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W M Brooks

Publications and source records attributed to W M Brooks.

At least 55 records · Page 3Linked 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

RAPID--a new method for fast imaging using a single slice of Z-magnetization.

A single slice of z-magnetization is used to generate high-speed images. The slice selection step is achieved using two sin-sinc pulses. This procedure eliminates the need for continual slice gradient reversal, a requirement for the FLASH technique. The RAPID imaging method has less inherent T1 and/or T2 dependence than current fast imaging methods and is more sensitive.

Humans↗
PubMed1987

Low-power NMR volume selection by slicing z magnetization.

A novel method for reducing the rf power requirements of selective pulses employed for z magnetization slice inversion in localized NMR spectroscopy is presented. Following slice preparation by the use of frequency-incremented sinc pulses, the slice gradient is reduced, which narrows the frequency width of the slice. This allows the use of relatively low-power selective inversion pulses, an important consideration for in vivo applications.

Bone Marrow↗
PubMed1986

Magnetic resonance imaging--first human images in Australia.

The use of magnetic resonance imaging, in the demonstration of internal human anatomy and in the diagnosis of disease, has the major advantages that the technique is noninvasive, does not require the use of ionizing radiation and that it can demonstrate neurological and cardiovascular lesions that cannot be diagnosed easily by other imaging methods. Magnetic resonance imaging is derived from the principle that certain atomic nuclei in a strong magnetic field will absorb pulses of radiofrequency energy; when the pulse is finished the nuclei will emit radiowaves at the same frequency. These radiowaves are received by specially designed aerials or coils and the information is collected by a computer which reconstructs an image of internal anatomy in a similar way to that of x-ray computed tomography (CT). By changing the strength of the magnetic fields and the frequency of the radiowave pulses, it is possible to examine different sections within the body. The first magnetic resonance images of humans were obtained in Australia in October 1985 on the research instrument of the Queensland Medical Magnetic Resonance Research Centre, which is based at the Mater Hospital in Brisbane, and is part of the University of Queensland's Department of Radiology.

Abdomen↗
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

In vivo determination of 31P spin relaxation times (T1, T2, T1 rho) in rat leg muscle. Use of an off-axis solenoid coil.

A probe using a solenoid coil tilted 45 degrees off-axis has been used to study the 31P NMR relaxation characteristics of the resonances arising from phosphorus metabolites in rats in vivo. T1, T1 rho and T2 values have been determined for phosphocreatine and ATP in leg muscle. The ratio of 31P T1(1700ms) to T2(12ms) for ATP was in excess of 200:1 compared with a ratio of 5:1 for 1H T1:T2. Of major significance was the observation that T2 values for phosphocreatine (230ms) were markedly longer than T2 values for ATP (12ms). Thus by use of appropriate delay times in spin echo sequences ATP signals can be nulled, and discrete 31P imaging of phosphocreatine in muscle may be possible provided the overall signal-to-noise is satisfactory.

Animals↗
PubMed1986

Relation between the phosphocreatine to ATP ratio determined by 31P nuclear magnetic resonance spectroscopy and left ventricular function in underperfused guinea-pig heart.

The relation between the PC/ATP ratio and left ventricular function was examined in the Langendorff-perfused guinea-pig heart over a range of perfusion flow rates. PC/ATP ratios were determined from the 31P-nuclear magnetic resonance spectra of hearts obtained at 80.98 MHz and ventricular function estimated by measuring pressure in the left ventricle. When flow rates were increased over the range 0.6 to 6.0 ml/min, the PC/ATP ratio increased from 0.64 +/- 0.05 at 0.6 ml/min to 1.82 +/- 0.12 at 3.8 ml/min with no further increase up to a flow rate of 6.0 ml/min. Developed pressure (DP) increased with the flow rate up to 6.0 ml/min but the end diastolic pressure (EDP) also increased. The DP/EDP ratio was found to correlate closely with the PC/ATP ratio over the range of flow rates examined. The PC/ATP ratio may be a practical index of myocardial function available to the clinician when the topical magnetic resonance technique is fully developed.

Adenosine Triphosphate↗
PubMed1986

Use of inversion spin transfer to monitor creatine kinase kinetics in rat skeletal muscle in vivo.

A simple multipulse sequence has been used to monitor creatine kinase kinetics in rat skeletal muscle in vivo. Using these procedures, the forward (ATP synthesis) and reverse fluxes (phosphocreatine synthesis) have been calculated to be 8.98 +/- 0.6 and 10.7 +/- 0.8 mumoles/g wet wt/s (n = 5) respectively. These results suggest that in resting skeletal muscle most of the gamma ATP observed in 31P NMR spectra is cytosolic and rapidly exchanging with phosphocreatine. The high flux rates reflect the high catalytic capacity of creatine kinase in skeletal muscle.

Adenosine Triphosphate↗
PubMed1985

In vitro metabolism of [2-13C]-ethanol by 1H NMR spectroscopy using 13C decoupling with the reverse dept polarization-transfer pulse sequence.

The metabolism of [2-13C]-ethanol by alcohol dehydrogenase purified from Drosophila melanogaster has been observed by proton nuclear magnetic resonance spectroscopy (NMR). The reverse-DEPT pulse sequence, with composite pulse 13C decoupling to simplify and increase the signal-to-noise of spectra, has been used to eliminate the strong water signal while still observing the proton signals of metabolites of interest. Using these techniques the rates of synthesis of acetaldehyde, its diol and acetate from [2-13C] ethanol by alcohol dehydrogenase were measured simultaneously.

Acetaldehyde↗
PubMed1985

Application of the reverse dept polarization-transfer pulse sequence to monitor in vitro and in vivo metabolism of 13C-ethanol by 1H-NMR spectroscopy.

