Hi,
I have been trying to compute the fieldmap for EPI correction using the command b0calc. The following are the commands I used (binaries are from neurodebian repository). The skull+tissue vs air segmentation image (EM_Map) was created from a T1-weighted MRI image.
fsl5.0-b0calc -i EM_Map_mask -o EM_Map_b0field --b0=3
fsl5.0-fslmaths EM_Map_b0field -mul 42575000 -mul 6.28318 EM_Map_b0field
Here are the links to the files in question. I have omitted the file $BMAP because of its size. EM_Map_fmap.nii.gz was extracted from EM_Map_b0field using a brain mask.
http://dl.dropbox.com/u/8460189/EM_Map_mask.nii.gz
http://dl.dropbox.com/u/8460189/EM_Map_b0field.nii.gz
http://dl.dropbox.com/u/8460189/EM_Map_fmap.nii.gz
However it seems that I must have made a mistake somewhere because in the final image, the light and dark areas don't appear to be in the right places? This is most obvious when comparing against the fieldmaps in for example Poyton et al, "Fieldmap-Free Retrospective Registration and Distortion Correction for EPI-Based Functional Imaging", 2009.
Any pointers are very much appreciated!
Cheers,
Louis.
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