Cost effectiveness of adding magnetic resonance imaging to the usual management of suspected scaphoid fractures

Objective: To determine the cost effectiveness of a magnetic resonance imaging scan (MRI) within 5 days of injury compared with the usual management of occult scaphoid fracture. Methods: All patients with suspected scaphoid fractures in five hospitals were invited to participate in a randomised controlled trial of usual treatment with or without an MRI scan. Healthcare costs were compared, and a cost effectiveness analysis of the use of MRI in this scenario was performed. Results: Twenty eight of the 37 patients identified were randomised: 17 in the control group, 11 in the MRI group. The groups were similar at baseline and follow up in terms of number of scaphoid fractures, other injuries, pain, and function. Of the patients without fracture, the MRI group had significantly fewer days immobilised: a median of 3.0 (interquartile range 3.0-3.0) v 10.0 (7-12) in the control group (p = 0.006). The MRI group used fewer healthcare units (median 3.0, interquartile range 2.0-4.25) than the control group (5.0, 3.0-6.5) (p = 0.03 for the difference). However, the median cost of health care in the MRI group ($594.35 AUD, $551.35-667.23) was slightly higher than in the control group ($428.15, $124.40-702.65) (p = 0.19 for the difference). The mean incremental cost effectiveness ratio derived from this simulation was that MRI costs $44.37 per day saved from unnecessary immobilisation (95% confidence interval $4.29 to $101.02). An illustrative willingness to pay was calculated using a combination of the trials measure of the subjects' individual productivity losses and the average daily earnings. Conclusions: Use of MRI in the management of occult scaphoid fracture reduces the number of days of unnecessary immobilisation and use of healthcare units. Healthcare costs increased non-significantly in relation to the use of MRI in this setting. However, when productivity losses are considered, MRI may be considered cost effective, depending on the individual case.

Fronto-parietal activation in attention-deficit hyperactivity disorder, combined type: functional magnetic resonance imaging study

A functional magnetic resonance imaging mental rotation paradigm was used to investigate the patterns of activation of fronto-parietal brain areas in male adolescents with attention-deficit hyperactivity disorder, combined type (ADHD-CT) compared with age-, gender-, handedness- and performance IQ-matched healthy controls. The ADHD-CT group had (a) decreased activation of the 'action-attentional' system (including Brodmann's areas (BA) 46, 39,40) and the superior parietal (BA7) and middle frontal (BA10) areas and (b) increased activation of the posterior midline attentional system. These different neuroactivation patterns indicate widespread frontal, striatal and parietal dysfunction in adolescents with ADHD-CT. Declaration of interest None.

Calculating current densities and fields produced by shielded magnetic resonance imaging probes

A method is presented for computing the fields produced by radio frequency probes of the type used in magnetic resonance imaging. The effects of surrounding the probe with a shielding coil, intended to eliminate stray fields produced outside the probe, are included. An essential feature of these devices is the fact that the conducting rungs of the probe are of finite width relative to the coil radius, and it is therefore necessary to find the distribution of current within the conductors as part of the solution process. This is done here using a numerical method based on the inverse finite Hilbert transform, applied iteratively to the entire structure including its shielding coils. It is observed that the fields are influenced substantially by the width of the conducting rungs of the probe, since induced eddy currents within the rungs become more pronounced as their width is increased. The shield is also shown to have a significant effect on both the primary current density and the resultant fields. Quality factors are computed for these probes and compared with values measured experimentally.

The structure of versutoxin (delta-atracotoxin-Hv1) provides insights into the binding of site 3 neurotoxins to the voltage-gated sodium channel

Background: Versutoxin (delta-ACTX-Hv1) is the major component of the venom of the Australian Blue Mountains funnel web spider, Hadronyche versuta. delta-ACTX-Hv1 produces potentially fatal neurotoxic symptoms in primates by slowing the inactivation of voltage-gated sodium channels; delta-ACTX-Hv1 is therefore a useful tool for studying sodium channel function. We have determined the three-dimensional structure of delta ACTX-Hv1 as the first step towards understanding the molecular basis of its interaction with these channels. Results: The solution structure of delta-ACTX-Hv1, determined using NMR spectroscopy, comprises a core beta region containing a triple-stranded antiparallel beta sheet, a thumb-like extension protruding from the beta region and a C-terminal 3(10) helix that is appended to the beta domain by virtue of a disulphide bond. The beta region contains a cystine knot motif similar to that seen in other neurotoxic polypeptides. The structure shows homology with mu-agatoxin-l, a spider toxin that also modifies the inactivation kinetics of vertebrate voltage-gated sodium channels. More surprisingly, delta-ACTX-Hv1 shows both sequence and structural homology with gurmarin, a plant polypeptide. This similarity leads us to suggest that the sweet-taste suppression elicited by gurmarin may result from an interaction with one of the downstream ion channels involved in sweet-taste transduction. Conclusions: delta-ACTX-Hv1 shows no structural homology with either sea anemone or alpha-scorpion toxins, both of which also modify the inactivation kinetics of voltage-gated sodium channels by interacting with channel recognition site 3. However, we have shown that delta-ACTX-Hv1 contains charged residues that are topologically related to those implicated in the binding of sea anemone and alpha-scorpion toxins to mammalian voltage-gated sodium channels, suggesting similarities in their mode of interaction with these channels.

