CT Imaging Evolution of Novel Coronavirus Pneumonia during Hospitalization

Object: To evaluate CT Features on serial thin-section computed tomographic (CT) scans in patients with conventional Novel Coronavirus Pneumonia (COVID-19) for the period during which they remained hospitalized. Methods: In this Retrospective study, we collected clinical information including Laboratory investigations and more importantly we focused on collecting imaging data of these 15 selected patients (8 men and 7 women, 22 - 70 years old, average age (45 ± 15)) with COVID-19 disease. The mean time between the initial and repeat thin-section CT scans was 3.3 ± 2.1 days, 7.9 ± 2.1 days, 14.2 ± 1.3 days after onset of symptoms in these 15 patients. Three experienced Radiologists reviewed the CT images independently and also in collaboration with each other for complicated or unique cases, for the Imaging characteristics like number and site of lesions, distribution of lesions whether it is lobular, lobar, unilateral or bilateral, and comparing the severity of disease in relation to the CT findings. The CT features were compared using the χ2 test and Fisher’s exact probability. Results: All of 15 patients had a history of visit to the endemic center i.e. Wuhan city or came in direct contact with an infected individual. Fever (93.3%) was the most common symptom. Majority of patients had a normal white blood cell count, and normal lymphocyte count although there were patients with leucopenia and lymphocytopenia. CT images showed predominate Ground-Glass opacities in the initial and repeat CT scans with a percentage of 90.6%, 53.9%, 44.2% respectively during the three spaced CT examinations; most patients had bilateral lung involvement (60%, 93.3%, 93.3%), the lesions predominantly involved the posterior (87.5%, 71.9%, 76.6%) and peripheral (90.6%, 84.3%, 85.7%) part of the lungs. There were more consolidation and mixed patterns in repeat CT scan Versus initial CT scan, the difference was statistically significant (P-values were ± 2.1 days) 63 (7.9 ± 2.1 days), and 57 (14.2 ± 1.3 days) respectively. The median percentage of pneumonia lesions of the whole lung volume in three times CT scan was 1.69% (4.59), 3.47% (5.46), 2.33% (4.75) respectively. Besides, “Tree-in-bud” sign, lung cavitation, and lymphadenopathy were absent. Conclusion: The Thin-slice Section CT Imaging features show uniquely different characteristics, each time the scans are taken. The most common findings in our study were bilateral multiple peripheral and mostly posterior ground-glass opacities (GGO), however the CT scan images that were taken in a timely manner to follow up demonstrated some remarkable changes, which undoubtedly play an important role in the diagnosis and management of the patient with COVID-19 disease.


Introduction
In December 2019, an epidemic of coronavirus disease (COVID 19) erupted in Wuhan City; China [1] [2] which has quickly spread all across the world and was declared as a global health emergency by WHO [3]. The number of patients is rapidly increasing outside of China. The World Health Organization (WHO) named the virus as SARS-COV-2 (severe acute respiratory syndrome coronavirus 2), and the infection it causes was termed as COVID-19 (Coronavirus disease-19) [4] the continuous expansion of COVID-19 has created a pandemic [5].
As of April 14, 2020, 1,844,863 confirmed and 117,021 deaths cases have been reported in Globally, China 83,696 confirmed and 3351 deaths cases have been reported [6].
According to the novel coronavirus pneumonia diagnosis and treatment plan (6 th trail version) issued by the National Health Committee of the People's Republic of China [7], COVID-19 is divided into four categories Mild, Moderate, Severe and dangerous. Although viral nucleic acid detection using real-time polymerase chain reaction (RT-PCR) remains the standard Laboratory test for the diagnosis of coronavirus disease, the fact cannot be ignored that the timely fashioned CT imaging studies is one of the core reference indexes in the process of COVID-19 diagnosis and treatment plan [8] [9] [10]. Since the majority of COVID-19 cases outside of Wuhan area are usually of Mild to Moderate nature, meaning that symptoms of this type of patients are not serious and the disease is itself not highly infectious and contagious [11], the purpose of this study is to retrospectively analyze the early CT imaging characteristics and then the follow up timely CT scans will clarify short-term evolution of Mild to Moderate COVID-19, to provide auxiliary decision-making for the diagnosis and treatment.

General Information
The study was approved by the medical ethics committee of the First Affiliated Hospital of Xi'an Jiao tong University, and the informed consent was taken from patients or their relatives. The clinical and imaging data of COVID-19 patients in our hospital since the end of January were analyzed retrospectively and a certain group of patients were selected for the study. Inclusion Criteria: 1) All the patients selected were confirmed as COVID-19.
2) Only patients who had positive symptoms of COVID-19, and had undergone thin layer CT scan images showing typical findings of the disease were included.
3) The selected patients did not have any other viral infection (e.g.: C.A.P.) 4) All selected patients were recently diagnosed and were still under treatment during the course of the study.
Exclusion criteria: 1) Patients with Poor quality CT images, not meeting the criteria to properly study the images and remark on it.
2) All those patients who have severe disease of other body systems, complicated by COVID-19 were excluded.
A total of 15 patients were selected for the study. With 8 males and 7 females, aged 22 -70 years, with a median age of 44 years.

