Hello all,

I have a question regarding the handling of fieldmap data in the presence of image wraparound (aliasing). The data are from a Siemens scanner, and I use epi_reg for B0 correction.

In the subject I am considering, the back of the head wraps around to the anterior edge of the image, and unfortunately does overlap to some extent with frontal brain voxels. Visually, this artifact can be detected in the phase and magnitude images, in addition to the BOLD data.

My understanding is that there's no easy way to correct the wraparound problem in this particular subject, since the wraparound voxels overlap with brain voxels. So, assuming that the fundamental problem cannot be fixed, I'm wondering how to best deal with the overlap territory when preparing my fieldmap data for epi_reg. Would it make sense to delete the corresponding voxels in the brain-extracted magnitude image? In other words, I'd be submitting to epi_reg a mask that not only excludes the background and noisy edge voxels, but also a chunk of frontal cortex. In this case, I'd be assuming that the remaining voxels in the masked phase image would provide sufficient information for FUGUE to make a reasonable estimate of the appropriate values of the voxels in the deleted region, via extrapolation. I could see how this assumption could be wrong, so, I thought I'd bring up the question here. Apologies in advance if I've missed something obvious in the documentation or previous listserv comments --

Karin