Magnetoencephalography using optically-pumped magnetometers*

Current magnetoencephalography (MEG) uses a helmet-shaped array of low-temperature superconducting quantum interference devices (SQUIDs) to image the magnetic field produced by the neural currents inside the head with millisecond temporal resolution. Moving the sensors closer to the scalp holds the promise of simultaneously increasing the spatial resolution of MEG. Our optically-pumped magnetometers (OPMs) are room-temperature sensors that work on the principle of laser spectroscopy of alkali atoms in a vapor cell. They can be microfabricated and placed in close proximity to the scalp for MEG. The MEG test system we present consists of 48 microfabricated OPMs, that are integrated into pairs on small flying lead sensor heads, such that they form 24 first-order gradiometers with a baseline of 2 cm. The gradiometer and magnetometer data are read out simultaneously. The sensors are assembled on a conformal 3D printed helmet with spokes that can be adjusted in the radial direction through a ratchet system. The magnetic field in the radial direction to the head is recorded with the magnetometers and radial gradiometers. We present first standard MEG recordings of resting-state measurements and evoked responses.