CARD: Calibration via Agreement in Reverse Diffusion for Out-of-Domain MRI Segmentation

2026-08-26

AI Summary

为解决域外MRI分割中模型自信度与准确性不匹配问题，提出CARD方法，通过反向扩散过程中的形状先验和类别分布差异来校准模型。

Abstract

Probability calibration aligns model confidence with predictive accuracy, enabling clinicians to identify unreliable segmentation regions. This alignment breaks down under domain shift, where artifacts and unseen protocols produce confident errors. Existing post-hoc methods adapt the correction at test time, conditioning on predictive entropy, the logit pattern, or augmentation response, but each proxy is read from the terminal prediction, the very quantity that shift corrupts. This motivates reliability evidence beyond the terminal prediction, which categorical diffusion provides in two ways. First, a generative shape prior keeps a capacity-limited reference intact when appearance is corrupted, so its disagreement with the primary segmentor highlights primary-model errors. Second, every reverse step yields a class distribution, separating persistent disagreement from transient discrepancy. Aggregated over the trajectory, this disagreement correlates with Dice at 0.788, against 0.521 for a matched discriminative control. We therefore propose CARD (Calibration via Agreement in Reverse Diffusion), which maps the temporal aggregate of this disagreement to a temperature field applied per pixel across all classes, so that confidence changes while the segmentation does not. Across cardiac, prostate and brain MRI shifts, CARD lowers calibration error in 45 of 49 comparisons against the strongest baseline in each setting.

Problem

• probability calibration
• domain shift
• out-of-domain MRI segmentation
• confident errors

Innovation

• probability calibration
• reverse diffusion
• generative shape prior
• temporal aggregate of disagreement
• temperature field