Chest CT of a COVID-19 Patient

Introduction:

COVID-19 is a spreading disease caused by the SARS-CoV-2 virus. It was declared a pandemic by the World Health Organization (WHO) on 11th March 2020. Initially, it was considered a global crisis as the morbidity and mortality rates were high, the diagnostic aids were minimal, and treatment was just palliative.

The virus is mostly transmitted from person to person through respiratory droplets. Symptoms include fever, cough, loss of smell, loss of taste, shortness of breath, body ache, malaise, and nasal congestion. However, severe cases of pneumonia and respiratory distress have also been reported, requiring hospitalization and invasive treatments. The elderly and patients with comorbidities are found to be at more risk. The treatment ranges from isolation and palliative care for simple cases to the use of ventilators in severely hospitalized patients.

Many new variants of the SARS-CoV-2 virus were reported after the initial outbreak. However, progressively, the diagnostic and therapeutic field of COVID-19 also observed some impressive evolution. Early detection of COVID-19 is essential for prompt treatment and also for confining the spread of the disease.

What Are the Different Diagnostic Aids in COVID-19?

Real-time RT-PCR (reverse transcription-polymerase chain reaction) remains the standard diagnostic tool for confirming the presence of COVID-19. It is usually performed by using a nasopharyngeal or oropharyngeal swab.

The role of radiological imaging, such as computed tomography (CT), has evolved to a great extent during the pandemic. Earlier, CT was used as a diagnostic tool at par with RT-PCR. However, current studies have advocated against the use of CT for primary screening in COVID-19. It may be used in severe cases of COVID-19, patients with comorbidities, and those patients experiencing respiratory distress.

Diagnostic tests such as chest X-rays, ultrasound, and immunological assays can be used to substantiate other findings associated with COVID-19.

What Is a Chest CT Scan?

A special X-ray machine is used in a chest CT scan which will take pictures of the patient’s lungs, blood vessels, heart, ribs, airway passages, and lymph nodes. A person is made to lie on a table and pillow and straps will hold them in place to prevent movement as that could result in a blurry image. A chest CT scan will help to find signs of infection, inflammation, injury, or disease of the lungs, major blood vessels, lymph nodes, and esophagus.

What Is the Role of Chest CT in COVID-19?

• Chest CT is the gold standard in advanced cases of COVID-19; to diagnose COVID-19 causing pneumonia.

• In patients with severe respiratory distress such as hypoxemia and severe dyspnea, CT is recommended irrespective of the RT-PCR test results.

• In elderly and co-morbidity-associated COVID patients, CT may help prevent disease progression, thus enabling early recovery.Related Topics

• The low sensitivity rate of RT-PCR (due to the difference in viral loading and disease staging) makes CT a more valuable diagnostic tool.

• However, increasing radiation exposure, high cost, and limited accessibility emphasize that CT should not be used for initial screening. It is recommended in cases where risk factors are associated with disease progression.

• CT helps distinguish COVID-19 pneumonia from other viral pneumonia.

What Are the CT Protocols Followed?

• Non-contrast material-enhanced CT is usually done.

• In case of associated pulmonary embolism, CT pulmonary angiography may be done.

• A low radiation dose is used based on the ALARA (as low as reasonably achievable) principle.

• The image is achieved during a single inspiratory breath.

• The radiological personnel are advised to follow all safety protocols and precautionary measures to prevent disease contamination.

• Using HEPA (high-efficiency particulate air) filtration in the examination room is helpful.

• Disinfection of CT examination rooms is mandatory.

What Is the Use Of CT Chest Scan With Contrast?

When a CT scan is made, around the body, an x-ray beam will move in a circle and will take images known as slices of the lungs and inside the chest. These images are processed by the computer and displayed on the computer. A contrast dye may be used during the test which will make parts of the body show up better in the image.

What Are the Various CT Findings and Their Importance?

Several studies have published reports on different CT findings in COVID-19 patients. They have found a direct correlation between CT findings and the stage and severity of the disease.

Other findings such as fibrosis, traction bronchiectasis, subpleural band, inverted halo, and vascular enlargement are also observed in the chest CT of COVID-19 cases.

What Are the Stages of COVID-19 Based on Chest CT?

Four stages of COVID-19 are described based on the chest CT findings:

What Are the CT Features in COVID-19 Pneumonia?

The Radiological Society of North America (RSNA) has laid down certain guidelines to report CT findings in COVID-19 pneumonia. Based on these findings, four categories are described below:

What Are the Various CT Scoring Systems?

There are two scoring systems:

1. CT Scan Severity Score (CTSS): It is used to determine the area of lung involvement. Three lobes are present in the right lung and two lobes in the left lung. Each of the five lobes is visualized and scored from one to five.

• Score 1: Less than 5 % lobar involvement.

• Score 2: 5 to 25 % lobar involvement.

• Score 3: 26 to 50 % lobar involvement.

• Score 4: 51 to 75 % lobar involvement.

• Score 5: More than 75 % lobar involvement.

The individual scores will be added up to obtain the final score, which will be out of 25. Based on the final score, the severity of the infection will be given as below:

• 1 to 8 score - Mild infection.

• 9 to 15 score - Moderate infection.

• More than 15 score - Severe infection.

The final score, when multiplied by four, gives the total lung involvement. Suppose the CTSS is 10; that means 40 % lung is involved (four multiplied by 10).

2. COVID-19 Reporting and Data System (CORADS):

It is used to determine the level of infection. The scoring is as given below:

Conclusion:

Chest CT has played a pivotal role in the existing battle against COVID-19. Though RT-PCR remains a standard in the screening of COVID-19, CT is indispensable in advanced and severe cases of respiratory distress. The prompt use of CT in advanced cases has helped physicians manage the most efficiently and swiftly possible. There is a slight ambiguity about the use of CT as a stand-alone diagnostic tool; however, in a scenario with limited resources and increasing cases, it is an important tool for rapid triage. With the disease evolving every day, innovation in the role of CT in disease diagnosis and management cannot be ruled out.