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New Patch Paves the Way for Continuous Brain Monitoring

A team of researchers led by Sheng Xu, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering, have created a wearable ultrasound patch that could deliver continuous, non-invasive monitoring of blood flow in the brain. These results were published in Nature.

New Patch Paves the Way for Continuous Brain Monitoring
This soft and stretchy ultrasound patch can be worn on the temple to provide continuous monitoring of blood flow in the brain. During use, the patch is connected through cables to a power source and computer. Image Credit: David Baillot/UC San Diego Jacobs School of Engineering.

The wearable ultrasound patch marks a significant advancement from the Transcranial Doppler ultrasound, the current clinical standard. This technique necessitates a qualified technician to hold an ultrasound probe against the patient's head. However, the procedure has drawbacks. Since it is operator-dependent, the operator’s skill level will determine how accurate the measurement is. It is also not feasible for continuous usage.

Xu's group created a tool to overcome these obstacles. Their wearable ultrasound patch provides a hands-free, reliable, and comfortable option that can be worn constantly throughout a patient's hospital stay.

The continuous monitoring capability of the patch addresses a critical gap in current clinical practices. Typically, cerebral blood flow is monitored at specific times each day, and those measurements do not necessarily reflect what may happen during the rest of the day. There can be undetected fluctuations between measurements. If a patient is about to experience an onset of stroke in the middle of the night, this device could offer information that is crucial for timely intervention.

Sai Zhou, Study Co-First Author and Ph.D. Candidate, Department of Materials Science and Engineering, University of California San Diego Jacobs

Geonho Park, a Ph.D. student in Xu’s lab studying chemical and nanoengineering and another co-first author, highlighted how patients undergoing and recuperating from brain surgery can also benefit from this technology.

The patch is made of silicone elastomer with many layers of flexible electronics implanted. It is about the size of a postage stamp. One layer is made up of a collection of small piezoelectric transducers that, when electrically activated, generate ultrasonic waves and receive waves that are reflected from the brain.

A copper mesh layer consisting of spring-shaped wires is another essential element that improves signal quality by reducing interference from the wearer’s body and surroundings. Elastic electrodes make up the remaining layers.

The patch must be connected to a computer and power supply to function. The researchers included ultrafast ultrasound imaging in the device to accomplish 3D monitoring. Ultrafast imaging records thousands of images per second, unlike standard ultrasound, which records 30 images per second.

The heavy reflection of the skull would cause poor signal strength from the piezoelectric transducers in the patch. Hence, this fast frame rate is required to obtain reliable data from them.

After that, the data are post-processed using unique algorithms to recreate 3D details, such as the position, size, and angle of the brain's major arteries.

The cerebral vasculature is a complex structure with multiple branching vessels. You need a device capable of capturing this three-dimensional information to get the whole picture and obtain more accurate measurements.

Xinyi Yang, Study Another Co-First Author and Ph.D. Student, Department of Materials Science and Engineering, University of California San Diego Jacobs

This study examined the patch's ability to monitor blood flow velocities in the major arteries that supply the brain—peak systolic, mean flow, and end-diastolic velocities—in 36 healthy participants. Participants performed blood-flow-affecting exercises, including hand-gripping, breath-holding, and reading. The patch’s measurements closely matched those obtained with a standard ultrasound probe.

The researchers intend to work with physicians at the UC San Diego School of Medicine to test the patch on individuals with neurological conditions that affect cerebral blood flow. Xu co-founded Softsonics to commercialize this technology.

National Institutes of Health (1R21EB025521-01, 1R21EB027303-01A1, 3R21EB027303-02S1, 1R01EB033464-01, 1R01HL171652-01) supported the study.

Journal Reference:

Zhou, S., et al. (2024) Transcranial volumetric imaging using a conformal ultrasound patch. Nature. doi:10.1038/s41586-024-07381-5.

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