Blum, MJ, Braun, M & Rosenfeld, D 1987, 'Fast magnetic resonance imaging using spiral trajectories.', Australas Phys Eng Sci Med, vol. 10, no. 2, pp. 79-87.
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Acquisition times in magnetic resonance imaging are typically in the order of minutes. These long acquisition times give rise to motion artefacts, preclude dynamic imaging and keep the patient throughput low. The authors investigate a fast imaging scheme which uses spiral trajectories in the spatial frequency domain. The entire domain can be sampled in a short time, requiring as few as one free induction decay (FID) acquisition. The scheme requires time varying gradients having the form of a ramped sinusoid. Several reconstruction methods are considered for forming the image from the spatial frequency domain data. The possibility of using multiple spirals to deal with the rapid decay of the FID signal is also examined in detail.
Blum, MJ, Braun, M, Rosenfeld, D, Dwyer III, SJ & Schneider, RH 1987, '<title>Fast Magnetic Resonance Imaging Using Spiral Trajectories</title>', SPIE Proceedings, vol. 767, pp. 40-46.
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Acquisition times in magnetic resonance imaging (MRI) are typically in the order of minutes. For an image of 256 × 256 pixels, the standard Fourier reconstruction technique used in most commercial imaging systems requires 256 separate free induction decay (FID) signals. While the FID signal itself is of relatively short duration, the successive FID signals are separated by long delays, of the order of seconds, to permit substantial relaxation of the signal before the next excitation. The resultant long acquisition times give rise to motion artefacts, preclude dynamic imaging and keep the patient throughput low. In this paper, we investigate a fast imaging scheme which uses spiral trajectories in the spatial frequency domain. The entire domain can be sampled in a short time, requiring as few as one FID acquisition. The scheme requires time varying gradients having the form of a ramped sinusoid. Several reconstruction methods are considered for forming the image from the spatial frequency domain data. The possibility of using multiple spirals to deal with the rapid decay of the FID signal is also examined in detail. © 1987 SPIE.
BRAUN, M & McCARTHY, AL 1987, 'Voxel Distortion in NMR Imaging with Non‐uniform Steady Fields', Australasian Radiology, vol. 31, no. 3, pp. 322-323.
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Braun, M & Rosenfeld, D 1987, 'Computer system architecture for NMR imaging.', Australas Phys Eng Sci Med, vol. 10, no. 2, pp. 64-71.
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NMR imaging makes extensive use of computers in data acquisition, image reconstruction, processing and display. Furthermore, in order to fully utilise the capability of the method, flexible control must be exercised over the radiofrequency and gradient pulse sequence. The requirements of operational flexibility and speed favour a distributed architecture with dedicated programmable devices taking on separate tasks under the overall control of a host computer. A fast, versatile pulse programmer is required to provide real-time control of a number of rapidly varying, experimental parameters. A state-memory-based, pulse programmer, having the architecture of a computer control unit, affords the optimum design for imaging applications. In image processing, array processors have a considerable speed advantage and will find increasing use in clinical imaging systems.
Ching, NH, Rosenfeld, D & Braun, M 1987, 'A novel compensating filter for resolution enhancement in ultrasonic imaging.', Australas Phys Eng Sci Med, vol. 10, no. 2, pp. 72-78.
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This study investigates the compensation of the spreading of ultrasonic pulses due to frequency-dependent attenuation by tissues. The effect of pulse spreading progressively degrades the axial resolution with increasing depth. A novel technique, using a time varying filter made up of a bank of tapped delay lines is proposed to compensate for this effect. The performance of the filter is evaluated by means of computer simulation and the limits of its application are discussed. Apart from improving the axial resolution (and, hence, the accuracy of axial measurements), the compensating filter could be used in implementing tissue characterisation algorithms based on attenuation data.
Ching, NH, Rosenfeld, D & Braun, M 1987, 'Resolution Enhancement In Ultrasonic Imaging By A Time-Varying Filter', SPIE Proceedings, vol. 768, pp. 79-84.
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The study reported here investigates the use of a time-varying filter to compensate for the spreading of ultrasonic pulses due to the frequency dependence of attenuation by tissues. The effect of this pulse spreading is to degrade progressively the axial resolution with increasing depth. The form of compensation required to correct for this effect is impossible to realize exactly. A novel time-varying filter utilizing a bank of bandpass filters is proposed as a realizable approximation of the required compensation. The performance of this filter is evaluated by means of a computer simulation. The limits of its application are discussed. Apart from improving the axial resolution, and hence the accuracy of axial measurements, the compensating filter could be used in implementing tissue characterization algorithms based on attenuation data. © 1987 SPIE.
Durance, G, Hogg, GR, Tendys, J & Watterson, PA 1987, 'Studies of equilibrium in the AAEC rotamak', Plasma Physics and Controlled Fusion, vol. 29, no. 2, pp. 227-244.
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Kane, E, McCabe, B & O'Brien, B 1987, 'Professional affiliations.', Nurs Adm Q, vol. 11, no. 4, pp. 33-34.
NG, TMJ & HOANG, DB 1987, 'JOINT OPTIMIZATION OF CAPACITY AND FLOW ASSIGNMENT IN A PACKET-SWITCHED COMMUNICATIONS NETWORK', IEEE TRANSACTIONS ON COMMUNICATIONS, vol. 35, no. 2, pp. 202-209.
