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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