Closed-Loop Pulse-Width Modulation Microwave Heating with Infrared Temperature Control for Perfusion Measurement

Measurement of blood flow/perfusion using temperature response of a heated region of tissue has been quite well-known, where the temperature of the tissue is raised by a heating device and the temperature response is recorded by a sensor. However, the existing methods are invasive (heating element/sensor embedded in the tissue) and/or rely on the conduction heating, which is sensitive to the heating element/sensor's contact with the tissue and the surrounding air convection. In this article, a system with a combined microwave heating (MWH) antenna and infrared (IR) temperature sensor, with closed-loop feedback control with pulse-width modulation (PWM), for noninvasive measurement of flow/perfusion, is introduced for the first time. Applying PWM is efficient and readily implementable and circumvents the need for expensive and complex power-adjustable microwave sources often used in MWH applications. A novel phantom is also introduced for the first time to be able to create quantifiable perfusion from flow circulated by a tubing system. For an MWH source with 2.1-W power at 2.4 GHz and a proportional feedback coefficient of $K_{p} = 0.88$ W/°C, the measurement results in terms of the phantom temperature read by the IR sensor and the average PWM voltage demonstrate a clear differentiation between perfusion values of 0.07 versus 0.23 mL/min/gr (0.5 °C and 0.5 V difference for temperature and average PWM voltage responses, respectively, within 2-3 min). These promising results signify the flexibility offered by the closed-loop temperature and PWM responses for low-cost evaluation of flow/perfusion using combined MWH and IR temperature sensing.