dear John, spm users ,
with reference to this specific thread, is it recommended to
use the inverse deformation toolbox that is provided by SPM, as a part of
some study. I have been curently using the inverse deformation toolbox
quite liberally over the past few months to get some results, and was
wondering what details i should keep in mind while performing this in the
most acceptable way?
further, is the inverse normalization a validated tool, and esp.
what are John's recommendations on using it as a component in some method?
In case it is safe to use, could somebody provide me with the
citations appropos to this work, to be mentioned in the paper?
regards,
Siddharth.
On Fri, 23 Aug 2002, Neggers, Bas wrote:
> Dear Satra and others,
>
> Dont have the (complete)solution, but perhaps some thoughts that might be
> helpful. I have also been thinking about this for a while, since i am
> planning to re-map normalised activation coordinates (from another study by
> someone else) to a subjects own brain (for stereotactic purposes.
>
> The problem is that the normalization (which isnt an affine transformation
> in the mathematical sense, by the way), is in principle not reversible, i.e.
> the inverse transformation doesnt (always) exist. If i understand it right,
> by the non-linear part of the normalization process 2 original locations
> could potentially be mapped to the same point in MNI space (John, is that
> true?), meaning that the inverse process is ambiguous. Th coregistration
> (linear) part, which is an affine transfromation (allowing rotations,
> translations, sheers and zooms) is reversible (the inverse matrix does
> exist). For the latter it is sufficient to load the affine transformation
> matrix (say M) from the mat-file, type inv(M) in Matlab and there you have
> the reverse of an affine transformation.
>
> During the SPM short course in London recently I asked John about this, and
> he told me, if i remember well, that the inverse of the normalization does
> in principle not exist, although in practice the non-linear coefficients do
> not reach the point where the process gets irreversable. Since i didnt
> examine the non-linear math of normalisation in detail yet, i cannot give
> you more detail. I plan to get into this in the near future, I'll keep you
> posted.
>
> Regards,
>
> Bas
>
>
> --------------------------------------------
> Dr. S.F.W. Neggers
> dept. of Psychonomics,Helmholtz Institute
> Utrecht University
> Heidelberglaan 2
> 3584 CS, Utrecht, the Netherlands
> Tel: (+31) 30 253 4582
> Fax: (+31) 30 253 4511
> E-mail: [log in to unmask]
> Web: http://www.fss.uu.nl/psn/pionier
> --------------------------------------------
>
>
>
>
> -----Original Message-----
> From: Satrajit Ghosh [mailto:[log in to unmask]]
> Sent: vrijdag 23 augustus 2002 4:39
> To: [log in to unmask]
> Subject: Inverse Affine Transform
>
>
> Dear Users,
>
> I have a very simple transform question. I have an affine normalized T1
> image from which I have extracted a brain surface. I would like to
> transform this image to its original space. So essentially I have the
> following:
> - *_sn3d.mat file
> - a set of vertices
>
> Is there a one liner to do this?
>
> Thanks,
>
> Satra
>
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