Shan Shen wrote:
> Hello! Everyone!
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> I want to compute the volume of gray matter in original images. I found
> following codes in previous emails from John, but I don’t understand
> what ‘voxvol = det(V(1).mat)/100^3;’ calculates. Since tot represents
> the sum of voxel intensities in modulated gray matter images, the total
> volume should be the sum multiplying by the product of the voxel size.
> If the modulated image has a voxel size as 1mmx1mmx1mm, is the product
> of the voxel size is equal to 1?
yes, 1mm³, but in the formula, it is in liters...
If you have the modulated GM image, you can use spm_global to have the
mean voxel value and then the global GM volume too - well, as far I as
know ;) -
> If I’d like to compute the global intracranial volume, shall I do all
> the same but only replace the modulated gray matter image to the
> modulated brain image?
> V = spm_vol(spm_get(1,'*.img'))
>
> tot = 0;
>
> for i=1:V(1).dim(3),
>
> img = spm_slice_vol(V(1),spm_matrix([0 0 i]),V(1).dim(1:2),0);
>
> tot = tot + sum(img(:));
>
> end;
>
> voxvol = det(V(1).mat)/100^3; % volume of a voxel, in litres
>
> tot = tot; % integral of voxel intensities
>
> tot*voxvol
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>
> Many thanks!
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> Dr shan shen
>
> Department of Psychology
>
> University of Surrey
>
> Guildford GU2 7XH
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> UK
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