[Insight-users] problems with geodesic active contour segmentation

[Sara Rolfe]

Hello,

I am attempting to find the external outline of a skull in a CT  
image.  I had been using active contours to do this successfully in  
MATLAB, but now I would like to change the implementation to ITK to  
improve the speed.  So far I have followed the  
GeodesicActiveContourImageFilter.cxx example using an extracted  
exterior outline for my feature image and the fast marching filter  
seeded with these edge points to initialize a distance map.  This does  
not seem to be working correctly since I am either getting (depending  
on my parameter selection) segmentations of large blobs around the  
skull edge or a single contour generally following the skull outline,  
but quite a bit larger.  I have tried the build-in edge feature image  
with similar results.  I have a couple of questions.

1.  Am I using the correct method to choose my seeds?  Do they need to  
be inside/outside the skull rather than on the edge?  I have tried  
both expansion 	  	directions.
2.  Is there a good method to get the segmentation to ignore the  
internal skull edge/brain?  In my MATLAB implementation I used region  
based contours.  Is 		there support for something similar in ITK?
3.  Is there something else I am doing incorrectly?  Can anyone  
explain the behavior that I'm seeing?

Thanks for your help!