Background and Purpose-Recovery from hemiparesis due to corticospinal tract infarction is well documented, but the mechanism of recovery is unknown. Functional MRI (fMRI) provides a means of identifying focal brain activity related to movement of a paretic hand. Although prior studies have suggested that supplementary motor regions in the ipsilesional and contralesional hemisphere play a role in recovery, little is known about the time course of cortical activation in these regions as recovery proceeds. Methods-Eight patients with first-ever corticospinal tract lacunes causing hemiparesis had serial fMRIs within the first few days after stroke and at 3 to 6 months. Six healthy subjects were used as controls. Statistically significant voxels during a finger-thumb opposition task were identified with an automated image processing program. An index of ipsilateral versus contralateral activity was used to compare relative contributions of the 2 hemispheres to motor function in the acute and chronic phases after stroke. Results-Controls showed expected activation in the contralateral sensorimotor cortex (SMC), premotor, and supplementary motor areas. Stroke patients differed from control patients in showing greater activation in the ipsilateral SMC, ipsilateral posterior parietal, and bilateral prefrontal regions. Compared with the nonparetic hand, the ratio of contralateral to ipsilateral SMC activity during movement of the paretic hand increased significantly over time as the paretic hand regained function. Conclusions-The evolution of activation in the SMC from early contralesional activity to late ipsilesional activity suggests that a dynamic bihemispheric reorganization of motor networks occurs during recovery from hemiparesis.

Positron emission tomography was used to measure local cerebral glucose utilization by the 1-[18F]fluoro-2-deoxy-D-glucose technique in 23 patients with cerebral gliomas. All 10 high-grade (III and IV) astrocytomas demonstrated a region of high activity with a glucose consumption of 7.4 +/- 3.5 (SD) mg/100 gm per minute. The 13 low-grade (I and II) gliomas had a glucose metabolic rate of 4.0 +/- 1.8 mg/100 gm per minute, with no distinctly visible hot spot. Thus, we found a correlation between rate of glycolysis and malignancy in primary cerebral tumors. Cerebral cortical glucose utilization was often depressed in areas adjacent to or neurally connected to the tumor site, and there was focal irregular delta wave EEG activity in these areas.

For patients with an eGFR lower than 15 mL/min, hemodialysis helped to prevent NSF. For patients with an eGFR lower than 30 mL/min who received a high dose of GBCA, acute renal failure, delayed hemodialysis after contrast agent injection, proinflammatory events, and hyperphosphatemia were associated with increased risk of NSF.

The hippocampal formation is composed of separate anatomical regions interconnected to form a circuit, and investigating abnormal hippocampal function is most revealing at the level of these regions. Until recently, regional analysis of the hippocampal formation could be performed only in animals or in human postmortem tissue. Here, we report a method using functional magnetic resonance imaging that evaluates the hippocampal regions in vivo, and we use this method to study elderly with normal memory, with isolated memory decline, and with probable Alzheimer's disease (AD). Although age‐related memory decline occurs commonly, the cause of this decline remains unknown, with disagreement as to whether this decline represents one or more etiologies. Analysis revealed two distinct patterns of regional dysfunction among elderly with isolated memory decline—one pattern similar to that found in elders with AD, involving all hippocampal regions, and a second pattern with dysfunction restricted to only one hippocampal region, the subiculum. These results offer direct evidence of hippocampal dysfunction associated with memory decline in the elderly, and implicate both predementia AD and non‐AD processes as possible underlying causes. Ann Neurol 1999;45:466–472

Memory function commonly declines in later life. Whether memory decline represents a disease process or whether it is part of normal aging remains unknown. Here we answer this question by assessing the function of multiple subregions that make up the hippocampal circuit across the human life span. A newly developed MRI approach--designed to detect functional changes in individual hippocampal subregions--was used to assess the hippocampal circuit in 70 subjects between 20 and 88 years of age. Using strict parametric criteria, analysis revealed that function in two hippocampal subregions--the subiculum and the dentate gyrus--decline normally with age. In contrast, function in the entorhinal cortex declines pathologically. Single-subject analysis revealed that hippocampal dysfunction, found in 60% of elders was selectively correlated with memory decline. These results show that memory decline is caused by different mechanisms and suggests how memory decline should be approached clinically.

