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At least 1,333 records · Page 74Linked to original sources
PubMed1988

MR evaluation of large intracranial aneurysms using cine low flip angle gradient-refocused imaging.

MR imaging has proved to be useful in evaluating large intracranial aneurysms. The parent artery and patent lumen can be identified as flow voids and differentiated from thrombus. However, in the presence of slow flow, even-echo rephasing, and motion artifact, increased intraluminal signal may be present, which may be difficult to distinguish from thrombus. Aneurysms are also dynamic lesions and exert pulsatile mass effect on adjacent structures. Further definition of vascular anatomy and physiology may aid in therapeutic planning and assessment. Cine MR is a new technique using a movie loop of sequential GRASS (gradient-recalled acquisition in the steady state) images obtained during various points in the cardiac cycle. The combination of GRASS images and cardiac gating thus allows cinegraphic display of vascular structures. A comparison of this method with routine T1- and T2-weighted MR imaging and angiography was made in a group of 13 patients with intracranial aneurysms greater than 1.5 cm in diameter. Eight of these patients underwent transvascular detachable balloon occlusion. With cine MR, flowing blood has high intensity due to flow-related enhancement. Turbulent and high-velocity flow can be recognized on the basis of signal loss, which occurs during systole. Thrombus demonstrated variable signal intensity, which remained unchanged during the cardiac cycle. Compared with routine MR sequences, there was less image degradation from phase-encoding artifacts and improved visualization of the neck of the aneurysm. Pulsatile mass effect was uniquely assessed. After transvascular embolization, cine MR demonstrated improved conspicuity of acute thrombus and higher contrast between flowing blood and the occlusion balloon when compared with routine MR. Confirmation of flow within the parent vessel, residual aneurysm lumen, and distal arterial branches is possible. If the parent vessel was occluded, cine MR yielded greater information than angiography. Cine MR provides additional anatomic and physiologic data in the evaluation and assessment of therapy of intracranial aneurysms. Information can be obtained that is not available with either routine MR or angiography. The inherent limitations of this new technique include partial-volume artifacts, less than optimal flow-related enhancement or spatial resolution, and poor data acquisition due to cardiac arrhythmias.

Adolescent↗
PubMed1998

Spatio-temporal fMRI analysis using Markov random fields.

Functional magnetic resonance images (fMRI's) provide high-resolution datasets which allow researchers to obtain accurate delineation and sensitive detection of activation areas involved in cognitive processes. To preserve the resolution of this noninvasive technique, refined methods are required in the analysis of the data. In this paper, we first discuss the widely used methods based on a statistical parameter map (SPM) analysis exposing the different shortcomings of this approach when considering high-resolution data. First, the often used Gaussian filtering results in a blurring effect and in delocalization of the activated area. Secondly, the SPM approach only considers false alarms due to noise but not rejections of activated voxels. We propose to embed the fMRI analysis problem into a Bayesian framework consisting of two steps: i) data restoration and ii) data analysis. We, therefore, propose two Markov random fields (MRF's) to solve these two problems. Results on three protocols (visual, motor and word recognition) are shown for two SPM approaches and compared with the proposed MRF approach.

Adult↗
PubMed2004

SENSE-DTI at 3 T.

While holding vast potential, diffusion tensor imaging (DTI) with single-excitation protocols still faces serious challenges. Limited spatial resolution, susceptibility to magnetic field inhomogeneity, and low signal-to-noise ratio (SNR) may be considered the most prominent limitations. It is demonstrated that all of these shortcomings can be effectively mitigated by the transition to parallel imaging technology and high magnetic field strength. Using the sensitivity encoding (SENSE) technique at 3 T, brain DTI was performed in nine healthy volunteers. Despite enhanced field inhomogeneity, parallel acquisition permitted both controlling geometric distortions and enhancing spatial resolution up to 0.8 mm in-plane. Heightened SNR requirements were met in part by high base sensitivity at 3 T. A further significant increase in SNR efficiency was accomplished by SENSE acquisition, exploiting enhanced encoding speed for echo time reduction. Based on the resulting image data, high-resolution tensor mapping is demonstrated.

Anisotropy↗
PubMed2005

Multi-Resolution FOCUSS: a source imaging technique applied to MEG data.

