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At least 415 records · Page 23Linked to original sources
PubMed2006

Applicability of the single equivalent moving dipole model in an infinite homogeneous medium to identify cardiac electrical sources: a computer simulation study in a realistic anatomic geometry torso model.

We have previously proposed an inverse algorithm for fitting potentials due to an arbitrary bio-electrical source to a single equivalent moving dipole (SEMD) model. The algorithm achieves fast identification of the SEMD parameters by employing a SEMD model embedded in an infinite homogeneous volume conductor. However, this may lead to systematic error in the identification of the SEMD parameters. In this paper, we investigate the accuracy of the algorithm in a realistic anatomic geometry torso model (forward problem). Specifically, we investigate the effect of measurement noise, dipole position and electrode configuration in the accuracy of the algorithm. The boundary element method was used to calculate the forward potential distribution at multiple electrode positions on the body surface due to a point dipole in the heart. We have found that the position and not the number of electrodes as well as the site of the origin of the arrhythmia in the heart have a significant effect on the accuracy of the inverse algorithm, while the measurement noise does not. Finally, we have shown that the inverse algorithm preserves the topology of the source distribution in the heart, thus potentially allowing the cardiac electrophysiologist to efficiently and accurately guide the tip of the catheter to the ablation site.

Action Potentials↗
PubMed1991

Material parameters and stress profiles within the periodontal ligament.

Levels and profiles of initial stress in the periodontal ligament after application of various force systems were studied. Two finite-element models, based on sections of human autopsy material, were developed to simulate one full and one partial mandible. The validity of the finite-element model was improved by identification of material parameters; the mechanical properties of the tissue were described by means of strain-gauge measurements of initial tooth movements in human autopsy material. The multiple modeling technique, in which data from a coarse global model are transferred to a more detailed one, was used to identify bone structure and boundary conditions. Parameters known to influence the results were varied to establish the validity of the finite-element model. Iterative calculation methods were used to gain stable results. However, optimizing features of the bone structure and boundary conditions did not influence the results significantly. The elastic stiffness of the periodontal ligament was determined to 0.07 MPa and tau = 0.49 (tau being the Poisson's ratio). Stress profiles were obtained for various force systems--as in tipping, translation, and root movement. As we expected, there was a marked variation in the stress distribution from cervix to apex when tipping forces were applied. Bodily movement of the tooth produced an almost uniform stress distribution; root movement produced stress patterns opposite to those observed during tipping; and masticatory forces alone produced stress patterns almost identical to those achieved by masticatory force in combination with orthodontic forces.

Adolescent↗
PubMed1985

Model identification and estimation of organ-function parameters using radioactive tracers and the impulse-response function.

Examination of the input-output events in functioning organs by the use of the impulse-response function (IRF) for a radioactive tracer is gaining more and more ground in nuclear medicine. This study summarizes the development of deconvolution analysis, laying special stress on the 'model-free' approach. System linearity and time invariance are discussed, and means of eliminating noise in IRFs originating from the input and organ-time-activity curves are outlined. Typical IRFs are illustrated by flow diagrams, time-domain curves, and their representation by Laplace transforms. The cases of nondiffusible and diffusible tracers as well as parenchymally extracted and transported substances are discussed. Methods for the derivation of models and for the calculation of physiologically important parameters from the IRFs are suggested.

Heart↗
PubMed2006

Identification of scanning slit-beam topographic parameters important in distinguishing normal from keratoconic corneal morphologic features.

PURPOSE: To identify morphologic parameters obtained using scanning slit-beam topography that help distinguish normal from keratoconic corneal morphologic features. DESIGN: Observational, retrospective, cross-sectional study. METHODS: This retrospective review examined 207 normal eyes of patients undergoing an initial consultation for primary refractive surgery and 42 eyes with clinical keratoconus (KCN). The following parameters were examined and compared between the two groups: astigmatism, central corneal power, irregularity indices at 3 mm (II3) and 5 mm (II5), maximal posterior elevation (MPE) magnitude and location, thinnest optical pachymetry (TOP) magnitude and location, anterior elevation best-fit sphere (ABFS), posterior elevation best-fit sphere (PBFS), the ratio of ABFS to PBFS, the difference between average inferior and average superior K values at 3 mm and 5 mm in both keratometric (I-S K3 and I-S K5) and tangential (I-S T3 and I-S T5) topographic maps, and skewed radial axis at 3 mm (SRAX3) and 5 mm (SRAX5) of the keratometric topography map. RESULTS: The II3, II5, MPE magnitude, TOP magnitude, ABFS, PBFS, ABFS-to-PBFS ratio, I-S K at both 3 mm and 5 mm, I-S T at both 3 and 5 mm, and SRAX at 3 mm and 5 mm values were significantly different among the two groups (P < .001). The least-correlated parameters were SRAX3, TOP magnitude, and II3 in the KCN group and I-S K3, amount of astigmatism and MPE magnitude in the normal group. CONCLUSIONS: Parameters obtained using scanning slit-beam topography may allow improved differentiation of keratoconic from normal corneal shapes, especially when the poorly correlated intragroup parameters are used.

