Thermography for Human Febrile Screening

The Covid-19 pandemic has had a tremendous and lasting impact on how humans as a race will perceive and treat infections. One probable effect of the pandemic will be that persons symptomatic of infection will be further examined on an urgent basis, and are likely to be isolated, especially from public spaces, until any potential risk is nullified.

One of the challenges that the authorities in public spaces will face is that symptoms may not be obvious to a passive observer i.e. someone with a mild fever or a nagging cough may not appear ill, but may still be symptomatic. This brings about an urgent need for “screening” machines, which are capable of identifying symptoms that humans may not perceive, in order to arrest the potential spread of infection. As an example, Figure 1 shows how a fever was the most commonly observed symptom for Covid-19 patients, and as such fever is an “invisible” and not easily observable trait.

Figure 1. Percentages of Covid-19 patients with various symptoms. 'Fever' was observed to be the most common symptom by a large margin.                   Source: JAMA 2020;323 (11):1061-1069.

Traditional methods of temperature measurement are contact-based and require a few minutes to obtain an accurate measurement. Instant, non-contact technologies have become more commonplace, but not all of them are safe or accurate. Table 1 shows a comparison of a few methodologies for temperature measurement.

The need of the hour is a fast, non-contact and accurate mechanism for fever screening, while also ensuring that the person operating the machine remains safe from the risk of infection.

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Infrared (IR) cameras, also commonly known as thermal cameras, measure temperature by capturing the infrared irradiance of any object, including humans. These cameras are suitable for long periods of continuous running - ideal for cases where every individual entering a crowded space needs to be screened. These cameras are:

  • FAST: capturing up to 60 frames per second
  • NON-CONTACT: measurements are taken while the subject is 0.5 m to 1.0 m away
  • ACCURATE: with sensitivities as low as 30 mK (or 0.03°C)

However, thermal cameras come in many forms and models, and not all of them are suitable for fever screening. The WHO has provided clear guidelines as part of the ISO/TR 13154 and BS EN IEC 80601-2-59, to which any device for human febrile screening must adhere.

The past two months have seen the influx of several technologies that use thermal cameras for fever screening. However, not all of these are safe/accurate as they do not adhere to the above WHO guidelines, and do not address the complex intricacies of thermography.

As a result of the above, when a choice is to be made for the installation of a fever screening device using an IR camera, decision makers must stay away from technology offerings that:

  • claim to screen multiple persons at once
  • claim to have a large focus area (anything more than 1.0 meter)
  • do not measure temperature at the inner corner of the eye
  • claim to provide “absolute” temperature without a rolling average reference

At Spookfish Innovations, the team have built on their experience with thermography to put together a compliant and cost-effective fever screening system. The name “Harlequin” was inspired by the fish that bears the same name and shows off colours similar to visual representations of the infrared spectrum.

Figure 2. Harlequin Fever Screening in action at a factory in the UK (left) and Indian (right).

Harlequin uses computer vision to accurately detect faces in focus, followed by precise localisation of the subject’s inner eye corners, where core body temperature is then measured. The face and eye detection algorithms are powered by the latest machine learning technologies. Further, the system seamlessly integrates with existing access control systems to ensure that anyone detected with high temperature is not allowed to enter the premises.

Spookfish’s prior experience in working with the pharmaceutical industry has helped make Harlequin a secure system, with watertight measures in place to ensure no manipulation or leakage of screening data. At the same time, screening reports and audit trails can be easily generated with a few clicks.

These systems have already been deployed across several countries including India, the UK, the UAE and the USA, to ensure the safety of factory workers, caregivers and persons in spaces with large numbers of people. Till date, over 200,000 screens have been completed, and a handful have even been isolated for further medical checks upon detection of high temperature.

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