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At least 595 records · Page 33Linked to original sources
PubMed1999

DENSE: displacement encoding with stimulated echoes in cardiac functional MRI.

Displacement encoding with stimulated echoes (DENSE) was developed for high-resolution myocardial displacement mapping. Pixel phase is modulated by myocardial displacement and data spatial resolution is limited only by pixel size. 2D displacement vector maps were generated for the systolic action in canines with 0.94 x 1.9 mm nominal in-plane resolution and 2.3 mm/pi displacement encoding. A radial strain of 0.208 was measured across the free left ventricular wall over 105 ms during systole. DENSE displacement maps require small first-order gradient moments for encoding. DENSE magnitude images exhibit black-blood contrast which allows for better myocardial definition and reduced motion-related artifacts.

Animals↗
PubMed1997

Preliminary experience with medical applications of rapid prototyping by selective laser sintering.

Rapid prototyping techniques, originally developed for building components from computer aided designs in the motor industry, are now being applied in medicine to build models of human anatomy from high resolution multiplanar imaging data such a computed tomography (CT). The established technique of stereolithography and the more recent selective laser sintering (SLS), both build up an object layer by layer. Models have applications in surgical planning, for the design of customised implants and for training. Preliminary experience of using the SLS technique for medical applications is described, addressing questions regarding image processing, data transfer and manufacture. Pilot models, built from nylon, included two skills (a child with craniosynoslosis and an adult with hypertetorism) and a normal femur which was modelled for use in a bioengineering test of an artificial hip. The dimensions of the models were found to be in good agreement with the CT data from which they were built-for the child's skull the difference between the model and the CT data was less than 1.0 +/- 0.5 mm in each direction. Our experience showed that, with care, a combination of existing software packages may be used for data conversion. Ideally, image data of high spatial resolution should be used. The pilot models generated sufficient clinical interest for the technique to be pursued in the orthopaedic field.

Adult↗
PubMed2002

Crystallization of a nickel-containing superoxide dismutase and preliminary phase determination by MAD at the Ni K edge.

Superoxide dismutases are metalloenzymes which catalyse the disproportion of superoxide radicals and thus play an important role in the protection of biomolecules from oxidative damage. Redox-active metal ions known to act as the catalytic centre of these enzymes are Cu, Mn or Fe. Recently, enzymes containing Ni have been found in various Streptomyces species, introducing a fourth type of metal ion to the superoxide dismutase family. NiSOD has been crystallized for the purpose of structure determination by X-ray crystallography using Ni as an anomalous scatterer in multiple-wavelength anomalous dispersion (MAD) experiments. Two crystal forms belonging to space group P2(1)2(1)2(1) and one belonging to space group R3 were obtained using ammonium sulfate as a precipitant. Patterson maps of one of the orthorhombic forms revealed the presence of pseudo-translation, which could be removed for the other orthorhombic form by using 10% glycerol in its crystallization conditions. In addition, this reduced the unit cell by half. Phase information which led to interpretable electron-density maps was derived from MAD data to 2.0 A resolution after density modification applying solvent flattening, histogram matching and NCS averaging. Phases were extended to 1.68 A resolution with a data set collected at a wavelength of 1 A. Model building based on the resulting electron-density maps is in progress.

Catalytic Domain↗
PubMed1974

Pulse code modulation telemetry in ski injury research. I. Instrumentation.

Measurement problems can be classified into instrumentation, data transmission and recording, and analysis. This paper focuses on the transmission of multichannel, high-volume, high-frequency, high-accuracy data. Boot-ski dynamometer and skier velocity anemometer data provide 13 channels of max. 8-mV signals requiring 8-microvolt resolution or 4.45-Newton dynamometer resolution. The data transmission system features durability, power consumption approx. 10 Watts, weight 4.54 kp, range greater than 3,500 m, frequency response 250 Hz, accuracy 1 per cent, temperature stability, dynamic range plus or minus 2 inches. The transducer signals are ampflified to plus or minus 10 V for the 100-kbps PCM system. Special AC amplifiers, driven by an amplitude-stabilized power oscillator, were designed for elimination of radio frequency interference (RFI), improved stability and high signal/noise. Sixteen words are sequentially sampled at 521/sec-13 data, 2 frame counters, and 1 sync. The ground station consists of the PCM decoder with real-time capability and an analog tape recorder. Data is subsequently buffered and formatted onto digital tape by mini-computer.