Adult↗
PubMed1997

Identification and correlation of human footfall load parameters using multivariate analysis.

This research had two main objectives: to identify and quantify the multiple reaction parameters of human footfall load histories for 24 subjects; and to seek statistical correlations of the reaction parameters with two gaits: fitness walking and running, with two footfall surfaces: rigid and mat, and with two subject attributes: gender and arch index. These reaction parameters, measured with a force plate, include the subjects' foot reaction forces in the three orthogonal directions and the particular features of these forces such as their duration, average values, peak values, and rates of loading. An automated data retrieval-software system evaluated these reaction parameters. The statistical correlations were made using principal component analysis (PCA), a method that projected the 13 identified footfall reaction parameters onto subsets of three or four parameters called principal components that contained most of the variance of the original thirteen. The results, among others, show couplings between the vertical and the peak medial load, but an uncoupling of the posterior-anterior loads with the loads in the other two directions.

Adult↗
PubMed1999

Biohumoral parameters and bone mineral content in the identification of high risk subjects for postmenopausal osteoporosis.

BACKGROUND: The aim of this study was to evaluate the possibility of identifying women with a high risk of postmenopausal osteoporosis by using computerised bone mineral analysis (CBMA) associated with markers of bone turnover in order to provide a valid and reliable screening test. METHODS: A total of 925 patients were evaluated, 252 of whom had already undergone a preliminary densitometric test six months earlier and were diagnosed as fast bone losers. 225 of them (89%) also showed altered bone turnover markers. CBMA was negative in the remaining 673 patients but 13 patients showed altered bone turnover markers and three of the latter then showed a positive CBMA 18 months later. The 673 patients who, after six months of study, were not fast bone losers were monitored over time. RESULTS: It emerges from these results that fast bone losers are characterised by higher levels of hydroxyprolinuria and calcium, lower levels of oestrone and estradiol, and reduced body weight compared to healthy subjects. CONCLUSIONS: This simplified method enabled 79% of the fast bone losers to be identified, whereas densitometry identified 87.5% of the high-risk subjects. The main advantage of our simplified method compared to the measurement of bone mineral content is that it identifies the majority of fast bone losers in the initial postmenopausal period, before a substantial reduction in BMC has taken place.

Bone and Bones↗
PubMed2002

Evaluation of parameters in peptide mass fingerprinting for protein identification by MALDI-TOF mass spectrometry.

Protein identification by peptide mass fingerprinting, using the matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS), plays a major role in large proteome projects. In order to develop a simple and reliable method for protein identification by MALDI-TOF MS, we compared and evaluated the major steps in peptide mass fingerprinting. We found that the removal of excess enzyme from the in-gel digestion usually gave a few more peptide peaks, which were important for the identification of some proteins. Internal calibration always gave better results. However, for a large number of samples, two step calibrations (i.e. database search with peptide mass from external calibration, then the use of peptide masses from the search result as internal calibrants) were useful and convenient. From the evaluation and combination of steps that were already developed by others, we established a single overall procedure for peptide identification from a polyacrylamide gel.

Bacterial Proteins↗
PubMed1977

Objective identification of cell cycle phases and subphases by automated image analysis.

