Not long ago I published an article about the use of computed tomography (CT) to scan chest organs in patients with suspected COVID-19. The article resonated with the audience while CT imaging was positively acknowledged both in Moscow and New York. Some readers, being also regular health care consumers, expressed concern about the safety of imaging studies in the article titled: “Computed tomography causes cancer”. Prof. Sergey Morozov, CEO of Moscow Center of Diagnostics & Telemedicine explained to Stanislav Samburskiy when CT can actually be harmful.
Why do we need CT?
Around 49% of the symptomatic patients who have positive PCR test results manifest chest CT imaging abnormalities common to COVID-19 pneumonia. The UpToDate recommendations suggest splitting patients into two groups with either less or more than 50% of the pulmonary involvement (this can be seen on radiography or computed tomography images). In order to monitor changes clinicians rely on the unified classification scheme that assesses pulmonary involvement based on a four-grade scheme. Mild changes correspond to the CT-1 grade and manifest with less than 25% pulmonary involvement. The moderate condition is graded CT-2 and is associated with 25 to 50% abnormal changes. The patients who developed severe stage present with from 50 to 75% pulmonary involvement and are assigned a CT-3 grade. Critical condition (CT-4) is observed when the area of pulmonary lesions exceeds 75%. Such changes can only be seen on a CT image. The patients in severe (CT-3) or critical (CT-4) conditions accompanied by typical symptoms are referred to inpatient setting in 99% of the cases. It is also a common practice to hospitalise patients with moderate lung lesions (CT-2) if they show signs of hypoxemia.
Routing the patients with suspected COVID-19
Amidst absolute uncertainty and contradictory international recommendations on the diagnosis of the COVID-19 infection, it was impossible to tell which diagnostic method worked better than the alternatives.
Currently, the international database of medical literature Pubmed (the USA) contains over 2,035 scholarly articles that can be found using the “COVID-19 CT” keyword (computed tomography for COVID-19). The key studies that focus on the efficacy of the computed tomography for the disease management and forecasting the severity of COVID-19 pneumonia, can be found in the high-impact journals such as Radiology (Pan et al., Bernheim et al.) and the American Journal of Roentgenology (Zhao et al., Li et al.) The health care system in China adopted a routing scheme that allows categorizing patients into the groups at lower or higher risk of COVID-19, and determining an optimal treatment strategy, which may involve outpatient or inpatient care (Radiology, Ai et al.; Miao et al.) In the UK specialists developed a different routing algorithm: based on the CT results clinicians make a decision whether the patient should be left at home or hospitalized (Clinical Radiology, Nair et al.) In presence of the typical CT findings and based on the clinical status, the patients would either be admitted to the hospital or quarantined. Those with imaging abnormalities are referred to urgent differential examination without interrupting their self-isolation.
As the pandemic continues creating a safe working environment in health care facilities becomes ever more vital. To accomplish this the authorities introduced comprehensive measures to secure the sanitary and epidemiological safety. The Moscow outpatient CT centers imposed emergency rules for visiting the CT offices, cleaning the equipment, and zoning the CT rooms (the Order of MHD №374).
The CT premises were divided into specific functional zones. Two radiology technicians would work in the “red” zones wearing the necessary protective gear: one would see patients, taking their medical history and positioning them on a CT table, while the other would ensure supervisory control during the imaging process. Nurses and volunteers would provide assistance to the radiology technicians. Meanwhile, radiographers would perform remote reading of the CT results without leaving the “green” zone. The incidence of COVID-19 among outpatient healthcare workers during the pandemic was up to 3%, which is a good sign that once the working conditions are set up in compliance with the epidemiological safety guidelines the risk of getting an infection is low.
During the pandemic, the personnel of the outpatient CT centers had unrestricted access to personal protective equipment and disinfectants. We would like to express our sincere gratitude and appreciation for our patrons. They made sure that the front-line workers from outpatient and inpatient CT centers had regular access to enough high-quality food.
Radiation dose in CT exams
In real-life practice Moscow radiology technicians encountered patients who deliberately asked for a CT exam, considering this method to be reliable and safe. Although this opinion does reflect the reality, while computed tomography is a safe procedure, it is administered based on the particular clinical indications (the justification principle).
The radiation dose from CT scan in the diagnosis of COVID-19 is similar to that for a regular lung examination. The effective dose varies between 1 and 7 mSv, depending on the study protocol, and the patient’s body mass and height. In some scenarios when tailoring special low-dose protocols the effective dose may be as low as 1.0 mSv, although one should keep in kind that it may negatively affect the quality of the resulting images.
In view of this, the radiation dose can not be considered a factor that limits the use of the computed tomography for COVID-19 in symptomatic patients. However, it is essential to remember that CT does not suit for medical screening.
In April and May, early diagnosis of the lung changes typical in COVID-19 pneumonia in the outpatient CT centers gave rise to an effective patient routing mechanism: some patients were quarantined and treated outpatiently in the comfort of their homes, while the others were hospitalized and received emergency medical care. In June the statistics showed a decrease in the overall number of chest CT studies conducted in the Moscow outpatient CT centers. At the moment, the operation of the CT and MRI facilities has been fully restored back to admitting medically ill patients. Wide application of the antibody testing for COVID-19 helped to shape a different system for the provision of medical care during the pandemic.