I have tried to use level sets plugin to execute fast marching algorithm on mammograms to detect the breast boundary. When I do that though the gray level is same the algorithm doesnt chose the correct region why is that? if any one using this plugin may be he or she can address on this issue.
I agree with @etadobson that autothresholding seems to work well for the image you posted, and that Level Sets will be more difficult to make work well.
Please clarify what you mean by “not enough.” If you simply mean that it does not select enough of the tissue here, you can try other autothresholding algorithms. To my eye, RenyiEntropy looks like a good match, but you can just for yourself using the Auto Threshold plugin with the “Try all” option checked.
I understand why you were trying the Level Sets plugin then as discussed on another thread. But as @iarganda mentioned on that thread, the Level Sets plugin does not do exactly what you are looking for out of the box. Unless you have the time to read and understand its source code, it will be difficult to compare and validate the plugin’s approach vs. the relevant MATLAB function.