The voxel sizes are not an issue and have been dealt with many times
on the mailing list. It is common to have a negative voxel size for
images in SPM. It simply indicates that the indices of the voxels
have a left-handed orientation and that a flipping of the coordinate
system is used to enable reporting of coordinates in MNI space.
Providing you just use NIfTI compliant software (and don't try to do
anything "clever", such as setting the voxel sizes to be positive
without flipping the data), then things should be OK.
As for the missing scans, I don't really have a good explanation. I
would suggest looking for any error messages, and maybe seeing if
there is some pattern that explains which processed scans are missing.
Maybe you filled up your disk or exceeded your quota.
Best regards,
-John
On 18 June 2012 12:36, Valentino Pironti <[log in to unmask]> wrote:
> Dear All,
> I just normalized my EPI images using dartel tool. Strangely the voxel size now is -1.5x1.5x1.5. I am puzzled to see there is a minus. Also instead to have the original 691 volumes I have now 505.
> Do you have any idea why this is happening?
>
> Looking forward to hearing from you
> Best wishes,
> Valentino
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