[Insight-users] Improving the BSplineDeformationTransform?

[Luis Ibanez]

Hi Motes,

Your understanding on how the BSplineDeformableTransform works
is correct.

The locations of the nodes are never modified.

The registration process only computes new values for the magnitude
and direction of the vectors associated with the nodes.

It may be possible to get more adjustable fields by moving the nodes
as well,... but then you have to deal with a new interpolation for computing
the deformation vectors in all the intermediate locations, and of course,
you should come up with the heuristic on how to move the node locations.

If you want to go down this road, you could as well try the Kernel
Transforms,
which will perform interpolations such as ThinPlate Splines.


In any case,

This will make a great paper for the Insight Journal   :-)


      Regards,


             Luis


-------------------------------------------------------------------------------------------
On Mon, Aug 10, 2009 at 4:12 AM, motes motes <mort.motes at gmail.com> wrote:

> When using the BSplineDeformationTransform something like this is typically
> done:
>
> ...
> ...
>     for( unsigned int i=0; i< SpaceDimension; i++ ) {
>       spacing[i] = fixedSpacing[i] * (fixedSize[i] - 1) /
> numberOfGridCells;
>     }
>     origin  = fixedOrigin - fixedDirection * spacing;
>     bsplineTransform->SetGridSpacing(spacing);
>     bsplineTransform->SetGridOrigin(origin);
>     bsplineTransform->SetGridRegion(bsplineRegion);
>     bsplineTransform->SetGridDirection(fixedDirection);
>     const unsigned int numberOfParameters =
> bsplineTransform->GetNumberOfParameters();
>     const unsigned int numberOfNodes = numberOfParameters / SpaceDimension;
> ...
> ...
>
>
>
> In the first loop the position of the deformation vectors are initialized.
> During the image registration process as I understand the position of the
> deformation vectors are not changed, only the magnitude and direction of the
> vectors are modified.
>
> But would the BSplineDeformableTransform not improve the registration
> result if it was somehow (based on a well chosen heuristic) possible to also
> move the position of the deformation vectors?
>
> Are there any articles or other ITK information that deals with a more
> flexible approach to the position of the deformation vectors?
>
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