Please see below:
On 16 September 2016 at 00:52, Seung Gul Kang <sg.kang...@gmail.com> wrote:
> Dear Freesurfer experts,
> 1. I want to compare the area and/or areapial between two groups in qdec
> I think that the eTIV or total surface area should be used as a covariate.
> Which is more appropriate between eTIV and total surface area?
Using and not using a global measurement tell each different things, and a
suggestion (I'd say a recommendation) is to run both ways, i.e., with and
without global area as nuisance, and use the results from both when reading
and interpreting the findings.
Regarding ICV, it has substantial correlation with area and it can be
included as nuisance in the same model in which global area is included. It
is not a problem that they are correlated as both go as nuisance in the
> 2. Is there any guideline or rule for the smoothing in the thickness,
> area, and volume comparison?
> How about the smoothing=5?
There is no specific rule. We have investigated with as little as 10 mm on
the sphere and the results of the default area processing in FS become
virtually indistinguishable from the exact method that we proposed in 2012.
Although we did not investigate 5mm, we did look also into the ic5 and ic3
resolutions and, particularly for the ic5 (that has vertices about 4 times
farther from each other compared to the default ic7), 10 mm smoothing is
fine, suggesting that 5 mm would likewise lead to similar results for the
ic7. A summary of these findings is in a manuscript that we have just
uploaded to bioRxiv: http://dx.doi.org/10.1101/074666 (for this particular
question the SI is probably more important).
All the best,
> Thank you.
> *Seung Gul Kang, M.D., Ph.D. *
> *Psychiatrist, Associate Professor*; Department of Psychiatry, Gil
> Medical Center, Gachon University, School of Medicine, 21, Namdong-daero
> 774 beon-gil, Namdong-gu, Incheon, 21565, South Korea
> *Research scholar*; Sleep Disorders Clinical Research Program, Department
> of Psychiatry, Massachusetts General Hospital, Harvard Medical School, 1
> Bowdoin Square, 9th floor, Boston, MA 02114, USA
> *Collaboration researcher*; Division of Sleep & Circadian Disorders,
> Brigham & Women's Hospital, Harvard Medical School, 221 Longwood Ave,
> Boston MA 02115
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