An automatic system for detecting and counting sister chromatid exchanges in human chromosomes has been developed. Metaphase chromosomes from lymphocytes which had incorporated 5-bromodeoxyuridine for two replication cycles were treated with the dye 33258 Hoechst and photodegraded so that the sister chromatids exhibited differential Giemsa staining. A computer-controlled television-microscope system was used to acquire digitized metaphase spread images by direct scanning of microscope slides. Individual objects in the images were identified by a thresholding procedure. The probability that each object was a single, separate chromosome was estimated from size and shape measurements. An analysis of the spatial relationships of the dark-chromatid regions of each object yielded a set of possible exchange locations and estimated probabilities that such locations corresponded to sister chromatid exchanges. A normalized estimate of the sister chromatid exchange frequency was obtained by summing the joint probabilities that a location contained an exchange within a single, separate chromosome over the set of chromosomes from one or more cells and dividing by the expected value of the total chromosome area analyzed. Comparison with manual scoring of exchanges showed satisfactory agreement up to levels of approximately 30 sister chromatid exchanges/cell, or slightly more than twice control levels. The processing time for this automated sister chromatid exchange detection system was comparable to that of manual scoring.
Sister chromatids of human metaphase chromsomes from cells which have replicated twice in medium containing 5-bromodeoxyuridine exhibit unequal fluorescence when stained with the dye 33258 Hoechst. Sister chromatid exchanges occurring in these chromosomes are apparent as interchanges of brightly and dully fluorescing chromatids. A technique for detecting such exchanges by computer analysis of chromsome images has been developed and found to campare favorably with manual methods. The exchanges have been localized in the context of quinacrine banding patterns.
A new approach to a system for chromosome karyotyping is presented. The system assembles the information about chromosomes from several cells at a time, thereby filtering out noise due to variations in the slide preparations. The system makes i possible to use metaphase spreads which are incomplete due to missing chromosomes, touching and overlapping chromosomes and stain particles. The system gives a precise description of the chromosome complement in terms of distribution function parameters, with the uncertainty of the parameters specificed. The system is adaptive with respect to the initial reference parameter set so that both recognition of normal chromosomes, in spite of the variation displayed among individuals, and identification of aberrant chromosomes are possible. The precise chromosome descriptors can be used to detect differences between the tested individual and various references, in order to find chromosomal abnormalities.
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