Medical image classification plays a vital role in disease diagnosis, tumor staging, and various clinical applications. Deep learning (DL) methods have become increasingly popular for medical image classification. However, medical images have unique characteristics that pose challenges for training DL-based models, including limited annotated data, imbalanced distribution of classes, and large variations in lesion structures. Self-supervised learning (SSL) methods have emerged as a promising solution to alleviate these issues through directly learning useful representations from large-scale unlabeled data. In this study, a new generative self-supervised learning method based on the StyleGAN generator is proposed for medical image classification. The style generator, pretrained on large-scale unlabeled data, is integrated into the classification framework to effectively extract style features that encapsulate essential semantic information from input images through image reconstruction. The extracted style feature serves as an auxiliary regularization term to leverage knowledge learned from unlabeled data to support the training of the classification network and enhance model performance. To enable efficient feature fusion, a self-attention module is designed for this integration of the style generator and classification framework, dynamically focusing on important feature elements related to classification performance. Additionally, a sequential training strategy is designed to train the classification model on a limited number of labeled images while leveraging large-scale unlabeled data to improve classification performance. The experimental results on a chest X-ray image dataset demonstrate superior classification performance and robustness compared to traditional DL-based methods. The effectiveness and potential of the model were discussed as well.
Histopathology whole-slide image (WSI) captures detailed structural and morphological features of tumor tissue, offering rich histological and molecular information to support clinical practice. With the development of artificial intelligence, deep learning (DL) methods have emerged to assist in automatically analyzing histopathology WSIs. It alleviates the need for tedious, time-consuming, and error-prone inspections by clinicians. Up to now, employing DL models for histopathology WSI analysis is still challenging due to the intrinsic complexity of histology characteristics of tumor tissue, high image resolution, and large image size. In this study, we proposed a transformer-based classifier with feature aggregation for cancer subtype classification using histopathology WSIs while addressing these challenges. Our method shows three advantages to improve classification performance. First, an aggregate transformer decoder is employed to learn both global and local features from WSIs. Second, the transformer architecture facilitates the decoder to learn spatial correlations among different regions in a WSI. Third, the self-attention mechanism of the transformer facilitates the generation of saliency maps to highlight regions of interest in WSIs. We evaluated our model on three cancer subtype classification tasks and demonstrated its effectiveness and performance.
High-resolution histopathological images have rich characteristics of cancer tissues and cells. Recent studies have shown that digital pathology analysis can aid clinical decision-making by identifying metastases, subtyping and grading tumors, and predicting clinical outcomes. Still, the analysis of digital histologic images remains challenging due to the imbalance of the training data, the intrinsic complexity of histology characteristics of tumor tissue, and the extremely heavy computation burden for processing extremely high-resolution whole slide imaging (WSI) images. In this study, we developed a new deep learning-based classification framework that addresses these unique challenges to support clinical decision-making. The proposed method is motivated by our recently developed adversarial learning strategy with two major innovations. First, an image pre-processing module was designed to process the high-resolution histology images to reduce computational burden and keep informative features, alleviating the risk of overfitting issues when training the network. Second, recently developed StyleGAN2 with powerful generative capability was employed to recognize complex texture patterns and stain information in histology images and learn deep classification-relevant information, further improving the classification and reconstruction performance of our method. The experimental results on three different histology image datasets for different classification tasks demonstrated superior classification performance compared to traditional deep learning-based methods, and the generality of the proposed method to be applied to various applications.
The COVID-19 pandemic continues spreading rapidly around the world and has caused devastating outcomes towards the health of the global population. The reverse transcription-polymerase chain reaction (RT-PCR) test, as the only current gold standard for screening infected cases, yields a relatively high false positive rate and low sensitivity on asymptomatic subjects. The use of chest X-ray radiography (CXR) images coupled with deep- learning (DL) methods for image classification, represents an attractive adjunct to or replacement for RT-PCR testing. However, its usage has been widely debated over the past few months and its potential effectiveness remains unclear. A number of DL-based methods have been proposed to classify the COVID-19 cases from the normal ones, achieving satisfying high performance. However, these methods show limited performance on the multi-class classification task for COVID-19, pneumonia and normal cases, mainly due to two factors: 1) the textures in COVID-19 CXR images are extremely similar to that of pneumonia cases, and 2) there are much fewer COVID-19 cases compared to the other two classes in the public domain. To address these challenges, a novel framework is proposed to learn a deep convolutional neural network (DCNN) model for accurately classifying COVID-19 and pneumonia cases from other normal cases by the use of CXR images. In addition to training the model by use of conventional classification loss which measures classification accuracy, the proposed method innovatively employs a reconstruction loss measuring image fidelity and an adversarial loss measuring class distribution fidelity to assist in the training of the main DCNN model to extract more informative features to support multi-class classification. The experiment results on a COVID-19 dataset demonstrate the superior classification performance of the proposed method in terms of accuracy compared to other existing DL-based methods. The experiment on another cancer dataset further implies the potential of applying the proposed methods in other medical imaging applications.
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