Relationship Between Skin Temperature and Blood Flow During Exposure to Radio Frequency Energy: Implications for Device Development

Abstract

Abstract Background Active Dynamic Thermography (ADT) is a novel technology for noninvasive measurement of blood flow rate in the microcirculation of the skin. The method utilizes the relationship between flow rate and tissue temperature increase during exposure to radio frequency energy. We are developing an ADT device to screen for peripheral artery disease (PAD). PAD is characterized by impaired blood flow to the legs, as reflected in the skin microcirculation. The ADT system incorporates a radio frequency transmitter and a handheld transducer to simultaneously heat the skin and measure the temperature response. The objective of this study is to determine the extent to which the magnitude and depth of heating as well as device sensitivity are functions of (i) frequency and (ii) dermis thickness. Methods Exposure of three heterogeneous computational models of human skin with varying blood perfusion rates to 10-94 GHz energy was simulated. RF exposure was simulated by (i) determining the specific absorption rate (SAR) using a discretized model of human skin and finite-difference time-domain software and (ii) incorporating the local SAR values in a thermal model that related RF absorption and other relevant factors to predict local tissue temperatures over time. Results Results show that it is feasible to measure blood perfusion levels with ADT technology. Surface temperature increases were found to be more dependent upon the magnitude of power absorption than location of absorption within the skin. While surface temperature response does depend upon radio wave frequency and thickness of the dermis layer, such dependencies are mild. Sensitivity to blood flow rate was found to be proportional to the magnitude of absorbed power. Conclusion Results show that it is feasible to discriminate between blood flow rates using ADT technology at frequencies within the 10-94 GHz range. All frequencies analyzed produced similar levels of sensitivity to flow rate despite significant differences in penetration depth. These results are being used in the development of a preclinical prototype for quick and easy detection of asymptomatic PAD in humans.