Hi Jesper:
I am well and I hope you are too.
Thanks for your answer. The whole issue of modulation and covarying for brain size is a difficult one. What happens if there is atrophy?
If we imagine that a brain is smaller because of added atrophy then wouldn't correcting by just affine scaling the brain negate this effect, i.e., it would make the brain bigger to fit the template but I don't think scaling alone could differentiate a normal small brain from a mildly shrunken brain.
Correcting by total intracranial volume (assuming that G+W+CSF is a good approximation to the original TIV) would not be affected by atrophy since it assumes that the brain should have originally filled out the intracranial space. Thus it should be more sensitive to atrophy in addition to any difference in brain size.
Darren.
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