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Biomedical subjects

S Crozier

Publications and source records attributed to S Crozier.

At least 55 records · Page 3Linked to original sources
PubMed1998

Lateralization of speech and auditory temporal processing.

To investigate the role of temporal processing in language lateralization, we monitored asymmetry of cerebral activation in human volunteers using positron emission tomography (PET). Subjects were scanned during passive auditory stimulation with nonverbal sounds containing rapid (40 msec) or extended (200 msec) frequency transitions. Bilateral symmetric activation was observed in the auditory cortex for slow frequency transitions. In contrast, left-biased asymmetry was observed in response to rapid frequency transitions due to reduced response of the right auditory cortex. These results provide direct evidence that auditory processing of rapid acoustic transitions is lateralized in the human brain. Such functional asymmetry in temporal processing is likely to contribute to language lateralization from the lowest levels of cortical processing.

Acoustic Stimulation↗
PubMed1997

Sample-Induced RF Perturbations in High-Field, High-Resolution NMR Spectroscopy

Conducting dielectric samples are often used in high-resolution experiments at high field. It is shown that significant amplitude and phase distortions of the RF magnetic field may result from perturbations caused by such samples. Theoretical analyses demonstrate the spatial variation of the RF field amplitude and phase across the sample, and comparisons of the effect are made for a variety of sample properties and operating field strengths. Although the effect is highly nonlinear, it tends to increase with increasing field strength, permittivity, conductivity, and sample size. There are cases, however, in which increasing the conductivity of the sample improves the homogeneity of the amplitude of the RF field across the sample at the expense of distorted RF phase. It is important that the perturbation effects be calculated for the experimental conditions used, as they have the potential to reduce the signal-to-noise ratio of NMR experiments and may increase the generation of spurious coherences. The effect of RF-coil geometry on the coherences is also modeled, with the use of homogeneous resonators such as the birdcage design being preferred. Recommendations are made concerning methods of reducing sample-induced perturbations. Experimental high-field imaging and high-resolution studies demonstrate the effect.

Journal Article↗
PubMed1997

Regional proton nuclear magnetic resonance spectroscopy differentiates cortex and medulla in the isolated perfused rat kidney.

Volume-localized proton nuclear magnetic resonance spectroscopy was used as an assay of regional biochemistry in the isolated perfused rat kidney. This model eliminated artifacts caused by respiratory and cardiac motion experienced in vivo. Immersion of the kidney under its venous effluent reduced the susceptibility artifacts evoked by tissue-air interfaces. The rapid acquisition with relaxation enhancement imaging sequence was used for scout imaging. This gave excellent spatial resolution of the cortex, outer medulla, and inner medulla. Spectra were then acquired in 10 minutes using the volume-selective multipulse spectroscopy sequence from voxels with a volume of approximately 24 microL located within the cortical or medullary regions. Spectral peaks were assigned by the addition of known compounds to the perfusion medium and by comparison with spectra of protein-free extracts of cortex and medulla. The medullary region spectra were characterized by signals from the osmolytes betaine, glycerophosphorylcholine, and inositol. The spectra from the cortex were more complex and contained lesser contributions from osmolytes.

Animals↗
PubMed1997

Direct visualisation of B1 inhomogeneity by flip angle dependency.

Inhomogeneities in the spatial distribution of the excitatory Radio Frequency (RF) field, are still a dominant source of artifacts and loss of signal to noise ratio in MR imaging experiments. A number of strategies have been proposed to quantify this distribution. However, in this technical note we present a relatively simple MR imaging procedure which can be used to visualise RF inhomogeneities directly either by means of the magnitude or the phase of an image. To visualise the RF field distribution in both the inner and outer volumes of the coil, we have performed experiments in which the entire coil is submerged in a non-conducting fluid. To the best of our knowledge this strategy has not been used previously in order to evaluate coil performance. Finally, we demonstrate that the method is sensitive enough to reveal the effects of the sample properties on the effective RF wavelength of the transmitted field.

Artifacts↗
PubMed1997

Religiosity and sphere-specific just world beliefs in 16- to 18-year-olds.

One hundred forty-three (31 female and 112 male) English school pupils, 16 to 18 years old, completed the Francis Scale of Attitudes towards Christianity (FSAC; Francis & Stubbs, 1987), the Global Belief in a Just World Scale (GBJWS; Lipkus, 1991), and the Multidimensional Belief in a Just World Scale (MBJWS; Furnham & Procter, 1992). The MBJWS yields three subscale scores: Sociopolitical Just World Beliefs (SJW), Interpersonal Just World Beliefs (IJW), and Personal Just World Beliefs (PJW). Scores on the FSAC were not associated with scores on the GBJWS, the SJW, or the IJW, but they were positively associated, albeit weakly, with scores on the PJW.

Adolescent↗
PubMed1996

[Traumatic spinal complications of cervical arthrosis].

