Monitoring Progression of Diabetic Foot Ulcer—A Phantom Study Using Distributed Sensors and Near Field Microwave Radiometry

Local elevation of plantar surface temperature has been reported as an indicator of diabetic foot ulcer (DFU). In this work, we investigate the feasibility of using near field microwave radiometry (MR) to monitor the progression of DFU. A distributed arrangement of microwave sensors on the plantar surface connected to 2.87 GHz switch-circulator Dicke radiometer is proposed for deep tissue sensing of DFU induced inflammation. The individual sensor is an active near-field patch antenna integrated with a low-noise amplifier. Foot models derived from volunteers were used to determine the sensor locations on plantar surface. Numerical simulations were used to determine the sensing depth and coverage for brightness temperature measurements inside the foot. MR measurements of localized hot source of 12 mm diameter at $2~^{\circ }$ C above the background temperature indicated $\gt 1~^{\circ }$ C change in the proximal sensor for hot source at 24 mm depth and $0.93~^{\circ }$ C– $1~^{\circ }$ C temperature change at 30 mm depth. Preliminary phantom study suggests that distributed sensing of plantar surface using near-field MR could be used to monitor the progression of DFU deep inside the foot.