Distilling Clinical Reasoning from Text Corpora for Explainable AI in Medical Imaging

While deep learning models have achieved remarkable diagnostic accuracy in medical imaging, their inherent "black box" nature severely impedes clinical adoption due to a lack of transparency and trust. Current eXplainable AI (XAI) methods, such as saliency maps, offer low-level feature attribution but fail to provide clinically meaningful reasoning. State-of-the-art vision-language models trained end-to-end on image-report pairs often learn to exploit superficial correlations from noisy data, generating plausible but clinically vacuous explanations. To address this critical gap, we propose K-Distill-XAI, a novel teacher-student framework that decouples visual feature learning from high-level clinical reasoning. We first train a domain-expert "teacher" Large Language Model (LLM) on a vast corpus of biomedical literature to generate canonical, text-based clinical rationales. Subsequently, we train a multimodal "student" vision-language model using a cross-modal knowledge distillation objective, compelling it to generate explanations that are semantically aligned with the teacher's expert reasoning. Extensive experiments on the public MIMIC-CXR dataset demonstrate the superiority of our approach. K-Distill-XAI significantly outperforms state-of-the-art baselines in clinical accuracy, achieving an 8% relative improvement in CheXbert F1 score for report generation. Furthermore, this distillation process also boosts classification performance and yields state-of-the-art micro-averaged AUC across 14 clinical conditions.