NMR structure and backbone dynamics of a concatemer of epidermal growth factor homology modules of the human low-density lipoprotein receptor

The ligand-binding region of the low-density lipoprotein (LDL) receptor is formed by seven N-terminal, imperfect, cysteine-rich (LB) modules. This segment is followed by an epidermal growth factor precursor homology domain with two N-terminal, tandem, EGF-like modules that are thought to participate in LDL binding and recycling of the endocytosed receptor to the cell surface. EGF-A and the concatemer, EGF-AB, of these modules were expressed in Escherichia coli. Correct protein folding of EGF-A and the concatemer EGF-AB was achieved in the presence or absence of calcium ions, in contrast to the LB modules, which require them for correct folding. Homonuclear and heteronuclear H-1-N-15 NMR spectroscopy at 17.6 T was used to determine the three-dimensional structure of the concatemer. Both modules are formed by two pairs of short, anti-parallel beta -strands. In the concatemer, these modules have a fixed relative orientation, stabilized by calcium ion-binding and hydrophobic interactions at the interface. N-15 longitudinal and transverse relaxation rates, and {H-1}-N-15 heteronuclear NOEs were used to derive a model-free description of the backbone dynamics of the molecule. The concatemer appears relatively rigid, particularly near the calcium ion-binding site at the module interface, with an average generalized order parameter of 0.85 +/- 0.11. Some mutations causing familial hypercholesterolemia may now be rationalized. Mutations of D41, D43 and E44 in the EGF-B calcium ion-binding region may affect the stability of the linker and thus the orientation of the tandem modules. The diminutive core also provides little structural stabilization, necessitating the presence of disulfide bonds. The structure and dynamics of EGF-AB contrast with the N-terminal LB modules, which require calcium ions both for folding to form the correct disulfide connectivities and for maintenance of the folded structure, and are connected by highly mobile linking peptides. (C) 2001 Academic Press.

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.

The stochastic design of force-minimized compact magnets for high-field magnetic resonance imaging applications

New designs for force-minimized compact high-field clinical MRI magnets are described. The design method is a modified simulated annealing (SA) procedure which includes Maxwell forces in the error function to be minimized. This permits an automated force reduction in the magnet designs while controlling the overall dimensions of the system. As SA optimization requires many iterations to achieve a final design, it is important that each iteration in the procedure is rapid. We have therefore developed a rapid force calculation algorithm. Novel designs for short 3- and 4-T clinical MRI systems are presented in which force reduction has been invoked. The final designs provide large homogeneous regions and reduced stray fields in remarkable short magnets. A shielded 4-T design that is approximately 30% shorter than current designs is presented. This novel magnet generates a full 50-cm diameter homogeneous region.

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.

Structural characterization of the N-terminal autoregulatory sequence of phenylalanine hydroxylase

Phenylalanine hydroxylase (PAH) is activated by its substrate phenylalanine, and through phosphorylation by cAMP-dependent protein kinase at Ser 16 in the N-terminal autoregulatory sequence of the enzyme. The crystal structures of phosphorylated and unphosphorylated forms of the enzyme showed that, in the absence of phenylalanine, in both cases the N-terminal 18 residues including the phosphorylation site contained no interpretable electron density. We used nuclear magnetic resonance (NMR) spectroscopy to characterize this N-terminal region of the molecule in different stages of the regulatory pathway. A number of sharp resonances are observed in PAH with an intact N-terminal region, but no sharp resonances are present in a truncation mutant lacking the N-terminal 29 residues. The N-terminal sequence therefore represents a mobile flexible region of the molecule. The resonances become weaker after the addition of phenylalanine, indicating a loss of mobility. The peptides corresponding to residues 2-20 of PAH have different structural characteristics in the phosphorylated and unphosphorylated forms, with the former showing increased secondary structure. Our results support the model whereby upon phenylalanine binding, the mobile N-terminal 18 residues of PAH associate with the folded core of the molecule; phosphorylation may facilitate this interaction.

