[Insight-users] Registration Problem

[Luis Ibanez]

Hi Sven,


A) It is very strange that two images that are already registered
    would become misaligned after running a registration process
    on them.


    This raises suspicions about:


     A) your method for converting the ITK image to VTK

     B) your method for visualizaing the VTK images

     C) The optimizer setting (Minimize vs Maximize).



B) Reporting that "nothing works" is not very informative.

    There are many parameters to fine tune in a registration
    process, and you clearly have only experimented with a
    small subset of the possible combinations.

    Such report would only be useful if it is accompanied
    by

        a) The images that you are registering

        b) The source code that you are using

        c) The list of sets for parameters that
           you have tried.


C) You should verify every step of your processing.

     1) Are you reding this image from DICOM files ?

     2) What are their

              * Pixel type ?
              * Origin coordinates ?
              * Pixel spacing values ?
              * Direction cosines ?

     3) Have you visualized the images directly
        using:

               * VV ?
               * Slicer ?
               * SNAP ?
               * Paraview ?
               * Osirix ?
               * Other ?

     4) Have you resampled the moving image using
        only the initial transform of the registration ?

        How are you computing the initialization of the
        Transform ?



   Please report to the list the answers to
   questions:  C.1, C.2, C.3. and C.4


       Thanks



          Luis


---------------------
Fischer, Sven wrote:
> Dear all,
> 
> I want to do an registration between CT and MRI images. I use RegularStepGradientDescentOptimizer with MutualInformationImageToImageMetric for that task. I begin with loading the DICOM images with vtk and transform it to an ITKImage with VTKImageToImage filter, I register the images and transform them with ResampleImageFilter and  AffineTransform and transform them back to VTK to display them.
> Now when I display the images I find that they aren´t registered. I tried different settings on the optimizer and metric but nothing worked. I even found that two images that are already registered will be misregistered afterwards. When I display the MI value during the iterations I find that it is geting worse sometimes and the final is not always the best that was found in an earlier iteration step. Shouldn't it go back into direction of the best value if it finds a worse? Is that a mistake in the Optimizer? Could you give me an advice which Optimizer to use and how to set the settings for Optimizer and Metric?
> Could it be up to transforming the images between VTK and ITK? Is it important which ImageTypes/PixelTypes I use for Transforming, registration and transform between VTK/ITK?
> 
> Regards
> Sven
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