Extension of Coronavirus Disease 2019 (COVID-19) on Chest CT and Implications for Chest Radiograph Interpretation

Choi, Hyewon; Qi, Xiaolong; Yoon, Soon Ho; Park, Sang Joon; Lee, Kyung Hee; Kim, Jin Yong; Lee, Young Kyung; Ko, Hongseok; Kim, Ki Hwan; Park, Chang Min; Kim, Yun-Hyeon; Lei, Junqiang; Hong, Jung Hee; Kim, Hyungjin; Hwang, Eui Jin; Yoo, Seung Jin; Nam, Ju Gang; Lee, Chang Hyun; Goo, Jin Mo

PURPOSE: To study the extent of pulmonary involvement in COVID-19 with quantitative CT (QCT) and to assess the impact of disease burden on opacity visibility on chest radiographs. MATERIALS AND METHODS: This retrospective study included 20 pairs of CT scans and same-day chest radiographs from 17 patients with COVID-19, along with 20 chest radiographs of controls. All pulmonary opacities were semi-automatically segmented on CT images, producing an anteroposterior projection image to match the corresponding frontal chest radiograph. The lung opacification mass (QCTmass) was defined as [(opacity attenuation value+1000 HU)/1000]*1.065(g/mL) * combined volume (cm(3)) of the individual opacities. Eight thoracic radiologists reviewed the 40 radiographs, and a receiver operating characteristics curve analysis was performed for the detection of lung opacities. Logistic regression analysis was done to identify factors affecting opacity visibility on chest radiographs. RESULTS: The mean QCTmass per patient was 72.4±120.8 g (range, 0.7-420.7), and opacities occupied 3.2±5.8% (range, 0.1-19.8) and 13.9±18.0% (range, 0.5-57.8) of the lung area on the CT images and projected images, respectively. The radiographs had a median sensitivity of 25% and specificity of 90% among radiologists. Nineteen of 186 opacities were visible on chest radiographs, and a median area of 55.8% of the projected images was identifiable on radiographs. Logistic regression analysis showed that QCTmass (p<0.001) and combined opacity volume (p<0.001) significantly affected opacity visibility on radiographs. CONCLUSION: QCTmass varied among COVID-19 patients. Chest radiographs had high specificity for detecting lung opacities in COVID-19, but a low sensitivity. QCTmass and combined opacity volume were significant determinants of opacity visibility on radiographs. An earlier incorrect version appeared online. This article was corrected on April 6, 2020.