If you have the RAS in a vector: v = [R A S 1]';
And the talairach.xfm matrix X, then MNI talairach cooridnates are:
vMNI = X*v;
These can be computed to something closer to true talairach coords using
the attached mfile, originally from Matthew Brett.
doug
Ajay Pillai wrote:
>
> Hello all,
>
> Does any one have a matlab routine to convert given coordinates from RAS
> to talarach space.
>
> If not atleas give an indication of how to do it?
>
> Ajay
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--
Douglas N. Greve, Ph.D.
MGH-NMR Center
[EMAIL PROTECTED]
Phone Number: 617-724-2358
Fax: 617-726-7422
function outpoints = mni2tal(inpoints)
% Converts coordinates from MNI brain to best guess
% for equivalent Talairach coordinates
% FORMAT outpoints = mni2tal(inpoints)
% Where inpoints is N by 3 or 3 by N matrix of coordinates
% (N being the number of points)
% outpoints is the coordinate matrix with Talairach points
% Matthew Brett 10/8/99
dimdim = find(size(inpoints) == 3);
if isempty(dimdim)
error('input must be a N by 3 or 3 by N matrix')
end
if dimdim == 2
inpoints = inpoints'; %'
end
% Transformation matrices, different zooms above/below AC
upT = spm_matrix([0 0 0 0.05 0 0 0.99 0.97 0.92]);
downT = spm_matrix([0 0 0 0.05 0 0 0.99 0.97 0.84]);
tmp = inpoints(3,:)<0; % 1 if below AC
inpoints = [inpoints; ones(1, size(inpoints, 2))];
inpoints(:, tmp) = downT * inpoints(:, tmp);
inpoints(:, ~tmp) = upT * inpoints(:, ~tmp);
outpoints = inpoints(1:3, :);
if dimdim == 2
outpoints = outpoints'; %'
end
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