Greetings everyone,
I'm new to the list, so I hope this is a proper posting; I've looked thru
the archives and haven't found any explicit answers to my questions.
It appears to me that the origin on the MNI template (any of them, 152, 305,
Colin) is not on the Anterior Commissure; and it seems that others agree:
http://www.mrc-cbu.cam.ac.uk/Imaging/Common/mnispace.shtml
"...the coordinates are reported in terms of the system that Talairach
developed, with coordinate 0,0,0 being at the anterior commissure (AC), and
with the anterior / posterior commissural line (AC/PC line) defining the the
plane where z = 0. (In fact the AC is not exactly at 0,0,0 in the MNI brain,
but about 4mm below...)"
My first question is: Why is the origin off, or how was the origin determined?
My second question is: Do people make a correction for this when reporting
MNI coordinates? I would like to begin reporting MNI coordinates, but I'm a
little troubled by the fact that the default coordinate values reflect an
incorrect AC-relative anatomical location.
My last question is: Does the non-linear formula provided on the webpage
indicated above take into account the differences in origins between the 2
reference brains? Or better yet, does anyone have suggestions as to how to
handle coordinate reporting between the 2 reference brains?
Suppose that you wanted like to provide tables of both coordinate systems.
Perhaps one could talairach the MNI brain and extract those as talairach
coordinates. One could provide the MNI coordinates from SPM also but add a
footnote that the coordinate do not reflect an AC-origin.
Much thanks to all, cheers
-christopher
--
J. Christopher May
University of Pittsburgh
Dept. of Psychology
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