Dear Dr Doug,

Thank you very much for the detailed answer! I like very much the idea to adjust surface area by eTIV. Kindly I have the following follow-up questions and I highly appreciate your input:

1. Can this adjustment be done in Qdec by including eTIV a covariate or nauisance factor?

2. The individual ROIs for an external statistical software (e.g. SPSS): Can the adjustment be done by measuring the percent volume or surface relative to eTIV then make the comparison between the groups ( i.e. adjusted ROI volume = ROI volume*100 / eTIV)

3. Which approach is recommended: Adjust volume or surface area by adding eTIV as a confounding factor in surface based analysis (e.g. in Qdec) or by comparing the adjusted volume and surface area for the ROIs in SPSS

Regards,

John

-----Original Message-----

From: freesurfer-bounces@nmr.mgh.harvard.edu [mailto:freesurfer-bounces@nmr.mgh.harvard.edu] On Behalf Of Douglas N Greve

Sent: Monday, May 8, 2017 5:55 PM

To: freesurfer@nmr.mgh.harvard.edu

Subject: Re: [Freesurfer] Surface area

Yes, I would recommend making some kind of adjustment. As with all such adjustments, the adjustment you choose will dictate how you interpret the results (eg, a eTIV adjustment means something different that an adjustment for whole brain volume). For surface area, I usually adjust the eTIV. It might seem strange to adjust surface area by a volume, but for a highly folded surface, the surface area actually goes up linearly with the volume. But adjusting by total surface area is ok too.

On 05/08/2017 02:29 PM, John Anderson wrote:

> Dear Freesurfer experts,

> I know that the grey or white matter volume measures for the ROIs

> reported in "wmparc.mgz" can be adjusted for the total intracranial

> volume.... Is is correct to do the same for surfaces? I mean can the

> surface of an ROI (e.g. precentral) be adjusted to total surface area?

> If yes, this must be done for total white right or total left

> depending on the ROI if it is left or right, correct?

> Thank you

> John

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