iPPSIS: implanted Passive Pressure Sensor Interrogated with (ultra)-Sound - ABSTRACT More than 1.3 million new patients are diagnosed each year with neurological conditions that may result in ele- vated intracranial pressure (ICP). In these patients, the limited ability to make accurate, stable pressure meas- urements with wireless, MRI compatible devices contributes to poor clinical outcomes. It is hypothesized that a novel ultrasound-based wireless transduction approach combined with an implanted pressure-sensitive target has the potential to nearly eliminate drift, improving patient management. Long recognized as an unaddressed clinical need, implanted pressure sensors that measure intracranial pressure have been proposed since the 1950’s. Unfortunately, nearly all neuro sensors rely on the same underlying technology: a thin membrane that can deflect directly adjacent to a sealed air chamber or vacuum. Due to the size scales involved and the material constraints with traditional radio-frequency approaches, all of these devices experience drift as air or water vapor diffuse across the thin membrane and/or induce stress in packaging materials. This fundamentally limits the usefulness of these devices. As an example, the gold standard implanted pressure sensor for neurosurgeons, the Codman Microsensor ICP Transducer is wired, MRI conditional, and has an average drift of 1 mm Hg over 1 week. While recent innovations have led to the development of fiber optic-based sensors and even dissolvable sensors, these devices still rely on the same fundamental approach, and do not address the need for long-term stable sensors. This proposal seeks to advance a new approach to clinical testing: using ultrasound to transduce information from an implanted microsystems target. Our novel approach combines: 1) a novel MRI compatible pressure sensor “target” filled with liquids and air that move in response to pressure, and 2) an ultrasound-based platform that can image the movement of this air and liquid, thereby enabling a quantitative measurement of pressure. In the target, a thin membrane adjacent to a liquid-filled chamber deflects in response to pressure. This deflection causes a connected serpentine channel to fill with liquid. Since air is easily visualized in the device with ultrasound due to the high acoustic impedance mismatch, and since the air movement is proportional to pressure, this combined system creates an easy to read quantitative pressure measurement. Therefore, this project aims to accomplish the following: Aim 1: Development and long-term in vitro testing of membrane-based pressure micro-sensor ultrasound target. Aim 2: Develop ultrasound-based readout of passive implanted pressure sensor. Aim 3: Validate in vivo implant procedure and sensor integrity in acute and multi-week porcine models. When complete, a new class of ultra-stable, testable, long-term ICP pressure sensors will be available to quan- titatively monitor patients at risk of elevated intracranial pressure. This will spare patients from inconclusive im- aging studies or ICP sensors implanted in the brain with a cable or tube exiting the skull. More broadly, the new paradigm of ultrasound telemetry of microfabricated targets can have wide usefulness in medical sensing.
