Characterization of the implantable neurostimulator-based wireless bioimpedance measurement technique

A system for wireless bioimpedance measurements in small localized volumes was investigated using a millimeter-sized implantable device powered by ultrasound energy. The minimally invasive implant is very simple, consisting of two passive components that receive and demodulate the ultrasound which then directly drives tissue currents. By varying the ultrasound drive level and its amplitude modulation frequencies, the implantable device, in addition to neurostimulation, can be used to perform impedance measurements, thus offering a potential to both therapeutically neurostimulate tissue as well as record tissue impedance changes resulting from the stimulation. The system communicates in the return path by volume conduction. Potentials detected by skin electrodes are used to construct tissue impedance plots. In this report we demonstrate the feasibility of wireless impedance measurements and characterize system performance in terms of the signal detectability over the distance.