A Hybrid Microwave-Optical Applicator for Local Muscle Warming and Monitoring

Local warming of human tissue causes vasodilation and therefore blood volume to increase. Such thermal blood volume response allows the assessment of microcirculation in tissue, providing clinically important information. The deep warming is provided by a novel microwave applicator, which has a annular-ring microstrip patch operating at 2450 MHz with a superstrate interface layer to improve the coupling of electromagnetic (EM) waves into the skin. The design is based on computer simulations of specific absorption rate (SAR) and thermal distribution of the EM waves in a biological medium. The simulation results show that the applicator can elevate the muscle temperature by 3 to $4^{\circ}\mathrm{C}$. The thermal response is measured by an integrated optical probe which measures tissue oxygenation changes in deep tissue using the near infrared spectroscopy technique.