Hello,
I am using feat/fugue to unwarp EPI images and I am wondering what the
correct input for the echo spacing (dwell time) field is when EPI images
(resolution = 64x64 voxel/slice) were acquired with an accelerated
sequence.
Specifically, I have images acquired with an acceleration factor of 2 and a
TE of 30ms. My (naive?) first thought was to enter 30ms/2 = 15ms as the
echo spacing.
However, the sequence does not only acquire 64/2 = 32 lines but an
additional 24 reference lines.
Does the number of reference lines influence what I should enter as echo
spacing time?
[When I account for the reference lines by calculating either
(a) unwarp_echo_spacing =
echo_spacing*(lines_per_slice/acceleration_factor +
reference_lines)/lines_per_slice as opp) or
(b) unwarp_echo_spacing = lines_per_slice/acceleration_factor)
results with (a) look often better, but I might of course simply shift voxels
to location that actually suffer from signal drop out…]
I’d be thankful for any tip.
Regards - Guido
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