Analysis of IR thermal imager for mass blind fever screening Eddie Y.K. Ng, a, * G.J.L. Kaw, b and W.M. Chang c a School of Mechanical and Production Engineering Nanyang Tech. University, Singapore 639798, Singapore b Department of Diagnostic Radiology, Tan Tock Seng Hospital, Singapore 308433, Singapore c Zugo Photonics Pte Ltd, Kaki Bukit Techpark II, Singapore 415976, Singapore Received 27 February 2004 Available online 1 July 2004 Abstract Background: Obtaining meaningful temperature for the human body requires identifying a body site that will provide reliable data across a large population. It is important to understand that skin temperature does not solely depend on body-core temperature and may be affected by other physiological and environmental factors. Currently, there is lack of empirical data in correlating facial surface temperature with body core temperature. Present IR systems in use at airports/immigration checkpoints have not been scientifically validated particularly in regards to the false-negative rate. As a result, they may create a false sense of security by underestimating the number of febrile (and possibly infected) individuals. This article evaluates the effectiveness of thermal scanner when it is being used for mass blind screening of potential fever subjects such as SARS or bird flu patients. Methods: Bio-statistics with regression analysis and ROC is applied to analyse the data collected (502) from the SARS hospital in Singapore and conclusive results are drawn from them. The results are vital in determining two very important pieces of information: the best and yet practical region on the face to take readings and optimal pre-set threshold temperature for the thermal imager. Results: (1) The thermal scanner can be used as a first line tool for the mass blind screening of hyperthermia, (2) the readings from the scanner suggest good correlation with the ear temperature readings, (3) an imager temperature threshold should be determined by the environmental factors, outdoor condition in particular, the physiological site offset and the performance characteristics of thermal imager to warrant the most accurate and reliable screening operation. Conclusions: The analysis suggested that the thermal imager used holds much promise for mass blind screening when the readings from a specific region have a good correlation with the ear temperature. From the regression analysis, the best reading is taken from the maximum temperature in the eye region, followed by the maximum temperature in the forehead region. With ROC analysis, a randomly selected individual from the fever group has a test value larger than that for a randomly selected individual from the normal group in 97.2% of the time. The test can distinguish between the normal and febrile groups and an optimum threshold temperature for the thermal imager can be found. The pre-set threshold cut-off temperature for the current thermal imager was found to be 36.3jC with reference to the associated environmental condition. Any temperature readings that exceed this reading will trigger off the alarm and a thermometer will be used to verify the whether the person is having fever. D 2004 Elsevier Inc. All rights reserved. Keywords: SARS; Avian flu; IR system; Bio-statistics; Fever; Threshold temperature Introduction The cardinal symptoms of SARS and bird flu are fever (de Jong et al., 1997; Ksiazek et al., 2003; Peris et al., 2003; Rota et al., 2003) and this has led to temperature monitoring being practised at healthcare institutions, public areas and private establishments where crowds are expected. These fever-screening stations employ personnel to take the aural or oral temperatures so as to pick out those with fever and send them for further clinical evaluation for SARS and hence curb community spread of the disease. Oral and aural temperature measurements are accurate but are fairly ‘‘in- vasive’’, time-consuming, labour-intensive and skill-depen- dent. The ideal device for fever screening should be speedy, non-invasive and be able to detect accurately those with fever with minimal inconvenience and disruption of human traffic. As a first line of defense, infrared (IR) thermal imaging has the potential to fulfil these functions and can serve as a tool for mass screening for fever. However, there is currently lack of scientific evidence to support this application. As quoted in the Canada National Post (Sep- 0026-2862/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.mvr.2004.05.003 * Corresponding author. School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. Fax: +65-6791-1859. E-mail address: mykng@ntu.edu.sg (E.Y.K. Ng). www.elsevier.com/locate/ymvre Microvascular Research 68 (2004) 104 – 109