Error in Region growing MRI volumetric data.

Sir i want to segment DICOM stack of 28 slices, for 2D single image segmentation it work fine but for 3D volumetric data it give error, please help me . . .

    tolerance = 20; 
    Igray = double(mri); % mri is series of DICOM images 

     x = 0;
     y = 0;
    if(x == 0 || y == 0)
    imshow(Igray(:,:,12),[min_level max_level]);
    [x,y] = ginput(1); % Selecting the seed point 
    end
    Phi = double(false(size(Igray,1),size(Igray,2)));
    ref = double(true(size(Igray,1),size(Igray,2)));
    PhiOld = Phi;
    Phi(uint8(x),uint8(y)) = 1;
    while(sum(Phi(:))) ~= sum(PhiOld(:))
    PhiOld = Phi;
    segm_val = Igray(Phi);
    meanSeg = mean(segm_val);
    posVoisinsPhi = imdilate(Phi,strel('disk',1,0)) - Phi;
    voisins = find(posVoisinsPhi);
    valeursVoisins = Igray(voisins);
    Phi(voisins(valeursVoisins > meanSeg - tolerance & valeursVoisins < meanSeg + tolerance)) = 1;
   end
   imshow(Phi(:,:,12))

[Walter Roberson]

Please post the complete error message, everything in red.

[Muhammad Shoaib]

Sir these are the errors which i am getting.

Subscript indices must either be real positive integers or logicals.

Error in segCroissRegion (line 59) segm_val = Igray(Phi);