In this paper, we proposed a novel mutual consistency network (MC-Net+) to effectively exploit the unlabeled hard regions for semi-supervised medical image segmentation. The MC-Net+ model is motivated by the observation that deep models trained with limited annotations are prone to output highly uncertain and easily mis-classified predictions in the ambiguous regions (e.g. adhesive edges or thin branches) for the image segmentation task. Leveraging these region-level challenging samples can make the semi-supervised segmentation model training more effective. Therefore, our proposed MC-Net+ model consists of two new designs. First, the model contains one shared encoder and multiple sightly different decoders (i.e. using different up-sampling strategies). The statistical discrepancy of multiple decoders' outputs is computed to denote the model's uncertainty, which indicates the unlabeled hard regions. Second, a new mutual consistency constraint is enforced between one decoder's probability output and other decoders' soft pseudo labels. In this way, we minimize the model's uncertainty during training and force the model to generate invariant and low-entropy results in such challenging areas of unlabeled data, in order to learn a generalized feature representation. We compared the segmentation results of the MC-Net+ with five state-of-the-art semi-supervised approaches on three public medical datasets. Extension experiments with two common semi-supervised settings demonstrate the superior performance of our model over other existing methods, which sets a new state of the art for semi-supervised medical image segmentation.

本文提出了一种新颖的互相关网络（MC-Net+），通过有效地利用未标记数据进行半监督医学图像分割。我们在三个公共医学数据集上比较了我们 MC-Net+ 模型的分割结果与五种半监督方法的结果，实验表明我们的模型在半监督下分割效果最优，树立了半监督医学图像分割的新标准。

半监督医学图像分割的互一致性学习