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

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.

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.

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.

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.