Hi Chris,
just one more point to consider:
> I have recently been attempting to perform a simple regression analysis
> on a set of fa maps from several children. The b0 images were normalized to
> the EPI template of spm 99 and this transformation was applied to the
> corresponding fa maps (all having values for each voxel between 0 and 1).
I think this is reasonable. However, remember that you are looking at
kid's data, which of course is inherently different from adult data. The
difference to the adult template is increasing with the age difference.
In other words, if you are looking at very young kids, this alone may
screw up your analysis.
> voxels scattered across the brain (p < 0.05), with some of the strongest
> correlation occuring in the noise outside the brain.
This is why I thought it may be a problem. While overall brain size does
not change dramatically after a certain age (say, 5-6 years), non-brain
tissue does. The correlation with age you see outside of the brain may
well be an artifact of changes in non-brain tissue. You can ignore that,
since I take it you have no a priori hypothesis on that :) However,
remember that brain masking should be enabled during normalization of
pediatric images since otherwise the non-brain tissue will interfere.
> Is there a better method of normalizing DTI data?
I do not know if this is better, but you could normalize your data based
on a T1-dataset (if you have one). Coregister DTI and, say, segmented
native space white matter, and normalize the white matter to a
(preferrably pediatric) white matter a priori map. This will ignore the
EPI-distortions (which is worse than in your procedure) but may be
better in terms of the contribution of non-brain tissue.
> Thank you for your assistance. My apologies if my questions are overly
> simple - I am relatively new to SPM.
Aren't we all...
Best of luck,
Marko
--
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Marko Wilke (Dr.med./M.D.)
[log in to unmask]
Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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