Multimodal neuroimaging with optically pumped magnetometers: A simultaneous MEG-EEG-fNIRS acquisition system.

Multimodal neuroimaging plays an important role in neuroscience research. Integrated noninvasive neuroimaging modalities, such as magnetoencephalography (MEG), electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS), allow neural activity and related physiological processes in the brain to be precisely and comprehensively depicted, providing an effective and advanced platform to study brain function. Noncryogenic optically pumped magnetometer (OPM) MEG has high signal power due to its on-scalp sensor layout and enables more flexible configurations than traditional commercial superconducting MEG. Here, we integrate OPM-MEG with EEG and fNIRS to develop a multimodal neuroimaging system that can simultaneously measure brain electrophysiology and hemodynamics. We conducted a series of experiments to demonstrate the feasibility and robustness of our MEG-EEG-fNIRS acquisition system. The complementary neural and physiological signals simultaneously collected by our multimodal imaging system provide opportunities for a wide range of potential applications in neurovascular coupling, wearable neuroimaging, hyperscanning and brain-computer interfaces.

Automatic coregistration of MRI and on-scalp MEG.

BACKGROUND: Recent progress in optically pumped magnetometers (OPMs) and high-temperature superconducting quantum interference devices (SQUIDs) has facilitated the development of an on-scalp magnetoencephalography (MEG) system that offers high signal intensity and flexibility at a lower cost. While the on-scalp sensor array has high flexibility, it brings new challenges to accurate sensor-to-brain coregistration, which is essential for MEG source localization. NEW METHOD: A novel automatic filtering algorithm based on plane segmentation was proposed to locate on-scalp MEG sensors in 3D images reconstructed from optical scanning. Global image registration was employed for the automatic alignment of anatomical images and sensor positions. RESULTS: Seventy-one sensor dummies on the scalp were located and registered to brain anatomical images. The deviations of the sensor location and orientation from the averaged result of 10 measurements were less than 1 mm and 0.6°, respectively. The entire process could be completed in less than 4 min. COMPARISON WITH EXISTING METHODS: Compared with existing methods that involve various manual procedures, such as moving digitizers to fiducials and repeatedly pulling out sensors, our proposed coregistration method is more efficient and accurate. CONCLUSION: An automatic method for the coregistration of anatomical structure and on-scalp sensors that will have a large impact on the practical use of on-scalp MEG is developed.

A high-performance compact magnetic shield for optically pumped magnetometer-based magnetoencephalography.

The rapid development of the optically pumped magnetometer (OPM) has offered a much more flexible method for magnetoencephalography (MEG). Without using liquid helium and its associated dewar device in the OPM detectors, the large and expensive magnetically shielded room (MSR) for traditional MEG systems could be replaced by a compact shield. In the present work, an economic and compact cylindrical shield was designed and built to meet the low-field working requirement of the OPM in detecting human brain neuronal activities. The performance of the compact shield was evaluated and further compared with that of a commercial MSR. Our results showed that the residual magnetic fields and background noise of the compact shield were lower than or comparable to those of the MSR. The remnant field in the shield is found to be 4.2 nT, a factor of 13 000 smaller than the geomagnetic field which is applied to the transverse direction of the shield, and the longitudinal shielding factors measured using a known alternating-current magnetic field are approximately 191, 205, and 3130 at 0.1 Hz, 1 Hz, and 10 Hz, respectively; in addition, the evoked dynamic waveforms in the human auditory cortex that were recorded separately in these two shields demonstrated consistency. Our findings suggested that a compact shield is feasible for OPM-based MEG applications with high performance and low cost.

Magnetoencephalography with a Cs-based high-sensitivity compact atomic magnetometer.

In recent years, substantial progress has been made in developing a new generation of magnetoencephalography (MEG) with a spin-exchange relaxation free (SERF)-based atomic magnetometer (AM). An AM employs alkali atoms to detect weak magnetic fields. A compact AM array with high sensitivity is crucial to the design; however, most proposed compact AMs are potassium (K)- or rubidium (Rb)-based with single beam configurations. In the present study, a pump-probe two beam configuration with a Cesium (Cs)-based AM (Cs-AM) is introduced to detect human neuronal magnetic fields. The length of the vapor cell is 4 mm, which can fully satisfy the need of designing a compact sensor array. Compared with state-of-the-art compact AMs, our new Cs-AM has two advantages. First, it can be operated in a SERF regime, requiring much lower heating temperature, which benefits the sensor with a closer distance to scalp due to ease of thermal insulation and less electric heating noise interference. Second, the two-beam configuration in the design can achieve higher sensitivity. It is free of magnetic modulation, which is necessary in one-beam AMs; however, such modulation may cause other interference in multi-channel circumstances. In the frequency band between 10 Hz and 30 Hz, the noise level of the proposed Cs-AM is approximately 10 f T/Hz1/2, which is comparable with state-of-the-art K- or Rb-based compact AMs. The performance of the Cs-AM was verified by measuring human auditory evoked fields (AEFs) in reference to commercial superconducting quantum interference device (SQUID) channels. By using a Cs-AM, we observed a clear peak in AEFs around 100 ms (M100) with a much larger amplitude compared with that of a SQUID, and the temporal profiles of the two devices were in good agreement. The results indicate the possibility of using the compact Cs-AM for MEG recordings, and the current Cs-AM has the potential to be designed for multi-sensor arrays and gradiometers for future neuroscience studies.