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G J Galloway

Publications and source records attributed to G J Galloway.

31 records · Page 2Linked to original sources
PubMed1987

A comparison of some gradient-encoded volume-selection techniques for in vivo NMR spectroscopy.

Four of the techniques proposed for in vivo volume-selected NMR spectroscopy have been compared using a simple phantom with a large background water signal which was outside the region of interest. The methods VSE, SPACE, SPARS, and DIGGER all use pulsed field gradients for spatial encoding and were tested with a symmetric and an asymmetric phantom. SPACE was used to obtain volume-selected 1H NMR spectra of a human leg, demonstrating excellent discrimination between bone marrow and muscle.

Humans↗
PubMed1987

On the calculation of magnetization slice profiles for NMR imaging and in vivo spectroscopy.

When developing new techniques for NMR imaging and in vivo spectroscopy it is a major advantage to be able to calculate the magnetization slice profiles, at any point during a pulse sequence in the presence of a field gradient. While this has frequently been done by treating the problem as a number of discrete resonances, it is sometimes necessary to consider the continuous nature of the magnetization profiles. This paper describes a method used to simulate the free-induction decay at any point during the NMR experiment.

Magnetic Resonance Spectroscopy↗
PubMed1987

The study of human organs by phosphorus-31 topical magnetic resonance spectroscopy.

The potential clinical use of topical magnetic resonance spectroscopy (volume selection by static magnetic field gradients) was tested in 50 studies in volunteers. Topical magnetic resonance spectroscopy (MRS) was shown to be a straightforward method for localising 31P spectra of brain and liver. However, the spherical shape and fixed position of the selected volume posed serious limitations to the study of heart and transplanted kidney by topical MRS. Phosphorus-31 spectra of approximately 30 cm-3 of brain or liver could be obtained in 8 min. Ratios of metabolite concentrations could be determined with a coefficient of variation ranging from 10% to 30%. The ratios of phosphocreatine/ATP and inorganic phosphate/ATP in brain were 1.8 and 0.3, respectively. The ratio of inorganic phosphate/ATP in liver was 0.9. Intracellular pH was 7.03 in brain and 7.24 in liver. The T1 relaxation times of phosphocreatine, inorganic phosphate and gamma-ATP in brain were 4.8 s, 2.5 s and 1.0 s, respectively.

Brain↗
PubMed1986

Are quenches dangerous?

There exists some uncertainty about the hazards which the quenching of a superconducting magnet would present to a subject undergoing an NMR examination. To investigate this problem, a 1.6-T whole-body magnet was quenched with an anesthetized pig lying in the bore. This paper reports our findings which, in the circumstances of this experiment, suggest that the risks are small.

Animals↗
PubMed1986

The utilization of two frequency-shifted sinc pulses for performing volume-selected in vivo NMR spectroscopy.

A new approach to volume-selected in vivo NMR spectroscopy uses two frequency-shifted sinc pulses, in conjunction with pulsed field gradients, to destroy the coherence of the unwanted signals. A hard pi/2 pulse can then be used to read the z magnetization in the region of interest. This method is independent of T2, provides complete volume selection in a single acquisition, and can be readily implemented on most high-field commercial imaging/spectroscopy systems.

Magnetic Resonance Spectroscopy↗
PubMed1986

Suxamethonium chloride and malignant hyperpyrexia.

Pure suxamethonium chloride does not produce in vitro contracture of skeletal muscle from swine which are susceptible to malignant hyperpyrexia (MH), but does induce MH in vivo. It is suggested that suxamethonium chloride induces MH because the fasciculations which it causes lead to an increase in the myoplasmic calcium concentration.

Animals↗
PubMed1986

Assessment of human liver metabolism by phosphorus-31 magnetic resonance spectroscopy.

Phosphorus 31 magnetic resonance (MR) spectroscopy was used for the study of liver metabolism in vivo in seven healthy subjects. Subjects were examined in a 1.6 T whole-body magnet using surface coils for data acquisition. The region of the liver from which MR signals were collected was selected by magnetic-field profiling. The concentration ratios of adenosine triphosphate (ATP), inorganic phosphate (Pi) and sugar phosphates contained in liver cells could be reproducibly assessed. Cytosolic pH and the free magnesium concentration were determined to be 7.18 and 300 microM, respectively. During intravenous fructose tolerance tests the hepatic concentrations of sugar phosphates, ATP and Pi altered markedly. During the first 5 min following bolus injection of 250 mg fructose/kg body weight the concentration of sugar phosphates increased sevenfold whereas Pi and ATP decreased by three- to fourfold. Metabolism of sugar phosphates was complete within 20 min and could be followed by 31P MR with a time resolution of 5 min. Thus, 31P MR spectroscopy yields insight into liver metabolism which has not been accessible so far using conventional non-invasive methods. In conjunction with intravenous fructose loading, 31P MR spectroscopy may provide a means for the functional assessment of the liver.

Adenosine Triphosphate↗
PubMedDate not supplied

A reproducible method for automated extraction of brain volumes from 3D human head MR images.

An automated method for extracting brain volumes from three commonly acquired three-dimensional (3D) MR images (proton density, T1 weighted, and T2-weighted) of the human head is described. The procedure is divided into four levels: preprocessing, segmentation, scalp removal, and postprocessing. A user-provided reference point is the sole operator-dependent input required. The method's parameters were first optimized and then fixed and applied to 30 repeat data sets from 15 normal older adult subjects to investigate its reproducibility. Percent differences between total brain volumes (TBVs) for the subjects' repeated data sets ranged from .5% to 2.2%. We conclude that the method is both robust and reproducible and has the potential for wide application.

Aged↗
PubMedDate not supplied

The effect of the calcium ion antagonist 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate on malignant hyperpyrexia-susceptible porcine skeletal muscle.

In malignant hyperpyrexia susceptible (MHS) porcine skeletal muscle, a low concentration (100 mumol/l) of the calcium ion antagonist 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate (TMB-8) inhibited KCl-induced contractures, but potentiated contractures induced by halothane, caffeine and succinylcholine. Higher concentrations of TMB-8 (333 mumol/l to 1 mmol/l) contracted MHS muscle, but had little effect on muscle tension in control preparations. Treatments which inhibit excitation-contraction coupling abolished TMB-8-induced hyper-reactivity in MHS muscle. TMB-8 (50 mumol/l and 1 mmol/l) did not alter 45Ca2+ levels in actively loaded microsomal preparations from MHS swine. These results suggest that in malignant hyperpyrexia the primary abnormality occurs proximal to the release of calcium from the sarcoplasmic reticulum, probably at the level of excitation-contraction coupling.

Animals↗