[Insight-users] FEMRegistration and metrics

[Bignalet Francois]

Hi all!

I am using the itkFEMRegistrationFilter class and I would have some questions to ask:

1) about Normalized Correlation Metric

It is written in the ITK Software Guide (p283) that itkNormalizedCorrelationImageToImageMetric returns the negative value of the correlation, and so that the optimum is the minimum.
In the other hand, in the itkFEMRegistrationFilter.h documentation, it is written that the direction associated with ncc is 'maximize'...
I tried both registration with ncc minimize and ncc maximize, and actually I don't see any big difference. Can anyone help me?

2) about MutualInformation

I tried too to use FEMRegistrationFilter with MI, but I don't manage to have good results. The final output is more different from the fixed image than the moving image input, though I tried maximize and minimize. 

3) about Loads and forces

I read carefuly the Guide and the inline documentation, but I don't really understand how the image loads are converted in forces, how the Jacobian of the metric is used, and how the forces are reconverted in loads after each iteration. Does anyone can tell me about a documentation about FEM applied to images?

Thanks a lot

François Bignalet-Cazlet