Current density mapping approach for design of clinical magnetic resonance imaging magnets

Novel current density mapping (CDM) schemes are developed for the design of new actively shielded, clinical magnetic resonance imaging (MRI) magnets. This is an extended inverse method in which the entire potential solution space for the superconductors has been considered, rather than single current density layers. The solution provides an insight into the required superconducting coil pattern for a desired magnet configuration. This information is then used as an initial set of parameters for the magnet structure, and a previously developed hybrid numerical optimization technique is used to obtain the final geometry of the magnet. The CDM scheme is applied to the design of compact symmetric, asymmetric, and open architecture 1.0-1.5 T MRI magnet systems of novel geometry and utility. A new symmetric 1.0-T system that is just I m in length with a full 50-cm diameter of the active, or sensitive, volume (DSV) is detailed, as well as an asymmetric system in which a 50-cm DSV begins just 14 cm from the end of the coil structure. Finally a 1.0-T open magnet system with a full 50-cm DSV is presented. These new designs provide clinically useful homogeneous regions and have appropriately restricted stray fields but, in some of the designs, the DSV is much closer to the end of the magnet system than in conventional designs. These new designs have the potential to reduce patient claustrophobia and improve physician access to patients undergoing scans. (C) 2002 Wiley Periodicals, Inc.

An inverse design of an open, head/neck RF coil for MRI

Radio-frequency (RF) coils are a necessary component of magnetic resonance imaging (MRI) systems. When used in transmit operation, they act to generate a homogeneous RF magnetic field within a volume of interest and when in receive operation, they act to receive the nuclear magnetic resonance signal from the RF-excited specimen. This paper outlines a procedure for the design of open RF coils using the time-harmonic inverse method. This method entails the calculation of an ideal current density on a multipaned planar surface that would generate a specified magnetic field within the volume of interest. Because of the averaging effect of the regularization technique in the matrix solution, the specified magnetic field is shaped within an iterative procedure until the generated magnetic field matches the desired magnetic field. The stream-function technique is used to ascertain conductor positions and a method of moments package is then used to finalize the design. An open head/neck coil was designed to operate in a clinical 2T MRI system and the presented results prove the efficacy of this design methodology.

Ellipsoidal harmonic (Lame) MRI shims

Ellipsoidal harmonics are presented as a basis function set for the design of shim coils for magnetic resonance imaging (MRI) or spectroscopy. MR shim coils may be either superconductive or resistive. Ellipsoidal harmonics form an orthogonal set over an ellipsoid and hence are appropriate in circumstances where the imaging or spectroscopic region of a magnet more closely conforms to an ellipsoid rather than a sphere. This is often the case in practice. The Cartesian form of ellipsoidal harmonics is discussed. A method for the design of streamline coil designs is detailed and patterns for third-order ellipsoidal (Lame) shims wound on a cylindrical surface are presented.

High-performance L-band series and parallel switches using low-cost p-i-n diodes

Low-cost UHF-band p-i-n diodes are used to develop high-performance L-band series and parallel switches. To stop the rectification of large RF, signals, the diodes are biased at a large reverse-bias voltage. Parasitic elements of the diodes are tuned out using LC circuits in biasing circuits without increasing the size of the switches. (C) 2002 John Wiley Sons, Inc.

Microstrip circular phased array design and development using microwave antenna CAD tools

The complex design and development of a planar multilayer phased array antenna in microstrip technology can be simplified using two commercially available design tools 1) Ansoft Ensemble and 2) HP-EEsof Touchstone. In the approach presented here, Touchstone is used to design RF switches and phase shifters whose scattering parameters are incorporated in Ensemble simulations using its black box tool. Using this approach, Ensemble is able to fully analyze the performance of radiating and beamforming layers of a phased array prior to its manufacturing. This strategy is demonstrated in a design example of a 12-element linearly-polarized circular phased array operating at L band. A comparison between theoretical and experimental results of the array is demonstrated.

Analysis of a circular patch antenna radiating in a parallel-plate radial guide

A field matching method is described to analyze a recessed circular cavity radiating into a radial waveguide. Using the wall impedance approach, the analysis is divided into two separate problems of the cavity and its external environment. Based on this analysis, a computer algorithm is developed for determining wall admittances as seen at the edge of the patch in the cavity, the radial admittance matrix for the two-probe feed arrangement, and the input impedance as observed from the coaxial line feeding the cavity. This algorithm is tested against the general-purpose Hewlett-Packard finite-element High Frequency Structure Simulator as well as against measured results. Good agreement in all considered cases is noted.

