Deep learning has demonstrated remarkable performance across various tasks in medical imaging. However, these approaches primarily focus on supervised learning, assuming that the training and testing data are drawn from the same distribution. Unfortunately, this assumption may not always hold true in practice. To address these issues, unsupervised domain adaptation (UDA) techniques have been developed to transfer knowledge from a labeled domain to a related but unlabeled domain. In recent years, significant advancements have been made in UDA, resulting in a wide range of methodologies, including feature alignment, image translation, self-supervision, and disentangled representation methods, among others. In this paper, we provide a comprehensive literature review of recent deep UDA approaches in medical imaging from a technical perspective. Specifically, we categorize current UDA research in medical imaging into six groups and further divide them into finer subcategories based on the different tasks they perform. We also discuss the respective datasets used in the studies to assess the divergence between the different domains. Finally, we discuss emerging areas and provide insights and discussions on future research directions to conclude this survey.

深度学习在医学影像中取得了显著的性能，但主要关注有监督学习。为了解决这些问题，已经开发了无监督领域自适应技术，用于从一个有标签的领域转移知识到一个相关但无标签的领域。本文从技术角度对医学影像中最新的深度无监督领域自适应方法进行了综述，并将其分类为六组，进一步根据所执行的不同任务进行了精细的子分类。还讨论了用于评估不同领域之间差异的研究中使用的相应数据集。最后，讨论了新兴领域，并提供了未来研究方向的见解和讨论，总结了这项调查。

医学影像领域中的无监督域适应深度学习: 最近的进展与未来展望