[Insight-users] demons \w MI and BSpline optimization

[Ruben Schilling]

Hi all,

I have two questions:

(1)
I am wondering whether there is an example out using some variant of  
mutual information with some demons algorithm. I didn't find anything  
in the software guide nor the examples. It seems, that it would be  
interesting to compare its performance to the BSpline + mutual  
information registration.
 From the literature I don't see why it wouldn't be possible, since  
the demons only rely on similarity measure and distance to compute  
the forces, which does not limit one to e.g. squared differences. Is  
there a reason in optical flow, why we couldn't use demons with  
mutual information? Can't we replace the intensity similarity of  
optical flow with mutual information similarity?
Has anyone tried this yet? Is there a reason why there is no example  
(I thought it would be a rather general demand to have it).


(2)
I am optimizing currently also the DeformableRegistration8.cxx  
example (under consideration of DeformableRegistration6.cxx). Are  
there any general guidelines in optimizing the LBFGSB optimizer used?  
I find it quite non-trivial, because I don't have the necessary  
background on non-linear optimization theory. Especially for using  
the BSplines I find it hard, I can imagine setting e.g. the right  
scalings in an affine transform, but for a BSpline grid the  
parameters are the displacements of the nodes, right? Are there any  
general hints/guidelines how to procede here?



To make my point clear, I am actually trying to solve a difficult  
practical problem with multi-modalities and I am not intending to  
start any debate on which elastic transform is better. I am combining  
the elastic transform with a quite successful rigid and affine "pre- 
registration", but still the remaining problem is difficult enough,  
this is why I would like to explore all techniques available (yes, I  
do also consider FEM but haven't started on it for now).


I would be grateful for comments on these matters.

best regards
Ruben