High-Field MR-Compatible Dense Array EEG using Polymer Thick Film Technology

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DESCRIPTION (provided by applicant): The long-term objective of the proposed project is to design a low-profile, high-resistive, MRI-compatible dense array EEG sensor net for simultaneous dEEG/fMRI recordings in fields as high as 7 Tesla. This novel sensor net (256-channel InkNet) will use innovative conductive ink leads printed on polymer thick film (PTF) developed at the Analog Brain Imaging Laboratory (ABILAB) at the A. A. Martinos Center of Massachusetts General Hospital. The InkNet will interface with dEEG MRI-compatible hardware and software recently developed at Electrical Geodesics Inc. (EGI). This proposed system will provide safe, noninvasive, and affordable dEEG/fMRI technology to both clinicians and researchers, thereby enabling routine multimodal imaging of human brain function with unprecedented spatiotemporal resolution. Application of this technology will enhance the understanding of healthy brain function, treatment of many neural pathologies, {and pre-surgical planning}. For Phase I, the first Specific Aim is to modify EEG electrodes for MR-compatible dense-array InkNet recordings. The new InkNet will take advantage of EGI's patented low-profile 256-channel geodesic sensor net (HCGSN) structure. Two electrode designs will be developed and tested. The first will miniaturize the existing 32-channel InkCap half-ring electrodes to fit the HCGSN structure by embedding the electrode directly into the harness design rather than using an adhesive. The alternative design will interface EGI's pellet electrode to PTF ink leads by gluing it to an interface pad printed with polyimide conductive glue. Both designs will be tested using two abrasion-free skin applications: EGI's current electrolyte-soaked sponges and a novel biopotential hydrogel. Performance tests for high signal-to-noise ratio (SNR) and low drift will determine the best electrode design for the Phase I prototype. The Second Specific Aim is to design new PTF traces for efficient routing of the 256 electrode leads. An autorouter program (SPECCTRA) will test nine router parameters to converge on the optimal trace width and length which will then used to determine the number vias and layers required. A fixed trace width of 5 mils to ensure manufacturability will be achieved by testing for spacing violations during the SPECCTRA routing iterations. The final prototype circuits will be printed using a custom mix of carbon and silver inks tested for optimal dielectric and conductive properties. The Third Specific Aim is to test the new dEEG/fMRI system for safety and data integrity. Safety tests will be performed using finite difference time domain (FDTD) numerical simulations with an anatomically accurate head model, followed by actual temperature measurements in the 7T scanner using a specially developed phantom (CHEMA), high-power TSE imaging sequences to induce RF heating, and a four-channel Fluoroptic Thermometer. After confirming safety, MRI and EEG data integrity will be tested at 3T and 7T field strengths using T1-weighted structural sequence, a resting EEG alpha protocol, and a visual processing study. Analyses will contrast MRI quality with and without the InkNet, and EEG quality within and outside the MR scanner. PUBLIC HEALTH RELEVANCE: The goal of this project is to develop a system for simultaneous measurement of brain activity using two complementary methods: electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). This state-of-the-art system will offer brain scientists and clinicians a safe, non-invasive tool for studying human brain function with unprecedented spatial and temporal precision. This knowledge will help us better understand healthy brain function, treat many disorders (e.g., epilepsy), and improve pre-surgical planning.