[Insight-users] modify transformation parameters by using itkBSplineDeformableTransform

[Luis Ibanez]

Hi Xi,


1) If you want to implement a Transform that behaves as
    a Translation (or Rigid) transform in some regions and
    as Deformable in others, there are better ways of
    implementing such class, than fiddling with the parameters
    of the BSplineDeformable transfrom.

2) But, just to answer your question. The parameter array
    of the BSpline transform has the components of the
    deformation vectors at every node of the BSpline grid.

    Given a BSpline grid with N nodes in 3D, you will have

                          3 x N        parameters

    and they are arranged as:

      X1,X2,X3....... Xn,  Y1,Y2,Y3.....YN,...Z1, Z2, Z3,... ZN


3) You can change those parameters manually.
    Simply have to figure out which BSpline nodes
    are on top of the regions for which you want to
    allow only Translations, and change those
    accordingly.




   Regards,


       Luis



---------------------------------------------
On Wed, May 5, 2010 at 6:58 AM, Xi Liang <liangxi1986317 at hotmail.com> wrote:
> Dear all,
> I want to change the some control point parameters got by running
> registration by using itkBSplineDeformableTransform.h. The reason is to
> manually modify a set of control points such that only translation is
> applied on the corresponding regions. The question I would like to ask is
> whether this should be done manually, or we have a filter to change those
> parameters?
> If I have to do this manually, I will have to understand of the format of
> parameters. I understand the number of parameters get
> from itkBSplineDeformableTransform is ImageDimension *
> (numberOfGridNodesInOneDimension + BsplineOrder). Which value is for
> lower/upper borders, and which are for nodes? I think I will only need to
> modify the node values to enforce the translation transformations.
> This method is introduced by Tanner in Volume and Shape Preservation of
> Enhancing Lesions when applying nonrigid registration to a time series of
> contrast enhancing MR breast Images. It couples the control points of a
> bspline deformation to enforce rigidity on certain structures.
> Kind regards,
> Xi
>
>
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