[Insight-users] Building shape model to be used with GeodesicActiveCountourShapePriorLevelSetImageFilter

[Zachary Pincus]

Based on Leventon's paper that initially described the shape model 
level sets ( 
http://www.ai.mit.edu/people/leventon/Research/0006-CVPR/cvpr00.pdf ), 
and looking at the ITK implementation thereof, this is correct.

Note that you need to use the signed level set output -- not binarized 
inside/outside version or single isocontours from the level sets -- as 
input to the ImagePCAShapeModelEstimator. As you probably know, and for 
the benefit of others reading this, the "shape model" training images 
need to be represented as signed distances from the edge of the shape. 
Fortunately, this is the stock in trade of level sets, so you can use 
that output raw.

I was looking around for a class in ITK that could compute signed 
distance maps from a binary image, in case that is all the input one 
has for training images (e.g. input from a non-level-set segmentation 
method). I can't find anything explicitly there (is there??) but of 
course one could create a signed distance image by two applications of 
the Danielsson Distance Map filter to a binarized inside/outside image 
and its complement, and subtracting the two.

Zach Pincus

Department of Biochemistry and Program in Biomedical Informatics
Stanford University School of Medicine


On Aug 8, 2004, at 1:40 PM, Lino Ramirez wrote:

> Dear ITK users,
>
> I would like to do segmentation of vertebrae in x-ray images using the 
> GeodesicActiveCountourShapePriorLevelSetImageFilter. I already had a 
> look at the example available in the CVS repository. However, in the 
> example, it didn’t explain how to make the models. For what I have 
> read so far, I guess that the following steps would help me make such 
> a model.
>
> 1.- Align the training images
> 2.- Segment each image using a level-set based method
> 3.- Use the output level set as the inputs for 
> ImagePCAShapeModelEstimator
>
> Do these steps make sense? Or is there some other approach or example 
> I should follow?
>
> Thank you and have a nice day
>
> Lino
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