It also appears (http://imaging.mrc-cbu.cam.ac.uk/imaging/MniTalairach#head-e3c85d11e6224727ab9a5a7d65ec8b1d17b3f4be) that the MNI brain was 269 males and 66 females... which explains why it might be bigger than a true random sample of the population, but still doesn't explain why ALL of my males have smaller skulls than that brain.
I don't mean to press the issue, I am just curious. Thank you for your help.
-Daniel
-----Original Message-----
From: FSL - FMRIB's Software Library on behalf of Steve Smith
Sent: Thu 6/11/2009 10:47 AM
To: [log in to unmask]
Subject: Re: [FSL] All sienax vscaling factors > 1?
Yes - this is known to happen - I think it's because of a slight bias
in the way that the MNI152 was constructed (or the choice of subjects)
- but I'm afraid I can't remember the details.......maybe Andrew Janke
can remind us?
Your FOV shouldn't make any difference to this - but if your scanner
calibration was a little bit off that might have contributed further
to this result.
Cheers, Steve.
On 11 Jun 2009, at 09:45, Daniel Schwartz wrote:
> Hi,
>
> I've just dumped the VSCALING factors for all 105 subjects in my
> sienax analysis. It appears that ALL of the subjects in the study
> have smaller skulls than the MNI brain. This seems statistically
> improbable. Any ideas about how this could've happened? Not all of
> my subjects had the same T1 FOV/Imaging matrix size, if that might
> be a clue... but that makes it MORE confusing for me. Thanks in
> advance for any advice/insight.
>
> -Daniel
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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