Asymmetric MRI magnet design using a hybrid numerical method

This paper describes a hybrid numerical method for the design of asymmetric magnetic resonance imaging magnet systems. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. A new type of asymmetric magnet is proposed in this work. The asymmetric MRI magnet allows the diameter spherical imaging volume to be positioned close to one end of the magnet. The main advantages of making the magnet asymmetric include the potential to reduce the perception of claustrophobia for the patient, better access to the patient by attending physicians, and the potential for reduced peripheral nerve stimulation due to the gradient coil configuration. The results highlight that the method can be used to obtain an asymmetric MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1.2 m in length. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries. (C) 1999 Academic Press.

A hybrid, inverse approach to the design of magnetic resonance imaging magnets

This paper describes a hybrid numerical method of an inverse approach to the design of compact magnetic resonance imaging magnets. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first, kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. The emphasis of this work is on the optimal design of short MRI magnets. Details of the hybrid numerical model are presented, and the model is used to investigate compact, symmetric MRI magnets as well as asymmetric magnets. The results highlight that the method can be used to obtain a compact MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1 m in length, significantly shorter than current designs. Viable asymmetric magnet designs, in which the edge of the homogeneous region is very close to one end of the magnet system are also presented. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)00303-5].

A transdisciplinary approach to adolescent forensic mental health

Objective: To examine new strategies which may be implemented to address the significant mental health and substance abuse problems of young people within the juvenile justice system. Method: Wide-ranging literature review of mental health problems within the juvenile justice population is given, illustrating the high prevalence of mental health problems within this cohort of young people. Reference is made to the differing demographics and agendas of the American justice system compared to that found in Australia. Results: It is suggested that new initiatives stemming from quality Australian studies are required in order to facilitate reform within adolescent forensic mental health. Psychiatrists need to be at the forefront of innovative policy delivery within the juvenile justice system. Conclusions: A transdisciplinary approach is required to meet the changing needs of young people within the juvenile justice system. Such a system of care recognizes that these young people and their families have multiple needs that cross traditional boundaries and a collaborative approach across agencies is essential at both the policy and practical level. Psychiatrists have an important role to play in the development of these services. A systemic process to address such needs is offered.

Mutation analysis to verify feature matrices for isolating errors in simulation models

Software simulation models are computer programs that need to be verified and debugged like any other software. In previous work, a method for error isolation in simulation models has been proposed. The method relies on a set of feature matrices that can be used to determine which part of the model implementation is responsible for deviations in the output of the model. Currrently these feature matrices have to be generated by hand from the model implementation, which is a tedious and error-prone task. In this paper, a method based on mutation analysis, as well as prototype tool support for the verification of the manually generated feature matrices is presented. The application of the method and tool to a model for wastewater treatment shows that the feature matrices can be verified effectively using a minimal number of mutants.

Work domain analysis for training-system definition and acquisition

Training-needs analysis is critical for defining and procuring effective training systems. However, traditional approaches to training-needs analysis are not suitable for capturing the demands of highly automated and computerized work domains. In this article, we propose that work domain analysis can identify the functional structure of a work domain that must be captured in a training system, so that workers can be trained to deal with unpredictable contingencies that cannot be handled by computer systems. To illustrate this argument, we outline a work domain analysis of a fighter aircraft that defines its functional structure in terms of its training objectives, measures of performance, basic training functions, physical functionality, and physical context. The functional structure or training needs identified by work domain analysis can then be used as a basis for developing functional specifications for training systems, specifically its design objectives, data collection capabilities, scenario generation capabilities, physical functionality, and physical attributes. Finally, work domain analysis also provides a useful framework for evaluating whether a tendered solution fulfills the training needs of a work domain.

An inverse design method for elliptical MRI magnets

An inverse, current density mapping (CDM) method has been developed for the design of elliptical cross-section MRI magnets. The method provides a rapid prototyping system for unusual magnet designs, as it generates a 3D current density in response to a set of target field and geometric constraints. The emphasis of this work is on the investigation of new elliptical coil structures for clinical MRI magnets. The effect of the elliptical aspect ratio on magnet performance is investigated. Viable designs are generated for symmetric, asymmetric and open architecture elliptical magnets using the new method. Clinically relevant attributes such as reduced stray field and large homogeneous regions relative to total magnet length are included in the design process and investigated in detail. The preliminary magnet designs have several novel features.

