How to use zero level set to obtain the segmented object?

Hello,

I have used active contours with level set to plot the contour around an object within an image.How can i use the zero level set points to extract the segmented region only for volume calculation. Any help in terms of coding will be appreciated...

For example i have so far got something on the lines given below ...

   c=contours(phi(:,:,slice(i)),[0,0]);
   [h, pt] = plot_contours(c, 'r', 'linewidth', 2);
    pause; delete(h); plot(pt(1,:),pt(2,:),'.');

Visually i can see the contour around the segmented region .But the remaining contents in the image are also present.How can i get the object inside the contour only in order to get the number of pixels inside it ?

Thanks

Please hep