NeuroImage
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Previous studies have established regional gray matter (GM) volume loss in multiple sclerosis (MS) but the relationship between development of white matter (WM) lesions and changes of regional GM volumes is unclear. The present study addresses this issue by means of voxel-based morphometry (VBM). T1-weighted three-dimensional magnetic resonance imaging (MRI) data from MS patients followed up for 12 months were analyzed using VBM. ⋯ Within the RRMS group, those patients with increasing T2 and T1 lesion burden (n=45) showed additional GM volume loss during follow-up in the frontal and parietal cortex, and precuneus. In contrast, patients lacking an increase in WM lesion burden (n=44) did not show any significant GM changes. The present study suggests that the progression of regional GM volume reductions is associated with WM lesion progression and occurs predominantly in fronto-temporal cortical areas.
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Cortical spreading depression (i.e. waves of cellular depolarization, CSD) causes the aura symptoms in classical migraine, and may contribute to delayed cellular damage after an ischemic or traumatic insult to the brain. In the latter cases, secondary neuronal injury may be worsened by some of the cerebral blood flow (CBF) changes that are associated with CSD. Here, we describe a new method for the simultaneous, live imaging of local cellular depolarization and CBF changes (i.e. two variables with well-defined and important biological significance), through a closed cranial window prepared in anesthetized rats. ⋯ In addition to the high temporal and spatial resolution of VS dye and LSC imaging, their novel combination allows to determine how CBF changes relate to a heterogeneous and evolving pattern of cellular depolarization, in any area of interest of the cortical region under study. This methodological development is especially pertinent and timely for investigations into the peri-lesion depolarizations that occur in models of focal brain injury, situations where their site of spontaneous elicitation and propagation pattern cannot be predicted. It should also help advance our knowledge in epilepsy, CBF pharmacology, and neurovascular coupling under normal and pathophysiological conditions.
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Comparative Study
Sensitivity of voxel-based morphometry analysis to choice of imaging protocol at 3 T.
The objective of this study was to determine which 3D T(1)-weighted acquisition protocol at 3 T is best suited to voxel-based morphometry (VBM), and to characterize the sensitivity of VBM to choice of acquisition. First, image quality of three commonly used protocols, FLASH, MP-RAGE and MDEFT, was evaluated in terms of SNR, CNR, image uniformity and point spread function. These image metrics were estimated from simulations, phantom imaging and human studies. ⋯ The required population sample size estimates to detect a difference in GM density in longitudinal VBM studies, i.e. based only on methodological variance, were lowest for MDEFT. Although MP-RAGE requires more subjects than FLASH, its higher cortical CNR improves the accuracy of the tissue classification results, particularly in the motor cortex. For cross-sectional VBM studies, the variance in morphology across the population is likely to be the primary source of variability in the power analysis.
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Abnormalities in the brain generally manifest on MRI as changes in shape (morphometry) or changes in the nature of the tissue (signal intensity). Voxel Based Morphometry (VBM) is a whole brain quantitative way of assessing morphometric changes. Voxel Based Relaxometry (VBR) directly assesses signal intensity changes in quantitative maps of T2 relaxation time, but this requires specialised multiple-echo acquisition sequences that are not usually available at clinical sites. ⋯ This opens the door to the use of a voxel-based analysis approach on the vast amount of T2-weighted image data that has been and is being acquired on MRI scanners. When a quantitative modality is not available, VBIS can be an effective way to quantify differences between groups. We expect the method could also assist quantitative analysis of other qualitative modalities such as T1-weighted MRI, SPECT and CT.
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Low-frequency fluctuations in fMRI signal have been used to map several consistent resting state networks in the brain. Using the posterior cingulate cortex as a seed region, functional connectivity analyses have found not only positive correlations in the default mode network but negative correlations in another resting state network related to attentional processes. The interpretation is that the human brain is intrinsically organized into dynamic, anti-correlated functional networks. ⋯ A combination breath holding and visual task demonstrates that the relative phase of global and local signals can affect connectivity measures and that, experimentally, global signal regression leads to bell-shaped correlation value distributions, centred on zero. Finally, analyses of negatively correlated networks in resting state data show that global signal regression is most likely the cause of anti-correlations. These results call into question the interpretation of negatively correlated regions in the brain when using global signal regression as an initial processing step.