to step 714 of fig7 edge detection is performed on the 2d binary projection image to extract the contour of the selected object for highlighting any one of several edge detection techniques can be employed in one embodiment given the binary projection image with size of i u00d7 j denoted by p i j the output binary image containing the extracted contour denoted by c i j where i 0 i u2212 1 j 0 j u2212 1 is computed using an edge filter as follows a pixel is detected as an edge pixel when any of its eight neighboring pixels in the three by three square centered by the pixel has a zero valued pixel and the pixel is assigned a value of one otherwise the pixel is assigned a value of zero denoting a non edge pixel referring to step 716 of fig7 the final display image is generated by compositing the rendered image of step 710 and the extracted contour of step 714 that is the contour pixels of the selected object as indicated by the binary contour image are replaced by a pre chosen highlighting color for the object and the other pixels from the rendered image remain the same for final display note that in this embodiment the final display image is directly generated at the frame buffer 645 of the gpu 644 as shown in fig6 in another embodiment of the present disclosure the extracted contour using an edge filter using the.