The Role of Chest Radiography in the Diagnosis of COVID

The Role of Chest Radiography in the Diagnosis of COVID-19

Author: Debra J. Poelhuis, M.S., R.T.(R) (M)

Chest radiography (CXR) is a widely available baseline radiological modality in evaluating symptomatic patients with suspected or confirmed cases of COVID-19. Serial changes can help in monitoring the patients in conjunction with the clinical status of these patients in a hospital setting. As radiologic technologists who image patients suspected of having or confirmed to have COVID-19, they are the lynchpins of COVID-19 diagnosis. With that in mind, this article is geared toward advancing radiologic technologist’s understanding of the role of chest radiography in the diagnosis of COVID-19. We’ll review chest anatomy and physiology, symptoms of COVID-19, and discuss the role of chest radiography, including computed tomography scans, in diagnosing COVID-19 cases.

Table of Contents

Chest Anatomy and Physiology

The chest is the area of origin for many of the body’s systems because it houses the heart, esophagus, trachea, lungs, and thoracic diaphragm. The lungs begin at the bottom of your trachea. The lungs, two spongy, pinkish organs, are the center of the respiratory system. The right lung is composed of three lobes. The left lung has only two lobes allowing space to make room for the heart.

The Role of Chest Radiography in the Diagnosis of COVID-19

Each lung has a tube called a bronchus that connects to the trachea. The trachea carries air into and out of the lungs. Forming an upside-down “Y” in the chest, referred to as the bronchial tree, are the trachea and bronchi airways. The bronchi branch off into smaller bronchi and then into smaller tubes called bronchioles. Like the branches of a tree, these tiny tubes stretch out into every part of the lungs and are only about the thickness of a hair. There are 30,000 bronchioles in each lung. These tubes end with a cluster of small air sacs called the alveoli which look like a tiny bunch of grapes. The lungs hold about six hundred million alveoli giving the lungs about a surface area equivalent to the size of a tennis court. This allows adequate room for oxygen to pass into the body.

A network of capillaries covers each alveolus. This is where the exchange of oxygen and carbon dioxide happens. The heart sends deoxygenated blood, blood that is carrying carbon dioxide rather than oxygen, to the lungs.

As the blood passes through the tiny, thin-walled capillaries, they get oxygen from the alveoli. They return carbon dioxide through the thin walls to the alveoli. The oxygen-rich blood from the lungs is returned to the heart, where it is pumped to throughout the entire body. The carbon dioxide is exhaled out of the lungs and alveoli through the mouth and nose.

The gist: Each lung is divided into lobes and connected to the trachea. The bronchial tree running through the lungs is made up of the windpipe, bronchi, bronchioles, and alveoli.


COVID-19

SARS-CoV-2 disease (COVID-19) is an infection caused by a new emerging coronavirus, first detected in Wuhan, China, in December 2019. Now a protracted pandemic, COVID-19 continues to pose a serious public health problem for all countries. Radiologic technologists are at the frontlines of the COVID-19 outbreak response and as such are exposed and at risk. Recent vaccines and masking in public areas have slowed the incidence of COVID-19. But many people remain unvaccinated and continue to contribute to its spread.

So, what exactly is COVID-19, and what about its variants? Coronaviruses are a large family of viruses, some causing cold-like illnesses in people, while others cause illness in certain types of animals, such as cattle, camels, and bats. This virus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, laugh, speak, sing, or breathe. These particles range from larger respiratory droplets to smaller aerosols. Proper respiratory etiquette, such as coughing into a flexed elbow and staying home to self-isolate if one feels unwell, are recommendations to help stop the spread.

COVID-19 affects people in diverse ways with most infected people developing mild to moderate illness and recovering without hospitalization. Recently the Delta variant, and now the emerging Omicron variant, has played a huge role in the increased incidence of COVID.

As of December 5, 2021, there were 742,928 current cases of COVID reported in the United States. Since the pandemic began, healthcare personnel accounted for 779,875 cases, with 2,968 deaths reported by the CDC. On average it takes 5–6 days after a person is infected with the virus for symptoms to show. However, it can take up to 14 days.

Symptoms of COVID-19

The most common symptoms of COVID-19 are fever, cough, fatigue, and loss of taste or smell. More serious symptoms which can appear are difficulty breathing or shortness of breath, loss of speech or mobility, confusion, and chest pain. People should seek immediate medical attention when presented with serious symptoms, especially children and the elderly.

COVID-19 and Pneumonia

There are many distinct types of pneumonia associated with the COVID virus. While all are slightly different, they are can be fatal if not properly treated.