Athletic Injuries↗
PubMed2006

Analysis of environmental samples by application of multivariate curve resolution on fused high-performance liquid chromatography-diode array detection mass spectrometry data.

Multivariate curve resolution-alternating least squares (MCR-ALS) is applied to solve coelution problems in liquid chromatograpy with diode array detection (DAD) and mass spectrometry (MS). Fusion of DAD and MS detector signals improved results versus those obtained using only one of the two detector signals. Application of wavelet transform to MS data before its fusion with DAD data, further help to facilitate the resolution and quantitation of the coeluted compounds under study, besides a decrease of time of analysis. Mixtures of biocide compounds in standard mixtures and in environmental samples (sediment and wastewater samples) were analyzed with estimated quantitation errors below 12%.

Chromatography, High Pressure Liquid↗
PubMed2005

High-resolution PET detector design: modelling components of intrinsic spatial resolution.

The development of dedicated small animal PET (positron emission tomography) scanners has led to significantly higher spatial resolution and comparable sensitivity to clinical scanners. However, it is not clear whether we are approaching the fundamental limit of spatial resolution. This work aims to understand what is currently limiting spatial resolution during data formation and collection and how to apply that knowledge to obtain the best possible resolution for small animal PET without sacrificing sensitivity. Monte Carlo simulations were performed of the interactions of a 511 keV photon in a variety of detector materials to evaluate the modulation transfer function of the materials. Positron range, non-colinearity and pixel size were modelled to determine the contribution of additional components of data formation and collection on the complete modulation transfer function of a PET system. These simulations are shown to predict the intrinsic detector resolution of current high resolution systems very well. They also show that current detectors are not limited by inter-crystal scatter. An intrinsic resolution of 0.5 mm can be achieved, but would require a detector with a pixel size of around 250 microm that can be read out unambiguously. It is shown that a range of different detector materials, both scintillators and semiconductors, can be used in these high-resolution detectors. While this design relies on thin (approximately 3 mm) pieces of material, stacks of the material are shown to simultaneously provide spatial resolution near 0.5 mm and 60% efficiency. This work has shown that detectors with significantly better resolution and sensitivity can be developed for small animal PET applications.

Computer Simulation↗
PubMed2005

Urban meteorological modelling for nuclear emergency preparedness.

The main objectives of the current EU project "Integrated Systems for Forecasting Urban Meteorology, Air Pollution and Population Exposure" (FUMAPEX) are the improvement of meteorological forecasts for urban areas, the connection of numerical weather prediction (NWP) models to urban air pollution and population dose models, the building of improved urban air quality information and forecasting systems, and their application in cities in various European climates. In addition to the forecast of the worst air-pollution episodes in large cities, the potential use of improved weather forecasts for nuclear emergency management in urban areas, in case of hazardous releases from nuclear accidents or terror acts, is considered. Such use of NWP data is tested for the Copenhagen metropolitan area and the Øresund region. The Danish Meteorological Institute (DMI) is running an experimental version of the HIRLAM NWP model over Zealand including the Copenhagen metropolitan area with a horizontal resolution of 1.4km, thus approaching the city-scale. This involves 1-km resolution physiographic data with implications for the urban surface parameters, e.g. surface fluxes, roughness length and albedo. For the city of Copenhagen, the enhanced high-resolution NWP forecasting will be provided to demonstrate the improved dispersion forecasting capabilities of the Danish nuclear emergency preparedness decision-support system, the Accident Reporting and Guidance Operational System (ARGOS), used by the Danish Emergency Management Agency (DEMA). Recently, ARGOS has been extended with a capability of real-time calculation of regional-scale atmospheric dispersion of radioactive material from accidental releases. This is effectuated through on-line interfacing with the Danish Emergency Response Model of the Atmosphere (DERMA), which is run at DMI. For local-scale modelling of atmospheric dispersion, ARGOS utilises the Local-Scale Model Chain (LSMC), which makes use of high-resolution DMI-HIRLAM NWP model data provided to DEMA by DMI four times a day under operational surveillance and covering Denmark and surroundings. The integration of DERMA in ARGOS is effectuated through automated on-line digital communication and exchange of data. The calculations are carried out in parallel for each NWP model to which DMI has access, thereby providing a mini-ensemble of dispersion forecasts for the emergency management.

