PICK: Predict and Mask for Semi-supervised Medical Image Segmentation

Pseudo-labeling and consistency-based co-training are established paradigms in semi-supervised learning. Pseudo-labeling focuses on selecting reliable pseudo-labels, while co-training emphasizes sub-network diversity for complementary information extraction. However, both paradigms struggle with the inevitable erroneous predictions from unlabeled data, which poses a risk to task-specific decoders and ultimately impact model performance. To address this challenge, we propose a PredICt-and-masK (PICK) model for semi-supervised medical image segmentation. PICK operates by masking and predicting pseudo-label-guided attentive regions to exploit unlabeled data. It features a shared encoder and three task-specific decoders. Specifically, PICK employs a primary decoder supervised solely by labeled data to generate pseudo-labels, identifying potential targets in unlabeled data. The model then masks these regions and reconstructs them using a masked image modeling (MIM) decoder, optimizing through a reconstruction task. To reconcile segmentation and reconstruction, an auxiliary decoder is further developed to learn from the reconstructed images, whose predictions are constrained by the primary decoder. We evaluate PICK on five medical benchmarks, including single organ/tumor segmentation, multi-organ segmentation, and domain-generalized tasks. Our results indicate that PICK outperforms state-of-the-art methods. The code is available at https://github.com/maxwell0027/PICK.