Patterns of gene expression are altered in the frontal and motor cortices of human alcoholics

Alcoholism is a major health problem in Western countries, yet relatively little is known about the mechanisms by which chronic alcohol abuse causes the pathologic changes associated with the disease. It is likely that chronic alcoholism affects a number of signaling cascades and transcription factors, which in turn result in distinct gene expression patterns. These patterns are difficult to detect by traditional experiments measuring a few mRNAs at a time, but are well suited to microarray analyses. We used cDNA microarrays to analyze expression of approximately 10 000 genes in the frontal and motor cortices of three groups of chronic alcoholic and matched control cases. A functional hierarchy was devised for classification of brain genes and the resulting groups were compared based on differential expression. Comparison of gene expression patterns in these brain regions revealed a selective reprogramming of gene expression in distinct functional groups. The most pronounced differences were found in myelin-related genes and genes involved in protein trafficking. Significant changes in the expression of known alcohol-responsive genes, and genes involved in calcium, cAMP, and thyroid signaling pathways were also identified. These results suggest that multiple pathways may be important for neuropathology and altered neuronal function observed in alcoholism.

Parasite distribution on client reef fish determines cleaner fish foraging patterns

Recent evidence suggests that cleaner fish Labroides dimidiatus effectively control parasite densities on client reef fish that actively visit them to have parasites and dead or infected tissue removed. These findings support the hypothesis that clients benefit from cleaning, However, they do not show how cleaners reduce the parasite load of their clients. Cleaners could selectively feed on parasites or parasite removal could be a side product of cleaners foraging indifferently on the client surface, resulting in the removal of healthy mucus and scales also. To investigate cleaner fish foraging behaviour, we infected individuals of the surgeon fish Ctenochaetus striatus, with parasitic monogeneans on one body side, while the other body side was parasite free. We then allowed these clients to interact with L, dimidiatus. We found that the duration of interactions depended on parasite load, and that cleaners spent both more time and took more bites per time unit on the infected than on the uninfected side, Our data thus support the idea that parasite abundance determines food patch quality for cleaners. The overall outcome of cleaning interactions is thus likely to benefit the clients.

Molecular rates parallel diversification contrasts between carnivorous plant sister lineages

In the carnivorous plant family Lentibulariaceae, the bladderwort lineage (Utricularia and Genlisea) is substantially more species-rich and morphologically divergent than its sister lineage, the butterworts (Pinguicula). Bladderworts have a relaxed body plan that has permitted the evolution of terrestrial, epiphytic, and aquatic forms that capture prey in intricately designed suction bladders or corkscrew-shaped lobster-pot traps. In contrast, the flypaper-trapping butterworts maintain vegetative structures typical of angiosperms. We found that bladderwort genomes evolve significantly faster across seven loci (the trnL intron, the second trnL exon, the trnL-F intergenic spacer, the rps16 intron, rbcL, coxI, and 5.8S rDNA) representing all three genomic compartments. Generation time differences did not show a significant association. We relate these findings to the contested speciation rate hypothesis, which postulates a relationship between increased nucleotide substitution and increased cladogenesis. (C) 2002 The Willi Hennig Society.

Patterns of change and stability in the gender division of household labour in Australia, 1986-1997

Recent research in Australia and overseas has suggested that we are witnessing a convergence of men's and women's time on domestic labour activities. But there is disagreement about whether this is due to women reducing their time on housework or men increasing their time on housework. This article addresses these issues using national survey data collected in Australia in 1986, 1993 and 1997. The results show some changes in the proportional responsibilities of men and women in the home with men reporting a greater share of traditional indoor activities. But overall both men and women are spending less time on housework. In particular, women's time on housework has declined by six hours per week since 1986. Hence, while the gender gap between men's and women's involvement in the home is getting smaller, it is not the result of men increasing their share of the load, but is due to the large decline in women's time spent on domestic labour. There is also evidence of change in the relationship. between paid and unpaid work for women. Women's hours of,paid labour had a greater impact on their involvement in domestic labour in 1997 compared to a decade earlier. The article concludes that women's increased labour force involvement in combination with changing patterns and styles, of consumption is leading to some changes in the gender-division:of household labour, but not in the direction anticipated by earlier commentators on the domestic division of labour.

Patterns of governance: The curious case of non-profit community services in Australia

Community has taken on a new significance in Australian social policy discourse. Seemingly sound and morally justifiable, in the context Of neo-liberalism the language of community positions non-profit delivery of services as superior to state-provided services. As a consequence, non-profit community services are being centrally positioned to mediate the relationship between the state and citizen subjects. In the first part of this paper we trace some of the key historical developments in Australia's welfare state and patterns of governance that are propelling the non-profit sector firm the margins to the centre. The second section examines the relationship between Australia's shifting political landscape and the emerging welfare regime. One key feature of this new regime is the attempt to relocate citizenship away from the domain of the state and into that of civil society. The article concludes by sketching out some research themes, focusing, for example, on the impact of devolution of governance in terms of client rights and public accountability.