Roughness feature of metaphase chromosome spreads and nuclei for automated cell proliferation analysis

As a step towards automation of mitotic index estimation for cell proliferation studies, a roughness feature of surface-intensity images is introduced: the mean depthwidth ratio of extrema (MDWRE). This feature allows identification of variable-shaped metaphases and interphase nuclei in the presence of many artefacts (one metaphase per hundreds of nuclei and thousands of artefacts). The texture of the cytological objects (seen as rough surfaces) is quantified by scanning, in one dimension, the lines contained in a closed contour. MDWRE proves to be suitable for image magnifications by a factor of as low as ten, making faster scanning of slides possible. The use of this feature gives +14%, +65%, +133% and +133% better performance figures than classical textural features derived from co-occurrence matrices, such as contrast, energy, entropy and angular second moment, respectively, and +51% better than the relative extrema density (RED). The MDWRE per object and the shape of the histogram of the depth-width ratio of grey-level roughs have been shown to be very useful as textural features for the classification of metaphase images.