Best practices for standardized performance testing of infrared thermographs intended for fever screening

Abstract

Infrared (IR) modalities represent the only currently viable mass fever screening approaches for outbreaks of infectious disease pandemics such as Ebola virus disease and severe acute respiratory syndrome. Non-contact IR thermometers (NCITs) and IR thermographs (IRTs) have been used for fever screening in public areas such as airports. While NCITs remain a more popular choice than IRTs, there has been increasing evidences in the literature that IRTs can provide great accuracy in estimating body temperature if qualified systems are used and appropriate procedures are consistently applied. In this study, we addressed the issue of IRT qualification by implementing and evaluating a battery of test methods for objective, quantitative assessment of IRT performance based on a recent international standard (IEC 80601-2-59). We tested two commercial IRTs to evaluate their stability and drift, image uniformity, minimum resolvable temperature difference, and radiometric temperature laboratory accuracy. Based on these tests, we illustrated how experimental and data processing procedures could affect results, and suggested methods for clarifying and optimizing test methods. Overall, the insights into thermograph standardization and acquisition methods provided by this study may improve the utility of IR thermography and aid in comparing IRT performance, thus improving the potential for producing high quality disease pandemic countermeasures.

Clinical Evaluation of Fever-Screening Thermography: Impact of Consensus Guidelines and Facial Measurement Location

“…The use of a blackbody for temperature compensation had a moderate impact on IRT screening ability. In our prior study 28 , such compensation vastly improved the stability of IRT-2, and enabled the system to meet IEC 80601-2-59 performance speci cations. Except to measure and compensate for long-term drift, the use of 3-frame averaging in the current study may have improved stability to the point where the blackbody was no longer critical.…”

“…IRT-1 and IRT-2, rather, two fever screening systems, (IRT-1 + BB) and (IRT-2 + BB). We have evaluated these two systems in our previous work 28 and found that their uniformity, stability, drift, minimum resolvable temperature difference, and laboratory accuracy all satis ed the standard requirements.…”

“…A blackbody (SR-33, CI Systems Inc.) with a 4 × 4 inch emitter (image size > 20 × 20 pixels) was set at 35°C then positioned perpendicular to the sight line of the cameras and placed within the frame alongside the subject's face for temperature drift compensation. We previously veri ed that blackbody drift and uncertainty satis ed relevant standards 28 . The subject-to-camera distance was 0.6-0.8 meters to ensure that both the subject's face and the blackbody were included in the WTP with a resolution that satis ed recommended speci cations.…”

“…We developed a graphical user interface (GUI) with MATLAB to simultaneously control the webcam and two IRTs, as well as to collect images and patient/environmental information. Both IRTs had 30 Hz frame rates, and detailed speci cations and fundamental performance testing results can be found in our prior study 28 . A blackbody (SR-33, CI Systems Inc.) with a 4 × 4 inch emitter (image size > 20 × 20 pixels) was set at 35°C then positioned perpendicular to the sight line of the cameras and placed within the frame alongside the subject's face for temperature drift compensation.…”

“…International standard IEC 80601-2-59:2017 23 provides recommendations for performance characterization of fever-screening IRTs. In a prior study, we implemented and evaluated these recommendations using two commercial IRTs 28 , but we are not aware of any prior IRT clinical study which has implemented this standard. A consensus technical report, ISO/TR 13154:2017 24 , describes best practices for IRT deployment, implementation and operation.…”