[Insight-users] Problem with BSplines-Registration and Mutual Information Metric

[Carola Schmidt]

Hi, itk users.

 I am implementing the BSpline Registration to register CT-Data of the 
abdomen. I use the LBFGSBOptimizer
and use the parameters of the deformableRegistration8.cxx file

    OptimizerType::BoundSelectionType 
boundSelect(transform->GetNumberOfParameters());
    OptimizerType::BoundValueType 
upperBound(transform->GetNumberOfParameters());
    OptimizerType::BoundValueType 
lowerBound(transform->GetNumberOfParameters());

    boundSelect.Fill(0);
    upperBound.Fill(0.0);
    lowerBound.Fill(0.0);

    optimizer->SetBoundSelection(boundSelect);
    optimizer->SetUpperBound(upperBound);
    optimizer->SetLowerBound(lowerBound);

    optimizer->SetCostFunctionConvergenceFactor( 1e+7 );
    optimizer->SetProjectedGradientTolerance( 1e-4 );
    optimizer->SetMaximumNumberOfIterations( 500 );
    optimizer->SetMaximumNumberOfEvaluations( 500 );
    optimizer->SetMaximumNumberOfCorrections( 12 );
    

As metrics I tried itkMeanSquaresImageToImageMetric and 
itkMattesMutualInformationImageToImageMetric. When I use the 
itkMeanSquaresImageToImageMetric the registration takes really long but 
the results are quite ok.
When I use itkMattesMutualInformationImageToImageMetric the registration 
only takes a few seconds but most of the time the warped image looks 
like a hardly deformed moving image. Since the registration time is very 
short, it seems that the registration stops after a few steps and warps 
the image then. I use those parameters for the mututal information:

    metric->SetNumberOfHistogramBins( 40 );
    const unsigned int numberOfSamples = 10000; 
//fixedRegion.GetNumberOfPixels()/ 10;
    metric->SetNumberOfSpatialSamples( numberOfSamples );
    metric->ReinitializeSeed( 76926294 );
    metric->SetMovingImage(m_itkimage);
    metric->SetFixedImage(m_itkatlas);
    metric->SetFixedImageRegion(fixedRegion);

Why does the Mutual Information Metric not work as expected? Should I 
change the parameters of the optimizer?
Thanks for an answer.

Ciao,
Carola