Hi Gari, this is expected because of the way that we estimate intracranial volume (based on registration to talairach space). But even in theory, you are only changing what is brain and not what is skull so eICV should not change.
doug

On 11/28/13 11:52 AM, Garikoitz Lerma-Usabiaga wrote:

Hi list,
I obtained cortical thickness and volumetric results before and after correcting them for defects.

I just did some wm edits and mostly controls points in the top of the head (some subjects had less signal so I put control points in order to allow for a good surface reconstructions).

When comparing the values:

EXPECTED

- Same volume values for subcortical structures, i.e.: same thalamic volume before and after

- Different CT values in the edited areas and only for the edited subjects, i.e.: lh_paracentral_thickness

- Different volumetric values only for the edited subjects in, for example: lhCortexVol, CortexVol, CorticalWhiteMatterVol

NOT EXPECTED

- Same values for EstimatedTotalIntraCranialVol.

I was controlling thalamic values with the eTIV, (using Raz 2005's formula)*, but before and after correcting almost half of the subjects, obviously, I obtain the same results.

- Should I use a different value other than the eTIV?

- Is normal that the eTIV doesn't change but the rest of the values are changing? The brain is definitely different after the control points, it grows a little bit upwards.

any information on this will be appreciated!

thanks,

Gari

PS:

* Volume (adj) = Vol(rawi)-b*(ICV(i)-mean ICV), where b is the slope of regression of an ROI volume on ICV
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