Underwater Ultrasonic Imaging of Microbubbles for Real-time Control of Decompression Procedures Using Wearable CMUT Arrays

Decompression sickness (DCS) is one of the major health risks for scuba divers even if they follow strict prevention schedules to stage their decompression. DCS is caused by intravascular or extravascular bubbles as a result of tissue supersaturation in inert gases during decompression, with symptoms varying in severity from skin manifestations to excruciating pain, paralysis and death. The risk of DCS is mitigated through probabilistic decompression models. These effectively limit the supersaturation rate by slowing the ascent of the diver (decompression) but cannot personalize decompression schedules to individual diver physiology. Detection of microbubbles in real time during diving could potentially provide the information needed to personalize decompression schedules and lower individual DCS risk. Clearsens Inc. is a start-up company that aims to translate capacitive micromachined ultrasonic transducer (CMUT) technology to marketplace for novel ultrasound applications. The company licensed from NC State University a technology that simplifies the manufacturing process and enables highly efficient, wideband, and small form factor CMUT arrays. Our goal is to tailor the patented technology to this Navy need. Our findings in Phase I Base show that the technology is well suited to make a low-power, wearable and pressure-compatible ultrasound imaging system while having the ability to implement both traditional (B-mode/Doppler) imaging and microbubble-specific imaging schemes developed in the context of clinical contrast-enhanced ultrasound (CEUS). In Phase I, we verified our hypothesis that the voltages necessary to achieve similar acoustic output would decrease with depth, in both simulations and experiments.  Pressure tests with the help of our academic partners demonstrated that the technology can operate reliably at a pressure corresponding to 90 meters depth. We also acquired both B-mode and microbubble-specific images on a flow tissue-mimicking material using a CMUT array connected to a desktop research ultrasonic imaging system, demonstrating multiplexed imaging capability. In Phase II, we propose to manufacture the fully-packaged wearable prototype (final wideband CMUT array packaged with electronics as a wearable capable of multiplexed imaging on various anatomical locations) to be tested and optimized in human chamber dive experiments for decompression stress quantification. We will continue to work with the same established team of experts in microbubble ultrasonic physics and detection, ultra-wideband CMUT design and fabrication, low-power ultrasound electronic interfacing, and diving and hyperbaric medicine, to achieve our goals.