skip to Main Content

Why Forehead Fever Scanners Don't Work?

Lately, much media has been discussed 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.

Forehead Thermometer Accuracy

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.”

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

As Dr Fauci mentioned, such substantial variance in human body surface temperature measurements 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, which may not reflect the body’s core temperature, which is crucial for accurate fever detection. That surface temperature is affected by ambient temperature, and forehead readings are inconsistent from person to person, according to the National Library of Medicine. Testing has shown that the forehead varies 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 temperatures of 98.3°F (36.8°C). At the same time, a reading on the forehead measures 90.6°F (32.6°C) – a difference of 7.7 °F.

Temperature readings through non-contact means, such as ear temperature measurement, are not straightforward.

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 to measure body temperature accurately. 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.” The goal of measuring body temperature accurately is achieved by analyzing temperature readings from the inner canthi.

Thermal imaging cameras measure an object’s radiated infrared energy and mathematically convert that to a temperature based on the object’s radiance. Each pixel on the camera has a calibrated temperature reading, emphasizing the importance of accurate temperature readings for effective fever screening. 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 the 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. They cannot report 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.

Why use ambient 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 indicate a fever (one of the symptoms of a viral infection). In addition to thermal imaging systems, infrared thermometers and non-contact infrared thermometers are commonly used for quick screenings in various settings, mercury thermometers offering a rapid and non-invasive way to measure body temperature. 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 appropriately used. 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 non-contact infrared thermometers on the market or more accurate than thermal imaging cameras?

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 tear ducts (inner canthi) are the reliable area on the face to obtain core body temperature.
  • 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 reads. If there is any error on the camera, the EBT system constantly corrects that within the software by re-calibrating the camera so that it reads correctly based on a known source. Additionally, ensuring the thermometer is kept steady, and the subject remains still during the measurement is crucial for accurate readings, mirroring the precision required in using forehead thermometers effectively.

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 subjects in the screening area and then measure their temperature. This process typically takes 1 to 3 seconds. If oral temperature during the measurement is below a certain threshold, the person will get an on-screen Pass result (or green box). If their temperature exceeds the set threshold, they will get a Fail result (red box on screen).

graphical user interface, website

Can the Viper system be tied into Access Control?

Yes. Since we use different communication 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.

A practical part of efforts to minimize exposure and prevent the spread

The primary objective of thermal screening is to measure temperature to identify individuals with elevated body temperature. As stated, thermal screening cannot detect COVID-19 or diagnose any viral infection. Still, it has been recognized by the FDA and ISO as a practical part of efforts to minimize exposure to infected individuals and help prevent the spread. If you or your organization are considering implementing thermal screening, 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?