Electronics
Imagine a world map with every border and coast flattened into straight lines and you will have some idea of what surgeons using traditional ECoG grids are navigating by. “It’s very important,” explains Raslan, “because, generally speaking, you want to perform resection where there’s no motor function, but if the boundary that you’re using to delineate that area is incorrect, you can make the wrong decision. That’s one of the very first things we learned. “Now, you can have basically a resection margin of half a millimetre,” Dayeh adds. “You can look at the curvilinear boundary of the tumour, and only resect the tumour and preserve function.” More than just helping surgery teams differentiate brain regions, that enables fine distinctions within each functional area. “We can really observe these boundaries at the millimetre scale, and even define correlates for finger movements.” Equivalent levels of precision are currently attainable in research contexts thanks to Blackrock Neurotech’s Utah Array. However, at scarcely 5mm2
,
that is not the best device for getting the wider understanding often needed in planning a resection. It is also an expensive, difficult to manufacture technology that only works by penetrating the surface of the brain – which makes it hard to use in the middle of an operation.
“Conventionally there have been trade-offs that made the Utah Array a research-grade device and the ECoG grid a clinical grade device,” explains Raslan. “If you want to record a small area of the surface of the brain, or from individual cells, you have to penetrate; and you can either get a very high resolution or a large surface area coverage, but you can’t get both.” Until now. “In essence, this grid brings the research capabilities that we had previously available in the Utah Array to the clinical space. It turns the operating room into a very advanced research laboratory.”
The crystal ball
That would not be possible if not for the years of near-obsessive attention that Dayeh’s team at UCSD has given to material and microfabrication. Their idea began with crystals of PEDOT embedded in polyimide, but it reached its fruition with platinum nanorods and parylene C. PEDOT, a one-dimensional crystal, was originally chosen because of its ability to sense volumetrically rather than simply on its surface. That lowers electromechanical impedance and increases sensitivity, which is important for moving from millimetre to micron scale ECoG sensors without introducing extra noise to their readings. PEDOT,
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Medical Device Developments /
www.nsmedicaldevices.com 67
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