A novel target-field method for finite-length magnetic resonance shim coils: I. Zonal shims

This paper presents a new approach for the design of genuinely finite-length shim and gradient coils, intended for use in magnetic resonance imaging equipment. A cylindrical target region is located asymmetrically, at an arbitrary position within a coil of finite length. A desired target field is specified on the surface of that region, and a method is given that enables winding patterns on the surface of the coil to be designed, to produce the desired field at the inner target region. The method uses a minimization technique combined with regularization, to find the current density on the surface of the coil. The method is illustrated for linear, quadratic and cubic magnetic target fields located asymmetrically within a finite-length coil.

Compact clinical MRI magnet design using a multilayer current density approach

In this work, a new method of optimization is successfully applied to the theoretical design of compact, actively shielded, clinical MRI magnets. The problem is formulated as a two-step process in which the desired current densities on multiple, cc-axial surface layers are first calculated by solving Fredholm equations of the first kind. Non-linear optimization methods with inequality constraints are then invoked to fit practical magnet coils to the desired current densities. The current density approach allows rapid prototyping of unusual magnet designs. The emphasis of this work is on the optimal design of short, actively-shielded MRI magnets for whole-body imaging. Details of the hybrid numerical model are presented, and the model is used to investigate compact, symmetric, and asymmetric MRI magnets. Magnet designs are presented for actively-shielded, symmetric magnets of coil length 1.0 m, which is considerably shorter than currently available designs of comparable dsv size. Novel, actively-shielded, asymmetric magnet designs are also presented in which the beginning of a 50-cm dsv is positioned just 11 cm from the end of the coil structure, allowing much improved access to the patient and reduced patient claustrophobia. Magn Reson Med 45:331540, 2001. (C) 2001 Wiley-Liss, Inc.

Inferring population history from microsatellite and enzyme data in serially introduced cane toads, Bufo marinus

Much progress has been made on inferring population history from molecular data. However, complex demographic scenarios have been considered rarely or have proved intractable. The serial introduction of the South-Central American cane Load Bufo marinas in various Caribbean and Pacific islands involves four major phases: a possible genetic admixture during the first introduction, a bottleneck associated with founding, a transitory, population boom, and finally, a demographic stabilization. A large amount of historical and demographic information is available for those introductions and can be combined profitably with molecular data. We used a Bayesian approach to combine this information With microsatellite (10 loci) and enzyme (22 loci) data and used a rejection algorithm to simultaneously estimate the demographic parameters describing the four major phases of the introduction history,. The general historical trends supported by microsatellites and enzymes were similar. However, there was a stronger support for a larger bottleneck at introductions for microsatellites than enzymes and for a more balanced genetic admixture for enzymes than for microsatellites. Verb, little information was obtained from either marker about the transitory population boom observed after each introduction. Possible explanations for differences in resolution of demographic events and discrepancies between results obtained with microsatellites and enzymes were explored. Limits Of Our model and method for the analysis of nonequilibrium populations were discussed.

A segmentation-based and partial-volume-compensated method for an accurate measurement of lateral ventricular volumes on T-1-weighted magnetic resonance images

Lateral ventricular volumes based on segmented brain MR images can be significantly underestimated if partial volume effects are not considered. This is because a group of voxels in the neighborhood of lateral ventricles is often mis-classified as gray matter voxels due to partial volume effects. This group of voxels is actually a mixture of ventricular cerebro-spinal fluid and the white matter and therefore, a portion of it should be included as part of the lateral ventricular structure. In this note, we describe an automated method for the measurement of lateral ventricular volumes on segmented brain MR images. Image segmentation was carried in combination of intensity correction and thresholding. The method is featured with a procedure for addressing mis-classified voxels in the surrounding of lateral ventricles. A detailed analysis showed that lateral ventricular volumes could be underestimated by 10 to 30% depending upon the size of the lateral ventricular structure, if mis-classified voxels were not included. Validation of the method was done through comparison with the averaged manually traced volumes. Finally, the merit of the method is demonstrated in the evaluation of the rate of lateral ventricular enlargement. (C) 2001 Elsevier Science Inc. All rights reserved.

