I am using spm12 for some of my analysis. I create images in subject's native space and firstly want to write them as Nifti images. So I use spm_write_vol. It's strange that the nifti image that I write is not the same as the image that I feed in the function!

Can anyone point out the mistake I am making or the solution they have.

Here is the code:

V = spm_vol(binaryMaskFile);% binaryMaskFile is one of the subject's files, e.g. their mask.nii created after the first level stats

% now I change the name of the file

V.fname = 'test.nii';

% generate random data

data = randn(96,96,72);

% save it

spm_write_vol(V,data);

% read in the written volume and find the difference

diffVol = spm_read_vols(spm_vol('test.nii')) - data;

max(diffVol(:)) % I get 4.4715 in one example