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High-Resolution Surgical Brain Monitor Demonstrated

Micro-electrode grid

Micro-electrode grid used n brain surgery (David Baillot, UC San Diego)

25 May 2017. Biomedical engineers demonstrated a higher-resolution device for mapping the brain during surgery to highlight healthy and diseased tissue. The team from University of California in San Diego, with colleagues from Massachusetts General and Brigham and Women’s hospitals in Boston, describe the device in the 12 May issue of the journal Advanced Functional Materials (paid subscription required).

The researchers from the labs of UC-San Diego engineering professors Shadi Dayeh and Vikash Gilja, and neuroscientist-radiologist Eric Halgren, sought a device that observes brain activity during surgery with more granularity and detail than those used today. Current devices, called electrode grids, are made of silicone or plastic and arrayed with electrodes, placed on top of the brain to capture neural activity. The device identifies regions in the brain where nerve cells are functioning and those with a likelihood of disease, which helps surgeons treat or remove only diseased tissue.

Current electrode grids, however, tend to be bulky and have not changed their basic design in about 20 years. “Our goal is to develop a tool that can obtain more reliable information from the surface of the brain,” says Dayeh in a UC-San Diego statement. Their design aimed for a thinner, more flexible device that packs in more sensors for mapping brain activity in more detail.

The team — including neurosurgeons, neuroscientists, electrical engineers, materials scientists, and systems integration specialists — created its micro-electrode grid from from a polymer known as PEDOT:PSS, short for poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate). PEDOT:PSS conducts electric current and is being used in a number electronic and energy applications. But the material is also transparent, as well as physically and chemically stable.

The researchers replaced traditional metal electrodes found in today’s electrode grids with those made from PEDOT:PSS, taking advantage of its its high conductivity and transparency. As a result, their micro-electrode grid is thinner, transparent, and more flexible, with more electrodes in the array to capture more detailed neural activity. “These electrodes occupy minuscule volumes, says Gilja. “Imagine Saran Wrap, but thinner.”

The engineering team asked their neurosurgeon colleagues to try out the micro-grid with 4 brain surgery patients at the UC San Diego medical center, as well as Mass. General and Brigham and Women’s hospitals. In their tests, the surgeons used the micro-grid as well as standard electrode grids in the same procedures and recorded the results. The two types of electrode grids were used with patients awake and unconscious. During epilepsy surgery, for example, both grids identified regions of the brain responsible for seizures, as well as normally functioning areas, but the micro-grid provided more detailed and higher-resolution readings. In another case, the micro-grid recorded activity in meninges layers of the brain in increments as small as 400 micrometers.

The findings overall show the micro-grid works as well or somewhat better than standard electrode grids, but with higher resolution and less noise. “In order to introduce a new electrode grid for clinical use,” notes Dayeh, “we first need to show that the device can yield the same information as that used in the clinic. Then we can build upon that work to make an even better product that can improve patient care.”

The next steps in the micro-electrode grid’s development are to increase the electrode density and test the length of time the device can operate safely in the brain.

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