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Detecting COVID-19 using HRCT scans

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HRCT Chest | Covid Testing

Coronavirus is a form of infectious diseases that causes illnesses ranging from common cold to more severe conditions like lung damage, organ failure, etc. COVID-19 is a novel coronavirus (not been previously identified in humans) spreads primarily through saliva droplets or discharged through the nose when an infected person coughs or sneezes.

Since the epidemic broke out, there have been multiple reports on the ways Covid-19 has affected the human body. There is still a lot to learn about the virus that’s affected more than 55 million people and caused more than 1.3 million deaths [1]. But the one thing that’s become quite certain is that COVID-19 has a devastating impact on the body, sometimes leaving people with health problems even after they’ve recovered.

How does COVID-19 affect the body?

Early symptoms include shortness of breath, sore throat, body aches, extreme tiredness, fever, cough, nausea, headache and diarrhoea. A majority of cases suffer from lung damage, but there have also been cases where affected patients have had damage to organs like their heart, kidneys, brain, gut and blood vessels {2]. These affected blood vessels could also be a major reason why patients with blood pressure and diabetes are at a higher risk.

It must also be noted that there have been instances of patients who have been completely asymptomatic (showing no symptoms) and yet be infected by COVID-19, as stated by the Indian Council of Medical Research (ICMR).

Diagnostic approaches for COVID-19

In the early stages of the pandemic, testing for the coronavirus in India was a challenge for the medical community as there were very few centres who had the capability to conduct tests for the disease, and providing accurate results would take days to come.

But with extensive R&D, we’re now at a stage where we have developed tests that are faster and more accurate [4] like:

  • Rapid Antigen Detection Test (RADT)
  • RT-PCR (Reverse Transcription-Polymerase Chain Reaction),
  • CT Scans

Rapid Antigen Detection Test

Rapid Antigen Detection Test (RADT) is a swab test through the nasal passage that directly detects the presence of coronavirus antigens in the patient’s body. This is a quick response test showing results in 30 minutes and is usually done to find out if a patient is currently infected with the virus or not. The ICMR states that a positive result should be taken as a true positive while a negative test should be immediately followed by RT-PCR to rule out the infection.

RT-PCR

RT-PCR tests are considered the Gold standard when it comes to confirming if a person is infected with the coronavirus. Swabs are taken from a patient’s throat or nose and sent to the lab, which can pick up miniscule amounts of the virus that causes COVID-19. The time taken for an RT-PCR test result can take anywhere between 4-6 hours to a day due to the time taken to transport samples to the lab.

Limitation of RT-PCR

  1. There are already more than seven different SARS-CoV-2 nucleic acid PCR tests
  2. It is also very important to learn from the previous MERS-CoV epidemic and reflect on that experience, especially that a single negative upper respiratory sample is not enough to rule out infection. lower respiratory samples may be better than upper respiratory samples
  3. Reasons for the low sensitivity of PCR may include insensitive nucleic acid detection methods, variations in the accuracies of different tests, low initial viral load or improper clinical sampling

CT Scans

CT Scans have always been a reliable method for doctors to pinpoint affected tissues and organs in the body. With COVID-19, these scans have once again proven to be a reliable source of testing, especially in the cases of asymptomatic patients. COVID-19 is a respiratory disease affecting the lungs and CT scans of the lungs gives an accurate finding. While RT-PCR tests are a reliable form of testing, they are only effective when there is a presence of the virus antigen in the throat or nose. CT scans on the other hand can detect presence of the virus in the lungs, irrespective of whether the patient is symptomatic or asymptomatic. [5]

Early differentiation between emergency department (ED) patients with and without corona virus disease (COVID-19) is very important. Chest CT scan may be helpful in early diagnosis of COVID-19. The accuracy of chest CT in symptomatic ED patients is high. CT can be used as a quick tool to categorize patients into “probably positive” and “probably negative” cohorts.

Plain CT chest scans have been the preferred type of CT scan in providing accurate results. CT scans provide results within 30 minutes while a RT-PCR test can take upto 24 hours to provide results.

How do CT scans detect COVID-19?

