Imaging Guidelines for COVID-19 Infection

• Because there is still no vaccine or therapeutic drug for COVID-19, early detection and subsequent isolation of infected patients are essential to limit the spread of the disease.
• Reverse transcription polymerase chain reaction (RT-PCR) assays provide definitive diagnoses.
• Massachusetts General Hospital uses portable chest X-ray only for imaging workups in patients admitted with COVID-19.
• Chest X-ray is not used to diagnose COVID-19. Confirmation with viral testing is required even if radiologic findings are suggestive of the disease, in accordance with recommendations by the United States Centers for Disease Control and Prevention (CDC).

In December 2019, an outbreak of pneumonia caused by a novel coronavirus was reported in Wuhan, Hubei province, China. Within weeks, the infection, named COVID-19 (Corona Virus Disease 2019), spread across China and began to impact other countries around the world. Healthcare facilities across the United States are now preparing for the possibility of large-scale outbreaks of COVID-19, which the World Health Organization (WHO) recently reclassified as a pandemic.

Massachusetts General Hospital is using imaging to supplement RT-PCR findings in patients with suspected COVID-19. When the patients arrive at the hospital, they undergo portable chest X-ray as part of their imaging workup. (Using portable technology will help minimize exposure to others associated with moving the patient to the imaging department.) For select cases, including patients with severe illness and complications such as diffuse lung injury (ARDS), the hospital will use computed tomography (CT). Neither chest X-ray nor chest CT is used to diagnose COVID-19. Rather, they are used to aid in patients’ clinical workup.

Figure 1: Massachusetts General Hospital is using chest X-ray and, in select cases, chest CT as part of the imaging workup in patients with suspected COVD-19. Shown here are chest X-rays from two recent patients: one with a classic peripheral airspace opacity COVID + on PCR (left), the other with COVID+ ARDS.

The Evolution of COVID-19 Diagnosis

Soon after the outbreak was reported in China, use of reverse transcription polymerase chain reaction (RT-PCR) assays was established as the reference standard for definitive diagnosis of COVID-19. However, healthcare facilities quickly noted limitations. Because of a high rate of false-negatives and a relatively long processing time, diagnosis with the technology and subsequent treatment were often delayed, hampering efforts to contain the disease. Adding to these challenges, the availability of RT-PCR kits became an issue as the epidemic grew. In many cases, healthcare facilities did not have enough kits to adequately address the spread of COVID-19.

As a result, a growing number of healthcare facilities in China began using chest CT to aid in diagnosis. In a February 13 retrospective study, researchers noted that the Guangdong province in China had seen an “unprecedented” use of CT in an infectious disease outbreak. The technology not only helped address the shortage of RT-PCR kits but also proved more sensitive in detecting COVID-19. Another study showed a sensitivity of 98%, as opposed to 71% for RT-PCR. Given this sensitivity, the National Health and Health Commission of China now recognizes positive CT findings as major evidence of clinical diagnosis in the Hubei province, the epicenter of the outbreak. There, the addition of chest CT has reportedly resulted in 14,840 confirmed new cases of COVID-19.

In the United States, the CDC and the American College of Radiology (ACR) do not currently recommend chest X-ray or CT for diagnosis of COVID-19. Confirmation with viral testing is required even if radiologic findings are suggestive of the disease.

Figure 2: Typical CT imaging manifestation of COVID-19. A 38-year-old male with fever (39.3 ?), dry cough and shortness of breath for 3 days. Image courtesy of Jin Y, Cai L, Cheng Z, et al.

COVID-19 Imaging Features

The imaging findings for COVID-19 can range from normal to diffuse lung opacities. The typical findings described in the literature thus far include multifocal, bilateral, patchy peripheral ground-glass and rounded opacities with lower lobe predominance. Other findings include consolidation and rounded opacities with peripheral increased density (reverse halo). In general cavitation, pleural effusions and tree-in-bud nodules are uncommon. Notably, though expectedly, the findings associated with COVID-19 bear substantial similarities to those associated with the Severe Acute Respiratory Syndrome (SARS) coronavirus, which was responsible for a 2003 epidemic that impacted 26 countries. The progression of lung changes on CT has been shown to be consistent between the two diseases, with both the ground-glass and consolidation either worsening or improving over several days.

Because imaging findings for COVID-19 overlap with those for other viral infections, such as influenza, interstitial lung diseases and drug-related pneumonitis, relying on imaging alone could result in false-positive results in patients with suspected COVID-19. At the same time, a chest CT can appear normal in confirmed COVID-19 infection. For these reasons, imaging findings should be considered in the context of clinical history, symptoms and other laboratory tests and used to support diagnoses of COVID-19, as well as assessment of severity of lung involvement.

Further Information

For more information about imaging in patients with suspected COVID-19, please contact Jo-Anne Shepard, MD, or Subba Digumarthy, MD. We would like to thank Drs. Digumarthy and Shepard, as well as Matthew Gilman, MD, for their advice and assistance in preparing this article. All three are with the Department of Radiology, Thoracic Imaging and Intervention Division, Massachusetts General Hospital.

References

Ai T, Yang Z, Hou H, et al. Correlation of Chest CT and RT-PCR Testing in Coronavirus Disease 2019 (COVID-19) in China: A Report of 1014 Cases. Radiology. 2020 Feb 26:200642. Epub ahead of print.

Fang Y, Zhang H, Xie J, et al. Sensitivity of Chest CT for COVID-19: Comparison to RT-PCR. Radiology. 2020 Feb 19:200432. Epub ahead of print.

Ng M-Y, Lee EYP, Yang J, et al. Imaging Profile of the COVID-19 Infection: Radiologic Findings and Literature Review. Radiology: Cardiothoracic Imaging. 2020 Feb 13. Epub ahead of print.

Zu ZY, Jiang MD, Xu PP, Chen W, Ni QQ, Lu GM, Zhang LJ. Coronavirus Disease 2019 (COVID-19): A Perspective from China. Radiology. 2020 Feb 21:200490. Epub ahead of print.