Expand the contour of structure

Hi,

I would like to create contour of structure in image and need to expand the contour in all directions by 10 pixels. I used edge and imdilate, but got wrong results. Any help or guidance will be appreciable.

[edge_im,th] = edge(image,'sobel'); % Boundary of structure
figure(1),imshow(edge_im);

se = ones(10,10);
dilate_im = imdilate(edge_im,se,'full'); % Dilate boundary by 10 pixels
figure(2),imshow(dilate_im);

[expand_im,th]=edge(dilate_im,'sobel'); % Boundary of expansion of aperture
figure(3),imshow(expand_im);

[Doug Hull]

what is a typical image (please attach)? What is the 'correct' results?