Towards Integration of Ultrasonic-Powered Implantable Devices for Physiological Monitoring, Stimulation, and Imaging in Soft Tissues Using a Handheld Scanning Probe

Abstract

Ultrasounds (US) are one of the most used imaging and sensing modalities in the medical field. Apart from therapeutic applications, most interactions between the acoustic waves and tissue occur passively without any substantial modification to the physiology of the later. However, US can also be used to power actively implanted devices with the same energy-carrying waves. In this article, we propose small-form implantable devices for monitoring of physiological parameters in soft tissue (bio-potential and temperature), together with electric stimulation using a specially designed handheld scanning probe. The ultra-low power consumption of the devices ( $110~\\mu \\text{W}$ in average) and operation with harvested voltage levels as low as 0.5 V, allows deployment up to 25 mm from the probe. Sensing data is then transmitted by an ON-OFF Keying modulation scheme (OOK) and detected by an overly sensitive demodulator with carrier-to-noise ratio of– 57 dB. We went further to incorporate electronic modules for tissue impedance imaging in situ for detection of impairment to the normal conductivity of tissues caused by inflammation, bacterial infection or cancer. Potential applications of this technology include the detection of endogenous and exogenous sources of electric potential, useful in the evaluation of soft tissue healing and recovery after surgery, as a diagnostic complement to the more traditional methods of US imaging or alternative to other implantable devices, which are limited by inductive and radiofrequency powering links.