提出基于熵的公平主动学习框架,降低脑部分割中不同群体的性能差距。
Exploring Entropy-based Active Learning for Fair Brain Segmentation

- 用加权熵策略根据群体表现调节选择不确定性
- 在强/弱偏倚下分别降低75%和86%的性能差异
- 适合资源受限下需公平性的医学图像分割任务
主动学习(AL)是降低医学图像分割高昂标注成本的关键策略。然而,标准不确定性主动学习通常只关注整体性能,忽视敏感属性分组间的性能不公。尽管分类任务中已有公平主动学习研究,但其在医学图像分割中的应用仍空白。本文提出一种公平感知的主动学习框架,采用加权熵选择策略,基于已标注集上各群体的表现估计动态调节不确定性。为分离认知不确定性与解剖体积差异,进一步引入仅限感兴趣区域的掩码缩放熵。在带有可控左尾状核偏倚的合成T1加权脑部MRI上评估,使用3D U-Net进行分割,初始标注集设置为人口学平衡或严重失衡。实验表明,相比随机采样和标准熵采样,该方法显著降低群体间性能差异。通过在主动学习周期中优先选择表现较差的子群体,该方法始终取得最高公平性尺度性能,在最终预算下使强偏倚场景下的差异指标降低75%,弱偏倚场景降低86%。本工作是首个针对医学图像分割的公平主动学习研究,为资源受限环境提供高效公平建模策略。
原文摘要 · Abstract (English)
Active learning (AL) has emerged as a crucial strategy for reducing the prohibitive costs associated with medical image segmentation. However, standard uncertainty-based AL methods typically focus on maximizing performance metrics, ignoring performance disparities or fairness across groups with sensitive attributes. While fair active learning has been explored in classification tasks, its intersection with medical image segmentation remains unaddressed. In this work, we introduced a fairness-aware active learning framework with a Weighted Entropy selection strategy that modulates uncertainty based on current group-specific performance estimates on the labeled set. To decouple true epistemic uncertainty from anatomical volume variances, we further utilized a masked, scaled entropy restricted to the region of interest. The framework was evaluated on synthetic T1-weighted brain MRIs with controlled left caudate bias in both strong and weak bias settings. A 3D U-Net was trained to segment the left caudate under several AL strategies, starting from both demographically balanced and strongly imbalanced initial labeled sets. Experiments demonstrated that our method markedly reduces performance disparities between groups compared to random sampling and standard uncertainty sampling. By prioritizing poorly segmented subgroups during the AL cycles, our method consistently achieved the highest equity-scaled performance and reduced the disparity metric by 75% (strong bias) and 86% (weak bias) relative to standard entropy at the final budget. Overall, this work is among the first studies on fair AL for medical image segmentation, offering an efficient strategy to train more equitable models in resource-constrained environments.
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