In outbreaks of infectious diseases, fever screening can be an useful tool to help identify cases and slow the spread. While it certainly cannot diagnose a condition such as Covid-19 (especially when not all cases show symptoms), detecting elevated skin temperature can help qualified frontline healthcare workers triage and assess potential patients. Doing so from a distance, without physical contact, has obvious advantages for both patients and practitioners--thus the rise in the use of spot meters and thermal cameras. Although the stereotypical test point has always been the forehead, best practice for temperature sampling 1,2,3 identifies the interior of the ear hole or the fovil (near the corner of the eye beside the nose) as the most accurate sites to test.
If you want to test from a distance, the face is much more accessible than the interior of the ear hole. For the face, spot meters are problematic: temperature varies across the face, so a single point might be an outlier while an average of a larger area can obscure important detail. Accuracy can also vary with distance.
A full-face imaging approach using thermal (long wave infrared) cameras has the potential to be more accurate, consistent, and thorough than a single point sampling approach. It also has the potential for higher throughput (more people screened more quickly) and lower exposure for front-line healthcare workers. A thermal image can include a temperature reference (from a black body radiator for example) in the scene for much higher accuracy and reliability, and an automated imaging system can free healthcare hands to do other important tasks.
Teledyne DALSA's Calibir GXM infrared camera platform offers powerful performance, as part of an imaging system, for critical applications like fever screening. With great sensitivity and precision, outstanding dynamic range for wide temperature coverage, and factory-calibrated radiometric performance, Calibir delivers accurate, repeatable temperature data. Calibir GXM uses Teledyne's own microbolometer detector and 21-bit ADC design for robust, reliable thermal imaging.
Calibir is supported by our Sapera and CamExpert software, providing power, control and flexibility in developing imaging applications.
Calibir GXM and its control software allow you to set your own LUTs (look up tables); with this control, you can mark certain temperatures with color while leaving the rest monochrome. For example, show everything between 38 and 41°C as red.
Calibir GXM supports a smart frame averaging feature that can be tuned to minimize read noise according to your tolerance to movement, allowing any detection system to reach extremely low NETD values.
The details in this thermal image of an electric heater element shows Calibir GXM's exceptional range (right) compared a third party detector (left). With a temperature range over 1500°C with consistent NETD <0.05°C, enabled by our advanced 21-bit ADC, Calibir GXM offers unprecedented radiometric detail. For the much smaller temperature range of fever detection (~30°C to 45°C), Calibir GXM can output an 8 bit (sub)range of values for convenient integration that still has 21-bit precision and accuracy.
Up to two Regions Of Interest (ROIs) can be defined inside the camera: size, location, and the Min/Max/Average temperatures in each ROI can be displayed as well as the Min/Max/Average indication on the entire image. All this information is available in an easy metadata protocol that can be used to launch alerts or to combine with other types of image sensor (like visible CMOS sensor for identification for example). Metadata with ROIs temp information can be added to the image buffer.
Calibir GXM has nonuniformity correction and is factory calibrated with a proprietary ﬂux/temp base algorithm to account for Planck’s Law (also known as black-body law, it describes how IR ﬂux from an object does not change linearly with object temperature). The result is camera output that is linear with IR ﬂux, and each output color or grey level corresponds to an unique object temperature, simplifying your system.
Many articles were published on fever detection after the SARS outbreak, generally focusing on alternative and mostly non-contact methods (to avoid the spread of the virus). The most mainstream methods are handheld thermal thermometers and thermal cameras. According to a cursory review of the relevant literature on the subject, thermal cameras seem to be much more reliable and accurate then the handheld thermal thermometers, but only by following the guidelines around how and where to perform the measurements.
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 ISO. ISO TR 13154: Medical electrical equipment—Deployment, implementation and operational guidelines for identifying febrile humans using a screening thermograph. International Organization for Standardization; 2009.
 IEC/ISO. IEC 80601-2-59: Particular requirements for the basic safety and essential performance of screening thermographs for human febrile temperature screening. Geneva, Switzerland: International Electrotechnical Commission (IEC) / International Organization for Standardization (ISO); 2017.
 CDC. Non-Contact Temperature Measurement Devices: Considerations for Use in Port of Entry Screening Activities. 2014.
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