Paracetamol versus paracetamol-codeine in the treatment of post-operative dental pain: A randomized, double-blind, prospective trial

Background: Codeine is frequently added to paracetamol to treat post-operative dento-alveolar pain; studies have shown effectiveness in relief of post-operative pain at high doses but at the expense of central nervous and gastrointestinal side effects. There has been no trial to compare the efficacy and safety of paracetamol 1000mg with paracetamol 1000mg combined with codeine 30mg. Method. A randomized, single centre, double-blind prospective parallel group trial was performed to compare paracetamol 1000mg with paracetamol 1000mg with codeine 30mg for the relief of pain following surgical removal of impacted third molars, and analysed on an intention-to-treat (ITT) basis. Eighty-two patients were assigned randomly to receive either drug for a maximum of three doses. Patients recorded their pain intensity one hour after surgery and hourly thereafter for 12 hours. Results: The average increase in pain intensity over 12 hours was significantly less in patients receiving paracetamol plus codeine than in those receiving paracetamol alone (p=0.03) -1.81cm/h compared with 0.45cm/h - a difference of 1.13cm/h (95 per cent Cl: 0.18 to 2.08). Of the patients who received the paracetamol codeine combination, 62 per cent used escape medication compared with 75 per cent of those on paracetamol alone (p=0.20). There was no significant difference between the two groups in the proportion of patients experiencing adverse events (P=0.5). Conclusion: A combination of 1000mg paracetamol and 30mg codeine was significantly more effective in controlling pain for 12 hours following third molar removal, with no significant difference of side effects during the 12 hour period studied.

Quantification of sulfur and sulfur-containing compounds in wastewaters by means of a combination of liquid chromatographic methods

Low-micromolar concentrations of sulfite, thiosulfate and sulfide, present in synthetic wastewater or anaerobic digester effluent, were quantified by means of derivatization with monobromobimane, followed by HPLC separation with fluorescence detection. The concentration of elemental sulfur was determined, after its extraction with chloroform from the derivatized sample, by HPLC with UV detection. Recoveries of sulfide (both matrices), and of thiosulfate and sulfite (synthetic wastewater) were between 98 and 103%. The in-run RSDs on separate derivatizations were 13 and 19% for sulfite (two tests), between 1.5 and 6.6% for thiosulfate (two tests) and between 4.1 and 7.7% for sulfide (three tests). Response factors for derivatives of sulfide and thiosulfate, but not sulfite, were steady over a 13-month period during which 730 samples were analysed. Dithionate and tetrathionate did not seem to be detectable with this method. The distinctness of the elemental sulfur and the derivatizing-agent peaks was improved considerably by detecting elution at 297 instead of 263 nm. (C) 2002 Elsevier Science B.V. All rights reserved.

Energy cost of activity assessed by indirect calorimetry and a (CO2)-C-13 breath test

Purpose: The aim of this study was to assess the accuracy of a (CO2)-C-13 breath test for the prediction of short-duration energy expenditure. Methods: Eight healthy volunteers walked at 1.5 km.h(-1) for 60 min followed by 60-min recovery. During this time, the energy cost of physical activity was measured via respiratory calorimetry and a C-13 bicarbonate breath test. A further eight subjects were tested using the same two methods during a 60-min cycle at 0.5 kp. 30 ipm followed by a 60-min recovery. The rate of appearance of (CO2)-C-13, (RaCO2) was measured and the mean ratio, (V) over dot CO2/RaCO2 was used to calculate energy expenditure using the isotopic approach. Results: As would be expected, there was a significant difference in the energy cost of walking and cycling using both methods (P < 0.05). However. no significant differences were observed between respiratory calorimetry and the isotope method for measurement of energy expenditure while walking or cycling. Conclusions: These data suggest that the C-13 breath test is a valid method that can be used to measure the energy cost of short duration physical activity in a field setting.

