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Why Forehead Fever Scanners Don't Work

There has been a lot of media discussion of late about “fever scanners” and other devices designed to measure skin surface temperature. Even Dr. Fauci, NIH Director, weighed in on the subject recently in an interview with the chief of medicine at Walter Reed Army Medical Center on August 13.

a screen shot of Anthony S. Fauci

Forehead scanners are “notoriously inaccurate,” according to Dr. Fauci. He referenced his local weather of 90+ degrees and how that affects skin temperature. “So I went into the White House the other day, my temperature was like 103 until I took it in the air-conditioned car, and it was 97.4.”

Clearly, the accuracy and effectiveness of temperature screening depends on many factors. Let’s address the measurement device and screening methods.

Such substantial variance in human body surface temperature measurements, as mentioned by Dr. Fauci, can be expected when utilizing a non-contact handheld single spot IR Thermometer (a.k.a. forehead scanner) as it is aimed at a person’s forehead or temple. These devices detect surface temperature. That surface temperature is affected by ambient temperature, and forehead readings are not consistent from person to person according to the National Library of Medicine. Testing has shown that the forehead varies on average from 2°F to 10°F lower than the body’s core temperature.

forehead scanner example

Note the image example, where the tear duct region is being measured and getting a reading of 98.3°F (36.8°C). At the same time, a reading on the forehead is measuring 90.6°F (32.6°C) – a difference of 7.7° F.

Determining a person’s core body temperature through non-contact means is not an easy or simple process.

Body Temperature vs. Skin Temperature

Since forehead scanners do not accurately reflect a person’s core temperature, thermal imaging cameras answer the need for a non-contact method of measuring core temperature. This is achieved by measuring a person’s tear ducts. According to IEC report 80601-2-59, “evidence indicates that the region medially adjacent to the inner canthi is the preferred site for fever screening due to the stability of that measurement site. This is because the region is directly over the internal carotid artery.”

Thermal imaging cameras measure the radiated infrared energy of an object and convert that mathematically to a temperature based on the radiance of an object being measured. Each pixel on the camera has a calibrated temperature reading. This is why the FDA advises adherence to the requirements set forth by the ISO and IEC for thermographic screening (FDA: Thermal Imaging Systems and Covid-19).

The Viper EBT System automatically seeks out and measures a small area adjacent to the inner canthi as prescribed and recommended by the FDA, per the ISO and IEC. Viper EBT software then characterizes the inner canthi surface area temperature into a high quality representation of human body core temperature. Low-cost handheld IR thermometers do not have the required optical resolution to measure the small area of the inner canthi and as such, are incapable of reporting accurate temperature measurements on a repeatable basis, person to person, day after day, month after month. The Viper EBT System is designed and proven to produce reliable measurements over extended periods of time.

Why use temperature screening at all?

As a means of helping to prevent the spread of Coronavirus (COVID-19), thermal imaging systems serve as a pre-screening device. They identify elevated body temperature (EBT) which could be indicative of a fever (one of the symptoms of a viral infection). While thermal imaging systems are not medical devices and do not replace conventional medical testing, they can be used to give an early indication when used properly. According to the CDC, 85% of those admitted to the hospital with confirmed cases of Coronavirus had fever symptoms.

ISO technical report 13154 states that screening thermography should be an element of the layered screening process to support the objective of pandemic prevention. Along with appropriate follow up (i.e. referral to a medical professional for clinical diagnosis), thermal screening “can be useful to separate potentially infectious individuals from others.” The report cites examples of locations for use:

  • Medical facilities

  • Critical infrastructure facilities

  • Workplaces

  • Schools

  • Government buildings

  • Police and fire stations

  • Communal locations

  • Public transportation

In a 5/13/2020 discussion of thermal imaging systems, the FDA suggests consideration of temperature screening for “airports, workplaces, grocery stores, concert venues” and “other areas where you are trying to screen large groups” as “part of a larger approach to risk management.”

How is the Viper EBT System more accurate than other systems on the market, or more accurate than using thermal imaging cameras on your own?

First, we understand the application and how to make the measurement correctly.

  • Setup and operations guides for Viper EBT systems align with best practices set forth by the FDA and IEC.

  • We know that by following these best practices, the reliable area on the face to obtain core body temperature is the tear ducts (inner canthi).

  • Screen one person at a time.

  • We understand the requirement for cameras to have a small spot size, and utilize the correct optics and distance measurement.

  • We utilize Calibrated Reference Emitters in the scene’s field of view (FOV). That temperature is fed back into the software and compared to what the thermal imaging camera is actually reading. If there is any error on the camera, the EBT system constantly corrects for that within the software by re-calibrating the camera to read correctly based on a known source.

By using these methods, the Viper EBT system can achieve better than 0.5°F accuracy.

Is the Viper EBT System Automated?

Yes. ViperVision software has integrated facial recognition to sense a subject in the screening area and then measure their temperature. This process typically takes 1 to 3 seconds. If the resulting measurement is below a certain threshold, the person will get an on-screen Pass result (or green box). If their temperature is elevated above the set threshold, then they will get a Fail result (red box on screen).

graphical user interface, website

Can the Viper system be tied in to Access Control?

Yes. Since we use different modes of Communications Protocols (Digital IO, OPC, Modbus, Ethernet IP), we can communicate with external devices (both input and output). ViperVision software also allows the system to be monitored remotely.

An effective part of efforts to minimize exposure and prevent the spread

As has been stated, thermal screening cannot detect COVID-19, or diagnose any viral infection for that matter, but it has been recognized by the FDA and ISO as an effective part of efforts to minimize exposure to infected individuals and help prevent the spread. If you or your organization are considering implementing thermal screening, be sure to do your due diligence. Research the vendor and the equipment used in the system. We hope this post has helped you know what to ask.

Do you have questions for us?