Thanks for the info Doug. My comments below.
On Mar 10, 2004, at 1:19 PM, Doug Greve wrote:
Ray Fix wrote:
Hello List,
Question 1:
Where does the sample average7 come from? I searched through the
manuals, googled, searched around a little but was unable to find any
info. For example, is this the averaged brains of 7 male subjects in
there 40s?
It's a 7th order icosahedron (163842 vertices). I think the orig
coordinates are supposed to be talariach coordinates averaged over some
subjects (but it does not overlay very well on the talairach brain).
Bruce can give you more details.
Wow. Interesting. I never would have guessed. Thanks.
(Aside: Let's see ... 20 * 7^2 is only 980 faces so I am not sure
where all of those vertices are coming from. Probably some different
definition of order 7.)
Question 2:
My plan is to create my own ICBM labels using average7 and then apply
them via mri_label2label to two groups of subjects (which happen to be
pediatric data). Does this stand any chance of working? I would be
very interested if their are any other approaches you recommend.
It all depends on how you're going to map the labels. What coordinate
system are the ICBM labels in?
I guess I have to look into this more. Any suggestion on what
coordinate system should I use? Perhaps talairach. To be honest my
only knowledge about labels comes from looking at the recon-all script
and the one Faq-O-Matic page.
I was told that the labels in FreeSurfer are sort of non-standard. The
whole motivation for reporting results in terms of ICBM labels is to
make the results meaningful a large audience without getting into a
huge discussion about label definitions.
That said, it is likely that deep consideration was given in coming up
with the current default labeling scheme. Maybe someone would like to
refute my assertion that they are non-standard. It is something I
would like to learn more about but am not sure how to find out.
Thank you very much for your comments.
Ray Fix
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