Voluntary human movement emerges from dynamic interactions between the brain, spinal cord, and sensory afferents. Spinal cord function has proven particularly difficult to study non-invasively in humans due to its deep anatomical location and narrow diameter. As a result, sensorimotor interactions are often studied using cortico-muscular coupling, which captures interactions between brain and muscle but cannot reveal how these signals propagate through the spinal cord. Here, we use concurrent brain and spinal cord imaging with optically pumped magnetometers (OPMs) and electromyography (EMG) to test whether endogenous synchronization within the human sensorimotor system can be detected and characterized non-invasively across cortical, spinal, and muscular levels. Participants (n = 9) performed a sustained isometric hand contraction while we recorded cortical and spinal cord magnetic fields using OPMs and hand muscle activity using EMG, and we compared rhythmic activity propagating through the cortico-spinal-muscular loop with the state at rest. We show that the spinal contribution to cortico-muscular coupling manifests as coherent 10-35 Hz activity linking the contralateral sensorimotor cortex, cervical spinal cord, and muscle. This synchronization forms a distributed, bidirectionally interacting network with physiologically plausible temporal delays. The spatial organization of this activity accords with known sensorimotor anatomy, localizing to cervical segments appropriate for upper-limb control. Our results provide the first direct, non-invasive magnetic field evidence in humans of coherent brain and spinal cord oscillations and demonstrate the feasibility of concurrent, spatiotemporally resolved imaging of the central nervous system to open new avenues for studying human sensorimotor physiology.
Meaghan E. Spedden, Maike Schmidt, George C. O’Neill et al.· Current Biology· 1 citation
OBJECTIVE
Parallel imaging is ubiquitous in MRI, enabling higher spatial and/or temporal resolution. However, successful unfolding is contingent on robust and accurate estimation of relative coil sensitivities, which often involves computation times that preclude online deployment. We present a computationally efficient method of robustly estimating coil sensitivities, and reconstructing under-sampled images using a data-driven regularised SENSE formalism that is commensurate with online deployment for Cartesian k-space acquisitions.
MATERIALS AND METHODS
The proposed image reconstruction method via Multiple Orthogonal Reference Sensitivity Encoding (MORSE) estimates multiple sensitivities per voxel to address issues, such as rapidly varying sensitivities, chemical shift artefact, or insufficient fields of view. It simultaneously provides a data-driven regularisation term for noise control providing inherent adaptability to diverse imaging contexts.
RESULTS
MORSE has been successfully deployed in multiple neuroimaging studies at both 3T and 7T, including functional studies of autobiographical memory processing, visual and auditory perception, and quantitative MRI studies of neurodegenerative diseases including Huntington's, Alzheimer's and Parkinson's. Exemplar image reconstructions are presented and compared with GRAPPA, ENLIVE, ESPIRiT and LORAKS. We also showcase application of MORSE outside of the brain via application in liver and knee imaging. MORSE consistently produced high-quality, artefact-free images with reconstruction times feasible for online deployment.
DISCUSSION
The proposed method of sensitivity estimation and unfolding regularisation is flexible and robust. It is made available to the community in open-source as a library of functions within the vendor-agnostic Gadgetron image reconstruction framework.
Oliver Josephs, B. Dymerska, Nadine N. Graedel et al.· MAGMA· 3 citations
Magnetoencephalography (MEG) offers non-invasive neuroimaging with high temporal and spatial precision - but its adoption is hampered by the prohibitive cost and infrastructure burden of a magnetically shielded room. We have overcome that burden and present a lightweight, low-cost, multichannel magnetoencephalography system that can image brain activity without needing a magnetically shielded room. The multichannel nature of the system facilitates not just detection but also localization of brain signals that are over 300 million times smaller than environmental interference, without requiring passive shielding. Our system weighs less than 75kg, more than 100 times lighter than a typical shielded room. This is made possible through low-cost active shielding and software-based spatial filtering. We also show that the signal to noise ratio of our in-vivo recordings is comparable to what can be obtained from a conventional cryogenically-cooled MEG system sited within a shielded room. This demonstration is a crucial step towards democratizing magnetoencephalography and making it a globally accessible neuroimaging technology for healthcare and discovery research.
Yulia Bezsudnova, N. Alexander, S. Mellor et al.· bioRxiv· 0 citations
