Separating lungs in CT scans for improved COVID19 detection

This paper outlines our submission for the 4th COV19D competition as part of the ‘Domain adaptation, Explainability, Fairness in AI for Medical Image Analysis’ (DEFAI-MIA) workshop at the Computer Vision and Pattern Recognition Conference (CVPR). The competition consists of two challenges. The first is to train a classifier to detect the presence of COVID-19 from over one thousand CT scans from the COV19-CT-DB database. The second challenge is to perform domain adaptation by taking the dataset from Challenge 1 and adding a small number of scans (some annotated and other not) for a different distribution. We preprocessed the CT scans to segment the lungs, and output volumes with the lungs individually and together. We then trained 3D ResNet and Swin Transformer models on these inputs. We annotated the unlabeled CT scans using an ensemble of these models and chose the high-confidence predictions as pseudo-labels for fine-tuning. This achieved the winning macro F1 score of 94.89% for Challenge 1 of the competition. It also achieved a second-best macro F1 score of 77.21% for Challenge 2.