  Chest X-ray is an essential diagnostic tool in the identification of chest
diseases given its high sensitivity to pathological abnormalities in the lungs.
However, image-driven diagnosis is still challenging due to heterogeneity in
size and location of pathology, as well as visual similarities and
co-occurrence of separate pathology. Since disease-related regions often occupy
a relatively small portion of diagnostic images, classification models based on
traditional convolutional neural networks (CNNs) are adversely affected given
their locality bias. While CNNs were previously augmented with attention maps
or spatial masks to guide focus on potentially critical regions, learning
localization guidance under heterogeneity in the spatial distribution of
pathology is challenging. To improve multi-label classification performance,
here we propose a novel method, HydraViT, that synergistically combines a
transformer backbone with a multi-branch output module with learned weighting.
The transformer backbone enhances sensitivity to long-range context in X-ray
images, while using the self-attention mechanism to adaptively focus on
task-critical regions. The multi-branch output module dedicates an independent
branch to each disease label to attain robust learning across separate disease
classes, along with an aggregated branch across labels to maintain sensitivity
to co-occurrence relationships among pathology. Experiments demonstrate that,
on average, HydraViT outperforms competing attention-guided methods by 1.2%,
region-guided methods by 1.4%, and semantic-guided methods by 1.0% in
multi-label classification performance.
