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.
We implemented prospective motion-correction (PMC) for line-scanning fMRI. In line-scanning, online motion correction is needed since 1-dimensional data do not allow motion detection in every dimension and the limited coverage makes this approach sensitive to spin-history artifacts or scanning outside the area of interest, in the presence of motion. We compared three versions of PMC and three ways of managing the T1-driven return to equilibrium (T1-transient) introduced by the navigators, in the functional data analysis. We opted for a water-excitation navigator as the best alternative, and showed that the T1-transient can be successfully overcome in the functional analysis.
Large scale efforts are being employed to link Major Depressive Disorder (MDD) to cortical alterations in gray and white matter, though often, limited resolution prevents conclusions regarding the source. Here we used quantitative 7T MRI to explore the myeloarchitecture of the cortex in people suffering from MDD in order to unravel potential mechanisms underlying the psychopathology of MDD. We find altered T1-profiles in the rostral ACC, lateral PFC and OFC in MDD compared to healthy controls, indicating changes in cortical myeloarchitecture. Overall, cortical T1 values were higher in MDD, suggesting lower cortical myelination.
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