Glassy Carbon Electrodes Safer Than Metal in MRIs, Study Suggests

Implantable electrodes made of glassy carbon may be safer for use in MRI scans than traditional electrodes made of metal for people who undergo deep brain stimulation, a new study shows.

The study, “Glassy carbon microelectrodes minimize induced voltages, mechanical vibrations, and artifacts in magnetic resonance imaging,” was published in Microsystems & Nanoengineering.

In cases where Parkinson’s patients are not responding well to medication, deep brain stimulation (DBS) can be used to treat motor symptoms associated with this neurodegenerative disease. The treatment involves surgically implanting an electrode directly in the brain, then using that electrode to electrically stimulate specific brain regions.

Traditionally, electrodes used for DBS have been made of metal, most typically platinum. But metal electrodes pose a problem when a person needs to undergo an MRI scan. Such scans can be used to image the brain using powerful magnets, but those magnets can interact badly with metal electrodes.

Specifically, the electrodes can lead to large “white spots” on the MRI images themselves, which can limit the utility of the images. Plus, the magnetic fields generated in MRI can cause electrodes to vibrate, or they can generate electrical currents that make the electrode heat up. These circumstances run the risk of causing damage or irritation in the brain.

In the new study, researchers wondered if electrodes made of glassy carbon, instead of metal, would be resistant to these issues. Glassy carbon (GC) is basically a bunch of very thin layers of carbon pressed together.

The researchers previously had created GC-based electrodes designed for DBS, and in a previous study, they showed that these electrodes were more durable than traditional platinum ones.

“Inherently, the carbon thin-film material is homogenous—or one continuous material—so it has very few defective surfaces. Platinum has grains of metal which become the weak spots vulnerable to corrosion,” Sam Kassegne, PhD, a professor at San Diego State University (SDSU) and co-author of both studies, said in a press release.

The researchers tested their GC electrodes in an MRI; but, rather than using actual human brains, they implanted the electrodes in a substance sort of like Jell-O. The researchers demonstrated that, while the metal electrode created a bright white patch on the MRI images themselves, the CG was nearly invisible — suggesting that, in an actual brain, this type of electrode would interfere with imaging far less.

They measured the currents generated in these electrodes during an MRI scan, as well as how much they vibrated, and compared these measurements to similar measurements obtained using traditional metal probes.

They found that the current generated in the GC electrodes was about 10 times lower than that in the metal probes. Similarly, vibrations in the GC electrode were about 40 times weaker than those in the metal ones, Researchers noted, however, that “for both types of microelectrodes, the measurable forces were below the detection limit” — that is, the vibrations were very small for both, even if they were smaller for the GC electrode.

“Our lab testing shows that unlike the metal electrode, the glassy carbon electrode does not get magnetized by the MRI, so it won’t irritate the patient’s brain,” said Surabhi Nimbalkar, study co-author and doctoral candidate at SDSU.

Although the researchers noted that they did not directly assess heating of the electrodes, which may be an avenue for further study, they nonetheless concluded that “GC microelectrodes demonstrate superior behavior with respect to MR safety compared to [platinum]-based electrodes.”

“Since GC has recently been demonstrated to have a compelling advantage over other materials for neural stimulation (…), this MRI compatibility validated in this study offers an additional advantage for long-term in vivo use in clinical settings,” they wrote.