Frequency distributions of integrated optical density, perimeter, projection, area, form factor, average optical density, and mean dispersion path of nuclear images of Feulgen-stained HeLa S3 cells were obtained by automated image analysis at the base threshold of 0.04 OD. The mean values and standard deviations of these geometric parameters were then computed versus increasing values of threshold (0.08--0.32 OD). There is clear evidence of differential chromatin dispersion and convolution during the cycle of synchronized HeLa S3 cells at different times after selective mitotic detachment. The combination of average OD, form factor, and mean dispersion path at base threshold with the threshold dependence of nuclear morphometric parameters permits objective identification of cell cycle phases and their subphases, by characterizing variations in chromatin geometry within and between phases, regardless of whether DNA content remains constant (early G1, middle G1, late G1), varies only slightly (late G1-early S or late S-G2 transitions), or varies significantly (early S-middle S).

Autoanalysis↗
PubMed1982

The extraction and identification of drugs in aviation toxicology.

The drug screen as used in Aviation Pathology is unique in toxicological analysis in that it seeks to identify the whole range of clinical drugs at or below therapeutic levels. Recently the introduction of proteolytic enzymes has enabled more efficient extraction of drugs from tissues. The measurement of the Gas Chromatographic Retention Index can provide an important parameter in the identification of drug substances.

Aerospace Medicine↗
PubMed2005

Quantifying and reducing uncertainty in life cycle assessment using the Bayesian Monte Carlo method.

The traditional life cycle assessment (LCA) does not perform quantitative uncertainty analysis. However, without characterizing the associated uncertainty, the reliability of assessment results cannot be understood or ascertained. In this study, the Bayesian method, in combination with the Monte Carlo technique, is used to quantify and update the uncertainty in LCA results. A case study of applying the method to comparison of alternative waste treatment options in terms of global warming potential due to greenhouse gas emissions is presented. In the case study, the prior distributions of the parameters used for estimating emission inventory and environmental impact in LCA were based on the expert judgment from the intergovernmental panel on climate change (IPCC) guideline and were subsequently updated using the likelihood distributions resulting from both national statistic and site-specific data. The posterior uncertainty distribution of the LCA results was generated using Monte Carlo simulations with posterior parameter probability distributions. The results indicated that the incorporation of quantitative uncertainty analysis into LCA revealed more information than the deterministic LCA method, and the resulting decision may thus be different. In addition, in combination with the Monte Carlo simulation, calculations of correlation coefficients facilitated the identification of important parameters that had major influence to LCA results. Finally, by using national statistic data and site-specific information to update the prior uncertainty distribution, the resultant uncertainty associated with the LCA results could be reduced. A better informed decision can therefore be made based on the clearer and more complete comparison of options.

Bayes Theorem↗
PubMed2005

Determination of the limits of identification and quantitation of selected organochlorine and organophosphorous pesticide residues in surface water by full-scan gas chromatography/mass spectrometry.

In this work, we report a reliable method for quantitation and determination of the limits of identification of 14 organochlorine and organophosphorous pesticide (OPP) residues in surface water. The method features the simultaneous identification and quantitation of targeted pesticides and the possibility of identification of any other eluting compounds. The method is based on liquid-liquid extraction (LLE) with a mixture of petroleum ether and dichloromethane (70:30, v/v) followed by gas chromatographic separation and a full-scan mass spectrometric detection (GC-MS). The method presents a new validation parameter, limit of identification (LOI) which is defined for our purpose as the lowest analyte concentration that yields a library searchable mass spectrum. The method is linear over the range 0.048-1.20microgL(-1) for nine pesticides and 0.024-0.60microgL(-1) for the other five pesticides. Correlation coefficients vary between 0.988 and 0.998. Limits of detection (LODs) vary between 0.005 and 0.05microgL(-1) for 4,4'-DDT and LOIs vary between 0.012 and 0.048microgL(-1).

Alkanes↗
PubMed2005

Optimization of protein identification from digests as analyzed by capillary isoelectric focusing-mass spectrometry.

Capillary isoelectric focusing (CIEF) is a high-resolution separation technique for the analysis of peptides and protein digests. When coupled to ion trap-mass spectrometry (CIEF-MS) the unique separation mechanism is combined with a highly efficient detection system. In an earlier report, we described aspects of separation and interfacing in connection to the analysis of a digest of set of standard proteins. Now, we report on different aspects of the process of protein identification. Sequest software parameters were optimized by using a standard protein digest. These settings were used for the analysis of periplasmic proteins from Escherichia coli. Since in CIEF peptides are focused according to their pI values, the mobilization time of a particular peptide is dependent on its pI value. Based on this relation, the identification of some peptides was facilitated. Furthermore, the Sequest settings that were used could be evaluated. In total, 159 proteins were identified in a single run.

