How to isolate the circle from the shaded area?

I would like to have only a shaded area from the picture. I want to remove the circle from the binary image. Any idea?

Answer 1

[Matt J]

How about

       A=imread('http://www.mathworks.com/matlabcentral/answers/uploaded_files/24735/D1.png');
       A=rgb2gray(A);

       outer=~imfill(A,'holes'); 
       outerd=imdilate(outer,ones(5));

      newImage = A&~outerd;

[Mahmoud]

Amazing!! That worked perfectly! Now, if I want to fill the isolated area to find the area in pixel using regionprops, how can I fill that region?

[Matt J]

    B=imerode(~A,ones(3));

    S=regionprops(B,'PixelIdxList','Area');

    [ar,idx]=sort([S.Area],'descend');

    tofill=vertcat(S(idx(1:2)).PixelIdxList);
     C=false(size(A));
     C(tofill)=1; 

     result=~imdilate(C,ones(5));