Wearable ultrasonic sensor technology for biomedical monitoring

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One of the particular and significant issues for elderly people is that once they experience a physical disorder, they are often placed on bed rest. This requires special and intense care from caregivers to maintain their daily activities. Also, musculoskeletal diseases impair a patient’s physical ability. Early diagnosis of such ailments is crucial for appropriate treatment in order to prevent further progression of the disease. In addition, mechanical properties of biological tissues, such as stiffness and viscosity, change due to the disease, aging, injury and fatigue. Thus, such properties contain significant and useful information for medical diagnosis. X-ray and MRI are capable of providing anatomical images with high spatial resolution for medical diagnosis. However, they are rather expensive and available only in clinics or hospitals. Ultrasound has been a powerful tool for medical diagnosis and is widely used since it is noninvasive, risk-free (no ionizing radiation exposure), and capable of capturing images in real-time at a high frame rate and at low-cost. Ultrasonic diagnostic techniques can provide not only static images of anatomical structures but also real-time dynamic information of internal tissue motion associated with physical and physiological activities. If one can obtain internal tissue motion and mechanical properties quantitatively, in addition to conventional qualitative images, such augmented information would greatly aid doctors in making fast, accurate, and appropriate diagnoses. In addition, it is beneficial if real-time and continuous ultrasonic monitoring and diagnosis could be performed outside of clinical facilities and laboratories, without restricting daily life activities. Current non-invasive, wearable and/or non-contact techniques employed for monitoring physical activities, such as muscle contractions, include mechanomyography, surface electromyography, and 3D motion capture. However, these techniques lack sensitivity/spatial resolution in the tissue depth direction, or are capable of only monitoring the external motion at the body surface but not the detailed motion of internal tissues. Therefore, it might be difficult or impossible to assess the individual muscle located deep in the body.The objective of this proposed research program is to develop a wearable ultrasonic sensor and associated signal processing algorithms that can continuously monitor internal tissue motion in real-time during physical activities. Features of this sensor are: lightweight, flexible, mass-producible, low-cost, and thus, disposable. Disposability of the sensor is desirable for a medical device that contacts a human body since it does not require disinfection or sterilization after its usage. The wearable ultrasonic sensor technology to be developed in this proposed research program is able to measure the mechanical behavior and properties of tissues of interest quantitatively. The developed technology will enable monitoring of physical conditions of a subject outside of hospitals, clinics and laboratories. Furthermore, people will be able to wear cost-effective ultrasonic sensors that will continuously monitor their health conditions. The applications of the develop technology are not only in the areas of medical diagnosis and health monitoring but also in rehabilitation, kinesiology and sports for effective and efficient physical training. Science, engineering and clinical researchers could have benefits from this new ultrasonic sensing technology to study and understand a human physiology by monitoring tissue motion of their interest during various physical activities.