A Window Inside the Body and COVID-19

Getting images of what’s happening inside of people’s bodies is helping health professionals to evaluate and better understand the COVID-19 disease, which is caused by a newly discovered coronavirus.

“Diagnostic imaging is a window into the body,” said Olivier Pellet, a radiologist at the IAEA. “It has allowed us to uncover complications, such as lesions, pneumonia or blood clots in the lungs. Every day we learn about the virus and its impact on the human body, while discovering new COVID-19-related signs and symptoms we have not seen before, even when a person may otherwise appear asymptomatic.”

X-rays are a type of radiation. Many people are most familiar with them for their use in diagnosing a broken bone or examining teeth.

Health care professionals can harness X-ray radiation using an X-ray machine. When a patient is placed in the machine, a carefully selected dose of X-rays passes through the targeted area of the body. The thicker and denser parts of the body, such as bone, let fewer X-rays through, while softer, thinner parts let more through. As the X-rays come out on the other side of the body, a specialized detector captures their pattern. This creates an image of the structures inside the body and their changes.

For evaluating COVID-19, X-rays are taken of a person’s chest to get a look at the lung tissue. This is used for patients with respiratory symptoms of COVID-19. X-rays are also used for monitoring the evolution of the disease and making treatment and follow-up decisions, such as whether to admit a patient to the hospital or send a patient with severe symptoms for a CT scan.

“Given that X-ray machines are often readily available in care centres, many health care professionals already have access to these tools to help their countries deal with COVID-19,” Pellet said. “Some X-ray machines are also portable, lightweight, and easy to handle and decontaminate, which is critical in a pandemic, particularly in medical triage areas or makeshift hospital environments.”

A computed tomography (CT) scan is a set of multiple X-ray images. A CT machine rotates around the patient and rapidly sends X-rays through the body from multiple angles. A ring of hundreds of specialized detectors around the body track the pattern of the X-rays. This is then processed by the machine’s powerful computer to create detailed images constructed out of very thin slices of the body, up to 0.3 mm wide, often in 3D. For a CT scan of the chest, which is the area of the body typically scanned when evaluating COVID-19, hundreds of images are generated to cover the whole chest area.

CT machines are more sophisticated, more expensive and not as widely available as X-ray machines. They are also harder to decontaminate, which can take more than 20 minutes, said Pellet. “CT scans provide highly detailed information and to do that they use more radiation than an X-ray machine. They should therefore only be used when appropriate for the patient’s case.”

Ultrasound machines use high-frequency soundwaves instead of radiation to create an image. A probe connected to an ultrasound machine sends and receives millions of soundwaves every second through the target area of the body, which, in the case of COVID-19 patients, is typically the lungs. When the waves hit a boundary, such as between soft tissue and fluid or soft tissue and bone, they echo back to the probe. The probe tracks the distance and intensities of the echoes and translates this into images.

Ultrasound machines are low cost and more widely available than X-ray and CT machines. Being small, portable and easy to decontaminate, they can be easily used at patient bedsides, in an ambulance or in a triage situation. Since radiation is not involved, they can also be used more often without posing additional risks to patients and health care workers.

As ultrasound images are dynamically and instantly displayed on a screen, a trained health care professional can evaluate a patient on the spot. Ultrasound imaging of the lungs is a good starting point for evaluating patients displaying respiratory symptoms that could be signs of COVID-19, as it can display images that are strongly suggestive of the disease. However, as lung ultrasound only explores the periphery of the lungs and is user dependent so concrete and detailed images provided through chest X-rays and chest CT scans are needed for a conclusive diagnosis of COVID-19, as well as to follow and monitor the evolution of the disease in the patient.