I think I can help you out with these ones.
> Hi all,
> I'm trying to solve some doubts about mat files and similar..so I have a few
> questions
>
> 1) What is the difference (if any) between matrix V.mat stored in the V
> structure obtained from
> V=spm_vol(spm_get(1,'*img','filename'))
> and the one stored in the filename.mat file.?
None. However, if the filename.mat file does not exist, the matrix
obtained with spm_vol contains a transformation by default.
> 2) let's say I have an original image "analyze.img" which I realign &
> reslice to some other image getting a "ranalyze.img" file
> Their mat files store the same matrix. Now since ranalyze was produced
> by realigning and reslicing I would expect that file to be a transformed
> version through the realignment parameters of the original "analyze.img"
> file. is that true?
> do they have the same mat file, cause they use the same transformation
> between voxel space and world space?
I think you are a little bit confused here. You have an original image
"analyze.img" with a certain matrix "T.mat". If to that you apply a
certain number of transformations you can: 1) Save the same image with
another name ( i.e. "ranalyze.img" ) and another transformation matrix
"T2.mat" that will take into account T.mat AND the new transformations
(the most common thing to do to avoid resampling an image each time
you apply a transformation). 2) Save the new image with a default
transformation matrix.
> 3) When loading a volume with
>
> VOLUME=spm_read_vols(spm_vol(spm_get(1,'*img','filename')))
> does that just load the content of raw .img file?
Yes (loads the contents of all the input images)
>does that take into
> account the information in the mat file associated with the image, or the
> matrix V.mat in the V structure (if there is any difference)?
No
> so when loading the volumes with
> VOLUME=spm_read_vols(spm_vol(spm_get(1,'*img','filename')))
> do volumes for the file analyze.img and ranalyze.img differ cause the actual
> values stored in correspondent voxels differ?
It depends on how you saved you images.
> but still do they have the same .mat file cuase they use the same
> transformation to get from voxel space to world space?
It depends on how you saved you images (bis)
> thanks in advance
I hope I have been able you help you.
Rafael
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