Operating room technology
Dayeh and his research team’s sensor-grid electrocorticography device.
that it can be used in conjunction with MRI and an injection of microbubbles to open the blood-brain barrier in a specific area. This makes it possible to inject a neurotoxin (in this case, quinolinic acid), that exclusively damages what Lee calls the “seizurogenic” neurons, leaving glial cells, blood vessels and axons of passage intact. “If you think of the example of surgery in the temporal lobe for epilepsy, those axons of passage would be a quadrant of your visual system that would have been spared,” he explains. “That’s the entire advantage of PING: you hit the culprits that are creating the seizures, but you functionally spare everything else in the area.”
As a result, PING can be used to expand the neurosurgery treatment envelope to areas that are currently too dangerous to treat surgically. Like other focused ultrasound techniques, it uses multiple sonications originating from all around the patient’s head to exclusively target even the most irregularly shaped areas of the brain. “It’s not easy work going in with a scalpel, but with focused ultrasound you can open the blood brain barrier in a specific shape contoured to your target and produce a conformal lesion,” adds Lee, who is quick to highlight what this means for patients. “Resection is a major surgery: you’re going to be in the hospital for a while, you’re going to be in recovery for months; focused ultrasound is pretty close to going to the orthodontist.”
Applying technology the right way All this can only happen when clinically approved. Lee’s PING procedure and Dayeh’s high-resolution ECoG arrays are still to go through clinical trials. Still, they give an interesting preview of how technology could change neurosurgery in the coming years. For one thing, Dayeh’s arrays, which also have a very clear use case as brain-machine interfaces, could be used to identify and introduce new clinical markers for epilepsy. Their higher resolution would also make
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them ideal for directing the use of a procedure like PING on a small subset of aberrant neurons. Then again, 100 times more information could either make your work 100 times easier or 100 times more difficult. “It’s our job as engineers to make this transition smoother,” says Dayeh. “And the main challenge is how to display and interpret data from 1,000 channels, as opposed to a few tens.” That is going to require a profound shift from the current practice, which usually involves a neurophysiologist copying ECoG readings of different brain regions from a computer screen onto a printed map. “The surgeon will then try to project based on the context or put a sterile paper on the surface of the brain to mark these regions and match them to the grid,” Dayeh explains. “There’s a lot of back and forth and shouting – and that’s already a big theme in the OR.”
His team is working to smooth the transition with real-time displays of ECoG readings that can zoom in or highlight certain channels to present surgical teams with only the information they need at any given moment in a procedure. “It would really simplify the procedure a lot if we’re able to have a real-time display either directly from the surface of the brain, using light-emitting diodes, or on a computer screen next to the surgeon, where he could visibly see the regions and correlate them with the anatomy on the brain surface.” As well as supporting better clinical decisions, Dayeh believes high-resolution ECoG sensors combined with real-time displays are a way to shorten and simplify procedures, which would mean lower costs, less risk and greater availability. “This is maybe the holy grail of doing this,” he stresses, “not only to have better assessment and delineation of brain activity, but also to be able to have patients from any background going through the procedure if they need it.”
Lee feels much the same way about PING, which he is confident has the chance to help increase the number of people who take advantage of brain surgery. It could also allow many more people to perform it. Given that they work almost entirely through imaging technologies, it is possible to imagine PING procedures being led by radiologists, who have already begun to play much more central roles in neurosurgery since the introduction of intraoperative MRI. “Who has his or her hands on the controls of the machine is a good question,” he says. “But you will always need the knowledge base leading up to deciding what the target is. There’ll always be a high-end epileptologist and a neurosurgeon involved in the planning process. And, I mean, I would prefer to have my neurosurgeon at the wheel.” Brain surgery looks like it’s getting a little less complex, but that might just put brain surgeons in even higher demand.
Practical Patient Care /
www.practical-patient-care.com
David Baillot / UC San Diego Jacobs School of Engineering
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