Image Registration using BSplines with order greater than 3

Engineering
1

Hi, I’m trying to do a registration using BSplines of order 4. However, when I set 4 to the parameter ‘order’ in the BSplineTransformInitializer constructor, I got the following message: “sitk::ERROR: Invalid Order: 4 only orders 0, 1, 2, and 3 supported!”.

So, Is There a way to do this registration using SimpleITK? And using ITK?

Thanks.

2

Most likely you can achieve sufficiently smooth displacement field with 3rd order spline and appropriately dense grid of control points. But if you really want to have higher-order spline then most likely you just need to add 2 lines of code to sitkBSplineTransformInitializerFilter.cxx in SimpleITK.

3

I suspect that ITK does not support 4th order b-splines. Maybe some filter’s or data representations do, but likely not enough for a complete workflow. SimpleITK supports 1, 2, and 3 order b-splines. Likely higher orders did not compile when this feature is added.

4

The fourth order b-spline can be enabled by adding a 4 for the VSplineOrder when building an itk::BSplineTransform, and this can be supplied to the itk::BSplineTransformInitializer. The ITK Python wrapping provides 3rd order transform support out of the box. In general, if the goal is to increase transform flexibility, it is better to use a denser bspline grid over a higher order transform.

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