Air Pollutants, Radioactive↗
PubMed2001

Thermodynamics of metal ion binding. 1. Metal ion binding by wild-type carbonic anhydrase.

Understanding the energetic consequences of molecular structure in aqueous solution is a prerequisite to the rational design of synthetic motifs with predictable properties. Such properties include ligand binding and the collapse of polymer chains into discrete three-dimensional structures. Despite advances in macromolecular structure determination, correlations of structure with high-resolution thermodynamic data remain limited. Here we compare thermodynamic parameters for the binding of Zn(II), Cu(II), and Co(II) to human carbonic anhydrase II. These calorimetrically determined values are interpreted in terms of high-resolution X-ray crystallographic data. While both zinc and cobalt are bound with a 1:1 stoichiometry, CAII binds two copper ions. Considering only the high-affinity site, there is a diminution in the enthalpy of binding through the series Co(II) --> Zn(II) --> Cu(II) that mirrors the enthalpy of hydration; this observation reinforces the notion that the thermodynamics of solute association with water is at least as important as the thermodynamics of solute-solute interaction and that these effects must be considered when interpreting association in aqueous solution. Additionally, DeltaC(p) data suggest that zinc binding to CAII proceeds with a greater contribution from desolvation than does binding of either copper or cobalt, suggesting Nature optimizes binding by optimizing desolvation.

Apoenzymes↗
PubMed2001

Quasistatic zooming of FDTD E-field computations: the impact of down-scaling techniques.

Due to current computer limitations, regional hyperthermia treatment planning (HTP) is practically limited to a resolution of 1 cm, whereas a millimetre resolution is desired. Using the centimetre resolution E-field distribution, computed with, for example, the finite-difference time-domain (FDTD) method and the millimetre resolution patient anatomy it is possible to obtain a millimetre resolution SAR distribution in a volume of interest (VOI) by means of quasistatic zooming. To compute the required low-resolution E-field distribution, a low-resolution dielectric geometry is needed which is constructed by down-scaling the millimetre resolution dielectric geometry. In this study we have investigated which down-scaling technique results in a dielectric geometry that yields the best low-resolution E-field distribution as input for quasistatic zooming. A segmented 2 mm resolution CT data set of a patient has been down-scaled to 1 cm resolution using three different techniques: 'winner-takes-all', 'volumetric averaging' and 'anisotropic volumetric averaging'. The E-field distributions computed for those low-resolution dielectric geometries have been used as input for quasistatic zooming. The resulting zoomed-resolution SAR distributions were compared with a reference: the 2 mm resolution SAR distribution computed with the FDTD method. The E-field distribution for both a simple phantom and the complex partial patient geometry down-scaled using 'anisotropic volumetric averaging' resulted in zoomed-resolution SAR distributions that best approximate the corresponding high-resolution SAR distribution (correlation 97, 96% and absolute averaged difference 6, 14% respectively).

Anisotropy↗
PubMed2003

Use of the orthogonal projection approach (OPA) to monitor batch processes.

