Hierarchical Consistency and Refinement for Semi-supervised Medical Segmentation

Abstract

Semi-supervised learning exploits unlabeled data to improve generalization ability with insufficient annotations. In recent years, Mean Teacher method (MT) obtained impressive performance using prediction consistency as regularization. However, severe ambiguity in medical images makes the targets in the teacher model highly unreliable in obscure regions, thereby limits the model capability. To address this problem, we propose a novel multi-task learning semi-supervised framework to gain hierarchical consistency through training process. Specifically, we introduce region and shape predictions as subtasks to obtain the coarse-grained location and fine-grained boundary information. Then we predict pixel-level segmentation by fusing the hierarchical feature. Since calculating consistency loss in more loose regions typically alleviates the degradation caused by learning from unreliable targets, our teacher model generate guidance from each of the subtasks. Moreover, we focus on the geometrical correlations in different tasks and proposed the constraint method to refine the segmentation for accurate guidance. Experiments on the left atrium segmentation dataset show our algorithm achieves state-of-the-art performance comparing with other semi-supervised methods.