RF infrasonics for internal tissue characteristics

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The change of tissue mechanical properties in internal organs, vessels, airway and larynx can serve as diagnostic and prognostic indicators for many disorders that cause swelling, inflammation, tumors and plague deposition. In addition to the self-initiated vibrations induced by vital signs and egophony, mechanical motions of internal tissues can be triggered through an external actuation, when the subsequent vibration responses and damping characteristics can be observed outside the body. Present devices based on auscultation or stethoscope can retrieve tissue vibration higher than 20 Hz, and portable ultrasound can retrieve motion details with characteristic frequencies lower than 2 Hz with a frame rate of 20 Hz. However, many important internal tissue vibration characteristics in the infrasound band between 2 – 20 Hz are difficult to be accurately measured by present tools, especially in primary care and at home. However, the infrasound band covers the typical vibration characteristics of main vascular and respiratory tissues. For example, when the lung has inflammation, such as in the COVID-19 pneumonia, the lung and bronchi tissues will contain more water, a condition called edema, and have a large change in their vibration and damping characteristics. When plague is deposited inside aortic and coronary arteries, the vibration feature also evolves. Ultrasound and stethoscopes have been perfected over the years, but improvement beyond the present capabilities to close the gap of the infrasound range would be challenging. This project will develop the required hardware and software to achieve new capabilities and test on a manikin with artificial tissues. The developed sensor tools can be used for telemedicine or with other conventional diagnostic and image tools to improve imaging quality. The research results will be translated into undergraduate courses on sensors, and into promotional materials for K-12 students and public. The major objective of this research is to develop a wearable or portable radio frequency (RF) sensor that can cover broad tissue vibration bandwidth including the critical infrasound band of 2 – 20 Hz, together with signal processing algorithms appropriate to retrieve the transient features in both temporal and spectral domains. The sampling rate for radio signals can cover a very broad range for detecting very slow to very fast tissue and organ motions. In comparison, fast tissue motion is difficult for internal imaging with limited frame rates, and slow motion does not make a sound for the stethoscope to pick up. As many internal tissues have high viscosity and anisotropy, multiple RF sensors can be deployed as a multiple-input-multiple-output (MIMO) network to improve the spatial resolution. This project will develop near-field MIMO RF sensing similar to the ground-penetrating radar, and the acoustic detection is similar to seismology. Specifically, the project will construct a body phantom with imitation internal tissues a MIMO RF sensor array on the phantom. Signal processing algorithms for vibration and damping characteristics with high temporal and spectral resolutions will be developed and benchmarked. A physical model from the tissue excitation to the RF transceiver outputs with scalable geometrical parameters will also be developed. Lastly, human study with healthy participants will be conducted to provide feedbacks for improvement on sensor design.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.