We apply advanced visual representation learning to improve diagnostic tools and automated healthcare systems. Our research includes self-supervised learning for COVID-19 chest X-ray classification using masked autoencoders, efficient training methods for Alzheimer's disease diagnosis with learnable weighted pooling for 3D PET brain image classification, and contrastive cross-modal pre-training strategies for small sample medical imaging. We also work on multi-modal data analysis combining imagery and genetic features for Alzheimer's disease diagnosis, breast cancer localization using weakly-supervised self-training, and automatic hand skeletal shape estimation from radiographs. Our work addresses challenges in medical imaging including domain adaptation, model calibration, and handling limited training data.