Chest radiography plays a significant role in diagnosing the following:
  • ARDS or acute respiratory distress syndrome can occur in those who are critically ill or who have significant injuries. It is often fatal, as the risk increases with age and severity of illness. People with ARDS have severe shortness of breath and often are unable to breathe on their own without support from a ventilator.
  • Pulmonary interstitial emphysema (PIE) is a rare disease which can be seen in adults but most frequently occurs in premature infants. Premature infants with pulmonary interstitial emphysema can develop respiratory distress syndrome. The pathology seen involves lung damage through the alveolar and airway with over-distention that can produce air leaks. It has a high morbidity and mortality rate if not diagnosed and treated promptly (Wong, et al., 2020).
  • Pneumomediastinum – The exact mechanism by which SP occurs in SARS-CoV-2 pneumonia is unknown. During the coronavirus pandemic, the number of patients requiring endotracheal intubation and mechanical ventilation has increased significantly. Pneumomediastinum (PM) is an uncommon potentially life-threatening accumulation of air within the mediastinum (O’Conner, et al., 2005).
  • The Role of Chest Radiography in the Diagnosis of COVID-19
  • Pneumothorax – As many as 1 in 100 hospitalized COVID-19 patients may experience a pneumothorax, or punctured lung, according to a multicenter observational case series published in the European Respiratory Journal. A newer study found that COVID-19 may cause cysts in the lungs that could lead to lung punctures. Doctors were advised to consider the possibility of punctured lungs in COVID-19 patients, even in those who do not fit the profile for it, as many study patients were diagnosed with this condition only by chance (Beusekom, 2020).
  • Air leak phenomena – Spontaneous air-leak syndromes have emerged as rare but significant complication of COVID-19 pneumonia in recent months. This complication has been documented in both spontaneous and mechanically ventilated patients (Sabharwal, et al., 2021). Pneumothorax, subcutaneous emphysema, and mediastinal emphysema are components of air-leak syndrome, documented to occur in ARDS.
  • Ventilator-associated pneumonia (VAP) – The increased risk of ventilator-associated pneumonia in COVID infections, as compared to other ARDS, may be due to multiple factors, such as less rigorous use of standard prevention strategies during COVID-19, disease and therapy-associated immune impairment, prolonged duration of mechanical ventilation, prolonged use of sedation, and more frequent need for prone ventilation (Wicky, et al., 2021). Some studies found an important rate of complicated VAP with lung abscesses and empyema.

The Role of Chest Radiography in the Diagnosis of COVID-19

Chest radiograph PA view of RT-PCR proven COVID positive patient showing patchy opacities in bilateral mid and lower zones involving the peripheral lung fields (left more than right).

The Role of Chest Radiography in the Diagnosis of COVID-19

Chest radiograph PA view of RT-PCR proven COVID positive patient shows showing ill-defined air space consolidations with reticular opacities (black arrows) in bilateral mid and lower zones.

Computed Tomography and COVID

Radiological imaging plays a significant role in the diagnosis and follow up of COVID-19 pneumonia. Chest computed tomography (CT) is valuable in detecting both alternative diagnoses and complications of COVID-19 (acute respiratory distress syndrome, pulmonary embolism, and heart failure). CT findings in COVID-19 are of patchy ground-glass opacities with a peripheral or posterior distribution, usually involving the lower lobes. Pleural effusion, pericardial effusion, lymphadenopathy, cavitation, CT halo sign, and pneumothorax are some of the uncommon findings that can be seen with disease progression.

Chest CT should be performed with strict precautions to minimize hazardous exposure of patients and healthcare professionals to SARS-CoV-2. When possible, a chest CT should be performed at sites with less traffic to avoid exposure of other patients and staff. Where more than one fixed CT scanner is available, dedicated use of only one CT scanner for patients with COVID-19 may be ideal. Another option is the use of a mobile CT scanner (Mossa-Basha, et al., 2020).

Patients referred for CT should undergo chest CT without contrast enhancement (Rodriquez, et al., 2020) unless CT pulmonary angiography is required to detect pulmonary embolism (PE). While some patients with COVID-19 may need to undergo a follow-up chest CT, non-enhanced chest CT should preferably be performed by using a low radiation dose protocol to minimize radiation burden.

CT use, scan protocols, and radiation doses in patients with COVID-19 pneumonia showed wide variation across health care sites within the same and between different countries. Many patients were imaged multiple times and/or with multiphase CT scan protocols. Healthcare sites varied on their CT protocols: some adopted a single-phase non-contrast protocol and performed only one chest CT examination. Some used a reduced-dose chest CT protocol, and some reduced radiation dose for follow-up chest CT compared with the baseline examination. Only one of 28 countries in a study coordinated by the International Atomic Energy Agency reported a median CTDIvol less than 3 mGy for chest CT examinations. (Homayounieh, et al., 2020).

Conversely, lower-dose chest CT examinations on newer scanners (installed between 2016 and 2020) and those with iterative reconstruction suggest proper scanner use. There are no specific recommended or target doses in patients with COVID-19 pneumonia, but when evaluation is limited to lung parenchyma, a CTDIvol less than 3 mGy, as recommended for low-dose chest CT for lung cancer screening, may be sufficient for COVID-19 pneumonia (Kalra, et al., 2020).

The Role of Chest Radiography in the Diagnosis of COVID-19

(A) Chest radiograph of a RT-PCR proven COVID positive patient shows no abnormality. (B) HRCT chest done on same day as patient was symptomatic revealed patchy areas of ground glass densities with interlobular septal thickening in posterior basal segment of right lower lobe and medial basal segment of left lower lobe.
Source: [Source]

The Role of Chest Radiography in the Diagnosis of COVID-19

Chest CT abnormalities of high prevalence in COVID-19. Axial, nonenhanced chest CT image (lung window) shows bilateral ground-glass opacities and dilated segmental and subsegmental vessels, mainly on the right, in a 70-year-old man with positive RT-PCR test results for SARS-CoV-2.
Source: [Source]

Conclusion

The chest X-ray as well as the CT Chest are important diagnostic tools in the detection and management of COVID-19 pneumonia. The chest X-ray is a useful tool in detecting changes which can suggest the diagnosis of COVID, but the CT chest has a higher sensitivity. The common CT findings of bilateral involvement of pneumonia, the peripheral distribution, and pathologies seen in the lower lobes were also appreciated on CXR which corresponded to other studies. Portable CXR used as a bedside modality can be used to monitor the progression and regression of lung changes (Jacobi, et al., 2021). It can also detect lung complications in the form of ARDS, barotrauma, ventilator-associated pneumonia and misplaced tubes and lines helping reduce the morbidity and mortality.

As of June 2020, the WHO guidelines gave conditional recommendations for using the CXR for diagnosis in symptomatic cases. Using a portable machine at the point of care can reduce the risk of cross-infection.


References and Images

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