The orthogonal projection approach (OPA) and multivariate curve resolution (MCR) are presented as a way to monitor batch processes using spectroscopic data. Curve resolution allows one to look within a batch and predict on-line real concentration profiles of the different species appearing during reactions. Taking into account the variations of the process by using an augmented matrix of complete batches, the procedure explained here calculates some prediction coefficients that can afterwards be applied for a new batch.

Algorithms↗
PubMed2004

Crystallization and preliminary analysis of active nitroalkane oxidase in three crystal forms.

Nitroalkane oxidase (NAO), a flavoprotein cloned and purified from Fusarium oxysporum, catalyzes the oxidation of neutral nitroalkanes to the corresponding aldehydes or ketones, with the production of H2O2 and nitrite. In this paper, the crystallization and preliminary X-ray data analysis of three crystal forms of active nitroalkane oxidase are described. The first crystal form belongs to a trigonal space group (either P3(1)21 or P3(2)21, with unit-cell parameters a = b = 103.8, c = 487.0 A) and diffracts to at least 1.6 A resolution. Several data sets were collected using 2theta and kappa geometry in order to obtain a complete data set to 2.07 A resolution. Solvent-content and Matthews coefficient analysis suggests that crystal form 1 contains two homotetramers per asymmetric unit. Crystal form 2 (P2(1)2(1)2(1); a = 147.3, b = 153.5, c = 169.5 A) and crystal form 3 (P3(1) or P3(2); a = b = 108.9, c = 342.5 A) are obtained from slightly different conditions and also contain two homotetramers per asymmetric unit, but have different solvent contents. A three-wavelength MAD data set was collected from selenomethionine-enriched NAO (SeMet-NAO) in crystal form 3 and will be used for phasing.

Crystallization↗
PubMed2004

Respiratory reordered UNFOLD perfusion imaging.

PURPOSE: To propose a respiratory reordered UNFOLD (RR-UNFOLD) imaging sequence to significantly reduce the amount of k-space data required for first-pass MR myocardial perfusion imaging. MATERIALS AND METHODS: Rapid acquisition of high-resolution imaging data is essential to detailed quantitative analysis of first-pass myocardial perfusion. Existing MR sequences have explored the full capacity of the imaging hardware to reduce the acquisition window within each cardiac cycle while maintaining the desired spatial resolution. Further improvement in perfusion imaging will require a more efficient use of the information content of the k-space data. The method uses prospective diaphragmatic navigator echoes to ensure that temporal filtering of UNFOLD is carried out on a series of images that are spatially registered. An adaptive real-time rebinning algorithm is developed for the creation of static image subseries related to different levels of respiratory motion. Issues concerning the temporal smoothing of tracer kinetic signals are discussed, and a solution based on oversampling of the central k-space is provided. The method is assessed in 10 normal subjects without the administration of contrast agent, and further validated by administration of Gd-DTPA in 10 patients at rest. RESULTS: The results of this study show that RR-UNFOLD significantly extends the applicability of UNFOLD to perfusion imaging, which yields a 40% reduction in image artifact when the same amount of k-space information is used. CONCLUSION: The scan efficiency achieved can be used in combination with MR hardware improvements for extending the three-dimensional spatial coverage and shortening the data acquisition window to provide detailed information on regional myocardial perfusion abnormalities.

Adult↗
PubMed1989

Estimation of single channel kinetic parameters from data subject to limited time resolution.

The limited responsiveness of single-channel recording systems results in some brief events not being detected, and if this is ignored parameter estimation from the observed data will be biased. Statistical methods of correcting for this limited time resolution in a two-state Markov model have been proposed by Neher (1983. J. Physiol. (Lond.). 339:663-678) and by Colquhoun and Sigworth (1983. Single Channel Recording. 191-263). However, a numerical study by Blatz and Magleby (1986. Biophys. J. 49:967-980) indicated differences of 3-40% in the corrected values given by the two techniques. Here we explain why Neher's method produces biased results and the Colquhoun and Sigworth approach, which is no more difficult, provides reasonably accurate estimates.

