Our study protocol was approved by the Institutional Review Board (IRB). Informed consent was waived for this retrospective study that evaluated the de-identified data and involved no potential risk to patients.
Patients
Our study protocol was approved by the Institutional Review Board (IRB). Informed consent was waived for this retrospective study that evaluated the de-identified data and involved no potential risk to patients.
This multi-center, retrospective and observational study was conducted at the designated hospitals to treat patients with COVID-19 pneumonia, including Jianghan Shelter Hospital (Wuhan, China), Guilin Nan-xi-shan Hospital (Guangxi, China), Liuzhou People’s Hospital (Guangxi, China), The medical records of 73 patients with laboratory-confirmed COVID-19 infections were retrospectively collected from February 5th, 2020 to March 8th, 2020.The diagnosis of COVID-19 infection was confirmed according to the following methods: isolation of SARS CoV-2, or at least two positive results of real-time RT-PCR assays for SARS-CoV-2, or the detection of a genetic sequence matched with SARS-CoV-2. The severity of COVID-19 infection was defined according to the Chinese Management Guideline for COVID-19(version 6.0)(22) In this study, a total of 73 patients, including 30 females and 43 males, with age ranging from 26 to 85 (mean, 51 ± 13) years, were enrolled. Thereafter, patients were divided into four groups according to the disease severity, including mild-, common-, severe-, and fatal-type. Additionally, the treatment regimens varied depending on the disease type, so the patients were re-grouped to non-emergency (mild- and common-type) and emergency (severe- and fatal-type) groups. Among these enrolled patients, 47 (mean age, 49 ± 12 years) were recruited into the non-emergency group, while 26 (mean age, 55 ± 15 years) were enrolled in the emergency group. Some researchers (X.L., Y.Z., M.D.) noted that the related clinical parameters included laboratory findings, date of symptom onset, indications for the scans, and presence of complications (such as pneumomediastinum, pneumothorax, and superimposed infections). Moreover, CT scans were categorized according to the time duration between the date of symptom onset and the dates of obtaining CT images at 1, 2, 3, 4, and over 4 weeks after symptom onset.
The discharge criteria were as follows, absence of fever for at least 3 days, substantial improvement in both lungs upon chest CT, clinical remission of respiratory symptoms, and two negative results in throat-swab tests for SARS-CoV-2 RNA obtained at an interval of at least 24 h.
CT Protocol
All thorax CT scans were performed using commercial multi-detector CT scanners at the single inspiratory phase (uCT550, Shanghai United Imaging Healthcare, Shanghai, China; Aquilion 16-slice, TOSHIBA Medical Systems; Tochigi, Japan; NeuViz 64in, Shengyang Neusoft medical system, Hunan, China; Somatom Definition AS, Siemens, Nurnberg,Germany; Brilliance 64, Phillips Medical System, Eindhoven, the Netherlands). To acquire CT images, the tube voltage was fixed at 120 kVp, the pitch was 1.075, and the collimator widths were 64 × 0.6 mm, 128 × 0.6 mm, 64 × 0.6 mm, and 40 × 0.55 mm. CT images were reconstructed based on the raw data with a matrix size of 512 × 512 as the axial images (thickness, 1.5 mm or 2 mm; increment, 1.5 mm or 2 mm) in the transverse slice direction. The images were taken at lung (window width, 1,000– 1,500 HU; window level, − 700 HU) and mediastinal (window width, 350 HU; window level, 35–40 HU) settings.
Chest CT Evaluation
CT images of 73 were evaluated by three fellowship-trained cardiothoracic radiologists (M.D., Y.Z. with 7and 5 years of experience in interpreting chest CT findings, respectively) using the institutional digital database system (Vue PACS, version 11.3.5.8902, Carestream Health, Canada). All Digital Imaging and Communications in Medicine (DICOM) images were interpreted from CT studies without access to clinical and laboratory findings. All images were reviewed by the radiologists independently, and the final decisions were reached by discussion and consensus. All chest CT images evaluated(16, 23–26) are shown in Table 1.
Table 1
CT imaging features of patients with COVID-19
CT Characteristics | Definition |
Lobe involvement | Categorized as right upper lobe, right middle lobe, right lower lobe, left upper lobe and left lower lobe involvement |
The lung segment involved Lung involvement | Each segment of the lung was reviewed for GGO, Consolidation and Reticular, respectively Categorized as unilateral or bilateral lung involvement |
Lesion location Extent of lesion involvement | Central, lesion located in the interior two-thirds of the lung; Peripheral, in the outer one-third of the lung; Both central and peripheral Categorized as focal, multifocal, diffuse |
Predominantly distribution of opacities | Septal/subpleural, involving mainly the subperipheral one-third of the lung; Perbronchovasular, surrounding mainly the peribronchovascular bundle. Random, without predilection for subpleural or peribronchovascular regions |
Predominantly CT pattern | GGO pattern, an area of hazy increased lung opacity, within which margins of pulmonary vessels may be indistinct; Consolidation pattern, a homogeneous increase in pulmonary parenchymal attenuation that obscures the margins of vessels and airway walls; Reticular pattern,a descniptive term usually associated with interstitial lung diseases; Mixed pattern,combination of GGO,consolidation, and reticulation |
Interlobular septal thickening | Including smooth interlobular septal thickening or irregular interlobular septal thickening |
Pleural effusion | Fluid in the pleural cavity |
Lymphadenopathy | arbitrary thresholds for the upper limit of normal of 1 cm in short-axis diameter for mediastinal nodes |
A semi-quantitative analysis was used to quantify disease severity.(11, 27). For each lung lobe, a score that represented the extent of lung superimposed involvement (GGO, consolidation and reticular) was visually rated from 0 to 5, as shown below, 0, none; 1, < 5% lobe involvement; 2, 5–25% lobe involvement; 3, 26–49% lobe involvement; 4, 50–75% lobe involvement; and 5, > 75% lobe involvement.
The single GGO, single consolidation, and single reticular CT score were evaluated, respectively, according to the same criteria described above. The total CT score ranged from 0 ~ 25, which represented none to maximum lung involvement and each of the three findings scored at each thin-section CT examination.
Statistical Analysis
Illness day 0 was defined as the day of initial symptom onset. The median values of superimposed involvement CT score, single GGO CT score, single consolidation CT score and single reticular CT score and number of zones involved as a function of time were plotted. The temporal changes of main CT patterns, subtypes of ground-glass opacity, and the distribution of lung abnormalities were also analyzed. Kruskal Wallis rank-sum test was used for the difference between the median values of CT lung quantification in different period, and Chi-square test was applied to compare the frequency of CT patterns in different period. P-value of < 0.05 was considered to be statistically significant. Statistical analyses were performed using R software (version 3.6.2, the R Foundation for Statistical Computing, Vienna, Austria).