Closed-Loop Triaxial Optically Pumped Magnetometers for High-Sensitivity and High-Bandwidth Magnetoencephalography Measurements of the Developing Brain - PROJECT SUMMARY/ABSTRACT
Non-invasive detection of gamma oscillations in infants will inform a broad range of studies examining neuro-
developmental and neurodegenerative disorders. As the highest frequency of the named neural oscillations,
they are also lowest in magnitude, making them difficult to detect. In the proposed work, the gamma oscilla-
tions of infants (6-months) will be measured using a non-invasive functional neuroimaging device with high
spatiotemporal resolution (~1 mm/10 ms) suitable for infants. These specifications suggest magnetoenceph-
alography (MEG) as the modality and optically pumped magnetometers (OPM) as the magnetic sensor of
choice. OPM-MEG systems allow individual positional adjustment of each sensor, maximizing detected signal
power. Current state-of-the-art OPMs do not have sufficient sensitivity and bandwidth to recover gamma oscil-
lations with high fidelity. In collaboration with our industry partner, QuSpin, Inc., we will develop a pulsed OPM
with a sensitivity of 2 fT/rt-Hz and a bandwidth of 220 Hz, making it capable of measuring the high frequency
gamma oscillations near the surface of the subject’s scalp. The proposed sensor measures three orthogonal
vector components of the magnetic field using the same sensing volume, a unique feature that is essential for
the effectiveness of interference rejection algorithms. Furthermore, the triaxial mode allows for triaxial closed-
loop operation, an integral feature for suppressing systematic error sources in OPMs. The overall objective of
this project is to develop an OPM-MEG system with unprecedented sensitivity, bandwidth, and accuracy. Fur-
thermore, the MEG system will be validated in a study of gamma oscillations and brain synchronicity in infants
with a comparison between our hybrid OPM array and a commercial SQUID system. Aim 1 will deliver the core
component of the proposed MEG system: a novel pulsed-OPM sensor. The proposed sensor features 1) ex-
ceptional gradiometrically inferred sensitivity (2 ft/rt-Hz), 2) wide bandwidth (220 Hz), and 3) triaxial signal de-
tection using a single sensing volume, and 4) closed-loop operation on all three axes. Aim 2 will deliver a hy-
brid OPM-MEG system by incorporating 10 of our triaxial pulsed-OPM gradiometers (two triaxial OPMs sepa-
rated by 20 mm) and 20 triaxial commercial OPMs into a hybrid MEG sensor array installed in a magnetically
shielded room. Supporting tasks include control electronics, laser system, and novel signal processing algo-
rithms development for noise rejection using the full magnetic field vector. Aim 3: the robustness and effective-
ness of the pulsed OPM-MEG will be put to test by employing it to study gamma oscillations in 30 infants
through visual, auditory, and resting-state testing paradigms. The unique features of the proposed MEG sys-
tem stem from its novel pulsed sensor, which will provide the most sensitive OPM for non-invasive measure-
ment of brain’s magnetic field. Through the industry partnership, we will design for manufacturability to deliver
a prototype that is near product ready and has been validated against a commercial SQUID MEG system while
future research will seek further sensor miniaturization and improved sensitivity.
