Thermal Imaging Systems and COVID-19

When used correctly, thermal imaging systems generally have been shown to accurately measure someone’s surface skin temperature without being physically close to the person being evaluated. Thermal imaging systems offer certain benefits in that other methods need a closer proximity or contact to measure temperature (for example, non-contact infrared thermometers or oral thermometers).

Temperature-based screening, such as thermal imaging, is not effective at determining if someone definitively has COVID-19 because, among other things, a person with COVID-19 may not have a fever. A diagnostic test must be performed to determine if someone has COVID-19.

Thermal imaging systems have not been shown to be accurate when used to take the temperature of multiple people at the same time. The accuracy of these systems depends on careful set-up and operation, as well as proper preparation of the person being evaluated.

Thermal imaging systems have been used by several countries during epidemics, although information about their effectiveness as part of efforts to reduce the spread of disease has been mixed.

The FDA issued the Enforcement Policy for Telethermographic Systems During the Coronavirus Disease 2019 (COVID-19) Public Health Emergency guidance to help expand the availability of thermal imaging systems and mitigate thermometer shortages during the public health emergency. The guidance sets forth an enforcement policy that is intended to apply to all thermal imaging systems that are intended for medical purposes for the duration of the public health emergency related to COVID-19, and provides recommendations regarding performance and labeling of such systems.

Figure one: A picture of an infrared thermal camera pointed at a woman standing by herself in a public space. The camera displays her thermal image on the camera screen. Her face is shown on the screen in a reddish orange color indicating her skin has a higher surface temperature than her clothing displayed as yellow and the distant background displayed as gray. The temperature displayed on the screen as 31.7o Celsius. photo FDA

Benefits of Thermal Imaging Systems

The person who handles the thermal imaging system is not required to be physically close to the person being evaluated. In fact, the person who handles the thermal imaging system could be in a different area or room.

The thermal imaging system may measure surface skin temperature faster than the typical forehead or oral (mouth) thermometer that requires a close distance or physical contact with the person being evaluated.

Scientific studies show that, when used correctly, thermal imaging systems generally measure surface skin temperature accurately.

Limitations of Thermal Imaging Systems

Although these systems may be in use for initial temperature assessment to triage individuals in high throughput areas (for example, airports, businesses and sporting events), the systems have not been shown to be effective when used to take the temperature of multiple people at the same time. They should not be used for "mass fever screening."

These systems measure surface skin temperature, which is usually lower than a temperature measured orally. Thermal imaging systems must be adjusted properly to correct for this difference in measurements.

These systems work effectively only when all the following are true:

    The systems are used in the right environment or location.

    The systems are set up and operated correctly.

    The person being assessed is prepared according to instructions.

    The person handling the thermal imaging system is properly trained.

Proper Use of Thermal Imaging Systems

The person who handles the system should follow all manufacturer instructions to make sure the system is set up properly and located where it can measure surface skin temperature accurately.

The person who handles the system should be trained to properly prepare both the location where the system will be used, and the person being evaluated, to increase accuracy. For details, see the standards and scientific papers listed under References below.

Preparing the Area where You will Use a Thermal Imaging System

Room temperature should be 68-76 °F (20-24 °C) and relative humidity 10-50 percent.

Try to control other items that could impact the temperature measurement:

    Avoid reflective backgrounds (for example, glass, mirrors, metallic surfaces) to minimize reflected infrared radiation.

    Use in a room with no draft (movement of air), out of direct sunlight and away from radiant heat (for example, portable heaters, electrical sources).

    Avoid strong lighting (for example, incandescent, halogen and quartz tungsten halogen light bulbs).

An illustration of a person standing at a fixed distance directly facing an infrared thermal camera. Behind the person is a low reflective background and calibrated black body at the person’s head height. The camera is connected to a laptop.

Figure 2 demonstrates the proper thermal imaging room setup. photo FDA

Preparing the Thermal Imaging System

Some systems require the use of a calibrated blackbody (a tool for checking the calibration of an infrared temperature sensor) during evaluation to make sure measurements are accurate. Check the manufacturer’s instructions to determine if a calibrated blackbody is needed. Some devices do not require one.

Turn on the entire system 30 minutes before use to warm it up.

Preparing the Person Being Evaluated

The person handling the system should make sure the person being evaluated:

Does not have any face obstructions before measurement (such as a mask, glasses, hat, headband, or scarf), the person's hair is pulled away from the face, and the person’s face is clean and dry.

Does not have a higher or lower face temperature from wearing excessive clothing or head covers (for example, headbands, bandanas) or from using facial cleansing products (for example, cosmetic wipes).

Has waited at least 15 minutes in the measurement room or 30 minutes after exercising, strenuous physical activity, bathing, or using hot or cold compresses on the face.

Picture of the infrared thermal image of a man standing in front of a plain wall with a small square blackbody background on the wall. His face is shown in a dark red color indicating a higher skin surface temperature than his clothing that is shown in blue and yellow. The blackbody background is shown in very dark brown indicating minimized reflection of infrared radiation. A temperature range scale bar to the right of the picture shows a color range from dark brown through the color spectrum to dark blue.

Figure 3 demonstrates the proper thermal imaging setup for processing of individual people using a calibrated blackbody background. photo FDA

Using the Thermal Imaging System

Measure only one person’s surface skin temperature at a time.

Position the person at a fixed distance (follow the manufacturer’s instructions for use) from the thermal imaging system, directly facing the camera.

The image area should include the person’s whole face and the calibrated blackbody, if using one.

If an increased temperature is seen using the thermal imaging system, you should use a different method to confirm a fever. Public health officials can help you determine if the fever is a sign of infection.
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