Amino Acid Sequence↗
PubMedDate not supplied

Quantitative assessment of power Doppler mapping in the detection of renal allograft complications.

PURPOSE: We evaluated the usefulness of power Doppler (PD) imaging with a quantitative parameter in the identification of renal transplant complications. METHODS: One hundred eight transplanted kidneys were subjected to PD examinations. The blood flow area ratio (BFAR), defined as the percentage of the area of color pixels within a given cross-sectional area placed over a region of a transplanted kidney, was measured using built-in color histogram software and used as a quantitative parameter for evaluating the status of allograft blood perfusion. The mean BFARs in the normal, acute rejection (AR), acute tubular necrosis (ATN), chronic rejection (CR), and cytomegalovirus infection (CMV) groups were compared. RESULTS: The BFAR in the normal group tended to decrease gradually with the time interval since transplantation, but the mean value, 0.68+/-0.08, was significantly higher than that in the complication groups: AR, 0.43+/-0.18; ATN, 0.43+/-0.14; CR, 0.15+/-0.14; and CMV, 0.36+/-0.10 (p < 0.01 for all). When a BFAR of 0.60 or greater was used as the diagnostic criterion for normal allografts, a sensitivity, specificity, and accuracy of more than 90% could be achieved in the diagnosis of complications. However, owing to overlapping BFARs among the complication groups, the BFAR alone had a limited ability to differentiate the types of complications. CONCLUSIONS: Although PD imaging has some limitations in identifying the nature of renal allograft complications, the use of the quantitative parameter BFAR in the PD assessment of renal allografts may be useful in detecting complications. Further studies are needed to explore the BFAR's clinical value.

Adult↗
PubMed2006

Gastrointestinal stromal tumour: spiral computed tomography features and pathologic correlation.

PURPOSE: Our purpose was to define the diagnostic accuracy of helical computed tomography (CT) in the identification, characterisation and evaluation of extension of gastrointestinal stromal tumours (GIST) through correlation with some pathological findings. MATERIALS AND METHODS: Between August 2000 and September 2004, we conducted a retrospective study of the abdominal CT of 15 patients with histological diagnosis of GIST - that is, the immunopositivity for c-kit (CD117) - on a surgical specimen of the primary disease. We used a helical CT single-slice (Toshiba, Asteion; rotation time 0.75 s) in ten cases and helical CT multislice (Toshiba, Aquilion; 4 slices/rotation; rotation time 0.5 s) in five cases. In all cases, we used an organ-iodate nonionic contrast agent intravenously at a concentration of 350-400 mgI/ml. All cases studied the entire abdomen. Site, morphology and tumour size (smaller than 5 cm, 5-10 cm and larger than 10 cm) were considered parameters for tumour identification. Size, partial or total extraluminal tumour growth, homogeneous or inhomogeneous lesion enhancement and the eventual presence of calcifications were assumed to be criteria for characterisation of a GIST. Hepatic, peritoneal and/or lymph node metastases were considered parameters of intermediate or high malignancy. We correlated the results with some pathological features derived from the analysis of surgical tissue: site, morphology and tumour size, tissue components and risk of malignancy of GIST (on the basis of the 2002 Fletcher classification). RESULTS: We demonstrated one substantial concordance between radiological and pathological valuation of site, morphology, tumour size and absence of intralesional calcifications of GIST. Nine of ten GIST smaller than 5 cm, the two 5-10 cm and the three larger than 10 cm presented extraluminal growth. Enhancement was inhomogeneous in five of ten lesions smaller than 5 cm and in all cases larger than 5 cm. At pathological analysis, in all cases of inhomogeneous enhancement, solid, hemorrhagic, necrotic and cystic areas were found. Of seven tumours of intermediate malignancy, six were smaller than 5 cm and only one larger than 10 cm; the two 5-10 cm were of high malignancy and all tumours superior of 10 cm were at intermediate or high malignancy. Of the two cases with metastases, one was of intermediate and one of high malignancy. In the other cases of intermediate or high malignancy, metastases were absent. CONCLUSIONS: The immunopositivity for c-kit is requisite for definitive diagnosis of GIST, but imaging, and particularly helical CT, has a primary role. In this study, CT is was reliable for tumour identification. All tumours larger than 5 cm presented extraluminal growth, inhomogeneous enhancement, absence of calcifications and lymph node metastases. Furthermore, the tumour larger than 5 cm showed extraluminal growth and inhomogeneous enhancement. Tumour size established with CT was not sufficient to determine the degree of malignancy. Metastases at the time of diagnosis were indicative of intermediate or high malignancy, but the absence of metastases did not allow classification of GIST in the group of low and very low risk of malignancy.

