BabyMEG: A whole-head pediatric magnetoencephalography system for human brain development research

Abstract

We developed a 375-channel, whole-head magnetoencephalography (MEG) system ("BabyMEG") for studying the electrophysiological development of human brain during the first years of life. The helmet accommodates heads up to 95% of 36-month old boys in the USA. The unique two-layer sensor array consists of: (1) 270 magnetometers (10 mm diameter, ∼15 mm coil-to-coil spacing) in the inner layer, (2) thirty-five three-axis magnetometers (20 mm × 20 mm) in the outer layer 4 cm away from the inner layer. Additionally, there are three three-axis reference magnetometers. With the help of a remotely operated position adjustment mechanism, the sensor array can be positioned to provide a uniform short spacing (mean 8.5 mm) between the sensor array and room temperature surface of the dewar. The sensors are connected to superconducting quantum interference devices (SQUIDs) operating at 4.2 K with median sensitivity levels of 7.5 fT/√Hz for the inner and 4 fT/√Hz for the outer layer sensors. SQUID outputs are digitized by a 24-bit acquisition system. A closed-cycle helium recycler provides maintenance-free continuous operation, eliminating the need for helium, with no interruption needed during MEG measurements. BabyMEG with the recycler has been fully operational from March, 2015. Ongoing spontaneous brain activity can be monitored in real time without interference from external magnetic noise sources including the recycler, using a combination of a lightly shielded two-layer magnetically shielded room, an external active shielding, a signal-space projection method, and a synthetic gradiometer approach. Evoked responses in the cortex can be clearly detected without averaging. These new design features and capabilities represent several advances in MEG, increasing the utility of this technique in basic neuroscience as well as in clinical research and patient studies.

Non-Invasive Functional-Brain-Imaging with an OPM-based Magnetoencephalography System

“…SQUID sensors operate at ~ 4 K and liquid helium is used to achieve cryogenic temperature. Regular costly maintenance is required to fill the helium reservoir and calibrate the SQUID-based MEG system, although recent advancements in helium recycling [18] is reducing maintenance costs. The main limitation of SQUID-based MEG system, which also stems from the use of cryogens, is fixed sensor position.…”

“…In commercial SQUID based MEG systems, the rigid helmet is designed to fit the 95th percentile head size; this fixed helmet size degrades the signal quality for smaller heads, e.g. children [18].…”

Short-range connections in the developmental connectome during typical and atypical brain maturation

“…Specific MEG systems tailored for infant brain has also been recently established (e.g. Roberts et al, 2014; Edgar et al, 2015; Okada et al, 2016). …”

Developmental Changes in Movement Related Brain Activity in Early Childhood

“…Magnetoencephalographic (MEG) recordings provide a well-established technique for studying the time course of brain activity during motor tasks, as well as the role of oscillatory networks in motor control (for review see, Cheyne 2013). With the introduction of customized MEG systems for smaller children, MEG can fill the current gap between our knowledge of early neural development and that of motor and cognitive abilities (Johnson et al 2010, Cheyne et al 2014, Roberts et al 2014, He et al 2015, Okada et al 2016, He and Johnson 2018). There are however, relatively few MEG studies of motor development, partly due to the challenges of recording motor responses in children and most studies to date have focused on older children and adolescents (Gaetz et al 2010, Wilson et al 2010, Huo et al 2011, Trevarrow et al 2018).…”