Improved physiology-induced temporal stability achieved with variable-flip-angle FLEET multi-shot Echo Planar Time-resolved Imaging (EPTI)

Motivation: EPTI is a new highly-efficient imaging approach that addresses limitations of EPI by providing high-resolution distortion- and blurring-free imaging for fMRI. However, shot-to-shot phase-variations induced by physiological processes in conventional multi-shot EPTI can introduce instabilities into the reconstructed time-series data. Goal(s): Improving physiology-induced temporal stability of multi-shot EPTI. Approach: Combing multi-shot EPTI with the VFA-FLEET method, which minimizes shot-to-shot phase-variations by reordering the multi-shot acquisitions while maximizing the signal level by using a variable-flip-angle train and recursive RF pulse design. Results: In vivo fMRI data acquired at 7T demonstrate that the physiological instabilities of multi-shot EPTI can be substantially reduced with proposed method. Impact: Here we test whether temporal instabilities in conventional multi-shot EPTI time-series caused by physiological variability can be reduced by combining EPTI with the variable-flip-angle FLEET method. This combination can improve the usability and robustness of EPTI for high-resolution fMRI studies.