Study design and participants
In this cross-sectional retrospective study, patients with a definite diagnosis of COVID-19 infection were recruited at the two main referral hospitals for COVID-19 from February through March 2020.
Inclusion criteria were as follows: A) having a proper history; B) Positive real-time PCR of SARS-CoV-2; C) having at least one non-contrast chest CT scan
We studied the demographic, clinical, laboratory and radiologic findings of the patients. The data from the patients were kept confidential through codes.
Computerized Tomography Scans
Non- contrast CT scan was performed in a supine position during full inspiration. Scanning was extending from thoracic inlet to the upper abdomen. The technical parameter included: 8 slice scanner (GE Medical Systems, Milwaukee, WI, and USA), 120Kvp, thickness of 1.25-2mm, 1.25 mm interval.
The primary chest CT scan was reviewed independently by four radiologists’, three of whom (SS, PI, SJ) were board-certified in general diagnostic radiology with approximately eight to fifteen years of practice experience and one in training (YE with four years of practice experience). The radiologists were blind to the primary impression, clinical symptoms, and the patient’s outcome and undertook the classification and categorization of scans. The CT findings were arbitrarily considered to be one of these four categories as ground-glass opacity (GGO), consolidation, crazy paving, and nodular opacities.
The definitions of these findings were determined based on the Fleischer Society guidelines (16). Consolidation and GGO were defined as hazy areas of increased attenuation with and without obscuration of the underlying vasculature, respectively. GGO with intra-lobular lines were defined as crazy paving and nodular opacities were identified when focal round opacities either solid or GGOs with a diameter less than 3 cm.
To assess the severity of pulmonary parenchymal involvement, we quantified the extent and nature of abnormalities. For this purpose, the area of lung involvement was scored in the axial CT images based on the method described previously by Ooi et al in 2004 for the severe acute respiratory syndrome (SARS) (17). In this method each lung was assessed in three levels; upper (above the carina), middle (below the carina up to the upper limit of the inferior pulmonary vein), and lower (below the inferior pulmonary vein). Also, the right and left lung were evaluated separately and summed up to conclude the final score of each level.
The percentage of lung involvement in each level was evaluated independently and categorized as follows: 0 as normal, 1as < 25% abnormality, 2 as 25–49% abnormality, 3 as 50–74% abnormality, and 4 as ≥ 75% of the pulmonary cross-section CT scan (Table.1).
The nature of abnormalities can also determine the severity of lung involvement (18, 19). In this regard, we arbitrarily established a 4-point scoring system for defining the pattern of lung abnormalities in CT scans that summarized in Table 2.
Then, the two scores (extent and nature of abnormality) were multiplied by each other (Figure1). After adding together the scores of all 6 levels (3 levels in each side), a final radiologic severity score (RSS) for parenchymal involvement with values ranging from 0 to 96 was determined for each patient (Figure 2-4).
Eventually, the final score was determined by consensus between all four radiologists.
Eventually, this severity score was compared between sever and non-sever patients according to American Thoracic Society guidelines for community-acquired pneumonia (20).
The collected data was summarized as means (±SD), and categorical data are presented as the count (percentage). Unpaired Student's t-test, chi-square test, or Fisher's exact test was used to compare the RSS of COVID-19 patients as appropriate. A P. value of less than 0.05 considered indicating statistical significance. All the statistical analyses were performed by the Statistical Package for Social Sciences (SPSS Inc., Chicago, Illinois, USA) version 26.0.