Fig. 1.

Typical cases of two non-severe (left) and two severe (right) patients with COVID-19, where infections often occur in small regions of the lungs in CT images. The similar imaging biomarkers (e.g., ground glass opacities, mosaic sign, air bronchogram and interlobular septal thickening) of both cases (denoted by red boxes) make the non-severe and severe images difficult to distinguish. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)