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Other studies focusing on the evolution of COVID-19 pneumonia concluded that the lung segments showed marked changes with decreasing of GGOs and increasing of crazy-paving pattern and consolidation. Patients recovering from COVID-19 can be tracked with CT to assess for long-term or permanent lung damage, including fibrosis.

Pan et al. investigated the time course of lung changes during recovery from COVID-19 pneumonia. The results showed that with the evolution of the disease, GGO would enlarge with a crazy paving pattern and partial consolidation. Lung involvement reached a maximum at about the 10th day after the onset, and the crazy-paving pattern was resolved entirely in the absorption stage about the 14th day after the disease onset, which means that the crazy-paving pattern may become an important indicator for evaluation of disease evolution.

Dynamic changes on chest CT

Chest CT can also evaluate the time course of COVID-19 and assess the evolution of disease severity. Chung et al. evaluated each of the five lung lobes and determined the degree of involvement and rated the severity of each lobe. The patients who had the highest score were admitted to the intensive care unit with multiple bilateral GGOs and subsegmental consolidation. 

Critical stage disease may show further expansion of consolidations, with the whole lung showing increased opacity, a so-called “white lung”. In recovery stage patients, the lesion area is reduced and absorbed, or only residual fibrous lesions are seen. Less common findings include pleural effusion, stretch bronchiectasis, and thoracic lymphadenopathy.

Typical features on chest CT

Typical features on chest CT include ground-glass opacity with a cloud-like change on chest CT, not obscuring the accompanying pulmonary vascular structures in lungs. Corresponding pathological changes are exudation in the alveolar cavity with partial filling of the air cavity, mainly from serous and fibrinous exudates, alveolar septal vascular congestion and edema. 

It is recommended to use volume CT with a maximum acquisition  slice thickness of 5mm (>16 slice multi-detector CT) and a reconstruction slice thickness  of 1.0-1.5mm. Multi-planar reformats (transverse, sagittal and coronal planes) are beneficial for the early detection of lesions in patients with negative nucleic acid tests.

The sensitivity and specificity chest X-ray for mild type patients are relatively low. It is not recommended for patients with early COVID-19 stage. Chest CT scans can demonstrate almost all abnormalities including early mild exudative lesions. Chest CT is the most valuable imaging tool for the clinical diagnosis  of early stage COVID-19 pneumonia when patient’s symptoms are aspecific, especially in Wuhan with unsufficient PCR tests in the early pandemic period.