CiSeg: Unsupervised Cross-Modality Adaptation for 3D Medical Image Segmentation via Causal Intervention
Peiqing Lv, Yaonan Wang, Min Liu, Zhe Zhang, Yunfeng Ma, Licheng Liu, Erik H. W. Meijering · IEEE Transactions on Medical Imaging · 2025
Unsupervised domain adaptation (UDA) addresses the domain shift problem by transferring knowledge from labeled source domain data (e.g. CT) to unlabeled target domain data (e.g. MRI). While state-of-the-art methods reduce domain gaps via image- or feature-level alignment, their reliance on spurious correlations in the training data often limits generalization across domains. To overcome this limitation, we propose the Causal Intervention Segmentation Network (CiSeg), a novel framework that first integrates causal inference into UDA. A Structural Causal Model (SCM) is first constructed for the source domain to disentangle causal variables from bias variables, alleviating the impact of spurious correlations. Based on this SCM, we introduce a Counterfactual Disentanglement (CD) module to decompose the source domain's latent features into distinct causal and bias components, effectively eliminating their mutual dependencies. To enhance cross-domain consistency, two auxiliary components are introduced: Prototype-guided Contrastive Learning (PCL) and Causal-bias Residual Alignment (CBRA). PCL aligns pixel-level representations with their corresponding semantic prototypes, promoting stronger intra-class consistency and clearer inter-class separability. CBRA employs adversarial learning to align causal and bias residual features across domains, further enhancing feature-level invariance. Extensive experiments on cardiac, abdominal multi-organ, and BraTS18 segmentation tasks demonstrate that CiSeg outperforms state-of-the-art methods, achieving superior segmentation performance and robust cross-domain generalization. Code and models are available at https://github.com/lvpeiqing/CiSeg.