Ion Channels↗
PubMed2005

Effects of spatial and temporal resolution for MR image-guided thermal ablation of prostate with transurethral ultrasound.

PURPOSE: To describe approaches for determining optimal spatial and temporal resolutions for the proton resonance frequency shift method of quantitative magnetic resonance temperature imaging (MRTI) guidance of transurethral ultrasonic prostate ablation. MATERIALS AND METHODS: Temperature distributions of two transurethral ultrasound applicators (90 degrees sectored tubular and planar arrays) for canine prostate ablation were measured via MRTI during in vivo sonication, and agree well with two-dimensional finite difference model simulations at various spatial resolutions. Measured temperature distributions establish the relevant signal-to-noise ratio (SNR) range for thermometry in an interventional MR scanner, and are reconstructed at different resolutions to compare resultant temperature measurements. Various temporal resolutions are calculated by averaging MRTI frames. RESULTS: When noise is added to simulated temperature distributions for tubular and planar applicators, the minimum root mean squared (RMS) error is achieved by reconstructing to pixel sizes of 1.9 and 1.7 mm, respectively. In in vivo measurements, low spatial resolution MRTI data are shown to reduce the noise without significantly affecting thermal dose calculations. Temporal resolution of 0.66 frames/minute leads to measurement errors of more than 12 degrees C during rapid heating. CONCLUSION: Optimizing MRTI pixel size entails balancing large pixel SNR gain with accuracy in representing underlying temperature distributions.

Animals↗
PubMed2001

Resolution of GC-MS data of complex PAC mixtures and regression modeling of mutagenicity by PLS.

The present work describes a strategy to predict the mutagenicity of very complex mixtures of polycyclic aromatic compounds (PAC) from gas chromatography-mass spectrometry (GC-MS) patterns of the mixtures, each containing 260 compounds on average. The mixtures, 13 organic extracts of exhaust particles, were characterized by full scan GC-MS. The data were resolved into peaks and spectra for individual compounds by an automated curve resolution procedure. Similarity between spectra was evaluated for peaks that appeared within a time interval of 4 min, using a similarity index of 0.8 to ascertain that the same compound was represented by the same variable name (retention time) in all samples. The resolved chromatograms were integrated, resulting in a predictor matrix of size 13 x 721, which was used as input to a multivariate regression model. Partial least-squares projections to latent structures (PLS) were used to correlate the GC-MS chromatograms to mutagenicity as measured in the Ames Salmonella assay. The best model (high r2 and Q2) was obtained with 52 variables. These variables covary with the observed mutagenicity, and may subsequently be identified chemically. Furthermore, the regression model can be used to predict mutagenicity from GC-MS chromatograms of other organic extracts.

Air Pollutants↗
PubMed1996

A method for determining high-resolution activation time delays in unipolar cardiac mapping.

This paper presents a method for determining activation time delays in unipolar cardiac mapping data to resolutions considerably smaller than the sample interval. The method involves taking two filtered, differentiated electrograms and computing the Hilbert transform of their cross correlation, which exhibits a negative-to-positive zero crossing at the delay time between the signals. Simultaneous endocardial/epicardial recordings of sinus rhythm were made in the swine right atrium using identical, precisely superpositioned electrode arrays. Data were amplified, lowpass filtered, and digitized at 1000 Hz. A window of data was chosen around each electrogram in an endocardial/epicardial electrogram pair. The windowed electrograms were differentiated and highpass filtered, and the Hilbert transform of the cross correlation between the electrograms was computed. The activation time delay was taken to be the first negative-to-positive zero crossing. Average activation time delays (+/- SD) were computed for 4-s sinus rhythm recordings from each endocardial/epicardial electrode pair. For a representative site, the average transmural activation time delay was 0.71 +/- 0.06 ms (n = 10 electrograms). Time delays estimated using the Hilbert transform method were compared with time delays estimated using the maximum negative slope criterion. The Hilbert transform results exhibited much smaller standard deviations, indicating that the Hilbert transform method may produce more accurate time delay estimates than the maximum negative slope method.

