[Insight-users] Question about resampling and warping

[Rosario Sance]

Hi everybody,

I´m dealing with a project of motion correction in 3D DCE-MRI series. Up to 
now, I´ve tried several elastic registration algorithms, using MI and 
different optimizers, and aplying multirresolution strategies. Since there 
are intensity changes in my series along the time, I think that the most 
appropriate approach is to use multimodality methods, in spite of I only 
work with MRI.

Every suggestion of my previous work will welcomed.

Now, my questions:

1) When I define a BSpline grid and obtain a transform from the 
registration process, I achieve the registered image using the 
<http://www.itk.org/Doxygen/html/itkResampleImageFilter_8h-source.html>itk::ResampleImageFilter. 
But since I´m working with 3D and respiratory motion, I have some 
difficulties in visualizing the deformation field and interpreting it. I 
have tried with the Glyph option of the Paraview tool. Would you recommend 
me another way?

2) I have also tried the code of 
Examples/Registration/DeformableRegistration2.cxx  and 
Examples/Registration/DeformableRegistration5.cxx, so I have checked the 
possibilities of  the DemonsRegistrationFilter and the 
LevelSetMotionRegistrationFilter. In principle it should not work because 
the dependence with the voxel intensity and the histogram, but I got 
surprised because these algorithms reached a good registration outcomes, 
correcting the position of the input images. However:
         - The resampled image looks absolutely fine about the position, 
but not about the intensities, which seem to be adapted/very similar to 
those in the reference image. Actually I am taking the spacing and origin 
of the fixed image, but since I´m applying the output of the warping filter 
on the moving image, shouldn´t be kept the intensities and corrected only 
the position? I can´t understand how does the warping filter works, in 
spite I have searched in the documentation...
         - On the other hand, I write the deformation field as an image of 
vectors from the output of the warping filter, and keep it in a .vtk file. 
But when I try to visualize it as I did with the deformation fields of the 
resample filter, I don´t get to see any field. How does this filter store 
the vectors field and could it been visualized? Which are the differences 
between the use of both of the filters?

Thanks a lot in advance.
Rosario




Rosario Sance Garzón
Dpto. Ingeniería Electrónica
E.T.S.I. Telecomunicación
Avda. Ciudad Universitaria s/n
E-28040 - Madrid (SPAIN)
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