The study was approved by the Research Ethics Committee of the Central People’s Hospital of Huizhou, and in accordance with guidelines outlined in the Declaration of Helsinki. Informed consent was waived for this study. We collected and analyzed data of these patients anonymously.
Patients
All of the patients with COVID-19 pneumonia in Huizhou city between January 22, 2020 and March 5, 2020 were under treatment in the Central People’s Hospital of Huizhou. The patients were diagnosed with COVID-19 according to the World Health Organization (WHO) interim guidance 19. A total of 62 consecutive patients in the hospital were enrolled in this retrospective study. Among the 62 patients, 3 patients did not have chest CT scans, while another 3 patients did not have abnormal chest CT imaging. We excluded the 6 patients and the remaining 56 patients were included. All patients enrolled have been discharged from hospital according to the discharge criteria formulated by National Health Commission 20,21.
Data on gender, age, clinical symptoms, laboratory findings, exposure history (resident of or having travelled to Hubei Province; having closely contacted with confirmed or suspected COVID-19 patients), comorbidities, the date of illness onset and the date of performing CT examination were collected for all patients by carefully reviewing their medical records. Disease duration was defined as the time interval between the date of symptom onset or on which the specimen of asymptomatic case was detecting positive for SARS-CoV-2 and the date of CT acquisition.
CT Protocol
Chest CT scans were obtained on a commercial 16-detector CT scanner (Philips MX16, Philips Medical Systems, the Netherlands). To reduce motion artifacts, the patients were required to hold breath during scanning. All of the patients were performed a spiral scan for the following parameters: 2-mm section thickness, 1-mm gap, 24-mmcollimation, 360-mm field of view, 512-mm matrix, 120 KV, automatic tube current modulation. From the raw data, CT images were reconstructed with a lung algorithm for parenchymal analysis.
Imaging Analysis
All images were reviewed by 2 experienced chest radiologists who had worked more than 5 years in this field blindly to the clinical information. They reviewed the images independently and reached a decision in consensus. The following image characteristics were recorded 14: (1) ground-glass opacities (GGO, defined as hazy increased opacity of lung without obscuration of the underlying vessels and airway walls), (2) consolidation (defined as homogeneous increase of lung parenchyma with obscuration of the underlying vessels and airway walls), (3) crazy-paving pattern (defined as GGO with superimposed thickened interlobular and intralobular lines), (4) interlobular septal thickening, (5) halo sign (defined as a nodule or mass surrounded by GGO), (6) reversed halo sign (defined as focal rounded area of GGO surrounded by a more or less complete ring of consolidation), (7) fibrous stripes, (8) air bronchogram, (9) atelectasis, (10) subpleural curvilinear line, (11) pleural or pericardial effusion, (12) thoracic lymphadenopathy (defined as lymphnode with short axis diameter ≥1cm). To estimate the extent of lung involvement of all these abnormalities, we used a semi-quantitative score to assign each of 5 lung lobes. Each lung was assigned a score from 0 to 4 (0: no involvement; 1: 1-25% involvement; 2: 26-49% involvement; 3: 50-75% involvement; 4: >75% involvement) 8. The CT scores of 5 lung lobes were summed up as the total CT score which measured the overall lung involvement, ranging from 0 (no involvement) to 20 (maximum involvement).
The distribution of lung abnormalities was also recorded: (1) peripheral (involving mainly the outer one-third of the lung), (2) peribronchovascular (abnormalities along the path way of bronchovascular bundle), (3) diffuse (continuous involvement without respect to lung segments), (4) both peripheral and peribronchovascular. Radiological manifestations and distribution of some glossaries were presented in Figure 4.
Subsequently, we classified the CT scans of 56 patients into 4 groups based on the date on which the CT scan was obtained at the 1st, 2nd, 3rd week and longer than 3 weeks after symptom onset. If a patient was asymptomatic, we categorized the scans of the patient according to the date on which the specimen of patient was detecting positive for SARS-CoV-2 instead of the date of symptom onset.
Patients with follow-up chest CT scans further revealed the time course of major lung abnormalities in patients. According to the extent of reduction of abnormities presented in CT imagines, we categorized the 45 patients which had at least 2 follow-up CT scans into 4 groups: Group A, patients whose lesions reduced ≥75%; Group B, those whose lesions reduced 50-75%; Group C, those whose lesions reduced 25-50%; Group D, those whose lesions reduced <25%).
Statistical Analysis
Clinical characteristics and laboratory findings of the 56 include patients were reported. In addition, imaging features of CT scans acquired at the 1st, 2nd, 3rd week and longer than 3 weeks after symptom onset were evaluated. Further, we compared hospitalization durations, age and total CT scores among patients with at least 2 CT scans which were divided into 4 groups based on the extents that lesions reduced. We summarized continuous variables as medians and interquartile ranges (IQRs) or ranges as appropriate, while categorical variables were expressed as counts and percentages. All statistical analyses were performed using R software version 3.6.2 (R Foundation for Statistical Computing).