Towards functional spin-echo BOLD line-scanning in humans at 7T

Abstract

Objective Neurons cluster into sub-millimeter spatial structures and neural activity occurs at millisecond resolutions; hence, ultimately, high spatial and high temporal resolutions are required for functional MRI. In this work, we implemented a spin-echo line-scanning (SELINE) sequence to use in high spatial and temporal resolution fMRI. Materials and methods A line is formed by simply rotating the spin-echo refocusing gradient to a plane perpendicular to the excited slice and by removing the phase-encoding gradient. This technique promises a combination of high spatial and temporal resolution (250 μm, 500 ms) and microvascular specificity of functional responses. We compared SELINE data to a corresponding gradient-echo version (GELINE). Results We demonstrate that SELINE showed much-improved line selection (i.e. a sharper line profile) compared to GELINE, albeit at the cost of a significant drop in functional sensitivity. Discussion This low functional sensitivity needs to be addressed before SELINE can be applied for neuroscientific purposes.

Scaling the mountains: what lies above 7 Tesla magnetic resonance?

“…Novel RF array designs include optimal combinations of loop-dipole building blocks, as well as dielectric resonators, with numerous studies demonstrating their added value at 7 T [32] and 10.5 T. This Special Issue highlights the merits of transmit RF arrays. Configurations using 2, 8, 16, or 32 transmit channels were successfully utilised for a spectrum of applications, ranging from functional brain mapping at 9.4 T with 1 mm spatial resolution [33] to high spatial and temporal resolution spin-echo line scanning that ensures microvascular specificity of functional responses [34], as well as high spatiotemporal resolution quantification of near-wall haemodynamic parameters in in vitro intracranial aneurysms [35], resolving wall shear stress patterns, and cardiac and body imaging in humans and large experimental models at 7 T [36] and 10.5 T [8].…”

“…Similar to the early mountaineers who relied on the help of the Sherpas, neuroscientists need ingenuity, endurance and faithful collaboration with the locals (MR physicists, mathematicians, data scientists, expert engineers and other related experts) to fully realise the potential of MRI above 7 T. This may include changing from 2D EPI to 3D EPI acquisitions to limit SAR, the development of dedicated head magnetic field gradients to achieve the necessary short readout times, or revisiting existing imaging principles to achieve high spatial and temporal resolution. One example is provided by Raimondo et al, who paved the way for spin-echo line scanning, which can achieve spatial and temporal resolutions of 0.25 mm and 200 ms, respectively as pointed out in [34] of this Special Issue. Alternatively, highly anisotropic FLASH acquisitions can provide spatial resolutions of 0.1 mm along one axis, to match the columnar or laminar structure of the cortex as demonstrated in [33] of this Special Issue.…”

A selection and targeting framework of cortical locations for line‐scanning fMRI

“…The line‐scanning functional acquisition used a modified multi‐echo 2D gradient‐echo sequence where the phase‐encoding gradients are removed and two OVS bands are used to suppress signals outside the line (Raimondo, Heij, et al, 2023 ; Raimondo, Knapen, et al, 2021 ). With this sequence, 94.3 ± 1.3% of undesired signal outside the region of interest is suppressed (Raimondo, Knapen, et al, 2021 , Raimondo, Priovoulos, et al, 2023 ).…”

“…The cortex of humans has a much more intricate folding architecture (Van Essen et al, 2019 ), complicating (automatic) planning procedures. In earlier work (Raimondo, Heij, et al, 2023 ; Raimondo, Knapen, et al, 2021 ; Raimondo, Priovoulos, et al, 2023 ), this was done by manually placing the line as perpendicular as possible to the cortical surface while maintaining a coronal slice orientation. As the procedure is based purely on anatomy, it remains unclear whether the functional task will activate the imaged area and how the signal is sampled across depth.…”

Identifying the distinct spectral dynamics of laminar-specific interhemispheric connectivity with bilateral line-scanning fMRI

“…Recently, both line-scanning BOLD and diffusion cortical mapping has been implemented to investigate layer-specific anatomical and evoked hemodynamic features in human brains. 46,[67][68][69][70] Also, a recent animal fMRI study coregistered the brain-wide rs-fMRI correlation pattern and 3D Allen mouse brain atlas, presenting axonal tracing-based layer-specific neuronal connections underlying the default mode network. 9,71 To date, no direct measurement of laminar fMRI signals has been performed on symmetric cortices of two hemispheres to differentiate circuit-specific regulatory sources with high spatiotemporal resolution.…”