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The role of Nuclear Medicine in COVID-19 can be increased by redirecting existing radiopharmaceuticals and developing new ones to target different aspects of the virus. The lung perfusion scan can provide helpful information to the referring physician.

Imaging could aid in screening or accelerate the speed of diagnosis, especially with limitations of RT-PCR. Research indicates that Computed Tomography (CT) has high sensitivity for diagnosis of COVID-19.

This course covers role of computed tomography in diagnosis of COVID-19.

Computed Tomography

Due to shortage of kits and high false-negative rate of RT-PCR (Nucleic acid testing method), CT scans are used for the clinical diagnosis for COVID-19.

Chest CT scans are non-invasive and involve cross-sectional images by repeating it at several angles (Figure 1). The images obtained are further analyzed by radiologists to look for abnormal features leading to the diagnosis.

Figure 1. Multi detector CT Scanner on chest x-ray background for diagnosis COVID-19
Figure 1. Multi detector CT Scanner on chest x-ray background for diagnosis COVID-19

The imaging features of COVID-19 are diverse and depend on the stage of infection after the onset of symptoms.

Bernheim et al. saw more frequent normal CT findings (56%) in the early stages of the disease (0–2 days) with a maximum lung involvement peaking at around 10 days after the onset of symptoms. De Wever et al. found that opacities were most prominent 0–4 days after symptom onset (Figure 2) .

Figure 2. Computed tomography scan in a patient with severe viral pneumonia caused by SARS-CoV-2
Figure 2. Computed tomography scan in a patient with severe viral pneumonia caused by SARS-CoV-2

As a COVID-19 infection progresses, in addition to ground-glass opacities, irregular-shaped paved stone pattern develops, followed by increasing consolidation of the lungs (Figure 3).

Figure 3. Selective Focus of CT Chest AXIAL MIP view for diagnostic Pulmonary embolism (PE), lung cancer and COVID-19.
Figure 3. Selective Focus of CT Chest AXIAL MIP view for diagnostic Pulmonary embolism (PE), lung cancer and COVID-19.

Based on these imaging features, several retrospective studies have shown that CT scans have a higher sensitivity (86–98%) and improved false negative rates compared to RT-PCR. The main disadvantage of using CT for COVID-19 is that the specificity is low (25%) because the imaging features overlap with other viral pneumonia.

Limitations

  • CT scans are far more expensive but they expose patients to a low dose of radiation.
  • Patients included in the evaluation of infection time course should also be evaluated for their clinical histories, especially where the precise time of symptom onset is unknown.
  • The selection criteria for patients in these studies are unclear, but there appears to be a bias toward people with more severe illness, those in the hospital, or both.
  • The false-positive rate of CT will be unacceptably high in most settings, where many other respiratory and/or other diseases are present. CT scans cannot easily distinguish between Covid-19, SARS, MERS, and other viral pneumonias, including from influenza.
  • Moving individuals/patients around the hospital to the CT scanner increases chances of exposing other patients and parts of the hospital to contamination with COVID-19.

There are several points of discussion and controversies in the diagnosis of this deadly disease, but we must keep in mind that the reason to diagnose COVID-19 is not “patient management,” it is pandemic management.

External Links:

https://pubs.rsna.org/doi/10.1148/radiol.2020200642

http://jnm.snmjournals.org/content/61/6/781.full