Radiologists follow a system of CO-RADS in CT scans, to confirm the level of severity of an infection. The extent of damage can be clearly seen in CT-scan when the virus infects the lungs while RT-PCR can’t determine the extent of damage, virus has done. Different stages of lung infection have been defined starting from CO-RAD 1 to CO-RAD 6. Suspicion of COVID inspection starts at CO-RAD 4 and levels 5,6 are positive indicators of COVID-19.

What do you need to get a CT scan done for COVID?

The sensitivity of the CT tends to be higher (100.0%) in those with severe risk pneumonia than in patients with low/medium risk pneumonia (88.3%, p = 0.38). In patients with sepsis, sensitivity is significantly higher than in those without sepsis. In other words, sensitivity of CT is higher for severely ill patients.

In a study of patients presented at the ED with a clinical suspicion of COVID-19, it was found that chest CT scan when compared to RT-PCR had a high sensitivity of 89%.

Choosing a centre for your CT Scan

While choosing a centre for getting CT scans done, look out for the following:

  1. Centres with highly experienced and trained specialists who are capable of identifying presence of the virus in the body. A trained specialist will be able to recognize signs and notice minute details which could be otherwise overlooked by amateur radiologists.
  2. COVID-safe centres following all Government mandated protocols like temperature checks, strict adherence to social distancing, providing hand sanitizers in common areas and regularly sanitising all facilities and equipment after being used.
  3. Centres with latest, state-of-the-art equipment which provide top quality and highly detailed reports following international standards
  4.  Lots of centres take advantage of patients’ ignorance when it comes to pricing for tests related to COVID-19. The Government has set price caps on tests for testing facilities to comply with. Be vigilant of centres trying to charge extra for tests covered under these Government caps.

CT Scan Procedure

A CT Scan uses computers and rotating X-ray machines to create cross-sectional images of the body part being scanned. These images provide detailed information about damaged tissues and organs. In some case, patients may be given a special dye to drink, called “Contrast Material”, to help show affected parts more clearly. This technique obtains images with detailed image of the lungs, ideal to assess if there has been lung damage due to the virus.

Here’s more information on CT scan procedure:

  • For CT scan without contrast, patients can eat and drink before their appointment. They can take prescribed medications, if any. If a doctor has ordered a CT scan with contrast, they should not eat anything for at least four hours before scan begins.
  • Before the test, patients will need to change into a hospital gown and remove any jewellery or metal objects that they are wearing.
  • If a contrast dye is used, it will be given to by mouth (oral contrast) or injected into a vein in the arm (intravenous). Some adults, and most frequently children, may be administered sedatives prior to scanning procedures.
  • If oral contrast has been given, they will need to wait for about 45 to 60 minutes before being taken to the scanning room. This waiting time is needed for the contrast to move through the digestive tract.
  • The CT scanning machine is shaped like a doughnut. Patients will be made to lie on the imaging bed. The technician present in the console room can see them through a glass window and guide them through the process.
  • The bed is moved slowly through the scanner and patients must lie still while the process starts. The X-ray machine will rotate around and produce several images of the body. When needed, the technician will instruct them to hold their breath for several seconds so that they remain still. A CT scan takes only a few seconds to complete.

The main purpose of CT scan is to identify whether lungs are infected by the virus and what is the severity of lung involvement. That can be an important prognostic indicator. The results are available immediately for doctors to evaluate, these reports are usually sent to patients through their email in a few hours or can be collected by them the next day.

Steps on prevention

Some of the ways to protect yourself from getting infected are {3}:

  1. Maintain minimum 6 feet distance from other people, usually termed as social distancing
  2. Wear a medical grade N95 mask or a thick layered mask that covers your entire nose and mouth when you are outside your home
  3. Always keep your hands clean by washing them thoroughly as often as possible or by using hand sanitizers with atleast 60% alcohol in it
  4. Never touch your face when outside, unless you’ve washed them thoroughly
  5. If you are above the age pf 65, suffering from diabetes or cancer, it is highly recommended not to leave your home
  6. If you are having community gatherings, try to limit the size to no more than 10 people

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