ProtoCLIP: Prototype-Aligned Latent Refinement for Robust Zero-Shot Chest X-Ray Classification

TL;DR

ProtoCLIP enhances zero-shot chest X-ray classification by refining CLIP models with curated data and anchor alignment, significantly improving accuracy and robustness across diverse findings.

Contribution

It introduces a novel refinement strategy combining data curation and representation distillation to improve zero-shot medical image classification.

Findings

ProtoCLIP improves AUC by 2-10 percentage points over baseline.

Achieves a state-of-the-art AUC of 0.94 for pneumothorax.

Effectively mitigates zero-shot transfer failures in medical VLMs.

Abstract

Zero-shot vision-language models (VLMs) have shown promise for chest radiograph classification, but their performance is often limited by confounding label co-occurrence, long-tail class imbalance, and transfer instability under domain shift. We propose ProtoCLIP, a refinement strategy for CLIP-style VLMs that improves zero-shot discrimination through targeted data curation and distilled anchor alignment. Specifically, we construct pathology-focused training subsets with curated negative samples to reduce co-occurrence bias. We also introduce a representation-preserving distillation objective to stabilize adaptation while maintaining semantic structure and improving discrimination of clinically relevant co-occurring pathologies. Evaluated on an unseen dataset VinDr-CXR, ProtoCLIP improves AUC by 2-10 percentage points over a strong CLIP-based baseline across multiple findings. For pneumothorax specifically, ProtoCLIP achieves a state-of-the-art AUC of 0.94. These results demonstrate that anchor-guided refinement, coupled with curated supervision and controlled adaptation, can mitigate common zero-shot transfer failures in medical VLMs without requiring large-scale retraining.