Application of source localization algorithms in magnetoencephalography: test on a new generation of magnetometers

Magnetoencephalography (MEG) is a noninvasive neuroimaging technique for measuring the activity in the brain. In the vicinity of the head it measures the magnetic field produced by the electric currents in neurons. From the measured magnetic field, using various computational techniques, we determine the location of the source. In this paper, we present the main methods for localizing activated areas in the brain with the data obtained from a 128-channel superconducting quantum interference (SQUID) system. Great emphasis is on solving the inverse problem, i.e. finding the source from the measured magnetic field around the head, with the minimization of the forward model for calculating the magnetic field inside a conducting sphere. We also demonstrate each step in the image processing of the magnetic resonance imaging (MRI), which we use for a more precise source localization. We address all the major drawbacks when using the SQUID gradiometers. As an alternative, we present the new generation of magnetometers, optically pumped magnetometers (OPM), which operate at room temperature. Compared to SQUIDs they can be placed closer to the head with the use of a custom 3D printed sensor holder. We also present the first test results with a custom system of 15 OPMs.