Why is a small # a problem? It simply represents the fraction of the total intracranial volume occupied by that structure.
cheers Bruce On Thu, 24 Oct 2013, Dorian P. wrote:
Thank you Douglas. The eTIV has values like 1543825. Dividing ROIs by this value would create very small values.
Is there a standard TIV (i.e. from the talairach brain) to use as denominator for creating a ratio value? Or what is the best way to create a reasonable factor (i.e. 0.7-1.3) to correct/normalize roi volumes?
Dorian
2013/10/24 Douglas N Greve greve@nmr.mgh.harvard.edu
On 10/24/2013 10:37 AM, Dorian P. wrote: > Dear all, > > Excuse if these are simple questions but I am a bit confused on the > significance of the volume measures. > > 1. Are the volumes of ROIs calculated after normalization?No, everything is done in native space.
- If volumes are calculated post-normalization, why is correction
for
eTIV needed?
- What is the quickest way to correct for eTIV?
Not sure what you mean by the "quickest". Usually the ROI volumes are divided by the eTIV or the eTIV is used as a regressor doug
Thank you. Dorian TJU
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