Assessing Foot Temperature Using Infrared Thermography

Abstract

Background: Previous reports recommended using skin temperature as a guide to monitor neuropathic feet during their rehabilitation course. However, the diagnostic usefulness was limited because of poor thermal measurement and procedures. The purpose of this study was to propose a standardized protocol to quantify foot temperature. Methods: An infrared image system was used to measure skin temperature. The first experiment was conducted on 16 healthy volunteers to study temperature variation with respect to time. This study mapped out six subregions of anatomic interest over the sole, and average temperature values for each were studied. The second experiment was conducted on 62 diabetic patients, with and without sympathetic skin response (SSR), to study proposed sole temperature normalization with respect to forehead temperature for clinical diagnosis.Results: In the first experiment, the temperature in each plantar subregion varied as a function of time. In the sole area, the highest temperature was noted in the arch region (29.3 ± 0.9 degrees C). The toes had the lowest temperature value (26.2 ± 1.2 degrees C) in all areas. Equilibrium was reached after 15 minutes for the mean plantar temperature (27.8 ± 1.0 degrees C). In the second experiment, the diabetic patients without SSR had a slightly higher mean plantar temperature (27.6 ± 1.8 degrees C) than those with SSR (26.8 ± 2.2 degrees C), but the difference was not statistically significant (p > 0.05). The SSR-absent group (0.19) and the SSR-present group (0.24) had significant differences in their normalized temperatures as proposed (p < 0.05). Conclusions: The mean temperature of the entire plantar area was found to be more stable than the individual subregions, serving as a more practical indicator for thermoregulatory functions. The study also found that the overall mean plantar temperature stabilized after 15 minutes, and, thus, this time was recommended for clinical thermographic measurements. The normalized temperature may have more useful application than the plantar absolute temperature, as exemplified by the better correlation in diabetic feet. The mean plantar temperature, the wait time to start measurement, and the proposed normalization are believed to play important roles in neuropathic foot disorders.