On Wed, 17 Aug 2005 20:54:11 +0200, Diana Tordesillas
<[log in to unmask]> wrote:
>
>Dear SPM users and developers,
>
> Before I normalize I would like to move the AC to the middle of the
> image (using display and reorient images). My question is whether the
> normalization process should begin with this transformed image (that it
> has some interpolation error on it) or whether it can read the
> transformation file (image.mat) so I could start with the raw image.
I'm not sure I understand the question.
Note that:
(1) There's no interpolation error if you use display and reorient,
because no reslicing is involved; only the position/orientation
information in the associated *.mat file is changed.
(2) If you reslice the image after reorienting it and before you spatially
normalize it, you *will* introduce interpolation error. Furthermore, it's
not necessary to reslice it.
(3) Almost all steps in SPM use the information in the *.mat file (if
there is one). So if you reorient an Analyze format image (i.e., a *.img
| *.hdr pair), the resulting *.mat file (which is either created if one
doesn't already exist, or modified from the previously existing one) will
be automatically read at the spatial normalization step.
So...if I understand your question correctly, my advice is go ahead and
reorient before normalization if you wish, and don't bother reslicing the
reoriented image first.
> I read in the notes of a SPM course in the web not to move the AC if it
> is not very off, how far away has to be to make this a necessary step in
> the normalization process?
That's an empirical question. It's possible it could be 2 or 3 cm off,
and the algorithm would still work well. If it doesn't work well, you'll
see---the resulting warped image will look really bad.
Just try and see.
>Thank you very much!!
>
>
>Diana
>
>
>
>
>---------------------------------
>
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