Abstract
Recent vision-language foundation models deliver state-of-the-art results in natural image classification, but falter in medical images due to pronounced domain shifts. Training a medical foundation model also requires substantial resources, including extensive annotated data and high computational capacity. To bridge this gap with minimal overhead, we introduce MedBridge, a lightweight multimodal adaptation framework that flexibly re-purposes arbitrary pre-trained foundation VLMs for medical image diagnosis. MedBridge comprises three novel core components. First, a Focal Sampling module that subsamples and extracts high-resolution local regions to capture subtle pathological features, compensating for the limited input resolution of foundation VLMs. Second, a Query-Encoder model with a small set of learnable queries to align the feature maps of frozen VLMs with medical semantics, without requiring retraining of the backbone layers. Third, a Mixture of Experts mechanism, driven by lear