Adult↗
PubMed2003

Combination of magnetic parameters: an efficient way to discriminate soil-contamination sources (south France).

Biplots combining magnetic parameters allow to identification and differentiation different pollutant emission sources. A major problem in soil pollution is the characterization of the relative contributions of different anthropogenic particles sources. This paper demonstrates the efficiency of magnetic techniques to provide identification and differentiation of contaminating emission sources. About 100 soil samples were collected across a mixed agricultural and industrial area (Crau plain/Berre-Fos basin) in southern France. Nine soil profiles were realized. They are aligned along a transect, from the Mediterranean cost to the north. Measurements of initial magnetic susceptibility (chi) and remanent magnetization (ARM, IRM) have been carried out at room temperature. Several ratios of magnetic parameters were calculated and tested. Bivariate analyses allow to characterize different pollution sources and graphic results suggest three dominant contributions originated from road traffic, airport and steel industry. Moreover, magnetic grain-size discrimination between surface-soil samples and bottom-soil samples is obtained. An increase of hard magnetic components from topsoil towards the bottom of the profiles is evidenced.

Environmental Monitoring↗
PubMed2003

Determination of fluoroquinolones in human urine by liquid chromatography coupled to pneumatically assisted electrospray ionization mass spectrometry.

The fluoroquinolones are synthetic antimicrobial agents widely used in human and veterinary medicine. The aim of this work was to develop a method of characterization and determination of three widely used fluoroquinolones (norfloxacin, ciprofloxacin and ofloxacin) in human urine by liquid chromatography (LC) coupled to pneumatically assisted electrospray ionization (ESI) mass spectrometry (MS). For this purpose, the operational parameters of the electrospray interface were optimized in order to obtain the best signal stability and the highest sensitivity of the fluoroquinolones. The three fluoroquinolones studied and enrofloxacin, used as internal standard, were extracted from human urine samples by solid-phase extraction (SPE) and the previously established LC-UV method was successfully coupled with the MS system. The mass spectra obtained provide adequate information for identification purposes. Quality parameters were determined and satisfactory results were obtained. Likewise, the method detection limit was about 10 ng ml(-1) for the three fluoroquinolones studied employing selected-ion monitoring mode.

Chromatography, Liquid↗
PubMed2003

Parametric analysis of carotid plaque using a clinical ultrasound imaging system.

We evaluated quantitative ultrasonic methods for assessment of carotid plaque content. In vitro measurements of fixed, carotid plaque specimens obtained by surgical endarterectomy were performed using a clinical Philips HDI 5000 imaging system connected to a radiofrequency (RF) signal-acquisition system. We acquired RF signals and grey-scale images from carotid specimens (n = 17) and a tissue-mimicking reference phantom. Imaged plaque sections were then classified according to histology. Parametric images were constructed from the integrated backscatter (IBS), and the midband, slope and intercept values of a straight-line fit to the apparent backscatter transfer function. Analysis was performed on 82 regions-of-interest (ROIs). The IBS values for collagen, lipid and hemorrhage plaques were 5.8 +/- 5.4, 3.9 +/- 3.7, 2.8 +/- 2.2 dB, respectively. Midband and IBS parameter images exhibited good agreement in morphology with histology, whereas the slope and intercept parameter images were noisy. Mean IBS, midband, and grey-scale values of complex plaques were found to be statistically different (p < 0.05) from lipid, hemorrhage and fibrolipid plaques. The bias and limits of agreement (1.3 +/- 4.9 dB) between the grey-scale and IBS methods, however, indicated that the two methods were not interchangeable. Results indicate necessary improvements, such as reduction of large measurement variances and identification of robust parameters, that will permit multiparametric characterization of carotid plaque under in vivo conditions.

Carotid Arteries↗