Unsupervised anomaly detection has gained significant attention in the field of medical imaging due to its capability of relieving the costly pixel-level annotation. To achieve this, modern approaches usually utilize generative models to produce healthy references of the diseased images and then identify the abnormalities by comparing the healthy references and the original diseased images. Recently, diffusion models have exhibited promising potential for unsupervised anomaly detection in medical images for their good mode coverage and high sample quality. However, the intrinsic characteristics of the medical images, e.g. the low contrast, and the intricate anatomical structure of the human body make the reconstruction challenging. Besides, the global information of medical images often remain underutilized. To address these two issues, we propose a novel Masked Autoencoder-enhanced Diffusion Model (MAEDiff) for unsupervised anomaly detection in brain images. The MAEDiff involves a hierarchical patch partition. It generates healthy images by overlapping upper-level patches and implements a mechanism based on the masked autoencoders operating on the sub-level patches to enhance the condition on the unnoised regions. Extensive experiments on data of tumors and multiple sclerosis lesions demonstrate the effectiveness of our method.

我们提出了一种新颖的蒙版自编码器增强扩散模型 (MAEDiff)，用于无监督异常检测脑部图像。MAEDiff包括分层补丁分割，通过重叠上层补丁生成健康图像，并在次级补丁上采用基于蒙版自编码器的机制来增强未加入噪声区域的条件。对肿瘤和多发性硬化症病灶的数据进行了大量实验证明了我们方法的有效性。

MAEDiff: 基于掩码自编码器增强扩散模型的无监督脑部图像异常检测