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
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.
The limitations of thermal imaging cameras
Fever is an important sign of COVID-19 infection, but will not always be present. An infectious person in the early stages of the disease may have no symptoms at all, or may have some symptoms but no fever.
For this reason, the UK regulator for medicines and health products warned that temperature screening cannot be performed when COVID-19 cases are detected.
However, there is clinical evidence for the use of thermal imaging cameras for fever testing. The reality is that with the right thermal imager, the right lens, and the right guidelines and standards, an effective screening tool can be used.
This is how you get the best results
To maximize the chances of success, thermal imagers should be positioned near and at eye level to capture a group of image pixels near the tear ducts.
The type of camera and lens is extremely important – an infrared radiometer with at least 320 x 240 pixels is considered a minimum requirement for a standard lens between 20 and 24 °. Ideally, the face should take up at least 75% of the picture. Therefore, a distance of 70 to 120 cm between the scanned person and the camera is recommended to achieve this.
If these distances are extended, the temperature will drop. You can see that the temperature difference of the same person at 600 cm leads to a drop of 1.6 ° C.
The regular calibration of the camera and the recording of the ambient temperature on the image are crucial, as changes in the room temperature and humidity also affect the result. Drafts and direct sunlight can also cause difficulties and should be avoided.
For those who are concerned about safety, the most important thing to know is that infrared cameras, like all other cameras, record the energy emitted by the body and do not generate radiation themselves. So there is no risk from them.
Although proper and careful use minimizes false negative and positive results, these problems do occur. It is important, therefore, to understand the limitations of this technology for screening and to use it in conjunction with other measures to limit the spread of coronaviruses. In addition to social distancing, wearing masks and washing hands, thermal imaging cameras can still be part of our arsenal in the fight against this disease.
This article was republished from The Conversation by Roderick Thomas, a lecturer at Swansea University and Hamish Laing, professor of improved innovation, engagement and results at Swansea University, under a Creative Commons license. Read the original article.
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