Sunday, April 17, 2011

Analysis of the orientation of a particle by erosion

A metaphase image contains randomly oriented chromosomes, possibly overlapping and sometime nuclei. An automatic cytogenetic application should be able to detect and resolve overlapping chromosomes, to display chromosomes vertically for further karyotyping.

A step in the chromosome shape analysis, is to detect the chromosome orientation. The following script takes an isolated chromosome image, thresholds it, counts how many vertical erosions are necessary to erase the particle, rotates the image and do it again for all the rotation angle from 0° to 180°.
 Several kind of particles were tested: a small chromosome, a metacentric one, two overlapping chromosomes and a nuclei. A peak in the curve corresponds to the main particle orientation in the image. Overlapping chromosomes may yield a two peaks curve.

One peak curve for the above chromosome.A rotation of 50°, yields the highest resistance to erosion.
A small chromosome
Signature of a small chromosome

Signature of overlapping chromosomes
Signature of a nuclei. 130 iterations are necessary to erase the particle, compared to 22 for the small chromosome.