[Insight-users] Multi-resolution: different pyramids for fixed and moving images?

[Karthik Krishnan]

Yes, I suppose that might be done although I have no clue how it might 
affect the registration results themselves.

You could achieve the same with filters too and some extra code using 
the PyramidImageFilter to generate pyramids for the fixed image and the 
moving image seperately

  // Create a multi-resolution pyramid with shrink factors of 4,2,1
  typedef itk::PyramidImageFilter < FixedImageType, MovingImageType> 
PyramidFilterType;
  typename PyramidFilterType::Pointer subsampleFixedImageFilter = 
PyramidFilterType::New();
  typename PyramidFilterType::Pointer subsampleMovingImageFilter = 
PyramidFilterType::New();
  subsampleFixedImageFilter->SetInput( fixedImage );
  subsampleFixedImageFilter->SetShrinkFactors(4);
  subsampleFixedImageFilter->Update();

  typename FixedImageType::ConstPointer fixedImage = 
subsampleFixedImageFilter->GetOutput();
  m_Registration->SetFixedImage( fixedImage ); 

  // Set initial transform for registration
  // Set other registration paramters.
  // Set Optimizer parameters....
  m_Registration->StartRegistration();

 
  subsampleFixedImageFilter->SetShrinkFactors(2);
  subsampleFixedImageFilter->Update();
  m_Registration->SetInitialTransformParameters(
      m_Registration->GetLastTransformParameters() );
  m_Registration->StartRegistration();

  // Do this again with Pyramid factors of 1, ie full resolution
 
  // now get the resulting parameters
  typename RegistrationType::ParametersType finalParameters =
    m_Registration->GetLastTransformParameters();




Li, George (NIH/NCI) wrote:

>Hi, itk users & developers,
>
>I have read the ITK user guide and wondered if ITK should
>Include another multi-resolution scheme that allow user to
>Set two different pyramids for the fixed and moving images.
>
>This thought is based on the case when I tried to register 
>CT image and PET image: the latter has much worse spatial
>Resolution than the former. Thus, it would be beneficial to
>Me to set two different pyramids, possibly to reach the best 
>registration.
>
>Can this effect be achieved by any existing ITK filters, so
>That I can use it to reduce the CT resolution prior to the
>Registration?  
>
>Thanks,
>
>George
>
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