Spherical Echo-Planar Time-resolved Imaging (sEPTI) for 3D highly-accelerated, distortion-free, time-resolved whole-brain T2* mapping

EPTI is a rapid time-resolved quantitative imaging method. In this work, we developed a spherical EPTI sampling trajectory (sEPTI) to improve its speed. To achieve fast imaging, sEPTI traverses a tight 3D spherical k-space using full ramp-sampling and variable echo-spacing, which also desirably increases its spatiotemporal incoherency. sEPTI was demonstrated in vivo to provide improved imaging performance over conventional block 3D-EPTI that requires 1.4x longer scan; achieving high-quality 1mm isotropic whole-brain proton-density and T2* maps in 48s. As part of this work, a novel and effective reconstruction approach to mitigate high-spatial-order ghosts in echo-planar acquisitions was also developed.