NeuroImage
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The mechanisms underlying the progressive course of multiple sclerosis (MS) are not fully understood yet. Since diffusion tensor (DT) MRI can provide quantitative estimates of both MRI-visible and MRI-occult brain damage related to MS, the present study investigated the value of DT MRI-derived measures for the assessment of the short-term accumulation of white and gray matter (GM) pathology in patients with primary progressive (PP) and secondary progressive (SP) MS. Fifty-four patients with PPMS and 22 with SPMS were studied at baseline and after a mean follow-up of 15 months. ⋯ Over a 1-year period of follow-up, DT MRI can detect tissue changes beyond the resolution of conventional MRI in the NAGM of patients with progressive MS. The accumulation of DT MRI-detectable gray matter damage does not seem to merely depend upon the concomitant increase of T2-visible lesion load and the reduction of brain volume. These observations suggest that progressive NAGM damage might yet be an additional factor leading to the accumulation of disability in progressive MS.
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Clinical Trial
Single-shot compensation of image distortions and BOLD contrast optimization using multi-echo EPI for real-time fMRI.
Functional magnetic resonance imaging (fMRI) is most commonly based on echo-planar imaging (EPI). With higher field strengths, gradient performance, and computational power, real-time fMRI has become feasible; that is, brain activation can be monitored during the ongoing scan. However, EPI suffers from geometric distortions due to inhomogeneities of the magnetic field, especially close to air-tissue interfaces. ⋯ We present the theory, implementation, and applications of this single-shot distortion correction. Significant reduction in geometric distortion is shown both for phantom images and human fMRI data. Moreover, sensitivity to the blood oxygen level-dependent (BOLD) effect is increased by weighted summation of the undistorted images.
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Clinical Trial
Combined MEG/EEG analysis of the interictal spike complex in mesial temporal lobe epilepsy.
We studied the functional organization of the interictal spike complex in 30 patients with mesial temporal lobe epilepsy (MTLE) using combined magnetoencephalography (MEG)/electroencephalography (EEG) recordings. Spikes could be recorded in 14 patients (47%) during the 2- to 3-h MEG/EEG recording session. The MEG and EEG spikes were subjected to separate dipole analyses; the MEG spike dipole localizations were superimposed on MRI scans. ⋯ Whereas all five patients with AMV dipoles became completely seizure-free postoperatively (Class Ia), two out of four patients with AMH dipoles experienced persistent auras (Class Ib). This difference, however, was not statistically significant. We therefore conclude that combined MEG/EEG dipole modeling can identify subcompartments of the temporal lobe involved in epileptic activity and may be helpful to differentiate between subtypes of mesial temporal lobe epilepsy noninvasively.
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Comparative Study
Spatial sensitivity and temporal response of spin echo and gradient echo bold contrast at 3 T using peak hemodynamic activation time.
Recent theoretical and experimental work has suggested that spin echo (SE) functional MRI (fMRI) has improved localization of neural activity compared to gradient echo (GE) fMRI at high field strengths, albeit with a decrease in blood oxygenation level-dependent (BOLD) contrast. The present study investigated spatial and temporal variations in GE and SE fMRI at 3 T in response to a brief visual stimulus. ⋯ Because BOLD changes in response to increased neuronal activity occur earlier in the microvasculature and then later propagate into the venous compartment, these results provide further evidence that SE-based BOLD contrast provides superior localization to the site of activation at 3 T. Spatial overlay of SE and GE PHAT maps onto structural images reveal markedly different spatial profiles and further support the interpretation that shorter peak times correlate to improved spatial sensitivity.
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We measured, with whole-scalp magnetoencephalography, evoked fields from 10 healthy subjects to 1-ms thulium-laser stimuli that selectively activated nociceptive nerve fibers. The stimuli were delivered to the dorsum of the subject's left hand. The earliest cortical responses peaked at 165 +/- 7 ms, agreeing with the conduction velocity of Adelta-fibers. ⋯ Additional activations to both types of stimuli were detected in the cingulate cortex (three subjects) and in the bilateral insular cortex (two subjects). These results implicate that the nociceptive inputs mediated by the Adelta- and C-fibers are processed in a common cortical network in different time windows. Reliable temporospatial characterization of cortical responses to first and second pain offers a unique tool for basic and clinical neuroscience to study the two distinctive pain fiber systems at cortical level.