A variety of techniques are available for imaging magnetoencephalographic (MEG) data to the corresponding cortical structures. Each performs a functional optimization that includes mathematical and physical restrictions on source activity. Unlike other imaging techniques, MR-FOCUSS (Multi-Resolution FOCal Underdetermined System Solution) utilizes a wavelet statistical operator that allows spatial resolution to be chosen appropriately for focal or extended sources. Control of focal imaging properties is achieved by specifying P in an l(P) norm distribution template used to construct the wavelets. In addition, incorporation of a multi-resolution wavelet operator desensitizes the mathematical algorithm to noise, (regularization). Like the FOCUSS imaging technique, an initial estimate of cortical activity is recursively enhanced to obtain the final high resolution imaging results. Studies of model MEG data representing all regions of a realistic cortical model are performed to quantify MR-FOCUSS imaging properties. These modeled data studies included single and multiple dipole sources as well as an extended source model. Thus, MR-FOCUSS is found to be very effective for imaging language processing for pre-surgical planning and provides a high-resolution method to image sequential activation of multiple correlated sources involved in language processing.

Algorithms↗
PubMed1997

VET imaging: magnetic resonance imaging with variable encoding time.

A methodology of MRI data acquisition is introduced which involves lengthening the duration of signal readout period with complementary shortening of the phase encode pulses, and vice versa, in sequences where gradient encoding time is limited by RF pulse spacing. This variable encoding time (VET) methodology can be used to increase spatial resolution or reduce data acquisition time in 2D and 3D FT MRI based on CPMG and gradient echo sequences. Advantages of higher image SNR and different spatial frequency distributions in k-space are discussed and evaluated in preliminary experiments.

Aged↗
PubMed1985

A practical, high-resolution, microcomputer-based method for the analysis of relaxation data exhibiting multicomponent exponential decays.

We have developed and tested a practical, rapid, high-resolution, microcomputer-based method for the analysis of multicomponent exponential decays. The analysis utilizes the Fourier deconvolution technique and includes methods to reduce noise both in the input data and in the results. The developed method is particularly well suited for analysing decays consisting of a wide range of decay times. The method resolves two exponential decays differing by a factor of two when the input data are mathematically generated and without noise, and resolves two decays differing by a factor of three when 2% Gaussian noise is present in the same data. The method lends itself to routine analysis of any relaxation process consisting of exponential decays, including biomedical applications such as enzyme kinetics, circulatory transport functions, pharmacokinetics, plasma exchange therapy, and analysis of compartmental models for any process.

Birefringence↗
PubMed1998

Energetic particle fluxes data base of "CORONAS-I" satellite observations.

The data base DB SCR uses data obtained by the SCR instrument package on the CORONAS-I satellite. DB SCR contains information about fluxes of relativistic electrons (0.5-124 MeV), protons (1-300 MeV), nuclei (1-19 MeV/nucl) and gamma-radiation (0.1-7 MeV) in the low altitude region (500 km). The time resolution of the data is 2.5 s. Magnetic field parameters (B, magnetic latitude and longitude), L-shell and local times (LT and MLT) are included in DB SCR. Since all parameters are equivalents it is possible to perform the multidimensional analysis for any set of DB SCR parameters. The additional DB SCR software packages may be used to develop different semi-empirical models.

Databases, Factual↗
PubMed2006

Rearranged gene order between pig and human in a quantitative trait loci region on SSC3.

A quantitative trait locus (QTL) for ovulation rate on chromosome 3 that peaks at 36 cM has been identified in a Meishan-White composite resource population with an additive effect of 2.2 corpora lutea. As part of an effort to identify the responsible gene(s), typing of additional genes on the INRA-University of Minnesota porcine radiation hybrid (IMpRH) map of SSC3 and comparative analysis of gene order was conducted. We placed 52 known genes and expressed sequence tags, two BAC-end sequences and one microsatellite (SB42) on a framework map that fills gaps on previous RH maps. Data were analysed for two-point and multipoint linkage with the IMpRH mapping tool and were submitted to the IMpRH database (http://imprh.toulouse.inra.fr/). Gene order was confirmed for 42 loci residing in the QTL region (spanning c. 17 Mb of human sequence) by using the high-resolution IMpRH2 panel. Carthagène (http://www.inra.fr/internet/departments/MIA/T/CarthaGene) was used to estimate multipoint marker distance and order using all public markers on SSC3 in the IMpRH database and those typed in this study. For the high-resolution map, only data for markers typed in both panels were used. Comparative analysis of human and porcine maps identified conservation of gene order for SSC3q and multiple blocks of conserved segments for SSC3p, which included six distinct segments of HSA7 and two segments of HSA16. The results of this study allow significant refinement of the SSC3p region that contains an ovulation rate QTL.

