This retrospective study used non-identifiable patient data for analysis and was approved by the institutional review board. Therefore, the requirement for informed consent was waived.
From January 21, 2020, to March 6, 2020, patients with confirmed COVID-19 were retrospectively reviewed. Inclusion criteria: (1) presence of at least two follow-up CT scans, (2) the patients’ clinical data were complete. Exclusion criteria: (1) patients without pulmonary lesions, (2) patients without lesions presenting as spherical GGOs on initial chest CT, and (3) the interval between initial and follow-up CTs was > 7 days.
All patients underwent a non-contrast CT upon admission to the hospital with follow-up CT scans at < 7 days. Chest CT scans were performed using two MDCT scanners (Philips Brilliance iCT and Siemens SOMATOM go.Top) with the following parameters: tube voltage, 120 kV; automatic tube current modulation; beam pitch, 0.758/1.5; detector collimation, 0.625/0.6 mm; rotation time, 0.5 s; matrix size, 512 × 512; and section thickness and interval, 5.0 and 5.0 mm, respectively. All patients were in a supine position and scanned from the thoracic inlet to the lung base at the end of inspiration. CT images were reconstructed using a medium sharp reconstruction algorithm with a section thickness of 1 mm.
Analysis Of Ct Characteristics
Image analysis was evaluated on a PACS workstation (Vue PACS, Carestream Health, Inc) by two experienced radiologists (Z.G.C and F.J.L with 10 and 20 years of experience in thoracic radiology, respectively). They were blinded to clinical data and independently reviewed the images on both lung (width, 1500 HU; level, − 500 HU) and mediastinal (width, 350 HU; level, 40 HU) settings. Discrepancies were resolved by consensus.
For each spherical GGO, the initial CT scan was evaluated for the following characteristics: (a) lesion location, (b) relationship with the pleura (close to pleura, under the pleura, distant from the pleura), (c) lesion size, (d) CT value, (e) consolidation (yes or no), (f) uniformity of density (homogenous or heterogeneous), and (g) lesion border (ill-defined or well-defined). The relationship between the lesion and the pleura was considered as under the pleura if the distance between lesion and pleura was ≤ 2 cm; if > 2 cm, it was considered as distant from the pleura. All patients underwent follow-up chest CT scans, and the following results were reviewed: (a) the size and density changes of previous spherical GGOs, (b) changes of lesion border, (c) changes of consolidation, (d) the appearance of air bronchogram, and (f) the manifestations of residual lesions on the latest CT scan. Based on the changes of initial lesions on follow-up CT scans, spherical GGOs were divided into two groups: those that showed progression and those that were directly absorbed.
Clinical and laboratory data of the patients were collected by one radiologist (W.J.L). Clinical data, including age, gender, clinical type, initial symptoms, length of hospitalization, numbers of scans, and the interval between the adjacent scans were recorded. Laboratory findings such as white blood cell count, neutrophil count and percentage, lymphocyte count and percentage, C-reactive protein, erythrocyte sedimentation rate, and lactate dehydrogenase, were also recorded. These laboratory tests were performed upon admission to the hospital.
All data were analyzed using SPSS 20.0 (SPSS, Chicago, Ill). Data were expressed as mean ± standard deviation for continuous variables and as numbers and percentages for categorical variables. The continuous variables used the analysis of Variance or Wilcoxon rank-sum test, and categorical variables were analyzed using the Pearson χ2 test or Fisher exact test. A p value of < 0.05 was considered significant.