Abstract
On March 11, 2020, the World Health Organization declared the coronavirus disease 2019 (COVID-19) pandemic. The expert organisations recommend more cautious use of thoracic computed tomography (CT), opting for low-dose protocols. We aimed at determining a threshold value of automatic tube current modulation noise index below which there is a chance to miss an onset of ground-glass opacities (GGO) in COVID-19. A team of radiologists and medical physicists performed 25 phantom CT studies using different automatic tube current modulation settings (SUREExposure3D technology). We then conducted a retrospective evaluation of the chest CT images from 22 patients with COVID-19 and calculated the density difference between the GGO and unaffected tissue. Finally, the results were matched to the phantom study results to determine the minimum noise index threshold value. The minimum density difference at the onset of COVID-19 was 252 HU (p < 0.001). This was found to correspond to the SUREExposure 3D noise index of 36. We established the noise index threshold of 36 for the Canon scanner without iterative reconstructions, allowing for a decrease in the dose-length product by 80%. The proposed protocol needs to be validated in a prospective study.
Highlights
On March 11, 2020, the World Health Organization declared the COVID-19 pandemic [1]
We reviewed the examinations of male and female patients with age ≥ 18 years referred for chest Computed tomography (CT) by their attending physicians due to suspected community-acquired pneumonia
This study presents an approach to applying automatic tube current modulation at SUREExposure 3D noise index 36 for filtered back-projection (FBP) CT reconstruction, the lung kernel, and 1.0-mm thickness to determine the presence of ground-glass opacities (GGO) in basal lung regions at the Th11–Th12 vertebral level in patients with body mass index 29 suspected for COVID-19
Summary
We obtained a density difference (ground-glass opacities minus visually unaffected tissue) of 252 HU (p < 0.001). A dose-length product reduction by 80% was obtained, and clinical validation is needed
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