Knowledge-Guided Cross-Modal Alignment and Progressive Fusion for Chest X-Ray Report Generation

The task of chest X-ray report generation, which aims to simulate the diagnosis process of doctors, has received widespread attention. Compared with the image caption task, chest X-ray report generation is more challenging since it needs to generate a longer and more accurate description of each diagnostic part in chest X-ray images. Most of existing works focus on how to extract better visual features or more accurate text expression based on existing reports. However, they ignore the interactions between visual and text modalities and are thus obviously not in line with human thinking. A small part of works explore the interactions of visual and text modalities, but data-driven learning of cross-modal information mapping can not break the semantic gap between different modalities. In this work, we propose a novel approach called Knowledge-guided Cross-modal Alignment and Progressive fusion (KCAP), which takes the knowledge words from a created medical knowledge dictionary as the bridge to guide the cross-modal feature alignment and fusion, for accurate chest X-ray report generation. In particular, we create the medical knowledge dictionary by extracting medical phrases from the training set and then selecting some phrases with substantive meanings as knowledge words based on their frequency of occurrence. Based on the knowledge words from the medical knowledge dictionary, the visual and text modalities are interacted by a mapping layer for the enhancement of the features of two modalities, and then the alignment fusion module is introduced to mitigate the semantic gap between visual and text modalities. To retain the important details of the original information, we design a progressive fusion scheme to integrate the advantages of both salient fused and original features to generate better medical reports. The experimental results on IU-Xray and MIMIC datasets demonstrate the effectiveness of the proposed KCAP.