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Simpson, AM & White, IG 1987, 'Interrelationships between motility, c-AMP, respiration and calcium uptake of ram and boar sperm', Animal Reproduction Science, vol. 15, no. 3-4, pp. 189-207.
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Uptake of radioactive calcium by washed ejaculated ram and epididymal boar spermatozoa was inhibited by theophylline and dibutyryl cyclic AMP (diBc-AMP) which increases cyclic AMP (c-AMP) levels in cells, by the uncouplers 2,4-dinitrophenol (2,4-DNP) and carbonylcyanide m-chlorophenylhydrazone (CCP), by sodium azide, rotenone and antimycin A and by ruthenium red and La3+. Nicotine, eserine and ouabain stimulated the calcium uptake of caput boar sperm and decamethonium inhibited it. Inhibition of calcium uptake was accompanied by a decrease in oxygen uptake in the case of the metabolic inhibitors (rotenone, antimycin A and sodium azide) and substances that interfere with cell calcium transport (ruthenium red and La3+). Respiration was increased in the presence of 2,4-DNP and CCP, and theophylline and diBc-AMP. The phosphodiesterase inhibitors (caffeine and theophylline), diBc-AMP, 2,4-DNP, bicarbonate ion and ouabain increased the motility of caput boar sperm. Most other substances depressed motility. The ionophore A23187 severely inhibited the motility of ram and boar sperm with an accompanying increase in their calcium and oxygen uptake which was largely unaffected by addition of inhibitors, activators and surfactants. This may be explained by the operation of competing mitochondrial and plasma membrane pumps. However, a selective increase in the permeability of the sperm plasma membrane on addition of the polyene antibiotic filipin released calcium accumulated in the presence of A23187. This provides further evidence for the lack of mitochondrial involvement in the influx of calcium produced by the ionophore.
Simpson, AM, Swan, MA & White, IG 1987, 'Calcium Uptake, Respiration, and Ultrastructure of Sperm Exposed to Ionophore A23187', Archives of Andrology, vol. 19, no. 1, pp. 5-18.
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Simpson, AM, Swan, MA & White, IG 1987, 'Susceptibility of epididymal boar sperm to cold shock and protective action of phosphatidylcholine', Gamete Research, vol. 17, no. 4, pp. 355-373.
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AbstractRapidly cooling (cold shocking) washed cauda boar sperm irreversibly reduced motility and respiration and greatly increased the uptake of 45Ca2+; the plasma membranes were removed and the acrosomes detached from nuclei. The motility, respiration, and calcium uptake of the less mature caput sperm were largely unaffected; and there was little damage to the ultrastructure. This indicates that boar sperm becomes less resistant to cold shock as they mature in the epididymis.The oxygen uptake, glucose breakdown, and lactic acid production of control caput sperm was less than that of cauda sperm. This suggest that the maturation of sperm in the epididymis of the boar involves an increase in both the glycolytic and oxidative phases of glucose metabolism.The presence of 2.0 mg/ml phosphatidylcholine (lecithin) in the medium prevented ultrastructural damage to cauda sperm on cold shock, and motility and respiration were maintained at levels similar to those of control sperm. Although the presence of phospholipid reduced the large calcium influx following cold shock, it was still greater that that of control sperm.The “protective” effect against cold shock was not maintained after rewashing the sperm free of phosphatidylcholine prior to cold shock, indicating a fairly “loose” interaction of the phospholipid with boar sperm membranes that was easily disrupted.
Town, G, Ching, N, Braun, M & Rosenfeld, D 1987, 'Design and construction of 'SUMRIS'--the Sydney University magnetic resonance imaging system.', Australas Phys Eng Sci Med, vol. 10, no. 2, pp. 58-63.
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Magnetic resonance imaging (MRI) is a highly versatile medical imaging modality which uses nuclear magnetic resonance (NMR) techniques to obtain the spatial distribution of a combination of tissue-dependent NMR parameters. The NMR Imaging Group at the School of Electrical Engineering, University of Sydney, has carried out a number of investigations into various aspects of magnetic resonance imaging, primarily in signal processing and image formation algorithms. To enable further development of these and other techniques it was found necessary to construct SUMRIS - the Sydney University Magnetic Resonance Imaging System, a flexible imaging and spectroscopy experimental facility. The appropriate design strategy adopted was to start by building a simple NMR apparatus and expand it in steps, progressing towards a complete imaging and spectroscopy system.
Town, G, Ching, N, Braun, M, Rosenfeld, D, Dwyer III, SJ & Schneider, RH 1987, '<title>Design And Construction Of 'SUMRIS' -The Sydney University Magnetic Resonance Imaging System</title>', SPIE Proceedings, vol. 767, pp. 55-60.
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A magnetic resonance imaging system for investigation and development of nuclear magnetic resonance (NMR) imaging techniques is being constructed by the NMR Imaging Group within the School of Electrical Engineering at the University of Sydney. The system will also be capable of spatially-localized in-vivo spectroscopy. Primary requirements of a research instrument are flexibility and low cost, precluding purchase of a commercial system and necessitating in-house construction. The appropriate design strategy adopted was to start by building a simple NMR apparatus and expand it in steps, progressing towards a complete imaging and spectroscopy system. © 1987, SPIE.