Integrable variant of the one-dimensional Hubbard model

A new integrable model which is a variant of the one-dimensional Hubbard model is proposed. The integrability of the model is verified by presenting the associated quantum R-matrix which satisfies the Yang-Baxter equation. We argue that the new model possesses the SO(4) algebra symmetry, which contains a representation of the eta-pairing SU(2) algebra and a spin SU(2) algebra. Additionally, the algebraic Bethe ansatz is studied by means of the quantum inverse scattering method. The spectrum of the Hamiltonian, eigenvectors, as well as the Bethe ansatz equations, are discussed. (C) 2002 American Institute of Physics.

Detection of human respiratory syncytial virus in respiratory samples by LightCycler reverse transcriptase PCR

Laboratory diagnosis of human respiratory syncytial virus (hRSV) infections has traditionally been performed by virus isolation in cell culture and the direct fluorescent-antibody assay (DFA). Reverse transcriptase PCR (RT-PCR) is now recognized as a sensitive and specific alternative for detection of hRSV in respiratory samples. Using the LightCycler instrument, we developed a rapid RT-PCR assay for the detection of hRSV (the LC-RT-PCR) with a pair of hybridization probes that target the hRSV L gene. In the present study, 190 nasopharyngeal aspirate samples from patients with clinically recognized respiratory tract infections were examined for hRSV. The results were then compared to the results obtained with a testing algorithm that combined DFA and a culture-augmented DFA (CA-DFA) assay developed in our laboratory. hRSV was detected in 77 (41%) specimens by LC-RT-PCR and in 75 (39%) specimens by the combination of DFA and CA-DFA. All specimens that were positive by the DFA and CA-DFA testing algorithm were positive by the LC-RT-PCR. The presence of hRSV RNA in the two additional LC-RT-PCR-positive specimens was confirmed by a conventional RT-PCR method that targets the hRSV N gene. The sensitivity of LC-RT-PCR was 50 PFU/ml; and this, together with its high specificity and rapid turnaround time, makes the LC-RT-PCR suitable for the detection of hRSV in clinical specimens.

Genetic and environmental contributions to cannabis dependence in a national young adult twin sample

Background. This paper examines genetic and environmental contributions to risk of cannabis dependence. Method. Symptoms of cannabis dependence and measures of social, family and individual risk factors were assessed in a sample of 6265 young adult male and female Australian twins born 1964-1971. Results. Symptoms of cannabis dependence were common: 11(.)0% of sample (15(.)1% of men and 7(.)8% of women) reported two or more symptoms of dependence. Correlates of cannabis dependence included educational attainment, exposure to parental conflict, sexual abuse, major depression, social anxiety and childhood conduct disorder. However, even after control for the effects of these factors, there was evidence of significant genetic effects on risk of cannabis dependence. Standard genetic modelling indicated that 44(.)7% (95% CI = 15-72(.)2) of the variance in liability to cannabis dependence could be accounted for by genetic factors, 20(.)1% (95 CI = 0-43(.)6) could be attributed to shared environment factors and 35(.)3% (95% CI = 26(.)4-45(.)7) could be attributed to non-shared environmental factors. However, while there was no evidence of significant gender differences in the magnitude of genetic and environmental influences, a model which assumed both genetic and shared environmental influences on risks of cannabis dependence among men and shared environmental but no genetic influences among women provided an equally good fit to the data. Conclusions. There was consistent evidence that genetic risk factors are important determinants of risk of cannabis dependence among men. However, it remains uncertain whether there are genetic influences on liability to cannabis dependence among women.

Low-density koala (Phascolarctos cinereus) populations in the mulgalands of south-west Queensland. I. Faecal pellet sampling protocol

Koala (Phascolarctos cinereus) populations in eastern Australia are threatened by land clearing for agricultural and urban development. At the same time, conservation efforts are hindered by a dearth of information about inland populations. Faecal deposits offer a source of information that is readily available and easily collected non-invasively. We detail a faecal pellet sampling protocol that was developed for use in a large rangeland biogeographic region. The method samples trees in belt transects, uses a thorough search at the tree base to quickly identify trees with koala pellets under them, then estimates the abundance of faecal pellets under those trees using 1-m(2) quadrats. There was a strong linear relationship between these estimates and a complete enumeration of pellet abundance under the same trees. We evaluated the accuracy of our method in detecting trees where pellets were present by means of a misclassification index that was weighed more heavily for missed trees that had high numbers of pellets under them. This showed acceptable accuracy in all landforms except riverine, where some trees with large numbers of pellets were missed. Here, accuracy in detecting pellet presence was improved by sampling with quadrats, rather than basal searches. Finally, we developed a method to reliably age pellets and demonstrate how this protocol could be used with the faecal-standing-crop method to derive a regional estimate of absolute koala abundance.

