Use of Acoustic Thermometry to Determine the Temperature Field in the Human Forearm

In this study, we used passive acoustic thermometry to measure the core (acoustic brightness) temperature in a subject's forearm while applying warming ointments to the skin. A decrease of 3–6°C in the acoustic brightness temperature was recorded in the first 5–10 min. After this, the acoustic brightness temperature returned to the level prior to application of the ointment. We attribute the decrease in core temperature to the use of a gel at room temperature in the measurements. On the one hand, the application of a cold gel to the skin should reduce the superficial blood flow. However, the use of warming ointments temporarily blocked this process. As a result, cold blood from near-surface capillaries entered the internal tissues of the forearm, cooling the tissue. The effect was taken into account in the heat conduction equation with blood flow by changing a parameter used in the equation: the temperature of flowing blood. The time dependence of the acoustic brightness temperature calculated with the heat conduction equation is consistent with the experimental data.