OBJECTIVES: Cervical spondylotic myelopathy is usually a chronic and progressive disease. In a few cases, however, dramatic tetraplegia sometimes occurs after even minor injury. METHODS: We report seven patients (6 males, 1 female, aged from 41 to 63), who suffered from acute myelopathy after an injury. RESULTS: In 5 cases, the injury revealed the cervical spondylotic myelopathy. A hyperextension of the cervical spine was found in 5 cases. The injury was severe in only one case, but there was no bony abnormalities, except arthrosis. The most common cause was a fall. In contrast, severe tetraplegia was found in 4 cases. Spontaneous, but incomplete, recuperation occurred in 4 patients. In all 7 cases, CT scan and MRI showed congenital cervical stenosis associated with cervical spondylosis. The level of disco-osteophytic changes was mainly in C4, C5, C6. On T2-weighted spin-echo image, an increased signal intensity was present in the cord of 3 patients, but was not correlated with the severity of the symptoms, nor with improvement. Surgical treatment was performed in 6 cases: 3 laminectomies, 3 anterior or antero-lateral approaches. Improvement after operative decompression was observed in all but one case, even when the motor or sensory deficit persists for more than one year. Motricity of the inferior limbs improved better than the other deficits, perhaps because of the location of non-reversible lesions in the spinal gray matter. CONCLUSION: The acute medullary syndrome of cervical spondylotic myelopathy is serious and can cause major handicaps. This complication justifies a preventive surgical attitude when medullar signs are moderate, and cervical imagery shows a spondylotic compression of the cord with congenital stenosis.

Accidents, Home↗
PubMed1996

[Cerebral thrombotic complications, arterial and venous, disclosing inflammatory bowel disease].

A 40 year old woman presented successively an arterial and a venous cerebral thrombosis, revealing an inflammatory bowel disease. Digestive manifestations were very poor until then. Stroke is a rare complication of inflammatory bowel disease, and is usually correlated with and active phase of the disease. The mechanism by which the thrombogenic process occurs is unclear. The possible prothrombotic role of hemostasis disorders and the role of an angiitic process are discussed.

Adult↗
PubMed1995

Image directed proton spectroscopy of gerbil brain at 7 tesla.

Image directed localized 1H NMR spectra were obtained at 7 T (300 MHz) from cubic volumes of less than 40 microL in the gerbil brain. Signals from cerebral metabolites commonly detected in other rodent species were easily assigned, and high resolution spectroscopy (360 MHz) of aqueous brain extracts assisted the tentative identification of partially overlapping resonances from lower concentration compounds like alanine, lysine, gamma-aminobutyrate, valine, leucine and isoleucine. Weak coupling at 7 T was manifest in the resolution of signals from the gamma-CH2 groups of glutamine and glutamate. Down-field of water, signals assigned to purine nucleotides were conspicuous in the extract spectra, but localized spectra acquired routinely in vivo, using selective excitation and gradient crushing (SUBMERGE) for water suppression, exhibited little or no signal from purines. When localized in vivo spectra were acquired without water suppression, however, or using a low power binomial excitation sequence rather than SUBMERGE, a broad signal appeared at the resonant frequency of purine aromatic protons. NMR experiments on the nucleotide adenosine 5'-monophosphate (AMP) in 90% glycerol/10% D2O solution demonstrated that pre-irradiation of the water signal even for less than 100 ms attenuated the nucleotide signal appreciably. This implies that the soft pulses required for selective excitation of water in sequences such as SUBMERGE induce spin-diffusion which eliminates or diminishes the signal from nucleotides in vivo.

Acetates↗
PubMed1995

The design of biplanar, shielded, minimum energy, or minimum power pulsed B0 coils.

By extending the formalism previously developed for the design of unshielded, biplanar gradient coils, shielded biplanar B0 coils optimized for homogeneity and either minimum energy or minimum power may be designed. We present results from an integrated approach to shielded biplanar coil design, the results of which are also applicable to gradient coils, enabling the design of shielded coils with a concomitant decrease in total inductance of the coil. Length constraints are also included in the integrated minimization procedure. Results from a preliminary design indicate that high-homogeneity, low-impedance, well-shielded coils result from this design approach.

Electronics↗
PubMed1995

A design methodology for short, whole-body, shielded gradient coils for MRI.

A series of designs is presented for restricted length, whole-body, shielded gradient coils. By using the real space optimization technique, simulated annealing (SA), it is possible to produce viable gradient sets with a length-to-diameter ratio (LDR) of just 1.0. Radially remote return paths for the transverse coils aid in producing such short coils. While the linear regions of such coils cannot be as large as longer coils, they produce homogeneous linear regions suitable for use in whole-body imaging. The coil sets are well shielded even at such small LDRs.

Magnetic Resonance Imaging↗
PubMed1994

High resolution high field rodent cardiac imaging with flow enhancement suppression.

A method that incorporates cardiorespiratory-gated 2DFT spin-echo imaging with blood flow enhancement suppression is described which enables high resolution microimaging of the rodent heart. This methodology was applied to obtain in vivo cardiac mouse and rat images with in-plane resolutions of 100-200 microns using high field vertical bore magnet systems. Suppression of intraventricular blood flow enhancement was achieved using a combined spin-echo/gradient-refocussed sequence to dephase magnetization from flowing spins prior to imaging.

Animals↗