The Principle of Temporal Artery Thermometer

This is a non-invasive scanning thermometer for measuring core body temperature. The measurement is based on scanning the area above the temporal artery using an IR detector.

The superficial temporal artery extends directly from the external carotid artery and travels in front of the ear. Anatomically, it is lying approximately 1 mm below the skin, readily accessible and maintains good blood perfusion. If we assume zero thermal loss to the environment, the skin surface over the temporal artery area would be at the same temperature as the arterial blood in the aorta, which is in essence equal to core body temperature. Since the surrounding area temperature is normally lower than the core body temperature, there is a cooling effect at the skin surface due to the radiative heat loss to the surrounding air. To account for errors due to the natural heat loss, the hand-held scanning thermometer measures the ambient temperature at the same time it measures the absolute temperature of the skin surface over the temporal artery and computes arterial temperature using a heat balance equation.

Related: Clinical Applications of NTC Thermistors