[Insight-users] Best way to re-initialize level set during filter operation?

[Zachary Pincus]

Hello all,

I'm planning on experimenting with how valuable periodic level set 
re-initialization is for my particular segmentation application.

An IsoContourDistanceImageFilter=>FastChamferDistanceImageFilter 
pipeline is perfect for re-initializing a level set image, so just I 
need to figure out how to apply this pipeline to a *currently-running* 
level set segmentation filter (e.g. GeodesicActiveContours or similar), 
via a callback.

Obviously, it's possible to just run the level set filter for n 
iterations, re-initialize, feed that as input to a "new" (or 
potentially recycled) level set filter, and repeat. This seems a little 
nastier than just calling re-initialization code from a callback, 
though.

Here is how I would envision such a callback working if it were 
possible: The "current" level set image is stored in the filter's 
output. So to re-initialize this image, I imagine I would need to grab 
the output, modify it, and put the output of the pipeline above (which 
cannot run in place) back as the "new" output.

Now, I have a few questions about such a procedure:
(1) Is there anything one needs to do to tell a level set filter that 
the output has been changed? I'm thinking about filters which use 
narrow banding or explicit "layers." Presumably, the layer locations 
would need to be updated based on the re-initialized image. How would I 
go about triggering such an update?

(2) What is the best way to sneakily change the output of a level set 
filter? I can see two paths:
  	- Grab the level set output image's pixel container. Stuff it in a 
new itk::Image. Run that image through the pipeline above. Take the 
resulting pixel container, and make that the output image's pixel 
container.
	- Grab the level set output image, and call DisconnectPipeline() on 
it. Run the image through the pipeline above. Disconnect the output of 
that pipeline and re-attach it to the level set filter with 
GraftOutput().
Is either a preferred option?

So: Can/should this task be accomplished via call-back as I described 
above? If so, does anyone have any thoughts as to my specific 
questions?

Thanks for your time,

Zachary Pincus

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