Hello,
there is a problem we have with the use of the fieldmaps toolbox in SPM2.
We acquired 10 ms and 30 ms gradient echo phase and magnitude images on a
Signa Excite 1.5 Tesla machine. Phase maps with original values from -100 to
about 8000 were rescaled to -pi to +pi using the script of Chloe.
Defaults are set correctly in the pm_defaults.m script, readout time is 32.7
ms. The fieldmap can be calculated and looks ok.
Settings are then 'non-EPI', coregistering between the magnitude image of the
fieldmap and the EPI is done. The voxel displacement map looks fine, with
large variance in it, so it seems that some unwarping should take place.
However, the resulting unwarped EPI looks very much like the original with
only a few spots being changed in the difference image.
Switching Jacobian modulation on and off does not change a lot.
Is there common source of error we are not aware of?
Thanks very much in advance,
Philipp Saemann
Max-Planck-Institute of Psychiatry
Munich
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