Original Research ARTICLE
IHC Colour Histograms for Unsupervised Ki67 Proliferation Index Calculation
- 1Ryerson University, Canada
- 2University of Guelph, Canada
- 3Ontario Veterinary College, University of Guelph, Canada
Automated image analysis tools for Ki67 breast cancer digital pathology images would have significant value if integrated into diagnostic pathology workflows. Such tools would reduce the workload of pathologists, while improving efficiency and accuracy. Developing tools that are robust and reliable to multicentre data is challenging, however, differences in staining protocols, digitization equipment, staining compounds and slide preparation can create variabilities in image quality and colour across digital pathology datasets. In this work, a novel unsupervised colour separation framework based on the IHC colour histogram (IHCCH) is proposed for the robust analysis of Ki67 and hematoxylin stained images in multicentre datasets. An “overstaining” threshold is implemented to adjust for background overstaining, and an automated nuclei radius estimator is designed to improve nuclei detection. Proliferation index and F1 scores were compared between the proposed method and manually labeled ground truth data for 30 TMA cores that have ground truths for Ki67+ and Ki67- nuclei. The method accurately quantified the PI over the dataset, with an average proliferation index difference of 3.25%. To ensure the method generalizes to new, diverse datasets, 50 Ki67 TMAs from the Protein Atlas were used to test the validated approach. As the ground truth for this dataset is PI ranges, the automated result was compared to the PI range. The proposed method correctly classified 74 out of 80 TMA images, resulting in a 92.5% accuracy. In addition to these validations experiments, performance was compared to two colour-deconvolution based methods, and to six machine learning classifiers. In all cases, the proposed work maintained more consistent (reproducible) results, and higher PI quantification accuracy.
Keywords: Colour deconvolution, Colour image processing, Hematoxylin, ki67, Colour Separation, Histogram, proliferation index (PI), breast cancer
Received: 26 Feb 2019;
Accepted: 03 Sep 2019.
Copyright: © 2019 Geread, Morreale, Dony, Brouwer, Wood, Androutsos and Khademi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. April Khademi, Ryerson University, Toronto, Canada, firstname.lastname@example.org