Abstract: Objective To compare and analyze the CT images of patients with coronavirus disease 2019（COVID-19）before and after their nucleic acid detection results turning from positive to negative, and to evaluate the value of CT in clinical diagnosis and treatment. Methods In this retrospective analysis, 32 cases of COVID-19 from the Affiliated Infectious Diseases Hospital of Soochow University were enrolled. Chest CT images were acquired before the last positive nucleic acid test and after the first negative test. The imaging findings of the two timepoints were compared and observed, and a semi-quantitative scoring system was used to quantitatively estimate the extent of lesion in each lung lobe, using rank sum test. According to the "Guidelines for Imaging Diagnosis of New Coronavirus Pneumonia (First Edition 2020)", whether the CT images of 32 cases entered the absorption stage after the first negative nucleic acid test were determined. Results The CT images of 32 cases of COVID-19 during the transition from positive to negative in nucleic acid detection results all showed signs of viral pneumonia. The lesions were mainly bilateral, asymmetric, and subpleural distribution. After the nucleic acid test result turned negative for the first time, the lesion was decreased in extent in 24 cases (75.00%), increased in 7 cases (21.87%), and showed no overt change in 1 case (3.13%); The lesion density was decreased in 13 cases (40.63%), increased in 12 cases (37.50%) and showed no overt change in 7 cases (21.88%). The occurrence of intralobular septal thickening, air bronchogram sign, and enlarged vasculature sign before the last positive nucleic acid test and after the first negative test were 87.50% vs 84.38%, 96.88% vs 87.50%, 46.88% vs 34.38%. Compared with the lesion extent before the last positive nucleic acid test, the overall lesion extent after the negative test were significantly decreased in the semi-quantitative scores of lesion extent (P<0.05). Based on CT images diagnosis after the nucleic acid test turned negative for the first time, and 27 cases (84.38%) entered the absorption stage. Conclusion sThere is certain difference in CT image findings during the transition from positive to negative in nucleic acid test in patients with COVID-19, and the CT image findings after the first negative nucleic acid test are mostly indicating the absorption stage, which can assist the clinical evaluation of therapeutic efficacy.

Key words: Coronavirus disease 2019, Nucleic acid, Tomography, X-ray computed