How to Undertake a Clinically Relevant Systematic Review in a Rapidly Evolving Field: Magnetic Resonance Angiography

Objectives: The aim was to determine which generations of the evolving technology of magnetic resonance angiography (MRA) are currently of clinical relevance in two clinical applications. Our purpose was to plan a systematic review that would be valuable both to purchasers driven by cost-effectiveness and to practicing clinicians. Methods: Information was gathered from a search of major bibliographic databases, from a short questionnaire sent to 500 U.K. vascular radiologists and vascular surgeons, and from local clinical The authors thank A. Jackson and all those who completed a questionnaire. This work was carried out with the financial support of the Secretary of State for Health under the NHS Health Technology Assessment Programme, project 97/13/04. The views and opinions expressed do not necessarily reflect those of the Secretary of State for Health. In part, this work was undertaken by the Leeds Teaching Hospitals NHS Trust, which received funding from the NHS Executive. The views expressed in this publication are those of the authors and not necessarily those of the NHS Executive.experts. We asked which of the MRA techniques were currently used and, assuming availability, what would be their technique of choice. Results: There were 206 published articles that satisfied preliminary inclusion criteria: 69 discussed 2D time of flight (TOF); 47, 3D TOF; and 38, contrast-enhanced techniques. There were 162 questionnaires returned (60 radiologists, 102 surgeons). Of the total respondents, 77/162 (48%) used MRA in the assessment of carotid artery stenosis; 47/77 (61%) used 2D TOF; 32/77 (42%), 3D TOF; and 26/77 (34%), contrast-enhanced techniques. Thirty-five of 162 (22%) respondents used MRA in the assessment of peripheral vascular disease (PVD); 15/35 (43%) used 2D TOF, 4/35 (11%) used 3D TOF, and 22/35 (63%) used contrast-enhanced techniques. For those wishing to use MRA, contrast-enhanced techniques were the method of choice. Conclusions: The TOF methods that represent earlier generations of the technology remain clinically relevant, and will therefore be included in our systematic review. To ensure complete and relevant coverage in reviews of other evolving technologies, it would be advisable to obtain data for guidance in a similar way

Use of magnetic resonance angiography to select candidates with recently symptomatic carotid stenosis for surgery: systematic review

Objective To determine if sufficient evidence exists to support the use of magnetic resonance angiography as a means of selecting patients with recently symptomatic high grade carotid stenosis for surgery. Design Systematic review of published research on the diagnostic performance of magnetic resonance angiography, 1990-9. Main outcome measures Performance characteristics of diagnostic test. Results 126 potentially relevant articles were identified, but many articles failed to examine die performance of magnetic resonance angiography as a diagnostic test at the surgical decision thresholds used in major clinical trials on endarterectomy. 26 articles were included in a meta-analysis that showed a maximal joint sensitivity and specificity of 99% (95% confidence interval 98% to 100%) for identifying 70-99% stenosis and 90% (81% to 99%) for identifying 50-99% stenosis. Only four articles evaluated contrast enhanced magnetic resonance angiography. Conclusions Magnetic resonance angiography is accurate for selecting patients for carotid endarterectomy at the surgical decision thresholds established in the major endarterectomy trials, but the evidence is not very robust because of the heterogeneity of the studies included. Research is to determine the diagnostic performance of the most recent developments in magnetic resonance angiography, including contrast enhanced techniques, as well as to assess the impact of magnetic resonance angiography on surgical decision making and outcomes

Basic Methods for Computing Special Functions

This paper gives an overview of methods for the numerical evaluation of special functions, that is, the functions that arise in many problems from mathematical physics, engineering, probability theory, and other applied sciences. We consider in detail a selection of basic methods which are frequently used in the numerical evaluation of special functions: converging and asymptotic series, including Chebyshev expansions, linear recurrence relations, and numerical quadrature. Several other methods are available and some of these will be discussed in less detail. We give examples of recent software for special functions where these methods are used. We mention a list of new publications on computational aspects of special functions available on our website

Stable water isotopes as tools for basin-scale water cycle: Diagnosis of the MurrayDarling

We examine the hypothesis that isotopic techniques are applicable to hydrological predictions in difficult-to-simulate semi-arid basins, using the Murray-Darling Basin as an example. Isotopic data from three aquifers in the Murray-Darling characterize precipitation intensity for evaluation of GCMs. Applying these to 'good' (water conserving) and 'poor' (non-water-conserving) climate model simulations of the Murray-Darling gives rise to large differences in rainfall amount (30-62%). Selecting only 'good' models shows a greater than 150 mm annual groundwater recharge loss in El Niño cf. La Niña climates. 2002-2003 El Niño drought data are used to refine isotopic calculation of water lost in evaporation from rivers and irrigation, giving a cumulative loss of 64% of river water during 2002 (cf. 80% using a previous method). This substantiates recent identification of this El Niño drought as evaporatively most extreme and we conclude that stable water isotopes, used synergistically with hydro-climate models, have great potential in future water resource predictions.10 page(s

Interactive Resource-Intensive Applications Made Easy

Abstract. Snowbird is a middleware system based on virtual machine (VM) technology that simplifies the development and deployment of bimodal applications. Such applications alternate between phases with heavy computationalresource needs and phases rich in user interaction. Examples include digital animation, as well as scientific, medical, and engineering diagnostic and design tools. Traditionally, these applications have been manually partitioned into distributed components to take advantage of remote computational resources, while still providing low-latency user interaction. Instead, Snowbird lets developers design their applications as monolithic units within a VM, and automatically migrates the application to the optimal execution site to achieve short completion time and crisp interactive performance. Snowbird does not require that applications be written in a specific language, or use specific libraries, and it can be used with existing applications, including closed-source ones, without requiring recompilation or relinking. Snowbird achieves these goals by augmenting VM migration with an interaction-aware migration manager, support for graphics hardware acceleration, and a wide-area peer-to-peer storage system. Experiments conducted with a number of real-world applications, including commercial closed-source tools, show that applications running under Snowbird come within 4 % of optimal compute time, and provide crisp interactive performance that is comparable to native local execution

Low-Dimensional Waveguide Grating Fabrication in GaN with Use of SiCl4/Cl-2/Ar-Based Inductively Coupled Plasma Dry Etching

Optimized fabrication of submicron-sized features in gallium nitride (GaN) with the use of inductively coupled plasma (ICP) dry etching, based on SiCl4/Cl-2/Ar gas mixture, is presented. Dense periodic patterns, i.e., 400-nm-period gratings, were transferred into a gallium nitride waveguide under different etching conditions. ICP power, radiofrequency (RF) power, chamber pressure, and Ar/Cl-2 gas mixing ratio were altered during the experiment. Depths of fabricated grating couplers up to 670 nm were achieved. The most suitable etching conditions are discussed with the assessment based on etching selectivity, scanning electron microscopy (SEM) observation of grating tooth slope, hard-mask erosion process, and etched surface morpholog