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Hi, The dimensions 1-3 are x,y,z in space, and 4 is time. The pixdims are the sizes of these dimensions (mm in x,y,z and seconds for time). If your image doesn't use dimensions higher than these then it is fine. In FSL we never actually use the pixdim4 value, as it has not been reliable in the past. If the qform_name is Unknown and the qform_code is 0 (the former is completely set by the latter) then it just means that there is no useful information in the qform and it should be ignored. If the sform is set validly (sform_code is non-zero) then you have spatial information and orientation encoded which is useful. If the qform_code is non-zero and so is the sform_code and the two transforms are very different then this is unusual, although only problematic if the determinants of the two matrices have opposite signs. You can find more information on qforms and sforms in the excellent documentation embedded in the $FSLDIR/src/niftiio/nifti1.h file. All the best, Mark On 6 Apr 2009, at 21:45, Martin M Monti wrote: > Hi, I'm comparing 2 ways of getting/transforming dicom files, and > there seem to be some differences in the header of the two final 4D > images. I don't know the meaning of some of these fields though, > could I get a little input please? > > The two 4D files differ mainly in the following fields > > PIXDIM[4-->7] Being 1,0,0,0 in one case and 2,1,1,1 in the other. > (there is also a little truncation in the X,Y,Z pixdim e.g. 3.00000 > v 3.0000014305) > qform_name Unknown in one case vs Scanner anat > qform_code 0 vs 1 > (the two sform fields are identical though) > qto_xyz[1-->3] are substantially different > qform_'x,y,z'orient are all different (although they appear > identical in FSLVIEW) > one of the two loses the "description" field information. > > The basic problem is that, not understanding all of these fields I'm > not sure if this is a non-problem or if it is! > > thoughts? > > martin >