> The deformation field can obtained via the Deformation toolbox of the SPM2,
> and the "Visualize deformation" can show the deformation of slices.
>
> My questions are:
> 1. A displayed deformation field (from *_sn.mat) is supposed to be figures
> looked like the left images of the Figure-2 of the article --
> "Ashburner & Friston, Nonlinear Spatial Normalization Using Basis
> Functions".
> However, the displayed images showed three imageds indicated smoothed
> varied deformation field! (3 images smoothed varied from left to right,
> from bottom to top, and from anterior to posterior)
> But the visualized deformation field did not indicate these!
> Why? Anything wrong?
There is nothing wrong. It is simply a different kind of representation. A
deformation field in a y_*.img file is of the form:
[ x + a11*b1(x,y,z) + a12*b2(x,y,z) + ... ,
y + a21*b1(x,y,z) + a22*b2(x,y,z) + ...,
z + a31*b1(x,y,z) + a32*b2(x,y,z) + ... ]
whereas the images in the figure are:
a11*b1(x,y) + a12*b2(x,y) + ...
a21*b1(x,y) + a22*b2(x,y) + ...
As the "a11*b1(x,y,z) + a12*b2(x,y,z) + ..." part is relatively small compared
with the "x" part, then it is not easily seen.
I have actually simplified this quite a bit, as there are a few affine
transform related things also included.
>
> 2. How to overlap the deformation field on a MR image?
> Or, Does any tool can help us to visualize the deformation field in a
> more observable way such as the right images of the Figure-2 of the
> article -- "Ashburner & Friston, Nonlinear Spatial Normalization Using
> Basis Functions"
> Does the Deformation toolbox support such functions?
It isn't so easy to visualise a 3D deformation field. The Deformations
toolbox of SPM2 tries to show what a deformation field should look like with
the "Visualise Deformations" option. It is still a little hard to see what
is going on though. I prefer to visualise the Jacobian determinants, which
give an idea about where expansions and contractions have taken place.
Best regards,
-John
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