Hi Dara,
this is hist how I understand things, which may well be wrong, but in my
view:
> Our understanding is that the manual / display approach is optimal
Not necessarily, considering that you spend a lot of time doing this and
the results may not show. Also, based on a principle aversion to manual
interaction ;) reviewers may point out that this step induces variance
into an otherwise automated procedure. And your graduate students may
add that they could do something less boring in the time needed for
manual alignment...
> on the fact that rigid-body co-registration is designed for
> intra-subject registration and therefore would involve potential
> additional (shears/zooming?) changes to the source image
No, it does not. Rigid body refers to the fact that the whole image is
moved around, but is otherwise not altered. No zooming or shearing
involved. The position of a rigid body is determined by the pposition of
its center of mass and by its orientation, which again is described by 6
parameters (I must admit I just looked this up again at
http://en.wikipedia.org/wiki/Rigid_body :)
> What kind of additional changes over and above manual reorientation does
> the rigid-body co-registration impart to the subjects MR properties
> (intensity, variance?). How might these changes affect subsequent
> segmentation/VBM analyses and to what extent if known?
None (as ar as I know), and they shouldn't. Another reviewer may point
out that careful manual alignment will always be better than an
automated procedure, but in the end, it is your choice, depending on a
number of factors (how many people you have, how many images, how bad is
the difference from the "expected" orientation etc). I do coregistration
(and seem to fare well regarding the segmentation results), but other
people disagree.
Best,
Marko
--
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Marko Wilke (Dr.med./M.D.)
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Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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