TOPOGRAPHIC MODELING OF #1 G-BANDED CHROMOSOME

Abstract

An approach to a quantitative description of bands and interbands, representing alternating visible zones of chromatin packaging is presented. The study is performed on selected human chromosome (#1) obtained from G-banded metaphases observed by the optical microscope. In order to segment the image into structures of interest a topographic approach is proposed: greytone images are seen as landsurfaces (i.e., the grey tone of a pixel is the elevation in that point) and structures to be detected are considered as topographic relieves. In the segmentation process a rewriting process translates the greytone digital image into an image where each pixel is labelled by a symbol denoting the type of structure to which the pixel belongs. Rewriting is performed by repeatedly applying the rules of Bidimensional Lindenmayer Systems (BLS) to the input image. In each step BLS rules are applied to evaluate a local property. The repeated application of the rules combine the local properties of pixels up to an arbitrary distance, simulating an information diffusion process that determines the emergence of global properties of sets of pixels of arbitrary shape. Detected Troughs and Lowlands are interpreted as tracks of bands and interbands and from their description there derives a set of geometrical attributes. These attributes are useful to measure the distances between bands and interbands and hence to follow the dynamic packaging of chromosomes before cell division. Finally, topographic labelling seems to enhance the resolution level of chromosome features, especially for faint bands, thus it is reasonable to expect that even microvariations important in cytogenetic pathology can be detected.