Are you correcting for eddy currents before applying the field map?
Peace,
Matt.
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Drew
Sent: Tuesday, September 16, 2008 2:50 PM
To: [log in to unmask]
Subject: [FSL] Field Map EPI correction
Hello FSL users
We are trying to use FUGUE to correct the B0 inhomogeneity EPI distortions
in our DTI datasets.
We are measuring success by rigidly registering the non-diffusion-weighted
(b=0) image, before and after FUGUE correction, to a standard T2 Fast Spin
Echo image, to see which one looks better.
For the most part, it seems to have succeeded in "stretching out" some of
the distortions we were finding at the back/bottom (posterior, inferior) of
the brain. However, we've noticed that there seems to be a small, but
noticeable shear in the corrected image that appears to make some of the
more superior slices actually LESS good than before correction.
Looking at our B0map, there does seem to be a corresponding difference in
the B0 field, so we are more or less confident that everything is working
well.
So I guess the question is why would the correction result in a poorer
alignment?
has anyone else run into this? Could there be a problem with our field map
acquisition/calculation? Or is this merely a "nothing's perfect" sort of
issue?
Any insights would be appreciated.
Thanks
Drew
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