I asked my Philips 3T MRI tech to add a field map sequence (gradient echo) for correcting EPI-related distortions in 32dir 2mm iso ax DTI data with FUGUE. I was expecting something on the order of 2-3min, but the data I received is ~6min. It looks like they chose NEX=2. Is there any reason to collect a field map with NEX=2 instead of NEX=1? Are there specific parameter ranges available somewhere I could check against to see if some tweaks here and there can be made to decrease the field map acquisition time to the 2-3min range?
Many thanks for any suggestions,
Jenifer
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