Using the reverse 13C----1H DEPT polarization-transfer pulse sequence the metabolism of 13C ethanol in vitro and in vivo has been monitored by 1H-NMR spectroscopy. Using yeast alcohol dehydrogenase, acetaldehyde, the hydrated form of acetaldehyde and acetate were identified as metabolites of [2-13C]-ethanol. The ratio of hydrated to free acetaldehyde was dependent upon the protein concentration of the reaction mixture. Binding of acetaldehyde in an irreversible Schiffs base resulted in optimal enzyme activity. Hepatocytes from rats fasted for 20 h, metabolised [1-13C] and [2-13C]ethanol in a linear fashion, but no [13C]acetaldehyde was detected. Metabolic integrity of the hepatocytes was confirmed with [2-13C]acetate. The addition of disulfiram (50 micron) to hepatocyte suspensions which had been incubated with [1-13C]ethanol, resulted in the resynthesis of [13C]ethanol. The amount of [13C]ethanol resynthesized under these conditions represents intracellular acetaldehyde whose concentration was in the range of 400-800 mumol/g wet weight of hepatocytes when 50 mM ethanol had been originally incubated with the hepatocyte suspension. These studies show how NMR-polarization transfer pulse sequences can be used to monitor the metabolism of 13C-ethanol in vivo, and provide a unique tool to measure in vivo concentrations of acetaldehyde. The studies also suggest that cytoplasmic aldehyde dehydrogenase may play a major role in hepatic ethanol metabolism.

Acetaldehyde↗
PubMed1985

Determination of intracellular pH in the Langendorff-perfused guinea-pig heart by 31P nuclear magnetic resonance spectroscopy.

The 31P NMR spectrum of freshly prepared guinea-pig heart perfused in the Langendorff mode at 37 degrees C with medium containing either glucose or pyruvate as an energy source exhibited no inorganic phosphate peak making the determination of intracellular pH from the chemical shift of this peak impossible. By incorporating 2-deoxyglucose-6-phosphate into the heart to act as an alternative pH indicator, intracellular pH was determined to be 6.98 +/- 0.02 (mean +/- S.E.M. for eight animals). 2-Deoxyglucose was not taken up and phosphorylated by guinea-pig heart in the presence of glucose. Uptake and phosphorylation did proceed if glucose was omitted from the perfusion medium, but a large inorganic phosphate peak was present in the initial spectrum prior to 2-deoxyglucose addition. With pyruvate as sole energy source, an inorganic phosphate peak was absent initially and 2-deoxyglucose was taken up and phosphorylated. During a 12 min period of global ischaemia at 20 degrees C, when inorganic phosphate was visible together with 2-deoxyglucose-6-phosphate, a close correlation was found between the pH estimated from the chemical shift of inorganic phosphate and 2-deoxyglucose-6-phosphate over the pH range 6.3 to 6.9.

Animals↗
PubMed1984

In vivo 13C nuclear magnetic resonance spectroscopy using a solenoid transmit/receiver coil.

Topical nuclear magnetic resonance spectroscopy (NMR) using a solenoid transmit/receiver coil has been used to monitor the kinetics of intragastric utilization of [1-13C] glucose in mice in vivo. Using a double-tuned solenoid coil, signal to noise response was excellent and the natural abundance in vivo 13C spectra obtained with acquisition times of 10-15 minutes compares more than favourably with comparable studies using surface or saddle coils. This study clearly shows the potential of solenoid coils to monitor the kinetics of 13C-labelled metabolites in vivo.

Animals↗
PubMed1984

Potential hazards of NMR imaging. No evidence of the possible effects of static and changing magnetic fields on cardiac function of the rat and guinea pig.

Clinical proton NMR imaging uses magnetic field strengths in the range 0.1 to 0.5 T. In addition to the large static magnetic field, patients are exposed to magnetic field gradients during imaging and under extreme conditions, such as power failure or quenching, the field may collapse precipitously. A potential source of hazard to patients under these conditions is the induction of thoracic currents which may trigger ventricular fibrillation. In the present experiments, a 0.16 T resistive magnet with a time constant of 60 ms, powered by a programmable power supply, was used to examine any possible effects of static and changing magnetic field on the ECG and arterial blood pressure of anesthetized rats and guinea pigs. Animals were exposed to the following field conditions: static fields of 0.16 T; sine, triangular, and square wave modulated fields from 0.1 to 2 Hz; rapid field switches in excess of 2.0 T/s for 25 ms timed to occur at different stages of the cardiac cycle, including the vulnerable period during ventricular repolarization; and AC fields of 50 Hz. No change was observed in the blood pressure, heart rate, or ECG under any of the field conditions examined.

Animals↗
PubMed1983

31P nuclear magnetic resonance study of the recovery characteristics of high energy phosphate compounds and intracellular pH after global ischaemia in the perfused guinea-pig heart.

The recovery of high energy phosphate compounds in perfused guinea-pig heart at 20 degrees C after a 12 min period of global ischaemia was examined using 31P-NMR with a time resolution of 12 s. This time resolution was achieved by overlaying the data acquired from five successive ischaemic periods by arresting and restoring the flow of perfusion fluid to the heart in synchrony with the data acquisition sequence. The rate of creatine phosphate resynthesis after the ischaemic period proceeded 14 times faster than its rate of loss during the ischaemic period. ATP levels did not decrease during ischaemia and ADP was undetectable at any time. Estimates of intracellular pH from the chemical shift of the inorganic phosphate peak were impossible in normal guinea-pigs since the inorganic phosphate peak was not clearly defined. During the ischaemic period the inorganic phosphate peak increased in size and shifted upfield. On restoration of flow, the inorganic phosphate peak collapsed in a complex way following a different path to its formation during ischaemia.

Acid-Base Equilibrium↗