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S Crozier

Publications and source records attributed to S Crozier.

At least 73 records · Page 4Linked to original sources
PubMed1994

Practical aspects of shielded gradient-coil design for localised in vivo NMR spectroscopy and small-scale imaging.

For a number of NMR applications the availability of screened gradients is crucial to minimize the effect of eddy currents on the NMR signal. In this paper we review two types of shielded gradient design: the target field and minimum inductance methods. The two designs are compared and construction details are presented. A novel coil design constructed with a double-sided primary and a single layered screen is outlined. Experimental results for both target field and minimum inductance coils are presented and compared.

Magnetic Resonance Spectroscopy↗
PubMed1992

Measurement of the T2 relaxation time of ethanol and cerebral metabolites, in vivo.

The SPACE volume selection technique was combined with a spin-echo sequence to measure the transverse relaxation time of the resonances of ethanol and cerebral metabolites in the dog brain, in vivo. The method was extended to measure brain metabolite T2 values in the rat using 1H NMR microspectroscopy. The T2 decays for the resonances of the metabolites N-acetylaspartate, creatine/phosphocreatine, and choline/phosphorylcholine were found to be biexponential with long T2 components of 490, 260, and 350 ms for the dog and 490, 220, and 355 ms for the rat brain, respectively. The existence of a second T2 component may originate from J-coupled nonresolved metabolite resonances. The relaxation decay for the ethanol triplet could be fitted to a single exponential giving a T2 relaxation time of 335 ms. However, given the large errors in the measurement of ethanol peak intensities at short echo times because of overlapping lipid signal and the effects of J-modulation, a biexponential decay with a long T2 component of 335 ms cannot be ruled out. Ambiguities regarding the reported partial detection of the 1H NMR signal of ethanol in the brain are discussed.

Animals↗
PubMed1990

High-field localized in vivo proton spectroscopy on micro volumes.

A water-suppressed volume-selected in vivo 1H spectrum of 0.2 ml of a rat brain has been obtained at 200 MHz using the SPACE localization method. Good signal-to-noise and spectral resolution were obtained by averaging 256 acquisitions. The spectrum shows little T2 weighting effect.

Animals↗
PubMed1990

Application of volume-selected, two-dimensional multiple-quantum editing in vivo to observe cerebral metabolites.

The volume selection technique SPACE has been combined with a two-dimensional multiple-quantum editing sequence to uniquely detect certain J-coupled cerebral metabolites. In vivo results demonstrating edited glutamate/glutamine and lactate from 0.4 ml of a rat's brain at 4.7 T are presented. The sequence was optimized to balance multiple-quantum generation and signal loss due to T2 relaxation. Without due regard to T2 relaxation little signal is observed.

Animals↗
PubMed1990

Signal-to-noise ratio improvements in in vivo high resolution micro-volume selected spectroscopy.

A system capable of in vivo volume selected 1H NMR spectroscopy of voxels as small as 0.2 cm3 is described. Signal-to-noise ratio improvements with probe design and a novel signal steering device are detailed. A high-resolution, image-directed proton spectrum from 0.2 cm3 of a rat's brain at 200 MHz obtained using the SUBMERGE/SPACE pulse sequence is presented. Single-scan voxel shimming was implemented to improve spectral resolution.

Animals↗
PubMed1989

In vivo high-resolution volume-selected proton spectroscopy and T1 measurements in the dog brain.

Successful in vivo NMR spectroscopy requires a combination of techniques to address the problems of volume selection, water suppression, and resolution. All this needs to be done in the very heterogeneous environment found in living organisms. Previously published techniques are used to obtain 1H spectra from a dog brain, observing metabolites with concentrations below 1 mM. Measurements of spin-lattice relaxation times (T1) are also presented. The 1H relaxation times are long (T1 greater than 1.0 s) yielding information about the fluidity of the molecular environment. Comments are made concerning the achievable linewidth in vivo and the deficiencies that phase-encoding spectroscopic methods may have in obtaining high-resolution 1H spectra.

Animals↗
PubMedDate not supplied

Correlation between high-field T2-weighted MR imaging and histology of ischemic lesions in gerbil brain.

Global forebrain ischemia in the Mongolian gerbil is a common animal model for use in stroke research. We produced lesions of graded severity in gerbil brains (after prescreening by MR imaging) by performing 6-minute bilateral carotid artery occlusions while monitoring pericranial temperature with a temporalis muscle thermocouple probe and maintaining the temperature at 32 degrees C, 36 degrees C, or 40 degrees C. Lesion severity was scored 4 days after occlusion from findings on spin-echo images acquired at 7 T and from histologic scores. Statistically significant correlation was observed between the MR imaging score and brain temperature and between the MR imaging score and the area of the CA region of the hippocampus measured by histology. In addition, because prescreening with MR imaging revealed abnormalities in the hippocampus of some of the animals, and these animals were rejected from the study, the statistical significance of the result could be strengthened.

Animals↗
PubMedDate not supplied

Application of high field localised in vivo 1H MRS to study biochemical changes in the thiamin deficient rat brain under glucose load.

In vivo, volume-selected 1H NMR spectroscopy employing the SPACE technique was used to monitor biochemical changes in the thiamin deficient rat brain in response to glucose loading. The concentrations of brain N-acetylaspartate, glutamate/glutamine/gamma-aminobutyric acid, lactate and glucose differed significantly from those of control animals. The results are consistent with a metabolic block at the reaction catalyzed by the thiamin dependent enzyme alpha-keto glutarate dehydrogenase soon after the onset of neurological symptoms of thiamin deficiency, and a further block at pyruvate dehydrogenase arising late in the course of thiamin deficiency.

Acidosis, Lactic↗
PubMedDate not supplied

In vivo localized 1H spectroscopy of the rat eye at 7 T: preliminary studies.

Preliminary in vivo proton spectroscopic studies of the posterior chamber of the rat eye have been undertaken at 7 T. The Spatial and Chemical shift encoded Excitation (SPACE) localization sequence was used to acquire signals from 10 microliter voxels and demonstrate the presence of metabolites associated with the vitreous humor, lens, retina, and the optic nerve. Localized T2 and T1 measurements of water in the vitreous humor indicate a relatively fluid environment. Susceptibility maps are used to demonstrate the difficulties of in vivo spectroscopic investigations in the anterior regions of the eye. Comments are made concerning the implications for spectral resolution in these regions.

Animals↗