[Insight-users] Geodesic Active Contours passing over edges

[Luis Ibanez]

Hi Ivan,

Are you sure that your Sigmoid is generating dark
values on the edges of structures ?

The GeodesicActiveContour uses the feature image
as one of the inputs to the speed computation.

Note that the advection term is computed in the
form of a force vector and therefore it has a
direction.  Normally this direction is pointing
to the lower values of the Feature image, thus
to the center of the edges of the original image.

Could you post some slices of your input image,
feature image and the output of the GAC in MyPacs ?

you can create an account for free at

    htt://www.mypacs.net

Once you post the slices, please let us know the
image ID that you get for them.


If you want to play with a prototype, VolView has
ITK plugins for GeodesicActive contours.

You can download the free version of VolView from

    http://www.kitware.com/products/volview.html



Thanks


    Luis



---------------------
Ivan Macia wrote:

> Dear ITK users :
> 
> I have a problem with segmenting the liver in a series of slices. I first
> used the pipeline in the ITKSoftwareGuide. When I set a small value for the
> distance to the seeds in the FastMarchingFilter (used here to generate a
> distance map) I get a quite nice result although the initial zero level-set
> is very far away from the edges of the liver. If I use a larger value, that
> approximates better the shape of the liver (being careful of not having any
> lacks in this initial level-set) it results in controlled lacks in the
> segmented region, which is somewhat senseless to me.
> 
> I have realised that what is happening really in my case is that the
> Geodesic Active Contours are lacking over the first edges they find in the
> Sigmoid filter (used here as Feature Image) and are trying to fit to the
> second edges they find. This means that if in the Sigmoid the object I want
> to segment is white, then, there is a separation in black surrounding this
> area and then there is a transition to white again, the GAC try to adjust to
> this last transition. The same happens when I try to use other prior
> segmentations that adjust better to the liver area instead of using a Fast
> Marching filter as initial level-set.
> 
> I tried to reduce the values of the propagation and advection terms in the
> GAC and increase the Curvature term, but it does not seem to take effect (I
> even tried with Advection = Propagation = 0.01 and Curvature = 30.0). How
> can I fix this? Is this a normal behaviour?
> 
> Sorry if I haven't explained myself clearly and thanks in advance.
> 
> Iván
> 
> ________________________________
> 
> Iván Macía Oliver
> Ing. Industrial
> Ing. en Automática y Electrónica
> Asociación VICOMTech
> http://www.vicomtech.es
> Paseo Mikeletegi 57, bajo
> 20.009 Donostia-San Sebastián
> (Gipuzkoa) SPAIN
> Tlfno: (00 34) 943 30 92 30
> Fax: (00 34) 943 30 93 93
> e-mail: imacia at vicomtech.es
> 
> ***Member of INI-GraphicsNet***
> http://www.inigraphics.net
> _______________________________
> 
> 
> 
> 
> _______________________________________________
> Insight-users mailing list
> Insight-users at itk.org
> http://www.itk.org/mailman/listinfo/insight-users
>