Multiple thresholding to segment aorta

I need to segment the white circle part and the grey part around it. I've tried smoothing it and using boundary tracing but I'm getting terrible results.

Any help would be greatly appreciated

http://i48.tinypic.com/16hwaxd.png

Answer 1

Shouldn't be too hard unless the noise is a problem. I'd do these steps:

1. Reduce noise - there are a variety of methods.
2. Threshold at a high level to find bright things.
3. Use bwareaopen to get rid of small objects.
4. Call bwlabel and regionprops and use perimeter^2/(4*pi*area) to find round objects.
5. Use ismember() to keep the round objects only. Now you have just the white circle part.
6. Threshold at a medium level to get medium bright things.
7. Use watershed if necessary to split apart touching blobs.
8. Use imreconstruct to get only the gray part that contains the white circle.

Here are some examples to help you:

http://www.mathworks.com/matlabcentral/fileexchange/25157-image-segmentation-tutorial-blobsdemo

http://blogs.mathworks.com/steve/2006/06/02/cell-segmentation/