Animals↗
PubMed1996

Phylogeography and population structure of the Atlantic and Mediterranean green turtle Chelonia mydas: a mitochondrial DNA control region sequence assessment.

Mitochondrial (mt) DNA sequences were analysed to resolve the phylogeography and population genetic structure of Atlantic and Mediterranean populations of green turtles (Chelonia mydas). Analysis of sequence variation over 487 base pairs of the control (D-loop) region identified 18 haplotypes among 147 individuals from nine nesting populations. Pairwise comparisons of haplotype frequencies distinguished most nesting colonies, indicating significant genetic differentiation among rookeries and a strong propensity for natal homing behaviour by nesting females. Comparison of control region sequence data to earlier restriction fragment length polymorphism (RFLP) data for the same individuals demonstrates approximately a sixfold higher substitution rate in the 5' end of the control region. The sequence data provide higher resolution both in terms of the number of mtDNA genotype variants and the phylogeographic relationships detected within the Atlantic region, and reveal a gene genealogy that distinguishes two groups of haplotypes corresponding to (i) the western Caribbean and Mediterranean, and (ii) eastern Caribbean, South Atlantic and West Africa. The data suggest that phylogeographic patterns in the Atlantic Ocean may be interpreted in terms of female nest site fidelity and episodic dispersal events. The distribution of mtDNA haplotypes within the region is thus explained by the geological and climatic alternations (glacial and interglacial) over the last million years.

Animals↗
PubMed2000

Crystal structure of FMN-dependent nitroreductase from Escherichia coli B: a prodrug-activating enzyme.

The FMN-dependent flavoprotein nitroreductase from Escherichia coli B (NTR) is used in cancer chemotherapy to activate a range of prodrugs. The crystal structure of this enzyme has been determined, using molecular replacement methods and refined at 2.06 A resolution. The recombinant 24-kDa enzyme was crystallized in the tetragonal space group P4(1)2(1)2, with unit cell dimensions of a = b = 57.74 A and c = 275.51 A and two molecules in the asymmetric unit. The structure has a final R factor of 20.3% (R(free) = 26.7%), for all data between the resolution ranges of 10-2.06 A, and includes 4453 protein atoms, 230 water molecules, and 2 flavin mononucleotide (FMN) molecules. The functional unit is a homodimer, which forms the asymmetric unit in the crystal structure. The tertiary structures of these two monomers and their subunit interactions are nearly identical. The molecular replacement search model, the crystal structure of the major NAD(P)H:FMN oxidoreductase of Vibrio fisheri (FRase 1), was selected on the basis of its high sequence identity to that of NTR. The final superposition of these two enzymes revealed a very similar overall fold, with variation in the structures focused around surface loops and helices near the FMN cofactor. Helix G is implicated in substrate specificity and is better resolved in the present NTR structure than in the previously reported FRase 1 structure. The FMN binding pocket is also well-resolved, showing the presence of two channels leading into the active site. The amino acid side chains and main chain atoms interacting with the FMN are well-ordered. The structure of the substrate binding pocket has been used to examine substrate specificity and enzyme kinetics for prodrugs used in antibody-directed enzyme prodrug therapy (ADEPT) and gene-directed enzyme prodrug therapy (GDEPT).

Amino Acid Sequence↗
PubMed1999

Applying epidemiology-based outcomes research to clinical decision-making. A hypothetical model of biotechnology therapy in gram-negative sepsis.

