Beyond sensitivity: what are the enabling opportunities of OPM-MEG?

Abstract

While optically-pumped magnetometer (OPM) technology offers a number of compelling advantages over its SQUID predecessor for magnetoencephalography (MEG), many studies and viewpoints focus on issues of (i) scalp placement, with commensurate increases in sensitivity to weak magnetic fields and (ii) room temperature operation (without the need for baths of liquid helium to maintain superconducting properties of SQUIDs). This article addresses another unique and tantalizing opportunity-the ability for the OPM array to be "wearable", and thus to move with the participant. This is critical in adoption of naturalistic paradigms that move beyond "laboratory neuroscience" toward "real world neuroscience". It is also critically important in application to pediatric populations who cannot or will not remain still during conventional MEG scan procedures. Application to the developing infant brain will be considered as well as application to pediatric neuropsychiatric and developmental disorders, such as autism spectrum disorder. Rather than present solutions, this article will highlight the challenges faced by conventional SQUID-based cryo-MEG and explore the potential avenues for OPM-MEG to make a positive impact to the field of pediatric neuroscience.

Keywords: auditory; autism; optically-pumped magnetometer (OPM); pediatric; wearable.

Figure 1

The amplitude of a representative subject's M100 component of the auditory evoked field (AEF) determined under three motion conditions [no motion, mild: single motion 1.3 cm, moderate: continuous motion (max 4.3 cm)] in a conventional cryo-MEG system. The net amplitude of the AEF is seen to decrease as coherent signal averaging is impaired by increasing motion.

Figure 2

(A): A head-mounted OPM-MEG array offers visibly-appreciable difference to the conventional rigid helmet of a cryo-MEG. It potentially will offer the benefits of magnetic electrophysiology with a form factor more closely approximately an EEG array, with increased sensitivity (through scalp placement of detectors) and motion tolerance (through the coupling of the detector array and the participant's head), mitigating motion “artifacts” as well as tolerating realistic movements. [Written release was obtained for the photographic image]. The lower panel presents feasibility data for a single healthy adult subject (B), during an AEF paradigm using an OPM-MEG array in (C,D): a motionless condition and (E,F): with data obtained during continuous 5–10 cm head movement. Bilateral source modeled auditory responses and localizations [e.g., crosshair on right hemisphere dipole source in (D)] look highly comparable between conditions, with environmental noise contributions “projected away” as pseudo- (or nuisance) sources, identified by simple principal component analysis (PCA), implemented in BESA Research 7, (BESA Gmbh, Graefelfing, Germany) and modeled as dipole sources [marked as X's—see crosshairs in (F)].