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Subject:

Re: how to determine voxel size in SPM5 ?

From:

Istvan Akos Morocz <[log in to unmask]>

Reply-To:

Istvan Akos Morocz <[log in to unmask]>

Date:

Mon, 11 Feb 2008 12:59:45 -0500

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 ```thank you, John, that was very helpful. if everything would be so easy in life... bye, pisti ----- www.pistikem.org [log in to unmask] On Mon, 11 Feb 2008, John Ashburner wrote: > > Here is a snippet of MATLAB code that may be informative: > >>> M = [-1.9945 -0.0499 -0.1399 70.8144 > -0.0891 1.9090 0.5896 -63.5382 > -0.1188 -0.5942 1.9060 -60.7934 > 0 0 0 1.0000]; >>> >>> sqrt(sum(M(1:3,1:3).^2)) > > ans = > > 2.0000 2.0000 2.0000 > >>> svd(M(1:3,1:3)) > > ans = > > 2.0000 > 2.0000 > 2.0000 > >>> > > And for figuring out if there is a flip, the following gives the volume of a > voxel: > >>> det(M(1:3,1:3)) > > ans = > > -8.0000 > > > Best regards, > -John > > On Monday 11 February 2008 06:01, Istvan Akos Morocz wrote: >> dear SPM list, >> >> here a quite silly question: how can one determine the correct voxel >> size in a given MRI volume in SPM5, for example by using spm_vol.m >> (like previously with SPM2). V.mat doesn't lead anymore to the >> desired information., like in the past by computing : >> >> myVox = abs([ V.mat( 1, 1) V.mat( 2, 2) V.mat( 3, 3) ]) ; >> >> for example, i expect to deal with 2x2x2mm, but Y.mat instead gives: >> >> -1.9945 -0.0499 -0.1399 70.8144 >> -0.0891 1.9090 0.5896 -63.5382 >> -0.1188 -0.5942 1.9060 -60.7934 >> 0 0 0 1.0000 >> >> that's now after rotation i guess (as no mat files anymore). looked >> through the codes and also in the archives - w/o prevail. >> >> >> thanks in advance, bye, >> >> pisti >> >> >> ----- >> www.pistikem.org >> [log in to unmask] ```

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