One medical visual tokenizer across 2D and 3D imaging, nine modalities and 24 benchmarks
AspireAI community · arXiv
Medical multimodal AI needs a shared visual interface, but existing medical visual tokenizers are tied to one dimension and one imaging modality, which forces fragmented representations. MedVTok maps 2D images and 3D volumes from diverse modalities into a unified token space, using slice differential regularization to model inter-slice anatomical coherence that per-pixel or per-voxel supervision misses, and multi-expert representation alignment to combine several medical expert encoders while keeping modality-specific knowledge. Trained on 28M images and 70K volumes across 9 imaging modalities, the tokenizer supports classification, retrieval, segmentation, synthesis, visual question answering and medical report generation, and the authors report state-of-the-art performance across 24 benchmarks. It is a domain-specific model for medical imaging only, and the state-of-the-art claim is the authors own evaluation across their chosen benchmark set.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.