Generating an inverse transform

[Andrea Borsic]

Dear All,

There are multiple posts on this list asking information about applying the inverse of a registration transform to a set of points, but there seem to be no answer those questions.

Can anyone kindly confirm whether it is possible or not possible in Elastix to apply/generate the inverse of the given transform? In case it is possible, can you kindly suggest whether there might be some documentation, example, or any information regarding this specific task?

Thanks in advance for the kind attention,

Best Regards,

Andrea

[M.St...@lumc.nl]

Hi Andrea,

 

·         Chapter 6.1.6 of the manual is about this topic.

·         In the elastix/Testing directory of the repository there is a program (elxInvertTransform.cxx) to invert translation, rigid and affine transformations. This can be done in closed form directly.

·         For the B-spline transform or other deformable transformation models you need another approach. You can take the approach from Section 6.1.6 using the DisplacementMagnitudePenalty metric. If I am not mistaken scripts for it can be found at http://elastix.bigr.nl/wiki/index.php/Par0012.

·         An alternative approach is to iteratively find the inverse using the tool pxdeformationfieldoperator from ITKTools, see https://github.com/ITKTools/ITKTools/blob/master/src/deformationfieldoperator/. It uses the itkIterativeInverseDisplacementFieldImageFilter.

 

Once you have the inverse transformation, you can apply transformix to transform  a (set of) points.

 

HTH, Marius

 

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