Weighted Stratification in Multi-label Contrastive Learning for Long-Tailed Medical Image Classification

Ying-Chih Lin, Yong-Sheng Chen

Abstract: Multi-label classification (MLC) in medical image analysis presents significant challenges due to long-tailed class distribution and disease co-occurrence. While contrastive learning (CL) has emerged as a promising solution, recent studies primarily focus on defining positive samples, overlooking the low gradient problem associated with single-disease representation and the impact of co-occurring diseases. To address these issues, we propose ws-MulSupCon, a novel weighted stratification method in CL for MLC. Our gradient analysis indicates that separating the single-disease cases can amplify their gradient contributions. Accordingly, we stratify training samples into single- and multi-disease cases to enhance the representation learning of each disease. Moreover, we design a weighted loss function based on class frequency and disease comorbidity, mitigating the dominance of prevalent diseases and improving rare disease detection. To further discriminate between the healthy and diseased samples, a dedicated CL for healthy cases is introduced, improving overall classification performance and preventing false positives. Extensive experiments on NIH ChestXRay14 and MIMIC-CXR demonstrate that ws-MulSupCon outperforms SoTA methods across nearly all disease classes, showing its superiority and the effectiveness of learning long-tailed distribution in multi-label medical image classification. The code is available at https://github.com/xup6YJ/ws-MulSupCon.

External IDs:dblp:conf/miccai/LinC25