Fully Test-Time Adaptation for Image Segmentation.

When adopting a model from the source domain to the target domain, its performance usually degrades due to the domain shift problem. In clinical practice, the source data usually cannot be accessed during adaptation for privacy policy and the label for the target domain is in shortage because of the high cost of professional labeling. Therefore, it is worth considering how to efficiently adopt a pretrained model with only unlabeled data from the target domain. In this paper, we propose a novel fully test-time unsupervised adaptation method for image segmentation based on Regional Nuclear-norm (RN) and Contour Regularization (CR). The RN loss is specially designed for segmentation tasks to efficiently improve discriminability and diversity of prediction. The CR loss constrains the continuity and connectivity to enhance the relevance between pixels and their neighbors. Instead of retraining all parameters, we modify only the parameters in batch normalization layers with only a few epochs. We demonstrate the effectiveness and efficiency of the proposed method in the pancreas and liver segmentation dataset from the Medical Segmentation Decathlon and CHAOS challenge.