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Unfortunately, you can’t correct efficiently the distortion of B0 without an appropriate sequence of acquisition. The
alternative to the fieldmap acquisition is to acquire a second EPI with opposite phase encoding direction (one sequence Anterior->Posterior and one sequence Posterior->Anterior).
If you don’t have these data available, you will have to deal with your data without unwarping. In this case, make sure
to integer realignment parameters in your 1st level model. It would compensate a bit the movement effect by not the voxel displacement of the regions you cite.
From: SPM (Statistical Parametric Mapping) <[log in to unmask]>
On Behalf Of Steve Petersen
Sent: jeudi, 12 décembre 2019 18:37
To: [log in to unmask]
Subject: [SPM] Epi distorsion correction without fieldmaps
Dear SPM users,
I was wondering if it is possible correct the epi distorsions of my functional scans caused by magnetic field inhomogeneities. These artifacts are mainly observed in some areas of the temporal and orbitofrontal cortex. Unfortunately we
did not incorporated a field map estimation in our acquisition protocol.
These data were acquiered in a Philips Achieva 3T scanner.
Any suggestion will be very appreciated.
Thanks in advance.
Best regards,