Hello,
I am attempting to do VBM/TBM analysis using the method outlined below,
which I found in the list archives, and I have a couple of questions.
> “ 1) Coregister early and late images together (no reslicing).
> 2) High-dimensional registration of early and late images.
> Assume that the late image is the source, and the early
> image is the reference (although it could be done the other
> way around - or ideally could be done in a symmetric way).
> - Deformations toolbox.
> 3) Write out the Jacobian determinants from the resulting warp.
> - Deformations toolbox.
> 4) Apply the warp to the late image.
> - Deformations toolbox.
> 5) Do a "soft-mean" of the images (possibly including some global
> scaling). This can be done with ImCalc: (i1+i2)./(eps + (i1~=0) +
> (i2~=0)) 6) Spatially normalise this mean image (possibly via a
> segmentation
> step, as in "optimised VBM").
> 7) Segment this spatially normalised mean image.
> 8) Apply the spatial normalisation parameters to the Jacobian determinants.
> 9) Use ImCalc, select the normalised GM, and the spatially normalised
> Jacobian determinants, and evaluate the following expression: i1.*(i2-1)
> 10) Modulate this result by the volume changes from the spatial
> normalisation. 11) Smooth the results by about 12mm.
> 12) Do some stats on these.”
>
I apologize if this has already been asked, but I could not find answers in the mail list archives.
My questions are:
1) In step (9) above, what is the purpose for doing (i2-1), instead of, e.g. log(i2)? Wouldn't log(i2) be more appropriate here?
2) Also in step (9) above, does multiplying by the GM probability at each voxel potentially confound the measure of interest, the Jacobian determinant?
Thanks in advance for any help,
Matt Senjem.
--
Matthew L. Senjem
Analyst Programmer - Imaging Systems
Mayo Clinic and Foundation
Mail Code: RO_CE_09_IMAGING
200 First St. SW
Rochester, MN 55901
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Fax: 507-284-9778
Phone: 507-538-0764
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