The fluorolysis assay, a highly sensitive method for measuring the cytolytic activity of T cells at very low numbers

We have developed a highly sensitive cytolysis test, the fluorolysis assay, as a simple nonradioactive and inexpensive alternative to the standard Cr-51-release assay. P815 cells were stably transfected with a plasmid expressing the enhanced green fluorescent protein (EGFP) gene. These target cells were coated with or without cognate peptide or anti-CD3 Ab and then incubated with CD8(+) T cells to allow antigen-specific or nonspecific lysis. The degree of target cell lysis was measured using flow cytometry to count the percentage of viable propidium iodide(-) EGFP(+) cells, whose numbers were standardized to a reference number of fluorochrome-linked beads. By using small numbers of target cells (200-800 per reaction) and extended incubation times (up to 2 days), the antigen-specific cytolytic activity of one to two activated CD8(+) T cells of a CTL line could be detected. The redirected fluorolysis assay also measured the activity of very few ( greater than or equal to6) primary CD8(+) T cells following polyclonal activation. Importantly, antigen-specific lysis by small numbers ( greater than or equal to 25) of primary CD8(+) T cells could be directly measured ex vivo. This exquisite sensitivity of the fluorolysis assay, which was at least 8-33-folds higher than an optimized 51 Cr-release assay, allows in vitro and ex vivo studies of immune responses that would otherwise not be possible due to low CTL numbers or frequencies. (C) 2002 Elsevier Science B.V. All rights reserved.

The efficiency and condition of oysters and macroalgae used as biological filters of shrimp pond effluent

Current shrimp pond management practices generally result in elevated concentrations of nutrients, suspended solids, bacteria and phytoplankton compared with the influent water. Concerns about adverse environmental impacts caused by discharging pond effluent directly into adjacent waterways have prompted the search for cost-effective methods of effluent treatment. One potential method of effluent treatment is the use of ponds or raceways stocked with plants or animals that act as natural biofilters by removing waste nutrients. In addition to improving effluent water quality prior to discharge, the use of natural biofilters provides a method for capturing otherwise wasted nutrients. This study examined the potential of the native oyster, Saccostrea commercialis (Iredale and Roughley) and macroalgae, Gracilaria edulis (Gmelin) Silva to improve effluent water quality from a commercial Penaeus japonicus (Bate) shrimp farm, A system of raceways was constructed to permit recirculation of the effluent through the oysters to maximize the filtration of bacteria, phytoplankton and total suspended solids. A series of experiments was conducted to test the ability of oysters and macroalgae to improve effluent water quality in a flow-through system compared with a recirculating system. In the flow-through system, oysters reduced the concentration of bacteria to 35% of the initial concentration, chlorophyll a to 39%, total particulates (2.28-35.2 mum) to 29%, total nitrogen to 66% and total phosphorus to 56%. Under the recirculating flow regime, the ability of the oysters to improve water quality was significantly enhanced. After four circuits, total bacterial numbers were reduced to 12%, chlorophyll a to 4%, and total suspended solids to 16%. Efforts to increase biofiltration by adding additional layers of oyster trays and macroalgae-filled mesh bags resulted in fouling of the lower layers causing the death of oysters and senescence of macroalgae. Supplementary laboratory experiments were designed to examine the effects of high effluent concentrations of suspended particulates on the growth and condition of oysters and macroalgae. The results demonstrated that high concentrations of particulates inhibited growth and reduced the condition of oysters and macroalgae. Allowing the effluent to settle before biofiltration improved growth and reduced signs of stress in the oysters and macroalgae. A settling time of 6 h reduced particulates to a level that prevented fouling of the oysters and macroalgae.

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.