Low-Dose CT Could Be COVID-19 Assessment Tool

April 23, 2020
Whitney J. Palmer

Submillisievert chest CT scans offer quick and accurate assessment, particularly in patients with symptoms more than 48 hours.

The struggle to determine whether chest CT scans can be helpful in assessing patients with COVID-19 infection continues to march on in new research that examines the use of low-dose CT imaging.

In an April 21 study published in Radiology: Cardiothoracic Imaging, researchers, led by Anthony Dangis, M.D., in the radiology department of Imelda Hospital in Bonheiden, Belgium, determined chest CT scans using a radiation dose of less than 1 mSv quickly and accurately I pinpoint COVID-19 infection in emergency room patients, especially among those who have exhibited symptoms for more than 48 hours.

These findings are a positive step for providers looking to make diagnoses quickly without unduly exposing patients to more radiation than is necessary. The results are also helpful, the team contended, because the gold standard for COVID-19 diagnosis, real time polymerase chain reaction (RT-PCR) can have sensitivity as low as 70 percent. And, according to some previously published research, chest CT can have more than 90-percent sensitivity.

“Given the widespread use of chest CT for COVID-19 detection, our results demonstrate the feasibility of using low-dose chest CT to achieve an important reduction in radiation dose on a population level during this pandemic,” the team wrote.

To test both how low of a dose could still provide effective diagnosis, as well as how quickly the scan could be completed, the team conducted a study, from March 14 to March 24, with 192 emergency room patients who presented with COVID-19 symptoms. The average age was 62 years, but patients who ultimately tested positive for the virus were slightly older - 67 years - and were more likely to have a fever (68.7 percent compared to 45.9 percent).

Dangis’s team performed low-dose submillisievert chest CT exams using this protocol: 100 kVp, 20 mAs, a pitch of 1.2, and a gantry rotation time of 0.5 seconds. Patients also received RT-PCR testing. And, according to results, 43.2 patients were COVID-19-positive, and 56.8 percent tested negative for the virus.

Overall, the team determined the low-dose chest CT offered diagnostically sound results, particularly when assessing patients who had exhibited symptoms for more than 48 hours. Among those patients, CT scans were more sensitive than in an overall group (95.6 percent to 86.7 percent). The images also had a slightly higher positive predictive value (91.5 percent to 91.1 percent) and a higher negative predictive value (96.5 percent to 90.3 percent). Accuracy was also better - 94.2 percent compared to 90.6 percent. Specificity was slightly lower, however, at 93.2 percent versus 93.6 percent.

According to the analysis of the results, the team also determined the mean effective radiation dose for the low-dose chest CT protocol was 0.56 mSv, and the median time between image capture and patient report was 25 minutes with a range of 13 minutes to 49 minutes.

Based on the CT performance and outcome measurements, the team recommended chest CT as a diagnostic tool for COVID-19, particularly under certain circumstances.

“Low-dose chest CT may play a complementary role to RT-PCR for the early triage of patients with possible COVID-19 infection,” they said. “Chest CT may have the additional advantage of offering alternative diagnoses in a significant subset of patients.”

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