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How thermal imaging cameras can play a key role in slowing the spread of corona viruses

In response to the coronavirus pandemic, the world has rapidly deployed infrared thermal cameras (also known as infrared radiometers) to measure people’s temperature, and technology has become big business.

Since the pandemic started, thermal imaging cameras have been used in areas with high pedestrian traffic such as airports, shopping centers, nursing homes, factories, office buildings, schools and even hairdressers. This raises questions about their safety and accuracy.

And although the accuracy of these devices depends on how they are used, we can safely say that the technology is harmless to people and is completely safe.

How do thermal imaging cameras work?

Infrared thermal cameras measure the energy radiated from an object surface, such as human skin, without having to touch this surface. Different temperatures are shown in a thermogram as different colors, which can change color at the threshold for fever (38 ° C), for example.

This idea dates back to 1

800 when William Herschel, the royal astronomer who was already famous for discovering the planet Uranus, first described the existence of infrared radiation. He let sunlight run through a glass prism and measured the temperature of each rainbow color with different thermometers. He noticed a higher temperature in a dark area and called it “radiant heat”: We now call this infrared radiation.

Early thermal imaging cameras became available around 1959 and were initially used to measure the increased heat over arthritic hips. Other medical uses have been the Raynaud phenomenon (which affects blood flow), diabetes symptoms and melanoma. However, screening for fever is the most common clinical application today.

In the past, fever was diagnosed with mercury thermometers, which for safety reasons were replaced by infrared devices that measure the temperature of the eardrum. However, these require close contact with the person, which is not ideal for screening for potential cases of coronavirus.

Today’s infrared cameras are extremely reliable, easy to use with very few moving parts, but to be precise, it is important that the user targets the correct area of ​​the face. The forehead was the target area in the 2009 swine flu pandemic, which led to misleading results.

The latest update of the thermographs from the International Organization for Standardization confirms that the region with the most stable results is near the inner canthi (tear duct) because it is located directly above a main artery. If this range is one or more degrees higher than the baseline average (37 ℃), there is a high probability that the person has a fever, which should then be checked in the usual way with a conventional infrared eardrum thermometer.

In the illustration below we see the difference between the appearance of a child without a fever (left) on a thermal imager and a child with a fever (right) when the camera is directed towards the tear ducts.

Two thermal images: one of a child without a fever and one of a child with a fever.