key: cord-1042596-n5ezpo9w
authors: Shi, Feng; Wei, Ying; Xia, Liming; Shan, Fei; Mo, Zhanhao; Yan, Fuhua; Shen, Dinggang
title: Lung volume reduction and infection localization revealed in big data CT imaging of COVID-19
date: 2020-11-03
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2020.10.095
sha: 30a5d4515e717e24320ccea4f8562be204c3f447
doc_id: 1042596
cord_uid: n5ezpo9w

The ongoing worldwide COVID-19 pandemic has become a huge threat to global public health. Using CT image, 3389 COVID-19 patients, 1593 community-acquired pneumonia (CAP) patients, and 1707 non-pneumonia subjects were included to explore the different patterns of lung and lung infection. We found that COVID-19 patients have a significant reduced lung volume with increased density and mass, and the infections tend to present as bilateral lower lobes. The findings provide imaging evidence to improve our understanding of COVID-19.

pneumonia (CAP) patients, and 1707 non-pneumonia subjects were included to explore the different patterns of lung and lung infection. We found that COVID-19 patients have a significant reduced lung volume with increased density and mass, and the infections tend to present as bilateral lower lobes. The findings provide imaging evidence to improve our understanding of COVID-19.

Keywords: COVID-19, community-acquired pneumonia, non-pneumonia subjects, lung, big data

The current outbreak of coronavirus disease 2019 (COVID-19) has become a serious global health crisis. Chest CT imaging, as a direct assessment tool for lung infection, shows that ground-glass opacity (GGO), increased crazy-paving pattern, and consolidation are the main signs of COVID-19 infections (1) . Clinicians observed that COVID-19 patients' lungs become smaller and stiffer (2) , and have a 20 to 30 percent decrease in lung volume. However, there is limited study that utilizes big data to explore the overall alterations of lung volume, density and mass, as well as the distribution of infections that caused by the coronavirus.

For this retrospective study, we identified 3389 CT scans from COVID-19 patients, 1593 scans from community-acquired pneumonia (CAP) non-viral patients, and 1707 scans from non-pneumonia subjects. The ages of the participants ranged from 12 to 98 years. All the CT images were acquired with slice thickness less than 2mm and were First, we evaluated the overall characteristics of volume, density and mass in the lung and 5 lung lobes in the three groups. Two-sample z-tests were adopted for comparing the mean difference of two groups. Second, for the infected regions, the volume, density, and mass were also obtained from 5 lung lobes to investigate their distinct inflammation distributions between COVID-19 and CAP patients.

In the overall region analysis, lung volumes of COVID-19 patients are significantly smaller than those of CAP patients as well as non-pneumonia subjects. Lung densities of COVID-19 patients are larger than those of CAP patients, and those of nonpneumonia subjects are the smallest. The mass has a similar pattern with the density. In the lung lobe analysis, COVID-19 patients' lung volumes are significantly smaller than the other two groups in L2, R1, and R3, while the lung densities are larger in all lung lobes. The mass of L2, R2 and R3 reveal higher in COVID-19. CAP patients are found with higher density of R3 (Figure 1 ). In line with the previous study where different degrees of alveolar collapse were found in 6 COVID-19 patients (5), our findings indicate that the COVID-19 are generally accompanied by reduced volume of the lung and lung lobes, with increased density and mass. The pattern of CAP is similar with non-pneumonia subjects, except that the density of CAP patients is relatively larger. The pattern of mass is similar to that of the volume (Figure 2 ). These findings revealed that the typical pattern of infection in COVID-19 and CAP patients is bilateral and involves multiple lobes. Compared to the middle and upper lobes, lower lobes are more affected, with slight predominance in the right lower lobe. These findings might because that the cells targeted by the coronavirus are mainly located in the bilateral lower lobe bronchus. Since the right bronchus is short and straight, the virus might tend to favor this location, which agrees with previous reports (6, 7) . Besides, the volume, density and mass patterns of COVID-19 are overall larger than those of CAP patients, which supports that COVID-19 patients have more severe pneumonia effects, and the relatively larger density distribution of COVID-19 might suggest that the manifestations of COVID-19 pneumonia could be more diverse.

There are some limitations in this study. Severity information and longitudinal follow-ups may allow the further exploration of the lung progresses in pneumonia patients. Also, CAP can be caused by different pathogens, such as bacteria, fungi, parasites, or viruses. Viral infection was reported with more similar patterns as J o u r n a l P r e -p r o o f compared to COVID19 pneumonia (8) . Future study could investigate the image patterns of CAP subtypes as well as with COVID-19.

In summary, using massive dataset we observed reduced lung volume and increased density and mass in COVID-19 patients compared to CAP patients and non-pneumonia subjects. In addition, pneumonia including COVID-19 tends to present as bilateral with a slight predominance in the right lower lobe, while there exist distinct infection distribution and severity between COVID-19 patients and CAP patients. We hope that our findings could provide imaging evidence in delineating lung abnormalities in pneumonia patients and would likely to improve the understanding of the radiological underpinning of COVID-19. 

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