The gold standard for diagnosing COVID-19 is reverse transcription polymerase chain reaction (RT-PCR), a technique for which its inventor, Kary Mullis, was awarded the Nobel Prize. As we have discovered over the past few hectic months, RT-PCR does have some drawbacks: results are not immediately available; the swabs to collect a tissue sample from the back of the nose and reagents are in short supply; and the test may give false-negative results about 30% of the time.
The image above right is a 3D model based on computed tomography (CT) scans and shows how COVID-19 wreaked significant damage – highlighted in yellow – on the lungs of a 59-year-old patient who later died of the disease (© George Washington University). Because COVID-19 is a respiratory disease, both lung CT and chest X-rays have been touted as alternative methods of diagnosis, but there has been disagreement in the literature. Radiologists from Iran – one of the countries hardest hit by the pandemic – reported in Academic Radiology that chest CT was superior to RT-PCR, while the American College of Radiology has recommended against using CT for screening and diagnosis.
Although chest X-rays are routinely used to identify lung infections such as pneumonia, a recent paper in the Journal of Urgent Care Medicine has suggested these images are not a reliable method to diagnose COVID-19. One of the drawbacks of 2D digital X-rays is that all structures, such as the ribs, are superimposed on one another, making it difficult to identify features that may indicate pathology. A technology that encompasses the benefits of X-rays – low dose and high spatial resolution – but supports 3D visualisation, is digital tomosynthesis (DT).
Seen above left is a standard DT setup: a patient lies on a bed, an X-ray detector is located beneath him and an X-ray tube moves through an arc above his chest. A research group from Ukraine has just published a paper in which they gathered a chest X-ray of a patient with confirmed COVID-19 and compared that with a frontal plane slice generated by tomosynthesis (see below, © Teleoptic).
The image shows the same ground-glass opacities that are the hallmark of early disease seen on CT, but at a higher spatial resolution and significantly lower dose. Now might be the time for medical imaging facilities to consider tomosynthesis as a modality that could contribute to fighting this pandemic, although the lungs are not the only organ affected. As highlighted in today’s edition of Science, while the lungs are ground zero, “COVID-19 also tears through organ systems from brain to blood vessels.”