NeuroImage
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Two different methodologies for obtaining PRESS-localized magnetic resonance spectroscopic imaging (MRSI) data from the mesial and lateral temporal lobes were investigated. The study used short echo times (30 ms) and long repetition times (3000 ms) to minimize relaxation effects. Inhomogeneity and spectral distortions from the proximity of the temporal bones precluded the attainment of consistently good-quality data from both temporal lobes at once. ⋯ The previously observed lower anterior ratios of NAA to creatine plus choline (NAA/(Cr + Cho) may instead have been due to higher anterior choline. Large differences in metabolite concentrations were seen between posterior lateral temporal lobe (predominantly subcortical white matter) and the posterior mesial temporal lobe, most notably lower creatine, glutamate/glutamine, and myo-inositol, and higher NAA/(Cr + Cho) in the lateral than mesial temporal lobe. This pattern was similar to that previously seen for grey/white matter differences in the frontal, parietal and occipital regions.
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Seventeen clinically stabilized monohemispheric stroke patients were studied in order to investigate the chronic topographical modifications induced on primary sensory cortical hand areas by a monohemispheric stroke within the middle cerebral artery territory. Magnetoencephalographic (MEG) localization of the cortical areas activated following electrical separate stimulation of the median nerve, thumb, and little fingers was integrated with magnetic resonance imaging. Spatial localization of Equivalent Current Dipoles (ECDs) of the short-latency cortical responses generated in primary sensory cortices, "hand area" (distance between 1st and 5th digits ECDs), interhemispheric differences of such parameters, as well as of somatosensory-evoked fields waveshapes were investigated and compared with a control population. ⋯ Interhemispheric ECDs strength differences were larger than normal in 25% of cases after both types of lesions; the strength in the AH being enlarged after all cortical, and only 24% of subcortical strokes. In a significant percentage of monohemispheric strokes, excessive interhemispheric differences were found between AH and UH, suggesting that brain areas outside the normal boundaries and usually not reached by a dense sensory input from the opposite hand and fingers may act as somatosensory "hand" centers. Correlation analysis between clinical outcome and cortical reorganization in the AH suggests that this mechanism is linked with hand sensorimotor recovery.
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Polygon-mesh representations of the cortices of individual subjects are of anatomical interest, aid visualization of functional imaging data and provide important constraints for their statistical analysis. Due to noise and partial volume sampling, however, conventional segmentation methods rarely yield a voxel object whose outer boundary represents the folded cortical sheet without topological errors. These errors, called handles, have particularly deleterious effects when the polygon mesh constructed from the segmented voxel representation is inflated or flattened. ⋯ By applying the same method to the inverse object, an alternative set of solutions is determined, correcting the errors by addition instead of deletion of voxels. For each handle separately, the solution more consistent with the intensities of the original anatomical MR scan is chosen. The accuracy of the resulting polygon-mesh reconstructions has been validated by visual inspection, by quantitative comparison to an expert's manual corrections, and by crossvalidation between reconstructions from different scans of the same subject's cortex.
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Most of functional magnetic resonance imaging (fMRI) time series analysis is based on single voxel data evaluation using parametric statistical tests. The result of such an analysis is a statistical parametric map. Voxels with a high significance value in the parametric test are interpreted as activation regions stimulated by the experimental task. ⋯ Spectral parameters such as coherence measure and phase lead can be estimated. The resulting maps give detailed information on brain regions that belong to a network structure and also show the temporal behavior of the BOLD response function. This paper describes the method and presents a visual fMRI experiment as an example to demonstrate the results.