This issue has come up in a couple of labs here, and I thought it warranted
feedback from the SPM group. We've run into problems using the SPM
co-registration process with patients having moderate or greater
atrophy...most often the result is a large difference in the pitch between
the functionals and anatomicals. So, this led us to wonder if one manually
reorients both the patient functional (3.75mm isotopic) and anatomical (1mm
isotopic) to the same origin in SPM, such that pulling up the resulting
images in "Check Reg" accords good overlap, does this pose a problem for
subsequent transformation? I suspect so, but just wanted to double-check.
Our current scheme is to segment the anatomical, then warp the grey segment
to a grey atlas space. The resulting warp transform parameters are then
applied to the functionals. Without prior co-registration, I would think
that the transform parameters based upon 1mm isotopic could not be directly
applied to 3.75mm functionals without serious error.
Since SPM co-registration is causing us problems with some subjects and our
functionals and anatomicals are reoriented and resliced to a common origin,
is there a way to mathematically change the 1mm-derived warp transformation
parameters to fit the 3.75mm functionals? Essentially, we would like to
skip co-registration while still correcting for voxel dimension differences
and using this step-wise warping approach.
Regards to all,
Jeff Browndyke
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