Hi,
Thanks for the explanation.
> (i) The distortions associated with deforming a source (individual) sphere to
> a target (template, or atlas) sphere can be visualized using a deformation
> field, as Donna notes. Alternatively, they can be viewed using an areal
> distortion map, computed using Surface: Measurements: Generate Distortion.
> This will compute the areal distortion (as log 2 values) between the surface
> in the main window and whatever currently loaded surface you choose from the
> pulldown menu.
>
> If you are using Core 6 landmarks and registering human individuals to the
> PALS-B12 atlas, the sphere-to-sphere distortions are generally pretty modest.
>
>
> ii) The issue of evaluating the 'distortions' of the original surface are
> conceptually not so straightforward. (I assume by 'original' you mean the 3D
> 'fiducial' or 'anatomical' surface configuration.)
>
Your asumption is right. Here is the analysis I want to do. I have a 3D
fiducial surface , based on this fiducial surface ,let's say, "template", I
generated some simulated fiducial surface with some deformation, let's say
"subject". So here I know the "deformation vectors" for each vertex between
the template and the subject in the original 3D fiducial surface "space". Then
I use Caret to do spherical registration from those subjects to the template. I
want to check how these " deformation vectors " I got from Caret are different
from my generated "deformation vectors". But the problem for me is, after
Caret registration, the " deformation vectors" is based on the spherical
space. While my generated "deformation vectors" are in the 3d fiducial surface
space, it's not comparible for these two vectors. That's why I want to know
whether I can put the deformed subject sphere back into the fiducial surface
representation. In that way, I can calculate the difference
in the fiducial space. While from your comments it seems that the answer is
no, could you give me some suggestions about how to calculate the difference of
the deformation vectors which are not in the same space? Generating the
deformation vectors in the spherical space is the last thing I want to do
because you never know how it likes in the real fiducial surface representation.
Hope for your suggestion.
Thanks a lot.
> Caret by default creates a 'deformed' fiducial surface as part of the
> registration process, but in this case 'deformed' is really an unfortunate
> misnomer. We now routinely describe it as a 'resampled' fiducial surface.
> It has the same fundamental shape as the original but is represented by a
> different surface mesh (tessellation) - namely, the 'standard mesh' of the
> target atlas (73,730 nodes for both the PALS-B12 human atlas and the macaque
> F99 atlas).
>
> Another source of distortions is the mapping between the fiducial surface and
> the spherical surface. Even after multi-resolution morphing is done, the
> areal distortions between the sphere and the fiducial surface are generally
> large and irregular. This is because the cortex contains a lot of intrinsic
> (gaussian) curvature (dimples and bulges) rather than being simply folded
> like a crumpled newspaper. And given the high degree of variability in
> folding patterns (especially humans), the pattern of areal distortions
> differs markedly across individuals.
>
> I hope this helps, at least to some degree. If you have additional
> questions, please clarify more specifically what it is you are trying to
> learn from this analysis.
>
> These issues are very much on my current front burner, as I am in the midst
> of analyzing and writing a paper that introduces a new version of our
> landmark- and surface-based registration algorithm.
>
> David VE
Jidan
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