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High B Value (high + b_value)

Distribution by Scientific Domains
Medical Sciences80%

Selected Abstracts

Predicting the Histopathological Grade of Cerebral Gliomas Using High b value MR DW Imaging at 3-Tesla

JOURNAL OF NEUROIMAGING, Issue 3 2008
Juan Alvarez-Linera MD
ABSTRACT BACKGROUND Our aim was to prospectively assess whether magnetic resonance (MR) diffusion-weighted (DW) imaging using high b values can predict better than b value of 1,000 s/mm2 the histopathological grade of cerebral gliomas. METHODS Fifty-four patients with histologically verified brain gliomas (35 high-grade and 19 low-grade gliomas) underwent MR DW imaging. Isotropic DW images and apparent diffusion coefficient (ADC) were obtained with b values of 1,000 and 3,000 s/mm2. Each tumor was evaluated as being hyperintense, iso-intense or hypointense to normal, contralateral-hemisphere white matter. RESULTS Most of the patients with high- and low-grade gliomas showed areas of increased signal intensity on their isotropic images, obtained with a b value of 1,000 s/mm2. However, with a b value of 3,000 s/mm2 the areas of increased signal intensity were seen in 97.1% of the high-grade gliomas, while 94.7% of the low-grade gliomas showed no area of increased signal intensity. The mean area under the ROC curve for ADC ratio, obtained with a b value of 3,000 s/mm2, was significantly higher than that obtained with 1,000 s/mm2 (.932 vs. .856, P= .04). CONCLUSION High b value DW MR might be useful as a complementary tool in preoperative assessment of the histopathological grading of cerebral gliomas. [source]

Highly diffusion-sensitized MRI of brain: Dissociation of gray and white matter

MAGNETIC RESONANCE IN MEDICINE, Issue 5 2001
Takashi Yoshiura
Abstract The brains of six healthy volunteers were scanned with a full tensor diffusion MRI technique to study the effect of a high b value on diffusion-weighted images (DWIs). The b values ranged from 500 to 5000 s/mm2. Isotropic DWIs, trace apparent diffusion coefficient (ADC) maps, and fractional anisotropy (FA) maps were created for each b value. As the b value increased, ADC decreased in both the gray and white matter. Furthermore, ADC of the white matter became lower than that of the gray matter, and, as a result, the white matter became brighter than the gray matter in the isotropic DWIs. Quantitative analysis showed that these changes were due to nonmonoexponential diffusion signal decay of the brain tissue, which was more prominent in white matter than in gray matter. There was no significant change in relation to the b value in the FA maps. High b value appears to have a dissociating effect on gray and white matter in DWIs. Magn Reson Med 45:734,740, 2001. © 2001 Wiley-Liss, Inc. [source]

Structural flexibility, an essential component of the allosteric activation in Escherichia coli glucosamine-6-phosphate deaminase

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2002
E. Rudiño-Piñera
A new crystallographic structure of the free active-site R conformer of the allosteric enzyme glucosamine-6-phosphate deaminase from Escherichia coli, coupled with previously reported structures of the T and R conformers, generates a detailed description of the heterotropic allosteric transition in which structural flexibility plays a central role. The T conformer's external zone [Horjales et al. (1999), Structure, 7, 527,536] presents higher B values than in the R conformers. The ligand-free enzyme (T conformer) undergoes an allosteric transition to the free active-site R conformer upon binding of the allosteric activator. This structure shows three alternate conformations of the mobile section of the active-site lid (residues 163,182), in comparison to the high B values for the unique conformation of the T conformer. One of these alternate R conformations corresponds to the active-site lid found when the substrate is bound. The disorder associated with the three alternate conformations can be related to the biological regulation of the Km of the enzyme for the reaction, which is metabolically required to maintain adequate concentrations of the activator, which holds the enzyme in its R state. Seven alternate conformations for the active-site lid and three for the C-terminus were refined for the T structure using isotropic B factors. Some of these conformers approach that of the R conformer in geometry. Furthermore, the direction of the atomic vibrations obtained with anisotropic B refinement supports the hypothesis of an oscillating rather than a tense T state. The concerted character of the allosteric transition is also analysed in view of the apparent dynamics of the conformers. [source]

Highly diffusion-sensitized MRI of brain: Dissociation of gray and white matter

MAGNETIC RESONANCE IN MEDICINE, Issue 5 2001
Takashi Yoshiura
Abstract The brains of six healthy volunteers were scanned with a full tensor diffusion MRI technique to study the effect of a high b value on diffusion-weighted images (DWIs). The b values ranged from 500 to 5000 s/mm2. Isotropic DWIs, trace apparent diffusion coefficient (ADC) maps, and fractional anisotropy (FA) maps were created for each b value. As the b value increased, ADC decreased in both the gray and white matter. Furthermore, ADC of the white matter became lower than that of the gray matter, and, as a result, the white matter became brighter than the gray matter in the isotropic DWIs. Quantitative analysis showed that these changes were due to nonmonoexponential diffusion signal decay of the brain tissue, which was more prominent in white matter than in gray matter. There was no significant change in relation to the b value in the FA maps. High b value appears to have a dissociating effect on gray and white matter in DWIs. Magn Reson Med 45:734,740, 2001. © 2001 Wiley-Liss, Inc. [source]

Predicting the Histopathological Grade of Cerebral Gliomas Using High b value MR DW Imaging at 3-Tesla

JOURNAL OF NEUROIMAGING, Issue 3 2008
Juan Alvarez-Linera MD
ABSTRACT BACKGROUND Our aim was to prospectively assess whether magnetic resonance (MR) diffusion-weighted (DW) imaging using high b values can predict better than b value of 1,000 s/mm2 the histopathological grade of cerebral gliomas. METHODS Fifty-four patients with histologically verified brain gliomas (35 high-grade and 19 low-grade gliomas) underwent MR DW imaging. Isotropic DW images and apparent diffusion coefficient (ADC) were obtained with b values of 1,000 and 3,000 s/mm2. Each tumor was evaluated as being hyperintense, iso-intense or hypointense to normal, contralateral-hemisphere white matter. RESULTS Most of the patients with high- and low-grade gliomas showed areas of increased signal intensity on their isotropic images, obtained with a b value of 1,000 s/mm2. However, with a b value of 3,000 s/mm2 the areas of increased signal intensity were seen in 97.1% of the high-grade gliomas, while 94.7% of the low-grade gliomas showed no area of increased signal intensity. The mean area under the ROC curve for ADC ratio, obtained with a b value of 3,000 s/mm2, was significantly higher than that obtained with 1,000 s/mm2 (.932 vs. .856, P= .04). CONCLUSION High b value DW MR might be useful as a complementary tool in preoperative assessment of the histopathological grading of cerebral gliomas. [source]