[Insight-users] Mutual Info-based Registration on Ultrasound image

[Thomas - Kuiran Chen]

Hi Luis, 

I've been trying to use ITK's implementation of viola's mutual information based registration (itk::MutualInformationImageToImageMetric) for ultrasound images.

The parameter settings of the matric in the example (ImageRegistration2) work well on MRI image, but when I tried with ultrasound images (I even tried two identical images), the result was interesting but somehow unexpected.  The bestValue from the optimizer was around 0.5 (mutual info entropy), and the program suggested a translation of (0.11, 0.09) along X and Y directions, and the number of iterations used was 200. 

The parameters need to be set are (as for the MRI image - BrainT1SliceBorder20.pgn, in the example):

1. for itk::MutualInformationImageToImageMetric:
- Fixed and moving image standard deviation, the example suggests 0.4;
- Number of Spatial Sample Bins, the example uses 50;

2. for itk::DiscreteGaussianImageFilter:
- Fixed and moving image smoother various, the example sets 2.0

3. for itk::GradientDescentOptimizer:
- learning rate: set to 20.0 in the example
- number of iterations: 200

Can you provide any hints/guidelines of how to play with these parameters for different image modality?  In particular, those work for ultrasound images?  Also is there any text I can find to explain these parameters in more details?

Thanks a lot,
Thomas