Inclusion Criteria:  Non-critically ill patients hospitalized in the COVID-19 Unit of the Centre Hospitalier Princesse Grace of Monaco Presenting with a sudden clinical deterioration defined by a respiratory rate impairment and/or a rise of oxygen flow to reach a peripheral capillary oxygen saturation (SpO2) of more than 95% during at least 48 hours a diagnosis of pulmonary embolism was discarded by CT pulmonary angiography no clinical or biological (procalcitonin levels) evidence of lung superinfection without clinical evidence for LV dysfunction  Exclusion Criteria:  Non confirmed COVID-19 pneumonia according to the WHO guidance by a positive result of RT-PCR assay of nasal and pharyngeal swabs, Patients without peripheral pulmonary ground-glass opacities or air-space consolidation on their chest CT scan at admission and common laboratory findings including lymphocytopenia, eosinopenia, significantly elevated markers of organ inflammation such as fibrinogen and C-reactive protein. Patients could not be included if their medical condition was unstable or precluded a safe transfer to the nuclear medicine department, if they were under mechanical ventilation (either non-invasive or invasive), if they required critical care unit, or in case of a pregnancy.