> I have reoriented MR images with SPM2 and the warning: "Shears involved"
> occured. In the SPM archives, I found one email concerning that problem
> in SPM99:
> http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind04&L=SPM&P=R377607&I=-3
>
> My question is: If shears are involved in reorientation but the following
> normalization works well then I could ignore this warning, right?
You can probably ignore the warning if the shears are very small. The
regularistion used by the spatial normalisation does tend to bias the
solution a little (so any incorrect information in the original headers or
mat files about voxel sizes, shears etc can in principle lead to
systematically different spatially normalised images), but I don't imagine
that the effect is very large.
Best regards,
-John
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