Hello!
Many thanks for Matthieu's reply.
I still don't understand what‘voxvol = det(V(1).mat)/100^3;’means. Why the
volume is equal to ' tot*voxvol ', not 'tot/100^3'? What does V.mat
represent?
Any suggestion will be appreciated.
I've read the script of spm_global. It only says to calculate the mean value
but not the volume. How does it calculate the volume then?
Also the question in my previous email. 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?
shan
-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On
Behalf Of Matthieu Brucher
Sent: 02 March 2005 08:46
To: [log in to unmask]
Subject: Re: [SPM] modulated GM in VBM
Shan Shen wrote:
> Hello! Everyone!
>
>
>
> 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
>
>
>
> Many thanks!
>
>
>
>
>
>
>
>
>
> Dr shan shen
>
> Department of Psychology
>
> University of Surrey
>
> Guildford GU2 7XH
>
> UK
>
>
>
|