐free multi‐contrast/quantitative imaging in the presence of fat signals.