Re: [Freesurfer] Volumes in native or normalized space, and eTIV

What is the problem with small values? You can multiply them by 100 to give you percent of brain. Or multiply them by 1000 to give you tenths of percents

doug

On 10/24/2013 12:58 PM, 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 mailto: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.
>
> 2. If volumes are calculated post-normalization, why is
correction for
> eTIV needed?
>
> 3. 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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