Quantum dynamics of two coupled qubits

We investigate the difference between classical and quantum dynamics of coupled magnetic dipoles. We prove that in general the dynamics of the classical interaction Hamiltonian differs from the corresponding quantum model, regardless of the initial state. The difference appears as nonpositive-definite diffusion terms in the quantum evolution equation of an appropriate positive phase-space probability density. Thus, it is not possible to express the dynamics in terms of a convolution of a positive transition probability function and the initial condition as can be done in the classical case. It is this feature that enables the quantum system to evolve to an entangled state. We conclude that the dynamics are a quantum element of nuclear magnetic resonance quantum-information processing. There are two limits where our quantum evolution coincides with the classical one: the short-time limit before spin-spin interaction sets in and the long-time limit when phase diffusion is incorporated.

Axial mixing in rotating drums using magnetic resonance imaging using bran as a model for solid state fermentations

Magnetic resonance imaging (MRI) is an easily automated, reliable technique to investigate axial mixing within rotating drums. Moist bran can be clearly differentiated from dry bran using MRI allowing a non-segregating tracer for axial mixing. For a 20-cm diameter drum, the axial dispersion coefficient in the particle bed was 0.51 cm s(-2). Axial dispersion is scale-dependent.

Hydrofluoric acid pre-treatment for improving 13C CPMAS NMR spectral quality of forest soils in south-east Queensland, Australia

Hydrofluoric acid (HF) was used to pre-treat forest soils of south-east Queensland for assessing the effectiveness of iron (Fe) removal, carbon (C) composition using C-13 cross-polarisation (CP) with magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) before and after the HF pre-treatment, and the improvement of C-13 CPMAS NMR spectra. Soil samples were collected from 4 experimental sites of different soil types, harvest residue management or prescribed burning, and tree species. More than 86% of Fe was in all soil types removed by the HF treatment. The C-13 NMR spectral quality was improved with increased resolution, especially in the alkyl C and O-alkyl C regions, and reduced NMR run-time (1-5 h per sample compared with >20 h per sample without the pre-treatment). The C composition appeared to alter slightly after the pre-treatment, but this might be largely due to improved spectrometer conditions and increased resolution leading to more accurate NMR spectral integration. Organic C recovery after HF pre-treatment varied with soil types and forest management, and soluble soil organic matter (SOM) could be lost during the pre-treatment. The Fourier Transform-Infrared (FT-IR) spectra of HF extracts indicated the preferential removal of carboxylic C groups during the pre-treatment, but this could also be due to adsorbed water on the mineral matter. The NMR spectra revealed some changes in C composition and quality due to residue management and decomposition. Overall, the HF treatment was a useful pre-treatment for obtaining semi-quantitative C-13 CPMAS NMR spectra of subtropical Australian forest soils.

Repeated three-dimensional magnetic resonance imaging of atherosclerosis development in innominate arteries of low-density lipoprotein receptor-knockout mice

Background-In vivo methods to evaluate the size and composition of atherosclerotic lesions in animal models of atherosclerosis would assist in the testing of antiatherosclerotic drugs. We have developed an MRI method of detecting atherosclerotic plaque in the major vessels at the base of the heart in low-density lipoprotein (LDL) receptor-knockout (LDLR-/-) mice on a high-fat diet. Methods and Results-Three-dimensional fast spin-echo magnetic resonance images were acquired at 7 T by use of cardiac and respiratory triggering, with approximate to140-mum isotropic resolution, over 30 minutes. Comparison of normal and fat-suppressed images from female LDLR-/- mice I week before and 8 and 12 weeks after the transfer to a high-fat diet allowed visualization and quantification of plaque development in the innominate artery in vivo. Plaque mean cross-sectional area was significantly greater at week 12 in the LDLR-/- mice (0.14+/-0.086 mm(2) [mean+/-SD]) than in wild-type control mice on a normal diet (0.017+/-0.031 mm(2), p

Review of time-domain polarization measurements for assessing insulation condition in aged transformers

This paper presents a review of the time-domain polarization measurement techniques for the condition assessment of aged transformer insulation. The polarization process is first described with appropriate dielectric response theories and then commonly used polarization methods are described with special emphasis on the most widely used return voltage(rv) measurement. Most recent emphasis has been directed to techniques of determining moisture content of insulation indirectly by measuring rv parameters. The major difficulty still lies with the accurate interpretation of return voltage results. This paper investigates different thoughts regarding the interpretation of rv results for different moisture and ageing conditions. Other time domain polarization measurement techniques and their results are also presented in this paper.