Wow, that’s a terrible correlation between two putative measures of head size.

What does the scatterplot of FS’s “eTIV” vs “SupraTentorialVol” look like? The latter is based on the surfaces, so a scatterplot of the two can be a good way to identify cases where the talairach.xfm file (from which “eTIV” is derived) isn’t very accurate.

cheers, -MH

-- Michael Harms, Ph.D. ----------------------------------------------------------- Conte Center for the Neuroscience of Mental Disorders Washington University School of Medicine Department of Psychiatry, Box 8134 660 South Euclid Ave. Tel: 314-747-6173 St. Louis, MO 63110 Email: mharms@wustl.edu

From: <freesurfer-bounces@nmr.mgh.harvard.edumailto:freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of Jeffrey Crawford <jcrawf29@jhmi.edumailto:jcrawf29@jhmi.edu> Reply-To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edumailto:freesurfer@nmr.mgh.harvard.edu> Date: Friday, December 16, 2016 at 11:56 AM To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edumailto:freesurfer@nmr.mgh.harvard.edu> Subject: [Freesurfer] V6 FS eTICV versus CAT12 TICV with Small Heads

Hello everyone!

I have some questions about FS eTICV. I read on the Wiki that eTICV is not the best measure of ICV and saw the same from other articles. The alternative I decided on was measuring the TICV using CAT12 from SPM. I decided to do a scatterplot of the eTICV from FS V6 and TICV from CAT12 to see how they match each other on measurment. FS is the variable on the Y-axis and CAT12 is the variable on the X-axis. If we assume that CAT12 is more accurate than FS, then it looks as though the FS begins to become more inaccurate as the head size gets smaller.

[cid:image001.png@01D2579B.8A615E30]

So here are my questions:

1. Is my interpretation of this scatterplot correct?

2. Does FS generally have more difficulty measuring smaller heads? If so, then why?

3. Is it more advised for me to use the CAT12 TICV measure as a covariate in my future analysis? Or maybe some other program that I don’t know about?

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