Facial thermal imaging: A systematic review with guidelines and measurement uncertainty estimation

The development of thermal imaging cameras has led to their widespread use, including for measuring facial skin temperature. However, the measurement protocol is not standardised, resulting in inaccurate and unreliable measurements. This systematic review of 315 papers selected according to the PRISMA guidelines aims to address this issue by reviewing how the papers reported key measurement parameters (type of thermal imaging camera, emissivity coefficient, measurement distance, ambient conditions, length of acclimatisation period) and how they analyse the thermograms. To make facial temperature measurements comparable within and between studies, we have proposed guidelines for accurate and reliable measurements and estimated measurement uncertainty for facial thermography as a result of this systematic review. Thus, a threshold of at least 0.3 degrees C is suggested to achieve a metrologically significant difference between experimental conditions or spatial or temporal points.