PaCL: Patient-aware contrastive learning through metadata refinement for generalized early disease diagnosis

Early diagnosis plays a pivotal role in effectively treating numerous diseases, especially in healthcare scenarios where prompt and accurate diagnoses are essential. Contrastive learning (CL) has emerged as a promising approach for medical tasks, offering advantages over traditional supervised learning methods. However, in healthcare, patient metadata contains valuable clinical information that can enhance representations, yet existing CL methods often overlook this data. In this study, we propose an novel approach that leverages both clinical information and imaging data in contrastive learning to enhance model generalization and interpretability. Furthermore, existing contrastive methods may be prone to sampling bias, which can lead to the model capturing spurious relationships and exhibiting unequal performance across protected subgroups frequently encountered in medical settings. To address these limitations, we introduce Patient-aware Contrastive Learning (PaCL), featuring an inter-class separability objective (IeSO) and an intra-class diversity objective (IaDO). IeSO harnesses rich clinical information to refine samples, while IaDO ensures the necessary diversity among samples to prevent class collapse. We demonstrate the effectiveness of PaCL both theoretically through causal refinements and empirically across six real-world medical imaging tasks spanning three imaging modalities: ophthalmology, radiology, and dermatology. Notably, PaCL outperforms previous techniques across all six tasks.