Image acquisition and analysis
All included patients underwent baseline chest non-contrast enhanced CT in a designated hospital (Guangzhou Eighth People’s Hospital). An Optima CT680 scanner (GE Medical Systems, Milwaukee, WI) was used and set at 210 mA and 120 kV, with the minimum slice thickness of 1 mm. All images were analyzed by two senior chest radiologists with 15–20 years of experience, in a consistent manner. Image analysis, focused on the lesion features of each patient, included (a) distribution characteristics, (b) number of lobes involved, (c) lobe of lesion distribution, (d) patterns of the lesion (e.g., ground glass opacification, consolidation, cavitation, crazy paving pattern), (e) other signs in the lesion (e.g., interlobular septal thickening, air bronchogram sign), and (f) other findings (e.g., adjacent pleura thickening, pleural effusion, pericardial effusion, thoracic lymphadenopathy, pulmonary emphysema). Thoracic lymphadenopathy was defined as lymph node size of ≥ 10 mm in short-axis; ground glass opacification was defined as hazy opacity that did not obscure underlying bronchial and vascular margins (Figs. 1 and 2); consolidation was defined as opacification with obscuration of bronchial structures and pulmonary vessels [7]; crazy paving pattern was defined as ground glass opacification with associated interlobular septal thickening [8] (Fig. 3). The alterations caused by underlying lung diseases (such as tuberculosis, lung cancer) were not included in this study.
Fig. 1 A 49-year-old man with history of recent travel to Wuhan presented with fever and cough for 6 days. a, b Non-contrast enhanced chest CT showed multiple peripheral patchy ground glass opacities in bilateral multiple lobular and subsegmental with obscure boundary (white arrows), as well as thickening of the adjacent pleura (black arrows). Besides, CT scan also demonstrated consolidation in the right lower lobe and air bronchogram sign in the lesion (red arrow)
Fig. 2 A 49-year-old woman with history of recent travel to Wuhan, presented with fever and cough for 8 days. a Non-contrast enhanced chest CT demonstrated multiple ground glass opacification in the both lower lobes (white arrows). b After 4 days, the follow-up CT scan showed enlarged lesions and increased density of the lesions compared with previous images, indicating disease progression (red arrows)
Fig. 3 A 62-year-old man with a history of exposure to a market in Guangzhou, presented with fever and cough for 11 days. a, b Non-contrast enhanced chest CT showed multiple ground glass opacification in the both lower lobes and thickening of the adjacent pleura. The interlobular septal thickening in regions of ground glass opacification, representing crazy paving pattern (red arrows)
Fifty-two patients underwent a second chest CT after 1–6 days (mean 3.5 days). These images were evaluated for lesions’ evolution by two senior radiologists, in a consistent manner. Changes in lung lesions were divided as no change, disease resolution, and disease progression.