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Development of an OPM MCoG Array

Kolloquium der Abteilung 8

Whole-head SQUID-based MEG instruments can accurately localize interictal spike foci but cannot map the extent of seizure activity. Such instruments are limited by the spatial frequencies they can resolve – a function of sensor spacing and distance to the cortex. Intracranial measurement (electrocorticogram) remains the standard for clinical presurgical mapping of seizures. Simulations reveal that decreasing sensor spacing and distance to the scalp could permit measurement of independent sources on the superficial cortical surface with resolution equivalent to that of 10 mm electrode grids. At present, the rubidium cells of OPM sensors can be placed as close as 5 mm from the scalp. The challenges of developing an OPM magnetocortigraphy (MCoG) instrument suitable for use in both clinical and basic neuroscience include: 1) Accurate calibration of sensor geometry and gain. 2) Mitigation of nonlinearity due to cross-axis projection error (CAPE). 3) Localization of the sensor array on the head. 4) Coregistration of the OPM MEG data with the subject’s structural MRI. 5) Reduction of artifacts, inherent in magnetometers, due to head motion. A 56-channel (7 x 8) OPM sensor array with 3 OPM reference sensors has been fabricated at the NIMH MEG Core Facility. The performance and limitations of this design will be discussed.