A comparative study of iterative Chebyshev and Lanczos implementations of the boundary inhomogeneity method for quantum scattering

We have recently developed a scaleable Artificial Boundary Inhomogeneity (ABI) method [Chem. Phys. Lett.366, 390–397 (2002)] based on the utilization of the Lanczos algorithm, and in this work explore an alternative iterative implementation based on the Chebyshev algorithm. Detailed comparisons between the two iterative methods have been made in terms of efficiency as well as convergence behavior. The Lanczos subspace ABI method was also further improved by the use of a simpler three-term backward recursion algorithm to solve the subspace linear system. The two different iterative methods are tested on the model collinear H+H2 reactive state-to-state scattering.

An advanced method for eliminating impacts from frequency deviations in power system signal processing

Frequency deviation is a common problem for power system signal processing. Many power system measurements are carried out in a fixed sampling rate assuming the system operates in its nominal frequency (50 or 60 Hz). However, the actual frequency may deviate from the normal value from time to time due to various reasons such as disturbances and subsequent system transients. Measurement of signals based on a fixed sampling rate may introduce errors under such situations. In order to achieve high precision signal measurement appropriate algorithms need to be employed to reduce the impact from frequency deviation in the power system data acquisition process. This paper proposes an advanced algorithm to enhance Fourier transform for power system signal processing. The algorithm is able to effectively correct frequency deviation under fixed sampling rate. Accurate measurement of power system signals is essential for the secure and reliable operation of power systems. The algorithm is readily applicable to such occasions where signal processing is affected by frequency deviation. Both mathematical proof and numerical simulation are given in this paper to illustrate robustness and effectiveness of the proposed algorithm. Crown Copyright (C) 2003 Published by Elsevier Science B.V. All rights reserved.

A simple, rapid method for mapping bathymetry of small wetland basins

Many tools exist for determining and mapping the bathymetry and topography of aquatic systems, such as freshwater wetlands. However, these tools often require time-consuming survey work to produce accurate maps. In particular, the large quantity of data necessary may be prohibitive for projects where determining bathymetry is not a central focus, but instead a necessary step in achieving some other goal. We present a method to produce bathymetric surface maps with a minimum amount of effort using global positioning system receiver and laser transit survey data. We also demonstrate that this method is surprisingly accurate, given the small amount of data we use to generate the bathymetry maps.

Australian veterinarians who work with horses: views of the future

Objective To give an account of the views held by Australian veterinarians who work with horses on the future of their professional field. Method Questionnaires were mailed to 866 veterinarians who had been identified as working with horses, and 87% were completed and returned. Data were entered onto an Excel spreadsheet, and analysed using the SAS System for Windows. Results Their future prospects were believed to be very good or excellent by >60% of equine veterinarians but by only 30% of mixed practitioners seeing < 10% horses. The main factors believed likely to affect these prospects were the strength of the equine industries and the economic climate affecting horse owners, followed by the encroachment of cities into areas used for horses, competition from other veterinarians including specialist centres and from non-veterinary operators, and their ability to recruit and retain veterinarians with interest, experience and skill with horses. Urban encroachment, competition and recruitment were especially important for those seeing few horses. Concerns were also expressed about the competence and ethical behaviour of other veterinarians, the physical demands and dangers of horse work, the costs of providing equine veterinary services and of being paid for them, the regulatory restrictions imposed by governments and statutory bodies, the potential effects of litigation, and insurance issues. For many veterinarians in mixed practice these factors have reduced and are likely to reduce further the number of horses seen, to the extent that they have scant optimism about the future of horse work in their practices. Conclusion Economic and local factors will result in an increasing proportion of equine veterinary work being done in specialised equine centres, and the future of horse work in many mixed practices is, at best, precarious. A key factor influencing future prospects will be the availability of competent veterinarians committed to working with horses.

