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By Remcom, Inc.

Researchers at the Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital (MGH), Charlestown, Massachusetts, are developing a special electroencephalography (EEG) cap for use with a research technique that integrates EEG with magnetic resonance imaging (MRI). This integrated technique offers the potential to improve investigations of brain activity. But the RF generated by MRI induces currents in the EEG electrodes. Concerns have arisen that this current could generate temperature increases in sensitive brain tissues. The researchers recognized that they would have to evaluate many different electrode types and arrangements in order to optimize the design of the cap. These experiments obviously cannot be performed on human volunteers. It would be expensive to build a physical model with properties close to a human head. On the other hand, virtual models can be developed with properties very similar to a human head and used to predict the RF fields and tissue exposure to RF. But virtual models cannot be used with confidence to predict the performance of various types of electrodes and leads until they have been verified by physical experiments. It is very expensive to build a matching physical model to verify the accuracy of such a virtual model.

The MGH researchers overcame this challenge by developing a relatively inexpensive physical model called a phantom that approximates the behavior of a human head in the vicinity of an electromagnetic field. They tested this physical model using EEG electrodes and a bird cage coil that produces a radiofrequency field similar to an MRI instrument. They simulated the effects of using different types of EEG electrodes and leads on the phantom using electromagnetic simulation software and the simulation results were compared to the physical testing results. "A number of different electrodes were evaluated on both the physical and virtual models to confirm that the virtual model can predict differences in their performance," said Leonardo Angelone, one of the MGH researchers. "Now the virtual model is being modified to more closely match human anatomy and reconfigured to evaluate many different types of arrangements of electrodes. This capability is aiding the process of designing the EEG cap by enabling the researchers to quickly evaluate the performance of design alternatives at a lower cost and higher accuracy than physical experiments alone."

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•White Paper: Electromagnetic Simulation Aids Development Of Unique EEG Cap