Dear Iven,
If you actually want the Intra*Cranial* Volume then you should
not use these measures. They are all based on the *brain*
volume and not the skull cavity. So if your brain is shrinking
due to atrophy and you normalised by these measures then
you'd get a constant (and hence remove all detectable atrophy).
Now that might not be a factor in your study, so I don't know if
it is a big issue or not, as these measures can give you a whole
brain volume that is a perfectly good normalisation for say
subcortical volumes. However, for looking at whole-brain atrophy
it is not useful.
The alternative is to use the vscaling value (saved in report.sienax)
as this is a volume scaling that *is* based on the skull. You can take
the ICV of the standard space template and divide it by this number
to get an estimate of the ICV of that subject. It isn't a highly accurate
estimate of the ICV but it is *not* based on the brain volume and so is
useful for normalising brain volumes and controlling for head size.
It is how sienax converts individual volumes to normalised volumes.
I hope this helps.
All the best,
Mark
On 12 Jul 2011, at 10:03, Iven Fellhauer wrote:
> Dear all,
>
> i have problems with the interpretation of the sienax results (brain volume). I execute the command with the following options: sienax imagename -B "-R -S -B" -r
>
> I get the following results:
>
> tissue volume unnormalised-volume
> pgrey 523846.13 311996.37 (peripheral grey)
> vcsf 107070.20 63769.71 (ventricular CSF)
> GREY 666438.50 396922.65
> WHITE 910137.07 542066.54
> BRAIN 1576575.57 938989.19
>
> The brain volume is in this case only the volume of GREY and WHITE. Is the pgrey volume a part of the GREY volume? I want to calculate the total ICV. Do I sum up the four tissue types? Sum up only BRAIN (GREY and WHITE) volume and vcsf volume?
>
> Best regards,
>
> Iven Fellhauer
>
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