The Reading Room

What we know (so far) about using chest CTs to diagnose coronavirus

by Ty Aderhold, edited by Marisa Deline

Patients and clinicians throughout the country continue to report difficulties accessing viral testing kits for COVID-19, the disease caused by the new coronavirus. In light of limited testing options, many imaging leaders are wondering whether they should prepare to use CT scans to diagnose COVID-19. Here's our latest take.

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Timeline of emerging evidence

  • February 4: A Mount Sinai study of CT scans from COVID-19 patients from China identified particular patterns in the lung that can serve as markers to help diagnose and stage the disease.

  • February 26: Researchers published another study of Chinese patients that found CT scans had a higher sensitivity than the current standard (reverse transcription polymerase chain reaction or RT-PCR) and found that positive CT features could be used to re-classify patients with negative RT-PCR into "probable cases."

  • March 10: A research study showed that radiologists were able to distinguish COVID-19 from other similar chest CT findings such as non-COVID-19-pneumonia with a high sensitivity and moderate specificity.

The debate over the data

Across all of these studies, the sensitivity of CT scans for diagnosing COVID-19 was relatively high, meaning that it was able to correctly identify those with the disease. However, one limitation these studies found was that CT scans had a relatively low specificity. In other words, it classified some patients without COVID-19 as having the disease. Furthermore, patients with very early stages of the disease may not have these markers on a chest CT, so a negative scan cannot completely rule out COVID-19.

However, some researchers suggest that this low specificity and limitations are less important in areas facing an epidemic. In a recently published study in Radiology, the authors wrote, "Compared to RT-PCR, chest CT imaging may be a more reliable, practical and rapid method to diagnose and assess COVID-19, especially in the epidemic area."

Use of CT in China

Based on some of these preliminary findings, Chinese health care providers began confirming COVID-19 cases without RT-PCR tests using CT scans to diagnose COVID-19. This rapidly increased the ability for providers to test for the disease, which contributed to a massive one-day spike in cases on February 13th. On that date, health officials confirmed 14,840 new cases, which was up from just 2,015 cases that had been confirmed on the day before.

Current and potential future use in US

On March 11th, the American College of Radiology (ACR) released a statement confirming the stance that CT should not be used “to screen for or as a first-line test do diagnose COVID-19” and should be deployed “sparingly otherwise in the outbreak, reserving it for hospitalized, symptomatic patients with specific clinical indications for CT.” As of March 13th, CDC does not recommend using chest CTs to diagnose the virus.

However, some online comments indicate that some hospitals, including Mount Sinai Health System, are considering using CT as one diagnostic tool to evaluate and risk stratify patients.

Ways to prepare, for now

  • Keep a close eye on emerging evidence. We will continue to share updates on our blog. We also recommend you keep an eye on CDC and ACR press releases, of course. Given the fast-moving nature of this outbreak, you might also consider closely monitoring your colleagues' social media accounts.

  • Be prepared to speak with hospital and health system leaders about benefits and drawbacks. All health care leaders are making decisions in a fast-moving situation. Imaging leaders should be ready to answer questions from health system leaders and public health departments about the benefits and drawbacks of this diagnostic approach. Here's our quick take:
    • Potential pros:
      • Higher sensitivity in diagnosing COVID-19 compared to viral tests;

      • Quicker time to diagnoses compared to viral tests; and

      • Overcomes current issues with shortage of viral tests.
    • Potential cons:
      • A negative CT scan cannot completely rule out COVID-19, as it may not catch very early stages of disease;

      • Lower specificity may lead to some non-COVID-19 cases of pneumonia being diagnosed as positive; and

      • Operational challenges to scanning, including managing ventilation and airflow and thoroughly cleaning and sanitizing machines and rooms between patients.
  • Prepare for increased use of CT, especially if you're in an epidemic area. If the current positions of the CDC and/or the ACR change, testing volumes will spike immediately. Radiologists need to be preparing to read CT scans for potential COVID-19 so that they know what signs and markers to evaluate when these scans hit work queues, and imaging leaders need to prepare departmental protocols for scanning patients and cleaning equipment.

Last, but not least—artificial intelligence may be able to help

Some radiology providers and vendors, perhaps in anticipation of the use of CT to diagnose COVID-19 in the U.S., are already preparing. USARad, a teleradiology service provider, recently announced a COVID-19 program that will use radiologists and AI algorithms to provide screening diagnostics for the disease. Furthermore, the ACR Data Science Institute has recently published an AI "use case" for COVID-19 to encourage and educate the AI developer community. Finally, in China, providers are already leveraging AI algorithms to decrease the report turnaround time on these exams.

If you or your organization is using chest CTs for diagnosis and staging, we would love to speak with you. Please email me directly at aderholM@advisory.com so that we can continue to share emerging evidence and practices.

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