Water-fat separation in diffusion-weighted EPI using an IDEAL approach with image navigator.

PURPOSE: Echo planar-based diffusion-weighted MRI (DW-MRI) requires robust suppression of fat signal. Fat suppression techniques such as inversion recovery or spectrally selective excitation with subsequent gradient spoiling can extend scan time or perform suboptimally in the presence of strong main field inhomogeneities. Chemical shift-encoded water-fat separation using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) is robust in areas of main field inhomogeneity but requires accurate phase information, which can be distorted by patient motion during diffusion-weighting gradients. A method is proposed to overcome this with the use of image navigators. THEORY AND METHODS: A spin echo planar imaging (SE-EPI) diffusion-weighted sequence was modified to incorporate IDEAL acquisition in combination with an image navigator to correct for patient motion-induced phase effects. Images were acquired in phantoms and in healthy volunteers in brain, pelvic, and abdominal regions.
RESULTS: Without navigator, diffusion-weighted IDEAL created artifacts in areas of motion. These were removed when the two-dimensional navigator was used to correct the phase, resulting in correct water-fat separation.
CONCLUSION: DW-EPI with IDEAL and an integrated image navigator allows for robust water and fat separation in different body areas and are a time-efficient alternative to standard fat-suppression techniques in DW-MRI.