Pathology detection and delineation enables the automatic interpretation of medical scans such as chest X-rays while providing a high level of explainability to support radiologists in making informed decisions. However, annotating pathology bounding boxes is a time-consuming task such that large public datasets for this purpose are scarce. Current approaches thus use weakly supervised object detection to learn the (rough) localization of pathologies from image-level annotations, which is however limited in performance due to the lack of bounding box supervision. We therefore propose anatomy-driven pathology detection (ADPD), which uses easy-to-annotate bounding boxes of anatomical regions as proxies for pathologies. We study two training approaches – supervised training using anatomy-level pathology labels and multiple instance learning (MIL) with image-level pathology labels. Our results show that our anatomy-level training approach outperforms weakly supervised methods and fully supervised detection with limited training samples, and our MIL approach is competitive with both baseline approaches, therefore demonstrating the potential of our approach.
Getting bounding box labels for pathology detection in chest X-ray images is expensive and time-consuming. Anaomical regions and corresponding texts (visual grounding) on the other hand, can be mined in an automatic fashion, and is, therefore, available at a large scale.
Fig. 1. Overview: Anatomical regions are first detected using a CNN backbone and a shallow detector. For each region, observed pathologies are predicted using a shared classifier. Bounding boxes for each pathology are then predicted by considering regions with positive predictions and fusing overlapping boxes.
Fig. 2. Qualitative results of Loc-ADPD, with predicted (solid) and target (dashed) boxes. Cardiomegaly (red) is detected almost perfectly, as it is always exactly localized at one anatomical region. Other pathologies like atelectasis (blue), effusion (green), or pneumonia (cyan) are detected but often with non-perfect overlapping boxes. Detection also works well for predicting several overlapping pathologies (second from left).
Tab. 1. Results on the NIH ChestX-ray 8 dataset. Our models Loc-ADPD and MIL-ADPD, trained using anatomy (An) bounding boxes, both outperform all weakly supervised methods trained with image-level pathology (Pa) and anatomy-level pathol- ogy (An-Pa) labels by a large margin. MIL-ADPD is competitive with the supervised baseline trained with pathology (Pa) bounding boxes, while Loc-ADPD outperforms it by a large margin.