A Novel Environment-Invariant Core Body Temperature Estimation for High Sensitivity and Specificity Fever Screening

We propose a novel concept for core body temperature estimation to improve sensitivity and specificity of a fever screening system under different environmental conditions based on an infrared thermal camera. The conventional approach of setting low temperature thresholds to determine presence of fever to increase sensitivity has led to highly-degraded specificity due to the low accuracy in core body temperature estimation. Two main causes are the moderate correlation between core body temperature and surface temperature data used to determine it, and the estimation algorithm that does not consider changes in the environment. Hence, in our novel concept, we eliminate the environmental effects by using direct and correcting temperature data, and thus improve the accuracy in estimating core body temperature. The direct data contain rich information about core body temperature through maximum temperatures obtained from the mouth, ear, around the eye and forehead, while the correcting data contain information related to the surroundings such as the cheek and nose temperatures to compensate for the environmental effect on the former. Since direct data can be easily affected by the environment and noise, multiple direct data are taken to minimize this problem. Through improved accuracy, both sensitivity and specificity will be automatically increased and the trade-off between them when adjusting the threshold values will be greatly relaxed. Analysis of the results shows improvement in both sensitivity and specificity from78.9% and 87.0%, respectively, in the conventional approach, to 84.2% and 91.3% in the proposed method when 37.5$^{o}\text{C}$ was set as the threshold. Data in the present study was obtained from a wide spectrum of ages (between 22 and 58 years), ethnicities (seven) and core body temperatures (36.0$^{o}\text{C}$ to 39.5$^{o}\text{C}$). Data were also collected at variable room temperatures ranging from 20.2$^{o}\text{C}$ to 30.8$^{o}\text{C}$.