Action Potentials↗
PubMedDate not supplied

Wavelet based multiresolution expectation maximization image reconstruction algorithm for positron emission tomography.

Maximum Likelihood (ML) estimation based Expectation Maximization (EM) [IEEE Trans Med Imag, MI-1 (2) (1982) 113] reconstruction algorithm has shown to provide good quality reconstruction for positron emission tomography (PET). Our previous work [IEEE Trans Med Imag, 7(4) (1988) 273; Proc IEEE EMBS Conf, 20(2/6) (1998) 759] introduced the multigrid (MG) and multiresolution (MR) concept for PET image reconstruction using EM. This work transforms the MGEM and MREM algorithm to a Wavelet based Multiresolution EM (WMREM) algorithm by extending the concept of switching resolutions in both image and data spaces. The MR data space is generated by performing a 2D-wavelet transform on the acquired tube data that is used to reconstruct images at different spatial resolutions. Wavelet transform is used for MR reconstruction as well as adapted in the criterion for switching resolution levels. The advantage of the wavelet transform is that it provides very good frequency and spatial (time) localization and allows the use of these coarse resolution data spaces in the EM estimation process. The MR algorithm recovers low-frequency components of the reconstructed image at coarser resolutions in fewer iterations, reducing the number of iterations required at finer resolution to recover high-frequency components. This paper also presents the design of customized biorthogonal wavelet filters using the lifting method that are used for data decomposition and image reconstruction and compares them to other commonly known wavelets.

Algorithms↗
PubMed1998

Dipolar recoupling NMR of biomolecular self-assemblies: determining inter- and intrastrand distances in fibrilized Alzheimer's beta-amyloid peptide.

We demonstrate a new method for investigating the structure of self-associating biopolymers using dipolar recoupling NMR techniques. This approach was applied to the study of fibrillar beta-amyloid (Abeta) peptides (the primary component of the plaques of Alzheimer's disease) containing only a single isotopic spin label (13C), by employing the DRAWS (dipolar recoupling with a windowless sequence) technique to measure 13C-13C distances. The 'single-label' approach simplified analysis of DRAWS data, since only interstrand contacts are present, without the possibility of any intrastrand contacts. As previously reported [T.L.S. Benzinger, D.M. Gregory, T.S. Burkoth, H. Miller-Auer, D.G. Lynn, R.E. Botto, S.C. Meredith, Proc. Natl. Acad. Sci. 95 (1998) 13407.], contacts of approximately 5 A were observed at all residues studied, consistent with an extended parallel beta-sheet structure with each amino acid in exact register. Here, we propose that our strategy is completely generalizable, and provides a new approach for characterizing any iterative, self-associating biopolymer. Towards the end of generalizing and refining our approach, in this paper we evaluate several issues raised by our previous analyses. First, we consider the effects of double-quantum (DQ) transverse relaxation processes. Next, we discuss the effects of various multiple-spin geometries on modeling of DRAWS data. Several practical issues are also discussed: these include (1) the use of DQ filtering experiments, either to corroborate DRAWS data, or as a rapid screening assessment of the proper placement of isotopic spin labels; and (2) the comparison of solid samples prepared by either lyophilization or freezing. Finally, data obtained from the use of single labels is compared with that obtained in doubly 13C-labeled model compounds of known crystal structure. It is shown that such data are obtainable in far more complex peptide molecules. These data,taken together, refine the DRAWS method, and demonstrate its precision and utility in obtaining high resolution structural data in complex biomolecular aggregates such as Abeta.

Amyloid beta-Peptides↗