OBJECTIVE: Sepsis occurs in a heterogeneous population. A prospective nationwide surveillance study found that populations stratified by infection type had significant differences in the incidence of sepsis syndrome, rate of complications and mortality. The objective of this study was to explore whether successful identification of population-specific risk factors for disease-associated morbidity and mortality may allow for more accurate assessment of the cost effectiveness of treatment strategies. DESIGN: A decision analytic model was developed using outcomes data on incidence and resolution of major complications in sepsis syndrome. Healthcare resource utilisation data were based on length of hospital stay, intensive care unit stay versus hospital ward stay, and cost of treating sepsis-related complications. SETTING: This modelling study, conducted from the perspective of the healthcare institution, used actual outcomes data on 2 infection-specific patient populations. PATIENTS AND PARTICIPANTS: The 2 populations studied were patients with nosocomial respiratory tract infection or community-acquired urinary tract infection who subsequently developed sepsis syndrome. INTERVENTIONS: Treatment options modelled were standard therapy plus biotechnology therapy versus standard therapy alone in the treatment of gram-negative sepsis complications. MAIN OUTCOME MEASURES AND RESULTS: The incremental cost-effectiveness ratios differed between the 2 study populations, due to differences in the incidence and rate of resolution of major sepsis-associated complications. The use of biotechnology therapy is always more cost effective in the respiratory tract infection population. CONCLUSIONS: Cost-effectiveness results for a therapy may change when the epidemiology of the disease state is known and incorporated into the decision analytic model. An infection-specific approach is important in the treatment of sepsis.

Decision Making↗
PubMed2004

Multislice CT angiography: a practical guide to CT angiography in vascular imaging and intervention.

The development of multidetector CT (MDCT) has revolutionized CT angiography (CTA). Not only are new techniques now in the remit of CTA, but all the studies previously performed on single slice or helical CT can now be done with better resolution. The advantage of MDCT relevant to CTA is the ability to acquire high resolution, near isotropic data sets in a shorter acquisition time. Also important is the ability to achieve a longer scanning range in the arterial phase, which has seen the introduction of CTA of the peripheral arterial system. Image processing techniques have also progressed rapidly, with simplification of a previously cumbersome process. The high spatial resolution and relatively non-invasive nature make MDCT angiography a strong and serious competitor to established vascular imaging techniques. The implication is that traditional diagnostic pathways for evaluation of the vascular system have changed.

Angiography↗
PubMed2005

Efficient inference of haplotypes from genotypes on a large animal pedigree.

We present a simple algorithm for reconstruction of haplotypes from a sample of multilocus genotypes. The algorithm is aimed specifically for analysis of very large pedigrees for small chromosomal segments, where recombination frequency within the chromosomal segment can be assumed to be zero. The algorithm was tested both on simulated pedigrees of 155 individuals in a family structure of three generations and on real data of 1149 animals from the Israeli Holstein dairy cattle population, including 406 bulls with genotypes, but no females with genotypes. The rate of haplotype resolution for the simulated data was >91% with a standard deviation of 2%. With 20% missing data, the rate of haplotype resolution was 67.5% with a standard deviation of 1.3%. In both cases all recovered haplotypes were correct. In the real data, allele origin was resolved for 22% of the heterozygous genotypes, even though 70% of the genotypes were missing. Haplotypes were resolved for 36% of the males. Computing time was insignificant for both data sets. Despite the intricacy of large-scale real pedigree genotypes, the proposed algorithm provides a practical rule-based solution for resolving haplotypes for small chromosomal segments in commercial animal populations.

Algorithms↗
PubMed2004

Assessment of rice fields by GIS/GPS-supported classification of MODIS data.

The new Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite image offers a large choice of opportunities for operational applications. The 1-km Advanced Very High Resolution Radiometer (AVHRR) image is not suitable for retrieval of field level parameter and Landsat data are not frequent enough for monitoring changes in crop parameters during the critical crop growth periods. A methodology to map areas of paddy fields using MODIS, geographic information system (GIS) and global position system (GPS) is introduced in this paper. Training samples are selected and located with the help of GPS to provide maximal accuracy. A concept of assessing areas of potential cultivation of rice is suggested by means of GIS integration. By integration of MODIS with GIS and GPS technologies the actual areas of rice fields in 2002 have been mapped. The classification accuracy was 95.7% percent compared with the statistical data of the Agricultural Bureau of Zhejiang Province.

Agriculture↗
PubMed2001

A riparian wildlife habitat evaluation scheme developed using GIS.

To evaluate riparian habitat for wildlife, we used a geographic information system (GIS) that prioritized individual streams (for acquisition or management) by habitat ranking. We demonstrate this methodology for the Vermilion River basin in east-central Illinois, USA. Three data sets were used to evaluate land cover encompassing 300 m on either side of the streams: (1) the US Geological Survey's land use and land cover information (LUDA), (2) land cover manually digitized from the National High Altitude Photography (NHAP) program, and (3) Landsat Thematic Mapper (TM) data classified into land cover. Each of 30 tributaries in the study area was ranked for habitat according to the data contained in each data set, and results were compared. Habitat ranking schemes were devised and analysis performed for three species guilds: forest, grassland, and mixed successional species. TM and NHAP each differentiated habitat scores (for forest, grassland, and mixed successional guilds) among tributaries in a similar and suitable way, while LUDA was not suitable, due to the coarse resolution of the data. Overall, it was shown that the methodology is suitable to rank streams based on riparian habitat quality. Even though more work is needed to test and verify the method, the project has shown the potential for such techniques to assist in evaluating, tracking, and improving the management of riparian wildlife resources. The method can easily be applied over large areas such as states if TM-based land cover and stream data are available.

Agriculture↗
PubMed2006

Crystal structures of thermoelectric n- and p-type Ba8Ga16Ge30 studied by single crystal, multitemperature, neutron diffraction, conventional X-ray diffraction and resonant synchrotron X-ray diffraction.

Comprehensive single-crystal structural investigations of n- and p-type Ba8Ga16Ge30 have been carried out using multitemperature neutron and conventional X-ray diffraction as well as resonant synchrotron X-ray diffraction. The data show that the guest atom positions and dynamics are very similar in the two structures, although the barium atoms are slightly more displaced from the cage centers in the p-type structure than in the n-type structure (Deltad = 0.025 A). For both structures Fourier difference maps calculated from very high-resolution neutron diffraction data (sin theta/lambda > 2 A-1) show that the Ba nuclear density at lowest temperatures (15 K) is distributed in a torus around the crystallographic 6d site with maxima in the 24j positions. At room temperature the maxima have shifted to the 24k position. Analysis of atomic displacement parameters give Einstein temperatures of approximately 60(1) K for both structures. Thus, the fundamental difference in the low temperature thermal conductivity observed for p- and n-type Ba8Ga16Ge30 appear not to be directly related to the guest atom behavior as is commonly assumed in thermoelectric research. The neutron data and the resonant synchrotron X-ray data facilitate refinement of Ga/Ge framework occupancies. The Ga atoms have a clear preference for the 6c site with the preference being somewhat stronger for the n-type structure.

Journal Article↗
PubMedDate not supplied

Modular methodology for determination of polychlorinated biphenyls in soil as Aroclors and individual congeners.

A comprehensive screening and confirmatory method was developed for monitoring polychlorinated biphenyls (PCBs), both as Aroclors and as individual congeners. This approach incorporates extraction, extract cleanup, and analysis modules designed to match cost, time, and data quality requirements. Soxhlet, sonication, supercritical fluid, and accelerated solvent extractions were evaluated. Carbon chromatographic cleanup procedures were used for separation of congeners on the basis of ortho substitutions, which permitted calculation of toxicity equivalents. Individual congener determinations, congener total histograms, and peak comparison techniques for Aroclor identification were elaborated by using high and low resolution mass spectrometric data. A screening procedure based on immunoassay using the Ohmicron PCB RaPID Assay kit gave results comparable to those obtained by gas chromatography with electron capture detection in the range 0.40-230 ppm, when the appropriate Aroclor calibrator was used.

Aroclors↗
PubMed2005

Crystal structure of a carbohydrate induced homodimer of phospholipase A2 from Bungarus caeruleus at 2.1A resolution.

This is the first crystal structure of a carbohydrate induced dimer of phospholipase A(2) (PLA(2)). This is an endogenous complex formed between two PLA(2) molecules and two mannoses. It was isolated from Krait venom (Bungarus caeruleus) and crystallized as such. The complete amino acid sequence of PLA(2) was determined using cDNA method. Three-dimensional structure of the complex has been solved with molecular replacement method and refined to a final R-factor of 0.192 for all the data in the resolution range 20.0-2.1A. The presence of mannose molecules in the protein crystals was confirmed using dinitrosalicylic acid test and the molecular weight of the dimer was verified with MALDI-TOF. As indicated by dynamic light scattering and analytical ultracentrifugation the dimer was also stable in solution. The good quality non-protein electron density at the interface of two PLA(2) molecules enabled us to model two mannoses. The mannoses are involved extensively in interactions with protein atoms of both PLA(2) molecules. Some of the critical amino acid residues such as Asp 49 and Tyr 31, which are part of the substrate-binding site, are found facing the interface and interacting with mannoses. The structure of the complex clearly shows that the dimerization is caused by mannoses and it results in the loss of enzymatic activity.

Amino Acid Sequence↗