Design, Development and in vivo Evaluation of a Wireless Platform for Intracranial Pressure Monitoring Using Inductive Passive Implants

Abstract

Implantable LC-based passive sensors can enable wireless measurement of physiological parameters in inaccessible locations of the human body through an RF inductive link. A typical LC sensor consists of an inductive coil connected to a capacitive pressure sensing element to form an LC resonator, whose resonance frequency changes in response to variation of the quantity being measured. In biomedical applications, they are intended to provide continuous measurement of the desired parameter in patients with chronic diseases without the need for an implanted battery. Considering their cost-efficient manufacturing and fully passive operation, they are considered promising alternatives to the existing catheter-based transducers and can be potentially used in a variety of applications, including intraocular pressure (IOP) monitoring, intracranial pressure (ICP) monitoring and cardiovascular pressure sensing.<br/><br/>Over the past few decades, there has been increasing number of research in the development of fully passive pressure sensors for biomedical applications. Although the previous studies advanced the possibility of wireless pressure readout across the tissue, further development is required to translate the concept to clinically approved devices. In this research work, a complete system for biotelemetric wireless ICP monitoring was designed, developed and evaluated through in vitro and in vivo studies. The proposed system includes an ICP implant, which is wirelessly interrogated by a hand-held external reader. The external reader communicates with the implant through separated wireless channels for concurrent excitation of the implant and collection of the received signal from the sensor. The simultaneous transmit and receive operation is realized through a novel dual-port planar antenna. The reader device is connected to a host PC through a Bluetooth link. The proposed system provides real-time monitoring of the ICP through a dedicated interactive PC software.<br/><br/>The in vivo performance of the implant was evaluated in a canine model. The findings of the in vivo study are consistent with the theoretical analysis of the proposed telemetry scheme as well as the data obtained from the in vitro experiments. The capability of the wireless pressure readout and detection of in vivo ICP variation has been proved through the animal study and the in vivo data was verified using a commercial ICP monitor. The promising outcome of the in-body assessment of the system indicates that the proposed platform can be further developed and potentially used in real-life clinical trials for early detection of increasing ICP in patients with traumatic brain injuries and chronic intracranial hypertension. In addition, the same platform with further modification and customization can be used for other biomedical applications.