Development and Validation of a Current-Based EEG System for Tangential Current Measurement
Date
2021-09-10
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Abstract
Voltage-based electroencephalography (vEEG) and magnetoencephalography (MEG) are among the state-of-the-art non-invasive methodologies to study the electrophysiology of the human brain. Both methodologies offer high temporal but limited spatial resolution. vEEG and MEG are sensitive to radially and tangentially oriented dipoles in the brain, respectively. This complementary information improves the achievable spatial resolution when used simultaneously in source localization applications (e.g., locating epilepsy foci). However, MEG is not as easily accessible as vEEG. The initial setup cost of an MEG system is in the order of millions of US dollars (USD), and the yearly operational cost can be hundreds of thousands of USD. Conversely, a high-end vEEG system can be acquired for tens of thousands of USD and require minimal maintenance. In some topologies, vEEG can measure from tangential dipoles, but suffers from fundamental limitations regarding signal strength. To address the technological need for a more accessible technology than MEG that can measure tangential dipoles in the brain, I developed a current-based EEG (cEEG) system. The cEEG has a front-end transimpedance amplifier to measure currents that are caused by tangential dipoles. A one-channel cEEG amplifier was conceptualized, designed, simulated, implemented, and characterized for validating the proposed current-based technology. The characterization met design goals set to reliably measure brain currents. Using phantom and simulation models, I found that cEEG is mostly influenced by tangential dipoles. Further, the cEEG was used to measure alpha waves during a resting, and steady-state visual evoked potentials paradigms to measure brain activity from ten healthy individuals. Statistical analysis of the experimental data showed that the cEEG could effectively measure brain activity. Towards the development of a multichannel system, a second cEEG was developed with a microcontroller for on-board digitization of the amplified and filtered signal. This implementation allows the cEEG to have isolated power supplies, which are required if multiple amplifiers were to be used. cEEG systems open up the possibility to understand brain activity from a different perspective in research and clinical applications.
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Keywords
Bioinstrumentation, Current-based Instrumentation, Electroencephalography, Alpha waves, Steady-state visually evoked potentials, Current dipole, Magnetoencephalography
Citation
Comaduran Marquez, D. (2021). Development and Validation of a Current-Based EEG System for Tangential Current Measurement (Doctoral thesis). University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca .