Background The role and performance of chest CT in the diagnosis of the coronavirus disease 2019 (COVID-19) pandemic remains under active investigation. Purpose To evaluate the French national experience using Chest CT for COVID-19, results of chest CT and RT-PCR were compared together and with the final discharge diagnosis used as reference standard. Materials and Methods A structured CT scan survey (NCT04339686) was sent to 26 hospital radiology departments in France between March 2 and April 24 2020. These dates correspond to the peak of the national COVID-19 epidemic. Radiology departments were selected to reflect the estimated geographical prevalence heterogeneities of the epidemic. All symptomatic patients suspected of having a COVID-19 pneumonia who underwent within 48 hours both initial chest CT and at least one RT-PCR testing were included. The final discharge diagnosis, based on multiparametric items, was recorded. Data for each center were prospectively collected and gathered each week. Test efficacy was determined by using Mann-Whitney Test, Student’s t-test, Chi-square test and Pearson’s correlation. A p value <.05 determined statistical significance. Results Twenty-six of 26 hospital radiology departments responded to the survey with 7500 patients entered; 2652 did not have RT-PCR results or had unknown or excess delay between RT-PCR and CT. After exclusions, 4824 patients (mean age 64, ± 19 yrs, 2669 males) were included. Using final diagnosis as the reference, 2564 of the 4824 patients were positive for COVID-19 (53%). Sensitivity, specificity, NPV and PPV of chest CT for diagnosing COVID-19 were 2319/2564 (90%, 95% confidence interval [CI]: 89, 91), 2056/2260 (91%, 95%CI: 91, 92%), 2056/2300 (89%, 95%CI; 87, 90%) and 2319/2524 (92%, 95%CI 91, 93%) respectively. There was no significant difference for chest CT efficacy among the 26 geographically separate sites, each with varying amounts of disease prevalence. Conclusion Use of chest CT for the initial diagnosis and triage of suspected COVID-19 patients was successful.

Iterative reconstructions can be used to improve the SNR and CNR at a constant dose or to reduce the dose by keeping the same SNR and CNR on abdominal CT images.

Purpose To determine the impact of the COVID-19 on the CT activities in French radiological centers during the epidemic peak. Materials and methods A cross-sectional prospective CT scan survey was conducted between March 16 and April 12, 2020, in accordance with the local IRB. Seven hundred nine radiology centers were invited to participate in a weekly online survey. Numbers of CT examinations related to COVID-19 including at least chest (CT covid) and whole chest CT scan activities (CT chest) were recorded each week. A sub-analysis on French departments was performed during the 4 weeks of the study. The impact of the number of RT-PCRs (reverse transcriptase polymerase chain reactions) on the CT workflow was tested using two-sample t test and Pearson's test. Results Five hundred seventy-seven structures finally registered (78%) with mean response numbers of 336 ± 18.9 (323; 351). Mean CT chest activity per radiologic structure ranged from 75.8 ± 133 (0-1444) on week 12 to 99.3 ± 138.6 (0-1147) on week 13. Mean ratio of CT covid on CT chest varied from 0.36 to 0.59 on week 12 and week 14 respectively. There was a significant relationship between the number of RT-PCR performed and the number of CT covid (r = 0.73, p = 3.10 −16) but no link with the number of positive RT-PCR results. Conclusion In case of local high density COVID-19, CT workflow is strongly modified and redirected to the management of these specific patients. Key Points • Over the 4-week survey period, 117,686 chest CT (CT total) were performed among the responding centers, including 61,784 (52%) CT performed for COVID-19 (CT covid). • Across the country, the ratio CT covid /CT total varied from 0.36 to 0.59 and depended significantly on the local epidemic density (p = 0.003). • In clinical practice, in a context of growing epidemic, in France, chest CT was used as a surrogate to RT-PCR for patient triage.

A 47-year-old man, with a 25-year history of frequent scuba diving, presented with a right-sided hypoglossal palsy 2 days after occipital head trauma. CT showed excessive occipito-temporal and atlas pneumatization, soft tissue emphysema, right-sided opacification of mastoid air cells, and a right-sided hypoglossal canal fracture (figures 1 and 2). Hypoglossal palsy resolved spontaneously 10 days later. Four months later, mastoid fluid collection disappeared on CT, and other abnormalities were stable. Repetitive positive pressure phenomena (e.g., Valsalva maneuver) are often associated with cranial bone pneumatization.1,2 The preexisting cranial bone pneumatization probably placed the patient at risk for cranial bone fracture of the thinned bone in the setting of minor head trauma.