NeuroImage
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Quantitative assessment of the myelin content in white matter (WM) using MRI has become a useful tool for investigating myelin-related diseases, such as multiple sclerosis (MS). Myelin water fraction (MWF) maps can be estimated pixel-by-pixel by a determination of the T₂ or T₂* spectrum from signal decay measurements at each individual image pixel. However, detection of parameters from the measured decay curve, assuming a combination of smooth multi-exponential curves, results in a nonlinear and seriously ill-posed problem. ⋯ To determine optimal weighting factors, we define a spatially independent neighborhood for each pixel and a distance with respect to decay rates that effectively includes pixels with similar decay characteristics, and which therefore have similar relaxation parameters. We recover the MWF values by using optimally weighted decay curves. We use numerical simulations and in vitro and in vivo experimental brain data scanned with a multi-gradient-echo sequence to demonstrate the feasibility of our proposed algorithm and to highlight its advantages compared to the conventional method.
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Transcranial Direct Current Stimulation (tDCS) is a non-invasive, low-cost, well-tolerated technique producing lasting modulation of cortical excitability. Behavioral and therapeutic outcomes of tDCS are linked to the targeted brain regions, but there is little evidence that current reaches the brain as intended. We aimed to: (1) validate a computational model for estimating cortical electric fields in human transcranial stimulation, and (2) assess the magnitude and spread of cortical electric field with a novel High-Definition tDCS (HD-tDCS) scalp montage using a 4 × 1-Ring electrode configuration. ⋯ We provide direct evidence in humans that TES with a 4 × 1-Ring configuration can activate motor cortex and that current does not substantially spread outside the stimulation area. Computational models predict that both TES and tDCS waveforms using the 4 × 1-Ring configuration generate electric fields in cortex with comparable gross current distribution, and preferentially directed normal (inward) currents. The agreement of modeling and experimental data for both current delivery and focality support the use of the HD-tDCS 4 × 1-Ring montage for cortically targeted neuromodulation.
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Trigeminal neuralgia (TN) is supposedly caused by an ectatic blood vessel affecting the trigeminal nerve at the root entry zone of the brain stem. Recent evidence suggests an additional central component within trigeminal pain-processing in the pathophysiology of TN. Therefore, we aimed to identify specific brain regions possibly associated with the development or maintenance of TN using magnetic resonance imaging (MRI) voxel-based morphometry (VBM). ⋯ No GM increase was found comparing patient subgroups with each other and with healthy controls. The observed changes probably reflect the impact of multiple, daily attacks of trigeminal pain in these patients similar to what was previously described in other chronic pain conditions and may be interpreted as adaptation mechanism to chronic pain in regard to neuronal plasticity. The ACC, parahippocampus and temporal lobe volume reduction in parallel with disease duration may point to a pivotal role of these structures in chronic pain.
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Neuroimaging results are typically graphically rendered and color-coded, which influences the process of knowledge generation within neuroscience as well as the public perception of brain research. Analyzing these issues requires empirical information on the display practice in neuroimaging. ⋯ We demonstrate a variety of display styles despite a remarkable dominance of few image production sites and software systems, outline some tendencies of standardization, and identify shortcomings with respect to color scale explication in neuroimages. We discuss the importance of the finding for knowledge production in neuroimaging, and we make suggestions to improve the display practice in neuroimaging, especially on regimes of color coding.
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Changes in cerebral perfusion and CO2 cerebrovascular reactivity during and immediately after a sojourn at high altitude remain unclear but may be critical for acclimatization. The aim of the present study was to assess the effects of 6days at 4350m on cerebral perfusion and cerebrovascular reactivity (CVR) to CO2 by arterial spin labeling (ASL) magnetic resonance imaging at sea level and to compare it with transcranial Doppler (TCD) results at altitude. Eleven healthy male subjects, non-acclimatized to altitude, stayed for 6days at 4350m (Observatoire Vallot, massif du Mont-Blanc). ⋯ In conclusion, prolonged exposure to high altitude significantly increases blood flow during the altitude stay and within 6h after returning to sea level. Decreased CO2 CVR after prolonged altitude exposure was also observed using ASL. Changes in cerebral hemodynamics with altitude exposure probably involve other mechanisms than the vasodilatory effect of hypoxia only, since it persists under normoxia several hours following the descent.