CT Examination Method
CT examination equipment is Philips 16 Slices CT. All patients were laid in a supine position for the scan, the scanning range was from the thoracic entrance to the cost-phrenic angle. The thickness of the layer was 1 mm and the layer spacing was 5 mm, the tube voltage was 120 kV, with automatic tube current, the matrix was 512 mm × 512 mm, and the standard algorithm was 1.0 mm thin-layer reconstruction. Lung window: window width WW = 1500 HU, window length WL = −800 HU. mediastinal window: window width WW = 400 HU, window length WL = 40 HU.

CT Interpretation
Three Senior radiologists with 20, 25, and 35 years' working experience respectively read the CT Images. Complicated cases with unusual findings were often discussed with each other.
Image evaluation includes: 1) Evaluation of lesion nature: The lesions were divided into four types according to GROUND-GLASS OPACITIES, (including pure GGO, GGO with enlarged interlobular septum), CONSOLIDATION, MIXED LESIONS (including GGO, consolidation, fibrosis), and FIBROTIC LESIONS, and other associated signs were recorded. The identification of signs was based on the definition of the Fleischner society [12]. Open Journal of Radiology 2) Evaluation of the distribution of the lesions: The lesions can be Unilateral or Bilateral (depending upon which lung is affected Rt or Lt); its location can also be Anterior, Posterior or central (to the mid-axillary line); the location of the lesion is also divided into Upper lung zones, Middle lung zones and Lower lung zones (based on lobar anatomy of lungs).
3) The severity of the lesion: Anatomically the lungs are divided into five lobes The total score is equivalent the total score of the five lung lobes. 4) Quantitative CT evaluation of the percentage of lesions in the total lung volume: The "digital lung TM" software was used for quantitative calculation, automatic segmentation of the volume of lesions and the total lung volume, and then the percentage of lesions in the total lung volume was obtained.

Statistical Methods
SPSS 22.0 statistical software was used for analysis. Frequency and rate were used for counting data. Normally distributed measurement data were expressed by mean ± SD, and median (interquartile interval) [M(q)] for skew distribution. χ 2 or Fisher's exact probability method was used for comparison with CT for change of pathological properties. P < 0.05 was statistically significant.    respectively. There is no significant difference in the distribution of the upper and lower lung fields, as shown in Table 2.

Changes in the Number, Distribution, and Severity of Lesions
Quantitative CT showed that the median proportion of pneumonia lesions to total lung volume was 1.69 (4.59%) in the first CT examination, 3.47 (5.46%) in the second CT examination and 2.33 (4.75%) in the third CT examination; the overall score of lung disease severity was 36, 63 and 57, respectively, suggesting that the imaging manifestation was aggravating the severity of the lesion around the first week of the course of the disease; the severity of the lesion gradually decreased after the second week, as shown in Table 2.    Table 3.

Other Accompanying Signs
Pleural effusion in 2 cases (13.3%), bronchiectasis in 2 cases (13.3%), no tree-in-bud sign reflecting small airway lesions, no cavity lesions, no obvious Open Journal of Radiology  mediastinal and hilar lymphadenopathy were seen.

Discussion
Similar to the previous reports [13] [14], this study found that at the time of ad- In previous studies on SARS, it was found that the fibrous cord is the residual sign in the lung after healing [18]. In this study, it was found that the fibrous  [19]. However, the common signs of community-acquired pneumonia, such as tree-in-bud sign, lymphadenopathy, and cavitation, are absent in CT images, which is helpful to reduce the spectrum of differential diagnosis. If the CT image of the patient shows multiple ground glass shadows in both lungs, the posterior and prepheral of the lung field distribution, and there is a corresponding epidemiological history, with fever and dry cough symptoms, the white blood cell count and lymphocyte count in the laboratory examination are reduced, COVID-19 should be highly suspected, and nucleic acid (RT-PCR) examination is required for the diagnosis.
Limitations of this study: the sample size is small, and the influence of COPD, Open Journal of Radiology cardiovascular disease, and other basic diseases on the change of pulmonary lesions is not considered. In addition, the patients included in this study were younger and had an age-related bias, and there was no complete agreement between the first time and the reexamination CT at the time, which may have some impact on the experimental results.

Conclusion
The most common findings in our study were bilateral multiple peripheral and mostly posterior ground-glass opacities (GGO), The CT imaging changes show a trend within two weeks after symptoms appear. Compared with clinical symptoms, there is a delay, consolidation and mixed lesions may be potential biological signs of disease development. CT Imaging examination and evaluation are advantageous for the diagnosis and management of COVID-19.