- Most national and international organizations recommend against routine use of imaging for the diagnosis of COVID-19 pneumonia unless there is a lack of availability or access to immunoassays or PCR testing
- Chest CT may be indicated for patients with moderate to severe symptoms of COVID-19, worsening respiratory status or suspicion of cardiopulmonary complications
- When indicated for patients with suspected or known COVID-19, chest CT should usually be performed with a single-phase, noncontrast, low-dose protocol using fast scanning techniques
The use of CT and other imaging to diagnose COVID-19 has become common because of false-negative results of reverse transcription polymerase chain reaction (PCR) tests, as well as limited access to PCR tests and immunoassays. Concerned about radiation doses, the International Atomic Energy Agency held a live webinar on April 9, 2020, to discuss how to optimize CT practice and protocols for COVID-19 pneumonia.
Mannudeep K. Kalra, MD, staff radiologist of the Division of Thoracic Imaging and director of the Webster Center for Quality and Safety in the Department of Radiology at Massachusetts General Hospital, and Fatemeh Homayounieh, MD, of the Webster Center for Quality and Safety, and colleagues review the proceedings in European Radiology. The webinar drew 977 attendees from 84 countries.
Indications for CT in COVID-19
- Most national and international organizations recommend against diagnostic imaging for COVID-19 when PCR tests and immunoassays are available and patients have mild symptoms; chest CT is thought to have low sensitivity in early COVID-19
- When the availability of diagnostic PCR and immunoassays is limited, chest radiography or CT can be used for patients who have moderate to severe symptoms of COVID-19 pneumonia
- CT should not be used to assess the severity of COVID-19
CT Techniques and COVID-19
Most studies of the efficacy of CT in suspected or known COVID-19 pneumonia involved single-phase, noncontrast, low-dose chest CT. Low dose implies CTDIvol <3 mGy in most small and average-size adults.
On the other hand, post-contrast chest CT may be helpful when there is:
- Clinical worsening of the cardiorespiratory status
- Suspected pulmonary embolism (exclude noncontrast phase CT and directly acquire CT pulmonary angiography using a single post-contrast protocol)
Faster scanning (gantry rotation ≤0.5 seconds and pitch value >1:1) is preferred for the substantial number of patients who are short of breath or coughing. The paper includes a table that suggests scan parameters for acquiring low-dose chest CT using four common brands of CT scanners.
CT and COVID-19 in Special Populations
Health care workers: Neither chest radiography nor CT should be routine because of the radiation exposure and lack of sensitivity in early disease. Imaging can be considered for workers who have moderate to severe COVID-19, certain comorbidities or worsening cardiorespiratory status.
Pregnant patients: Chest CT must be reserved for suspected complications of COVID-19 or worsening respiratory status. If pulmonary embolism is suspected, direct CT angiography must be performed from lung apices to lung bases (without extension into the upper abdomen).
Children: The indications are the same as in adults. For children weighing up to 50 kg, CTDIvol can be as low as 1 mGy.
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