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Activation Studies (activation + studies)

Distribution by Scientific Domains

Medical Sciences	33%

Selected Abstracts

Perfusion MR imaging with pulsed arterial spin-labeling: Basic principles and applications in functional brain imaging

CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2002
Yihong Yang
Abstract Basic principles of the arterial spin-labeling perfusion MRI are described, with focus on a brain perfusion model with pulsed labeling. A multislice perfusion imaging sequence with adiabatic inversion and spiral scanning is illustrated as an example. The mechanism of the perfusion measurement, the quantification of cerebral blood flow, and the suppression of potential artifacts are discussed. Applications of the perfusion imaging in brain activation studies, including simultaneous detection of blood flow and blood oxygenation, are demonstrated. Important issues associated with the applications such as sensitivity, quantification, and temporal resolution are discussed. © 2002 Wiley Periodicals, Inc. Concepts Magn Reson 14: 347,357, 2002 [source]

Odor processing in multiple chemical sensitivity

HUMAN BRAIN MAPPING, Issue 3 2007
Lena Hillert
Abstract Multiple chemical sensitivity (MCS) is characterized by somatic distress upon exposure to odors. As in other idiopathic environmental intolerances, the mechanisms behind the reported hypersensitivity are unknown. Using the advantage of the well-defined trigger (odor), we investigated whether subjects with MCS could have an increased odor-signal response in the odor-processing neuronal circuits. Positron emission tomography (PET) activation studies with several different odorants were carried out in 12 MCS females and 12 female controls. Activation was defined as a significant increase in regional cerebral blood flow (rCBF) during smelling of the respective odorant compared to smelling of odorless air. The study also included online measurements of respiratory frequency and amplitude and heart rate variations by recording of R wave intervals (RR) on the surface electrocardiogram. The MCS subjects activated odor-processing brain regions less than controls, despite the reported, and physiologically indicated (decreased RR interval) distress. In parallel, they showed an odorant-related increase in activation of the anterior cingulate cortex and cuneus-precuneus. Notably, the baseline rCBF was normal. Thus, the abnormal patterns were observed only in response to odor signals. Subjects with MCS process odors differently from controls, however, without signs of neuronal sensitization. One possible explanation for the observed pattern of activation in MCS is a top-down regulation of odor-response via cingulate cortex. Hum. Brain Mapp, 2007. © 2006 Wiley-Liss, Inc. [source]

Reflections on the application of 13C-MRS to research on brain metabolism

NMR IN BIOMEDICINE, Issue 6-7 2003
Peter Morris
Abstract The power of 13C-MRS lies in its unique chemical specificity, enabling detection and quantification of metabolic intermediates which would not be so readily monitored using conventional radiochemical techniques. Examples from animal studies, by examination of tissue extracts from the whole brain, brain slices and cultured cells, include observation of intermediates such as citrate and triose phosphates which have yielded novel information on neuronal/glial relationships. The use of 13C-labelled acetate as a specific precursor for glial metabolism provided evidence in support of the view that some of the GABA produced in the brain is derived from glial glutamine. Such studies have also provided direct evidence on the contribution of anaplerotic pathways to intermediary metabolism. Analogous studies are now being performed on the human brain, where 13C-acetate is used to quantitate the overall contribution of glial cells to intermediary metabolism, and use of 13C-glucose enables direct calculation of rates of flux through the TCA (FTCA) and of the glutamate,glutamine cycle (FCYC), leading to the conclusion that the rate of glial recycling of glutamate accounts for some 50% of FTCA. The rate of 0.74,,mol,min,1,g,1 for FTCA is compatible with PET rates of CMRglc of 0.3,0.4,,mol,min,1,g,1 (since each glucose molecule yields two molecules of pyruvate entering the TCA). Our brain activation studies showed a 60% increase in FTCA, which is very similar to the increases in CBF and in CMRglc observed in PET activation studies. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Implantation damage recovery and carrier activation studies of Si-implanted Al0.18Ga0.82N by temperature dependent Hall-effect measurements

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007
Mee-Yi Ryu
Abstract N-type activation studies of Si-implanted Al0.18Ga0.82N have been made as a function of anneal temperature and ion dose to obtain maximum possible activation efficiency. Nearly 100 and 95% electrical activation efficiencies were obtained for Si-implanted Al0.18Ga0.82N with doses of 5x1014 and 1x1015 cm,2 and annealing at 1250 and 1200 oC for 25 min, respectively. The room temperature sheet resistivity decreases from 528 to 196 ,/square with increasing anneal temperature from 1150 to 1250 oC for a dose of 5x1014 cm,2. Both sheet carrier concentration (activation efficiency) and mobility increase with anneal temperature, indicating an improved implantation damage recovery with anneal temperature. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Fragmentation pathways of 2,3-dimethyl-2,3-dinitrobutane cations in the gas phase

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2009
Martin R. L. Paine
2,3-Dimethyl-2,3-dinitrobutane (DMNB) is an explosive taggant added to plastic explosives during manufacture making them more susceptible to vapour-phase detection systems. In this study, the formation and detection of gas-phase [M+H]+, [M+Li]+, [M+NH4]+ and [M+Na]+ adducts of DMNB was achieved using electrospray ionisation on a triple quadrupole mass spectrometer. The [M+H]+ ion abundance was found to have a strong dependence on ion source temperature, decreasing markedly at source temperatures above 50°C. In contrast, the [M+Na]+ ion demonstrated increasing ion abundance at source temperatures up to 105°C. The relative susceptibility of DMNB adduct ions toward dissociation was investigated by collision-induced dissociation. Probable structures of product ions and mechanisms for unimolecular dissociation have been inferred based on fragmentation patterns from tandem mass (MS/MS) spectra of source-formed ions of normal and isotopically labelled DMNB, and quantum chemical calculations. Both thermal and collisional activation studies suggest that the [M+Na]+ adduct ions are significantly more stable toward dissociation than their protonated analogues and, as a consequence, the former provide attractive targets for detection by contemporary rapid screening methods such as desorption electrospray ionisation mass spectrometry. Copyright © 2009 Commonwealth of Australia. Published by John Wiley & Sons, Ltd. [source]