Jesper,
Smacked on the fingers by a reviewer. Hmm....
IMHO the state of the field, in this regard, is such a mess it would hardly
seem possible to say anything but Talairachish or to paraphrase Prince (we
could just call it "T" for the anatomic space formerly known as Talairach).
As you point out the EPI template is not the same as the T1 template.
Although papers routinely report coordinates as "Talairach" this can mean
anything from 1) MNI coordinates but the authors misunderstand this to be
Talairach, 2) MNI transformed to Talairach using Matthew Brett's
approximately correct algorithm (not a 'diss to Matthew as approximate
refers to the transformation not the algorithm and he has said it is just
an approximation), 3) a lab's own version of normalization based on either
their own algorithms or a local template, which is an approximation to the
approximation of some other template, etc.
I think coordinates are "understood" to be an approximation and any attempt
to use those coordinates in a meta-analysis or as a reference should be
given wide latitude as to localization. Although there has been discussion
over the years about probabilistic atlases these do not seem to be in
widespread use. Furthermore even if an atlas was available how would one
deal with cases in which local templates are generated?
Sorry to provide more questions than answers,
Puss Darren
At 06:28 AM 9/21/2005, Jesper Andersson wrote:
>Dear John and others,
>
>I have a question regarding how we should describe the space instantiated
>by the SPM2 EPI template. When using one of the MNI templates it seems to
>be quite accepted to write something like "The Talairach space as defined
>by the MNI template". How should we refer to the space that is defined by
>the EPI template? Correct me if I'm wrong, but isn't this template based
>on a large handful (10-15?) subjects scanned with the old 2T FIL scanner,
>and certainly can't be referred to as the MNI space.
>
>We tried to pass it off as "approximate Talairach space", but got smacked
>on our fingers by the reviewer for being too inprecise. Any thoughts anyone?
>
>Puss Jesper
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Darren R. Gitelman, M.D.
Cognitive Neurology and Alzheimer¹s Disease Center
Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611
Voice: (312) 908-9023 Fax: (312) 908-8789
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