[Insight-users] Initialization of BSpline transformation with deformation vector field

[Jochen Cammin]

I want to register two 3D images using the BSplineDeformableTransform. I
have an estimate for the transformation which I want to use to
initialize the BSpline transformation. As far as I can see from the
documentation, the transform can only be initialized with BSpline
coefficients.

However, my initial estimate is in the form of a deformation vector
field. Therefore, I need to transform the initial deformation vector
field into BSpline coefficients.

I thought that I could use the BSplineDecompositionImageFilter for this
purpose. Is the following way a good approach?

      1. create three 3D images from the initial deformation vector field
         (one for each component of the vectors).

      2. use the BSplineDecompositionImageFilter on each of the three
         images to calculate the BSpline coefficients for each dimension

      3. initialize the transformation with these parameter images


Is this approach correct? When I looked at two examples that use the
BSplineDecompositionImageFilter (DeformableRegistration6.cxx and
DeformableRegistration15.cxx) it looks like
BSplineDecompositionImageFilter works directly on the coefficient images
of the coarser transformation, never on the actual deformation vector
field. That's why I'm not sure if my approach will give the correct results.

Thanks for any feedback,
Jochen