Development of a hybrid microwave-optical deep muscle warming monitor

Elevating the temperature in tissue leads to vasodilation and therefore an increase in blood flow to reduce the excessive heat in the region, a physiological mechanism known as thermoregulation. These thermal responses have been used in various clinical applications to monitor the conditions of the spinal cord injury, vascular responses and free flap reconstruction. Currently blood flow measurements such as laser doppler flowmetry (LDF) are restricted to the skin, a rather superficial layer. To allow the investigation into deeper tissue such as the muscle, a new hybrid microwave-optical system has been developed. The deep warming is provided by a novel microwave applicator, which has a microstrip patch design operating at 2.45 GHz with a superstrate interface layer to improve the coupling of electromagnetic (EM) waves into the skin. Its 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 is capable of elevating the muscle temperature by 3-4 °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. The hybrid microwave-optical system has been built and tested on human calves in vivo. In the talk, we will present the development of this new type of non-invasive microwave applicator for deep tissue warming.