Cancer is one of the leading causes of death, thereby, contributing to their quick diagnosis or treatment is of greatest importance. Nowadays, tumours are mainly diagnosed and graded histologically using biopsies. Since the images need to be sharp to distinguish biological structures, samples are thinly sliced (3-5 μm) to avoid scattering and contrast is obtained using highly absorbance dyes (e.g., Haematoxylin and Eosin (H&E)). RGB (Red-Green-Blue) cameras have been widely employed to acquire those images, while new approaches, such as Hyperspectral (HS) Imaging (HSI), have been arising to obtain a greater amount of spectral information from the samples. However, in order to have diffuse light for the HS cameras to capture it, the thickness of the sample should be bigger than the ones employed in conventional microscopy. This work aims to characterize the influence of tissue thickness of histology breast samples sectioned at 2 and 3 μm on their spectral signatures. Based on the H&E transmittance spectra peaks, HS images were segmented into three structures: stroma (eosin-stained), nuclei (haematoxylin-stained), and background (non-stained). Results show that, spatially, in 3 μm samples there are more cells imaged than in 2 μm samples. Moreover, spectrally, 3 μm samples proportionate higher spectral contrast than 2 μm samples due the greater interaction of light with tissue, denoting them as more suitable for microscopic HSI.
KEYWORDS: RGB color model, Tumors, Principal component analysis, Tissues, Cancer detection, Object detection, Visualization, Hyperspectral imaging, Data modeling
The current advances in Whole-Slide Imaging (WSI) scanners allow for more and better visualization of histological slides. However, the analysis of histological samples by visual inspection is subjective and could be challenging. State-of-the-art object detection algorithms can be trained for cell spotting in a WSI. In this work, a new framework for the detection of tumor cells in high-resolution and high-detail using both RGB and Hyperspectral (HS) imaging is proposed. The framework introduces techniques to be trained on partially labeled data, since labeling at the cellular level is a time and energy-consuming task. Furthermore, the framework has been developed for working with RGB and HS information reduced to 3 bands. Current results are promising, showcasing in RGB similar performance as reference works (F1-score = 66.2%) and high possibilities for the integration of reduced HS information into current state-of-art deep learning models, with current results improving the mean precision a 6.3% from synthetic RGB images.
Hyperspectral (HS) imaging (HSI) is a novel technique that allows a better understanding of materials, being an improvement respect to other imaging modalities in multiple applications. Specifically, HSI technology applied to breast cancer histology, could significantly reduce the time of tumor diagnosis at the histopathology department. First, histological samples from twelve different breast cancer patients have been prepared and examined. Second, they were digitally scanned, using RGB (Red-Green-Blue) whole-slide imaging, and further annotated at cell level. Then, the annotated regions were captured with an HS microscopic acquisition system at 20× magnification, covering the 400-1000 nm spectral range. The HS data was registered (through synthetic RGB images) to the whole-slide images, allowing the transfer of accurate annotations made by pathologists to the HS image and extract each annotated cell from such image. Then, both spectral and spatial-spectral classifications were carried out to automatically detect tumor cells from the rest of the coexisting cells in the breast tissue (fibroblasts and lymphocytes). In this work, different supervised classifiers have been employed, namely kNN (k-Nearest-Neighbors), Random Forest, DNN (Deep Neural Network), Support Vector Machines (SVM) and CNN (Convolutional Neural Network). Test results for tumor cells vs. fibroblast classification show that the kNN performed with the best sensitivity/specificity (64/52%) trade-off and the CNN achieved the best sensitivity and AUC results (96% and 0.91, respectively). Moreover, at the tumor cells vs. lymphocyte classification, kNN also provided the best sensitivity-specificity ratio (58.47/58.86%) and an F1-score of 74.12%. The SVM algorithm also provided a high F-score result (70.38%). In conclusion, several machine learning algorithms provide promising results for cell classification in breast cancer tissue and so, future work must include these discoveries for faster cancer diagnosis.
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