  Purpose
  To alleviate the spatial encoding limitations of single-shot EPI by
developing multi-shot segmented EPI for ultra-high-resolution fMRI with reduced
ghosting artifacts from subject motion and respiration.
  Methods
  Segmented EPI can reduce readout duration and reduce acceleration factors,
however, the time elapsed between segment acquisitions (on the order of
seconds) can result in intermittent ghosting, limiting its use for fMRI. Here,
"FLEET" segment ordering--where segments are looped over before slices--was
combined with a variable flip angle progression (VFA-FLEET) to improve
inter-segment fidelity and maximize signal for fMRI. Scaling a sinc pulse's
flip angle for each segment (VFA-FLEET-Sinc) produced inconsistent slice
profiles and ghosting, therefore, a recursive Shinnar-Le Roux (SLR) RF pulse
design was developed (VFA-FLEET-SLR) to generate unique pulses for every
segment that together produce consistent slice profiles and signals.
  Results
  The temporal stability of VFA-FLEET-SLR was compared against
conventional-segmented EPI and VFA-FLEET-Sinc at 3 T and 7 T. VFA-FLEET-SLR
showed reductions in both intermittent and stable ghosting compared to
conventional-segmented and VFA-FLEET-Sinc, resulting in improved image quality
with a minor trade-off in temporal SNR. Combining VFA-FLEET-SLR with
acceleration, we achieved a 0.6-mm isotropic acquisition at 7 T--without zoomed
imaging or partial Fourier--demonstrating reliable detection of BOLD responses
to a visual stimulus. To counteract the increased repetition time from
segmentation, simultaneous multi-slice VFA-FLEET-SLR was demonstrated using
RF-encoded controlled aliasing.
  Conclusions
  VFA-FLEET with a recursive RF pulse design supports acquisitions with low
levels of artifact and spatial blur, enabling fMRI at previously inaccessible
spatial resolutions with a "full-brain" field of view.
