Infrared thermographs (IRTs) have been used for fever screening during infectious disease epidemics. However, their performance is inconsistent in literature, due to wide quality/implementation variations. We overview standards and FDA guidance for IRT performance evaluation, implementation, and regulation policies. Additionally, we present results from a large-scale clinical study of fever-screening IRTs and discuss impact of consensus guidelines and facial measurement location on performance. We found that: high-quality IRTs implemented according to international standards can help to accurately measure temperature; current standards can be improved to further enhance IRT performance. Overall, fever screening is only one element in infectious disease detection.
Significance: Infrared thermographs (IRTs) have been used for fever screening during infectious disease epidemics, including severe acute respiratory syndrome, Ebola virus disease, and coronavirus disease 2019 (COVID-19). Although IRTs have significant potential for human body temperature measurement, the literature indicates inconsistent diagnostic performance, possibly due to wide variations in implemented methodology. A standardized method for IRT fever screening was recently published, but there is a lack of clinical data demonstrating its impact on IRT performance.
Aim: Perform a clinical study to assess the diagnostic effectiveness of standardized IRT-based fever screening and evaluate the effect of facial measurement location.
Approach: We performed a clinical study of 596 subjects. Temperatures from 17 facial locations were extracted from thermal images and compared with oral thermometry. Statistical analyses included calculation of receiver operating characteristic (ROC) curves and area under the curve (AUC) values for detection of febrile subjects.
Results: Pearson correlation coefficients for IRT-based and reference (oral) temperatures were found to vary strongly with measurement location. Approaches based on maximum temperatures in either inner canthi or full-face regions indicated stronger discrimination ability than maximum forehead temperature (AUC values of 0.95 to 0.97 versus 0.86 to 0.87, respectively) and other specific facial locations. These values are markedly better than the vast majority of results found in prior human studies of IRT-based fever screening.
Conclusion: Our findings provide clinical confirmation of the utility of consensus approaches for fever screening, including the use of inner canthi temperatures, while also indicating that full-face maximum temperatures may provide an effective alternate approach.
Infrared thermography (IRT) – a non-contact, non-invasive technique – has been used for mass screenings to identify febrile individuals at transportation nodes (e.g., airports) during infectious disease pandemics such as SARS (Severe Acute Respiratory Syndrome), H1N1 virus, and Ebola outbreaks. Despite the potential of IRTs, the field lacks a well-established consensus methodology to ensure temperature measurement accuracy and reliability. This study aims to investigate the use of IRTs in a controlled setting to determine the effectiveness of IRT and the most reliable facial region for estimation of core temperature. We conducted a large clinical study, acquiring facial thermographs of 1,109 febrile and non-febrile subjects using Screening Thermographs (STs). Regression analyses between the reference oral temperature and different areas of the face, specifically the forehead and canthi, were carried out. The coefficients of determination of each regression were compared to determine how well facial and core body temperatures were correlated. Receiver operating characteristic (ROC) curves were constructed to compare the effectiveness of using different facial areas to identify febrile patients. Results show that the maximum temperature of the overall face has the best linear trend, followed by the maximum temperature at the inner canthus region. Both of these values show better correlations than forehead temperatures, which are commonly used as a target by non-contact infrared thermometers. For any chosen facial area, the maximum temperature collected always showed a stronger correlation than a specific point in that area. Results indicate that IRT performance is substantially approved when applying optimal measurement methodology.
KEYWORDS: Infrared radiation, Black bodies, Body temperature, Minimum resolvable temperature difference, Data processing, Image acquisition, Standards development
Infrared thermographs (IRTs) have been implemented for mass fever screening in public areas such as airports during outbreaks of infectious disease pandemics such as Ebola virus disease, yet the approach has not been entirely successful. There has been increasing evidence in the literature that IRTs can provide greater accuracy in estimating core body temperature, if qualified systems are used and appropriate procedures are consistently applied. In this study, we addressed the issue of system qualification by implementing and evaluating a battery of test methods for objective and quantitative performance assessment of two commercial IRTs based on a recent international standard (IEC 80601-2-59). We evaluated stability and drift, image uniformity, minimum resolvable temperature difference, and measurement accuracy of the IRTs and illustrated how experimental and data processing procedures affect results. For instance, we demonstrated that offset temperature compensation, achieved using an external blackbody, is essential to meet the standard’s recommendations for temperature drift and stability. Additionally, we identified methods that can be implemented to optimize IRT evaluation. As an example, we identified a less burdensome approach to characterize image uniformity with a single image acquisition of a uniform blackbody. Overall, the insights into thermograph standardization and acquisition methods provided by this study may improve the utility of this technology and aid in comparing IRT performance, thus improving the potential for high quality disease pandemic countermeasures.
Thermal modalities represent the only currently viable mass fever screening approach for outbreaks of infectious disease pandemics such as Ebola and SARS. Non-contact infrared thermometers (NCITs) and infrared thermographs (IRTs) have been previously used for mass fever screening in transportation hubs such as airports to reduce the spread of disease. While NCITs remain a more popular choice for fever screening in the field and at fixed locations, there has been increasing evidence in the literature that IRTs can provide greater accuracy in estimating core body temperature if appropriate measurement practices are applied – including the use of technically suitable thermographs. Therefore, the purpose of this study was to develop a battery of evaluation test methods for standardized, objective and quantitative assessment of thermograph performance characteristics critical to assessing suitability for clinical use. These factors include stability, drift, uniformity, minimum resolvable temperature difference, and accuracy. Two commercial IRT models were characterized. An external temperature reference source with high temperature accuracy was utilized as part of the screening thermograph. Results showed that both IRTs are relatively accurate and stable (<1% error of reading with stability of ±0.05°C). Overall, results of this study may facilitate development of standardized consensus test methods to enable consistent and accurate use of IRTs for fever screening.
Fever screening based on infrared thermographs (IRTs) is a viable mass screening approach during infectious disease pandemics, such as Ebola and Severe Acute Respiratory Syndrome (SARS), for temperature monitoring in public places like hospitals and airports. IRTs have been found to be powerful, quick and non-invasive methods for detecting elevated temperatures. Moreover, regions medially adjacent to the inner canthi (called the canthi regions in this paper) are preferred sites for fever screening. Accurate localization of the canthi regions can be achieved through multi-modality registration of infrared (IR) and white-light images. Here we propose a registration method through a coarse-fine registration strategy using different registration models based on landmarks and edge detection on eye contours. We have evaluated the registration accuracy to be within ± 2.7 mm, which enables accurate localization of the canthi regions.
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