Journal of neuroimaging : official journal of the American Society of Neuroimaging
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Functional imaging is beginning to outline the brain's functional architecture and mechanisms of recovery from injury. I will review primarily the motor-function literature from normal populations, learning trials, stroke recovery, and rehabilitation with a neural network approach that may prove fruitful in further advancing our understanding of brain plasticity in response to focal lesions. A key consideration in this review will be how the development of distributed motor networks might constrain recovery as a function of the altered connectivity between damaged and nondamaged areas. It will be argued that this connectivity is central to both recovery from injury and response to treatment.
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In the last decade, the use of magnetic resonance imaging (MRI) has led to a reevaluation of the pathogenesis and the natural history of multiple sclerosis (MS). This has been driven to a significant degree by results of proton magnetic resonance spectroscopy (1H-MRS) studies. By providing evidence of early neurodegeneration (based on levels of N-acetylaspartate), results of 1H-MRS studies have led to a reconsideration of the role of axonal damage in MS. ⋯ However, despite the pathological specificity of 1H-MRS and the relatively large number of clinical 1H-MRS studies on patients with MS, measures provided by this MR technique are not used routinely for assessing and monitoring MS patients. This is due to technical difficulties and limitations that are at present not entirely solved. We will review here the most relevant results in MS studies that have used 1H-MRS measures, the clinical importance of these results and the pending issues that need to be solved for a larger and more reliable use of 1H-MRS in clinical MS studies.
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During the past 10 years, conventional magnetic resonance imaging (cMRI) has become an established tool for the assessment of patients with multiple sclerosis (MS) and to monitor treatment trials. This is mainly due to the sensitivity and reproducibility of cMRI in the detection of MS-related damage. ⋯ Despite the fact that the role of cMRI in MS has been profoundly obviated by the advent of modern and quantitative MR techniques, several issues are still unresolved. Technical development in acquisition and postprocessing, as well as the introduction of high-field magnets in the clinical arena, are likely to increase our understanding of disease pathobiology, mainly through an increased ability to quantify the extent of gray matter damage.
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Merrill P Spencer and John M Reid applied the Hagen-Poiseuille law, continuity principle, and cerebrovascular resistance to describe a theoretical model of the relationship between the flow velocity, flow volume, and decreasing size of the residual vessel lumen. The model was plotted in a graph that became widely known as the Spencer's curve. Although derived for a smooth and axis-symmetric arterial stenosis of a short length in a segment with no bifurcations being perfused at stable arterial pressures and viscosity, this model represents a milestone in understanding cerebral hemodynamics with long-lasting practical and research implications. This review summarizes several hemodynamic principles that determine velocity and flow volume changes, explains how the model aids interpretation of cerebrovascular ultrasound studies, and describes its impact on clinical practice and research.
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Review Case Reports
Evidence of acute ischemic tissue change in transient global amnesia in magnetic resonance imaging: case report and literature review.
Transient global amnesia is a benign syndrome of sudden-onset alteration of behavior with temporary dysfunction of anterograde and recent retrograde memory. Its neural substrates remain uncertain. ⋯ The authors report a case of a 62-year-old man with a transient attack of memory disturbance, suggestive of transient global amnesia, in which magnetic resonance imaging performed 48 hours after onset showed left mesial temporal lobe signal changes on diffusion-weighted imaging and fluid-attenuated inversion recovery images. The findings and a literature review lend further support to the ischemic pathogenesis of transient global amnesia as a possible etiology, and underscore the role of diffusion-weighted imaging in the diagnosis of this condition.