The neural basis for perceptual grouping operations in the human visual system, including the processes which generate illusory contours, is fundamental to understanding human vision. We have employed functional magnetic resonance imaging to investigate these processes noninvasively. Images were acquired on a GE Signa 1.5T scanner equipped for echo planar imaging with an in-plane resolution of 1.5 x 1.5 mm and slice thicknesses of 3.0 or 5.0 mm. Visual stimuli included nonaligned inducers (pacmen) that created no perceptual contours, similar inducers at the corners of a Kanizsa square that created illusory contours, and a real square formed by continuous contours. Multiple contiguous axial slices were acquired during baseline, visual stimulation, and poststimulation periods. Activated regions were identified by a multistage statistical analysis of the activation. for each volume element sampled and were compared across conditions. Specific brain regions were activated in extrastriate cortex when the illusory contours were perceived but not during conditions when the illusory contours were absent. These unique regions were found primarily in the right hemisphere for all four subjects and demonstrate that specific brain regions are activated during the kind of perceptual grouping operations involved in illusory contour perception.Our goal is to identify areas of human cortex involved in the operation of perceptual grouping of local features into a global percept. We used functional magnetic resonance imaging (fMRI), a noninvasive neuroimaging technique which relies on local variations in blood supply and 02 concentration during neural activity (1-3), to investigate these processes. Neural activation within the cerebral cortex is believed to be associated with an increase in blood flow that is out of proportion to the 02 consumption, thus decreasing the capillary 02 extraction fraction and delivering more oxyhemoglobin to the local venous circulation (4-7). The resulting decrease in the local capillary and venous deoxyhemoglobin concentration results in an increase in the T2* weighted magnetic resonance signal due to the decreased paramagnetic effects of deoxyhemoglobin (8, 9). These local changes in blood chemistry can be observed without the use of exogenous contrast enhancing agents on clinical magnetic resonance scanners (3,(10)(11)(12), which has enabled fMRI localization of visual (10-16), motor (3,(17)(18)(19), auditory (20), speech (21), taste (22), and olfactory (23) processing in the human brain. Since fMRI is now established as a method for exploring the functional organization of the human brain (24), we applied this technique to investigate the global processes of perceptual grouping in vision.Borders between visual objects and their background are usually defined by changes in luminance or color. However, perceptual borders can be created by inducing elements distant from the perceived border, as in Kanizsa's triangle (25). The phenomena of perceived visual borders not associated with net lumi...

Circuits within the hippocampal formation are active during memory processing. Here we used functional magnetic resonance imaging (fMRI) to examine multiple sites across the long axis of the hippocampal formation while subjects performed different phases of an associative memory task, learning to associate faces with names. Viewing faces and hearing names in isolation resulted in separate hippocampal activation patterns. Pairing faces with names resulted a spatially redistributed activation pattern, rather than a simple summation of the activation patterns resulting from viewing faces and hearing names in isolation. Recalling names when cued with faces reactivated a pattern similar to that found during paired training. Finally, the activation patterns representing faces and names were found to be experience dependent, emerging with repeated exposure. Interpreted in the context of hippocampal anatomy and physiology, these findings reveal hippocampal circuit mechanisms that underlie memory encoding and retrieval.

Purpose:To determine radiation doses from coronary computed tomographic (CT) angiography performed by using a 320-detector row volume scanner and evaluate how the effective dose depends on scan mode and the calculation method used. Materials and Methods:Radiation doses from coronary CT angiography performed by using a volume scanner were determined by using metaloxide-semiconductor fi eld-effect transistor detectors positioned in an anthropomorphic phantom physically and radiographically simulating a male or female human. Organ and effective doses were determined for six scan modes, including both 64-row helical and 280-row volume scans. Effective doses were compared with estimates based on the method most commonly used in clinical literature: multiplying dose-length product (DLP) by a general conversion coeffi cient (0.017 or 0.014 mSv·mGy 2 1 ·cm 2 1 ), determined from Monte Carlo simulations of chest CT by using single-section scanners and previous tissue-weighting factors. Results:Effective dose was reduced by up to 91% with volume scanning relative to helical scanning, with similar image noise. Effective dose, determined by using International Commission on Radiological Protection publication 103 tissue-weighting factors, was 8.2 mSv, using volume scanning with exposure permitting a wide reconstruction window, 5.8 mSv with optimized exposure and 4.4 mSv for optimized 100-kVp scanning. Estimating effective dose with a chest conversion coeffi cient resulted in a dose as low as 1.8 mSv, substantially underestimating effective dose for both volume and helical coronary CT angiography. Conclusion:Volume scanning markedly decreases coronary CT angiography radiation doses compared with those at helical scanning. When conversion coeffi cients are used to estimate effective dose from DLP, they should be appropriate for the scanner and scan mode used and refl ect current tissue-weighting factors.q RSNA, 2010