A novel method for quantifying shape deformation applied to biocompatibility testing

Cytotoxicity tests are important for the screening and evaluation of biocom patibility of artificial organs. Morphologic changes of cells that were con tacted biomaterials or biomaterial extracts indicate their toxicity. Howeve r, information on cytotoxic effects is still obtained by subjective visual inspection of microscopic samples. In this article, a novel computer assist ed method is introduced. The automatic analysis of digitized micrographs is achieved in several stages: segmentation, separation, classification, and measurement The segmentation of the image is provided by a new local adapti ve thresholding technique, which adapts the threshold window sizes onto loc al gray level distribution and yields optimal window sizes. The actual thre shold is obtained by maximizing interclass variances and minimizing intracl ass variance. For the separation of connected cells, the binarized samples are cleaned from "false" markers by morphologic filtering. The subsequent s eparation is a two phase approach. Information levels are generated top-dow n by successively applying an enhanced erosion operator, which yields marke rs and filters noise usually evolving from multiple erosions. The converse bottom-up integration of the eroded markers is performed by successively ap plying an enhanced dilation operator, which reconstructs the cells and prev ents merging of already separated objects. The subsequent measuring provide s quantitative parameters of the distribution of size and compactness of th e cells contained within the sample. The method was evaluated by L-929 fibr oblasts that were in contact with 0%, 5%, and 10% concentrations of ethanol . For each concentration, 268 images of the cell populations were captured. The obtained quantitative parameters are highly correlated to the common v erbal description of morphologic changes. Therefore, the proposed automatic method has several advantages compared with subjective examinations. The r e suits allow an objective comparison of the quantification of phenomena; t he subjective influence of the observer is eliminated; and the laboratory s taff is relieved of time consuming routine work.