Dear SPM users
I tried to calculate the volumes of the GM/WM/CSF segments.
1. I tried it with the N vox value by multiplying the n vox value
with the whole boundingbox volume (customised) and divide them by
the determinant from the affine registration.
e.g. for GM (0.1996 * 4.985 liters)/0.4375 = 2.274 liters????
In my opinion, there must be a error in the matrix from which
I have calculated the determinant.
The matrix from the affine registration looks like this
-0.984652397319312 -0.01601706430295645 -0.002118768348360404
201.0153957960537
0.009009810452331476 -0.40483913770032703 -0.7711390007527495
192.507048140182
-9.784690721137174E-4 -0.48843170079109083 0.16698600269962102
100.13643261690986
0.0 0.0 0.0
1.0
the determinant of this matrix is 0.4375 which seems very strange
what happens with that matrix???
what would it mean when the determinant becomes negative?
2. To get segment volumes I have also tried the following function from John
V = spm_vol(spm_get(1,'*_seg*.img'));
vol = 0;
for i=1:V.dim(3),
img = spm_slice_vol(V,spm_matrix([0 0 i]),V.dim(1:2),0);
vol = vol + sum(img(:));
end;
fprintf('%g voxels, %g litres\n', vol, vol*det(V.mat(1:3,1:3))*1e-6);
for GM: 838197 voxels, -0.838197 litres
for WM: 553626 voxels, -0.553626 litres
for CSF: 1.01618e+006 voxels, -1.01618 litres
why there is a negative foresign?
it is not plausible that the whole brain volume (GM/WM/CSF) is about 2.397
liters!!!
3. Is there an other way to get GM/WM/CSF volumes from normalised MR images?
Thanks a lot in advance
best regard
Juergen
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Juergen Haenggi, Ph.D. student
Division of Psychiatry Research
Psychiatric University Hospital
University of Zurich, Switzerland
P.O. Box 1931
Lenggstrasse 31, 8032 Zurich
0041 44 384 26 10 (office phone)
0041 76 445 86 84 (mobile phone)
0041 44 384 26 86 (fax)
H 115 (office room number)
[log in to unmask] (division email)
http://www.dpr.unizh.ch/ (division website)
http://www.juergenhaenggi.ch (private website)
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