Australian veterinarians who work with horses: attitudes to work and career

Objective To describe the attitudes to their work and career of those Australian veterinarians who work with horses. Method Questionnaires were mailed to 866 veterinarians who had been identified as working with horses, and 87% were completed and returned. Data were entered onto Excel spreadsheets, and analysed using the SAS System for Windows. Results The main attractions of veterinary work with horses were the horses themselves and the equine industries, but working outdoors and with rewarding clients, and the satisfaction of successful outcomes were attractions for many. The list of disadvantages was longer, and included unreasonable and disagreeable clients as well as those who provided inadequate facilities, could not control their horses or did not care for them. The physical demands and risks of injury, the amount of time required, low rates of return and difficulties in collecting payment, were other major disadvantages. Some mentioned concerns about litigation, unethical behaviour, and recruiting and retaining veterinarians competent with horses. For many in mixed practice, the difficulties in affording modern equipment, and of developing and maintaining their own competence with horses, was a real concern. More than three-quarters of the respondents reported that their careers had lived up to expectations and that they would become veterinarians again; 70% of equine veterinarians would become an equine veterinarian again. Almost all (93%) of the respondents were either very glad, or 'generally glad though with some misgivings' that they had done the veterinary course. Older veterinarians reported suffering less stress, and being more content with their career, than younger colleagues. Conclusions The advantages of doing veterinary work with horses outweigh the disadvantages for most veterinarians, especially those well advanced in their careers.

Public and private psychiatry: Can they work together and is it worth the effort?

Objective: Partnerships in mental health care, particularly between public and private psychiatric services, are being increasingly recognized as important for optimizing patient management and the efficient organization of services. However, public sector mental health services and private psychiatrists do not always work well together and there seem to be a number of barriers to effective collaboration. This study set out to investigate the extent of collaborative 'shared care' arrangements between a public mental health service and private psychiatrists practising nearby. It also examined possible barriers to collaboration and some possible solutions to the identified problems. Method: A questionnaire examining the above factors was sent to all public sector mental health clinicians and all private psychiatrists in the area. Results: One hundred and five of the 154 (68.2%) public sector clinicians and 103 of the 194 (53.1%) private psychiatrists returned surveys. The main barriers to successful collaboration identified by members of both sectors were: 'Difficulty communicating' endorsed by 71.4% of public clinicians and 72% of private psychiatrists, 'Confusion of roles and responsibilities' endorsed by 62.9% and 66%, respectively, and 'Different treatment approach' by 47.6% and 45.6%, respectively. Over 60% of private psychiatrists identified problems with access to the public system as a barrier to successful shared care arrangements. It also emerged, as hypothesized, that the public and private systems tend to manage different patient populations and that public clinicians in particular are not fully aware of the private psychiatrists' range of expertise. This would result in fewer referrals for shared care across the sectors. Conclusions: A number of barriers to public sector clinicians and private psychiatrists collaborating in shared care arrangements were identified. The two groups surveyed identified similar barriers. Some of these can potentially be addressed by changes to service systems. Others require cultural shifts in both sectors. Improved communications including more opportunities for formal and informal meetings between people working in the two sectors would be likely to improve the understanding of the complementary sector's perspective and practice. Further changes would be expected to require careful work between the sectors on training, employment and practice protocols and initiatives, to allow better use of the existing services and resources.

On the equivalence of weighted Country-Product-Dummy (CPD) Method and the Rao-System for multilateral price comparisons

The country-product-dummy (CPD) method, originally proposed in Summers (1973), has recently been revisited in its weighted formulation to handle a variety of data related situations (Rao and Timmer, 2000, 2003; Heravi et al., 2001; Rao, 2001; Aten and Menezes, 2002; Heston and Aten, 2002; Deaton et al., 2004). The CPD method is also increasingly being used in the context of hedonic modelling instead of its original purpose of filling holes in Summers (1973). However, the CPD method is seen, among practitioners, as a black box due to its regression formulation. The main objective of the paper is to establish equivalence of purchasing power parities and international prices derived from the application of the weighted-CPD method with those arising out of the Rao-system for multilateral comparisons. A major implication of this result is that the weighted-CPD method would then be a natural method of aggregation at all levels of aggregation within the context of international comparisons.

A community nurse referral system for HMRs: Can it work?

The HMR model contains a mechanism whereby anyone who is concerned about the risk of medication misadventure can request a HMR from the patient's GP. Since nurses are widely involved in a range of triage and gatekeeping roles, utilising their primary care skills to identify patients for a HMR is a logical extension of this role. Furthermore, community nurses visit their clients in the home situation and see many difficulties the client may be experiencing at first hand. They are therefore well placed to request specialist assistance for the client. Blue Care in Brisbane, a community nursing service, approached its local Division of General practice to determine how best to request HMRs for its clients. The Division contacted The University of Queensland which initiated this study to engage the health care team to tailor the established HMR request process to the needs of community nurses and test the system developed. (non-author abstract)