Fig. 4

Example of quantitative lung CT analysis for a patient with severe COVID-19 receiving steroid therapy. A 69-year-old female complained of fever for 19 days accompanied with dyspnea and fatigue. After admission to hospital, she received high-flow nasal cannula oxygen therapy, arbidol, and steroid therapy. At admission, intravenous methylprednisolone was initiated with 40 mg every 12 h (1.31 mg/kg/d) for 5 days, followed by gradual tapering by 0.5 mg/kg every 5 days. Methylprednisolone was withdrawn at hospital day 15. Chest CT scans were performed at admission (A), day 3 (B), day 9 (C), day 16 (D), and day 22 (E). Chest CT scans (a), illustration of automated lung segmentation (b), 3D volumetric representation of the bilateral lungs (c), and comparison among different quantitative CT parameters (d) are shown in Fig. 3 at each stage. Yellow areas represent hyperinflated regions (%HI, − 901 to − 1000 HU); blue areas indicate normally aerated regions (%NAL, − 501 to − 900 HU); green areas represent poorly aerated regions (%PAL, − 101 to − 500 HU); red areas indicate nonaerated regions (%NNL, 100 to − 100 HU). The compromised lung volume was calculated as the sum of NNL and PAL. During the treatment process, the compromised lung volume decreased significantly over time from 39.01% (A-d) at admission to 27.49% (E-d) at stage 5