Dear John,
Interesting, but it would seem to me that this doesn't explain why they are so much crisper than the old a priori maps?
All the best, A
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]On
Behalf Of Ashburner John (PSYCHOLOGY)
Sent: 20 November 2006 12:51
To: [log in to unmask]
Subject: Re: [SPM] ICBM452 T1 apriori maps in VBM5 toolbox
There's a bit more info in spm_templates.man ...
%
_______________________________________________________________________
% /TPM/ DIRECTORY
% Contains Tissue probability maps provided by the International
% Consortium for Brain Mapping, John C. Mazziotta and Arthur W. Toga.
% http://www.loni.ucla.edu/ICBM/ICBM_TissueProb.html
%
% The 452 subjects were between 20 and 32 years old, and were
% approximately 50-50 male/female.
%
% The original datasets were affine transformed to match the MNI152
% space (by affine registration of the grey matter with the grey
% matter image in the apriori directory: smosrc=8, smoref=0,
% regtype=mni, cutoff=Inf).
%
_______________________________________________________________________
All I know about the original data is the stuff on the ICBM web site...
ICBM Tissue Probabilisitic Atlases
All 452 ICBM subject T1-weighted scans were aligned with the atlas
space, corrected for scan inhomogenities, and classified into gray
matter, white matter, and cerebrospinal fluid. The 452 tissue maps were
separated into their separate components and each component was averaged
in atlas space across the subjects to create the probability fields for
each tissue type. These fields represent the likelihood of finding gray
matter, white matter,or cerebrospinal fluid at a specified position for
a subject that has been linearly aligned to the atlas space.
Best regards,
-John
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
On Behalf Of Ged Ridgway
Sent: Friday, November 17, 2006 1:31 PM
To: [log in to unmask]
Subject: Re: [SPM] ICBM452 T1 apriori maps in VBM5 toolbox
Hi Juergen,
Seems I spoke too soon...
Juergen Haenggi wrote:
> (under the Custom option) there is following statement:
>
> The original data are derived from 452 T1-weighted
> scans, which were aligned with an atlas space,
> corrected for scan inhomogeneities, and classified
> into grey matter, white matter and cerebrospinal
> fluid. These data were then affine registered to the
> MNI space and downsampled to 2mm resolution.
Right, I was just thinking about the template for some reason... So I
am pretty certain that the spm5/templates/T1.nii is the MNI/ICBM152
template, not the 452 version, but...
The TPMs in SPM5 might well come from the ICBM452 rather than 152,
sorry about my confusion here. Since the SPM5 TPMs are quite sharp,
I'm guessing that they are the 5th order polynomial warped version
that you spoke of (but it's just a guess, I should really wait for JA
to reply...)
> Do you have any idea what the difference between the
> a priori maps located in the tpm and that located
> in the apriori folder is?
The apriori folder contains the much smoother SPM2 priors. What I
don't know is whether these are smoother due to using the
affine-registered ICBM452 version, or maybe the 152 version, or
whether they were simply Gaussian smoothed versions of the sharper
SPM5 TPMs.
Hopefully John Ashburner will clear up this mess that I have gotten us
into... ;-)
Ged.
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