Magnetoencephalography Without a Shielded Room

Wearable magnetoencephalography in an open environment

Birth of the Coil: another Milestone towards a fully reproducible low-field MRI scanner for head-imaging

This work presents an open-source, optimized solenoid head coil tailored for the 50 mT open-source scanner (OSII ONE v2.1), set the basis for a fully reliable and reproducible component for the open-source OSII ONE MRI scanner.

Motion tolerance in wearable OPM-MEG using dynamic field nulling

Wearable magnetoencephalography (MEG) enabled by optically pumped magnetometers (OPMs) promises improved comfort and motion tolerance. This is particularly beneficial when measuring brain activity in children who cannot sit still for long periods of time. Compared to cryogenic MEG, wearable MEG allows larger head movements, but they result in artifacts due to uncompensated background fields and reduce source localization accuracy. Spatial filtering methods can partially compensate these motion-induced artifacts, but they are most effective when used in combination with background field nulling. This is because accurate spatial filtering relies on an accurate estimate of the sensor gain and orientation of its sensitive axis. Through simulations, we first deduce the target residual background field that is necessary for accurate dipole localization (< 1 cm) in the presence of head movements. Our simulations indicate that smaller background fields enable larger head movements. Then, we used our open-source printed circuit board (PCB) coils to develop a method to dynamically null the background field. We demonstrate that our dynamic field nulling method allows improved localization of somatosensory evoked fields (SEFs) by maintaining the background field below the target residual fields established in the simulations. Our study highlights the importance of tracking both the background field and the head position relative to the background field for quality assurance in wearable MEG.

Modular Arrays for High Precision Wearable MEG

Optically pumped magnetometers (OPMs) can be used for magnetoencephalography (MEG) with equivalent or improved signal to noise ratio, relative to cryogenic MEG, when sensors are placed close to the scalp. OPM-based MEG can also be used in mobile contexts if sensors are placed in lightweight, wearable arrays. Individually tailored, rigid helmets known as scannercasts are currently the only method capable of achieving on-scalp, mobile recordings with high precision. However, these scannercasts are expensive to produce, require structural imaging in advance of the experiment, and can incur lengthy downtime while sensors are transferred between scannercasts. Here, we introduce a solution to these challenges that retains the advantages of scannercasts. We provide detailed steps for constructing a modular, cap-based design, suitable for all head sizes. Using simulations, we compare the leadfield power of this array against an idealised array and a commercially available mobile solution. We then validate our proposed solution empirically, in five participants, and provide a complete data preparation and analysis pipeline. Our design expands the accessibility of OPM-based MEG, and increases participant throughput to levels comparable to other imaging modalities. Crucially, it removes the trade-off between signal quality, mobility and practicality, promoting the unique potential of OPM-based MEG as a tool for studying naturalistic behaviour, and clinical assessment with high precision.

A review of advances in magnetocardiography with second generation quantum sensors

Abstract Magnetocardiography (MCG) offers a non-invasive, contactless, and radiation-free method for detecting the heart’s electrophysiological activity with high spatial and temporal resolution. Despite its diagnostic potential, clinical adoption has been limited by the technological and economic constraints of current sensing platforms. Superconducting quantum interference devices (SQUIDs) remain the gold standard for sensitivity but require cryogenic cooling and costly magnetic shielding, while optically pumped magnetometers (OPMs) provide room-temperature operation but face challenges such as dead zones, thermal management, and limited miniaturization. Recently, nitrogen-vacancy (NV) centers in diamond have emerged as a promising alternative. NV-based magnetometers combine solid-state robustness, miniaturization potential, and scalability, enabling prospects for portable and high-density sensor arrays. Current prototypes, however, remain two orders of magnitude less sensitive than clinical requirements. This paper reviews the state of SQUID, OPM, and NV technologies for MCG and highlights the technical advantages and limitations of each. Strategies for improving NV sensitivity are discussed as pathways toward bridging the sensitivity gap. While NV-based sensors are not yet clinically viable, their combination of robustness, scalability, and cost-reduction potential positions them as a compelling candidate for next-generation MCG systems, with the prospect of expanding cardiac diagnostics.

Intracranial Validation of Magnetoencephalography Across Oscillatory Frequency and Depth

Non-invasive, whole-brain neuroimaging methods such as functional magnetic resonance imaging, electroencephalography (EEG), and magnetoencephalography (MEG) are essential tools for studying the basis of human cognition in health and disease. MEG offers the opportunity to study neural activity at its intrinsic timescale, by recording the magnetic fields generated by electrical currents within the brain from outside the skull. Moreover, recently developed optically pumped magnetometers (OPMs) allow these recordings to take place in new settings, for example during naturalistic behaviour and in previously inaccessible populations. These breakthroughs have led to a shift in the neuroimaging landscape, with a global increase in the adoption of MEG. Crucially, however, the extent to which MEG recordings can measure different features of neural activity remains unclear. To address this issue, we leveraged a unique and rare dataset of concurrent MEG and intracranial EEG recordings from a cohort of epileptic patients. We found that group-level inferences of spontaneous oscillatory dynamics made with source-localised MEG, i.e. estimates of power and bursts, accurately reflected the underlying neural activity. As expected, the agreement was strongest for lower-frequency activity (delta, theta, and alpha) and superficial sources, and weakest in the gamma range. Crucially, however, MEG was also sensitive to deep structures: it captured oscillatory power and burst dynamics in the hippocampus, most robustly in the theta band. These findings demonstrate that MEG is sensitive to physiologically meaningful activity in cortical and subcortical regions and establish a foundation for the interpretation of future MEG studies across a wide range of research domains.