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PubMed1984

Quantification of regional extravascular lung water in dogs with positron emission tomography, using constant infusion of 15O-labeled water.

Continuous infusion of 15O-labeled water allows a quantitative measurement of the total water pool in the chest region by positron emission tomography (PET). By subsequent inhalation of 11CO the intravascular space (blood pool) can be quantitated as well. After a suitable normalization of the intravascular activities the extravascular water can be determined by subtraction of the blood pool from the water pool. The regional extravascular lung water distribution can be visualized in tomographic slices. The method was validated in an animal experiment using five dogs. They were measured before and after induction of a lung edema by IV injection of oleic acid. The increase of extravascular lung water was monitored by the thermo-dye-dilution method (TDD). The correlation of extravascular lung water as measured by TDD with PET measurements is good (r = 0.94). The PET values agree also with gravimetric lung water determinations. An absolute quantitation of regional extravascular lung water is possible after absorption correction of the PET data via transmission measurements and calibration of the camera system. The uncertainty in the absolute quantification is +/- 20%. In the experiments described here the mean extravascular lung water was 0.13 g/cm3 before and 0.25 g/cm3 after induction of lung edema.

Animals↗
PubMed2001

Application of micellar electrokinetic capillary chromatography for quantitative analysis of quercetin in plant materials.

A simple method for the routine determination of quercetin in biological samples was developed. The method consists of hydrolysis of bonded quercetin, its isolation and preconcentration on solid-phase extraction (SPE) column and a final analytical step using micellar electrokinetic capillary chromatography. The working range, linear range, the limit of quantification, and the measurement uncertainty were tested in validation. The method is suitable for quercetin determination in fruit and vegetable samples.

Brassica↗
PubMed2025

An integrated multiscale air quality modelling framework for industrial park pollution: Linking local emissions to regional transport.

Capturing the spatiotemporal distribution of pollutants in industrial parks remains challenging for regional air quality models because of their coarse resolution (3 km), resulting in uncertainties in local emission quantification. To address this, we developed the Integrated Multiscale Air Quality Modelling System for Industry (IAQMS-Industry), coupling the regional Nested Air Quality Prediction Modelling System (NAQPMS) with a city-scale chemical transport model. This framework integrates point-source locations and Gaussian plume dispersion to simulate particulate matter with a diameter smaller than 2.5 micrometres (PM2.5) at 100 m resolution. Applied to the Beijing Yi Zhuang and Tangshan industrial parks and evaluated against observations. The coupled model achieved a normalized mean bias (NMB) ranging from 3.1 % to 6.2 %, improving upon NAQPMS (-16.9 % to -7.7 %). Spatial analysis revealed that coarse regional grids underestimated the PM2.5​ concentrations at industrial sites by smoothing gradients, whereas IAQMS-Industry successfully resolved spatial patterns. Industrial point emissions accounted for 22.9 %-26.4 % of PM2.5 in the coupled model, which was significantly greater than the regional model estimates of 1.6 %-13.7 %. These findings indicate that regional models overestimate pollutant dispersion processes in industrial parks while underestimating local industrial impacts. By explicitly resolving point-source dynamics and linking them to regional transport, IAQMS-Industry provides a robust tool for designing targeted emission controls in industrial cities and balancing local air quality improvements with minimized regional pollution outflow. This study underscores the necessity of multiscale modelling for accurate source apportionment and informed environmental governance in industrial zones.

Air Pollution↗
PubMed1994

In search of power and significance: issues in the design and analysis of stochastic cost-effectiveness studies in health care.

Application of techniques such as cost-effectiveness analysis (CEA) is growing rapidly in health care. There are two general approaches to analysis: deterministic models based upon assumptions and secondary analysis of retrospective data, and prospective stochastic analyses in which the design of a clinical experiment such as randomised controlled trial is adapted to collect patient-specific data on costs and effects. An important methodological difference between these two approaches is in the quantification and analysis of uncertainty. Whereas the traditional CEA model utilizes sensitivity analysis, the mean-variance data on costs and effects from a prospective trial presents the opportunity to analyze cost-effectiveness using conventional inferential statistical methods. In this study we explored some of the implications of moving economic appraisal away from deterministic models and toward the experimental paradigm. Our specific focus was on the feasibility and desirability of constructing statistical tests of economic hypotheses and estimation of cost-effectiveness ratios with associated 95% confidence intervals. We show how relevant variances can be estimated for this task and discuss the implications for the design and analysis of prospective economic studies.

Confidence Intervals↗
PubMed2001

Expression of results with uncertainty for the determination of pesticides in melon--experience in a proficiency test.

The expression of results with an uncertainty through the "bottom-up" approach, involving the estimation and combination of all the sources of uncertainty, represents a challenge when the analytical method includes mass transfer steps (MTS). These steps (e.g. extraction, evaporation, digestion, etc.) with inherently different from 100% recoveries lack models capable of describing their precision and efficiency. Recently, a new methodology was published aimed at the estimation of the performance of these critical steps. Comparison of the experimental dispersion from the replicated analysis of spiked samples with the combination of the uncertainty associated with gravimetric, volumetric and instrumental quantification steps (described by well established models) allows the estimation of the MTS uncertainty. Evaluation of the behaviour of the MTS within the analytical range supports the use of developed estimations over a wide concentration range. This methodology was applied, with success, to the determination of pesticide residues in melon in one particular proficiency test organised by the Food Analysis Performance Assessment Scheme (FAPAS) between November 2000 and February 2001.

Chromatography, Gas↗
PubMed1995

Non-T1-weighted 31P chemical shift imaging of the human liver.

A 31P chemical shift imaging (CSI) protocol was developed for human liver studies. It is shown that at the commonly used repetition time (TR) of 1 s T1-weighting reduces the integrated intensities of liver phosphate metabolite signals by 18 +/- 15% (inorganic phosphate, Pi) to 46 +/- 10% (phosphodiester, PDE), that is for an RF pulse angle of 60 degrees (weighted average) in liver. The loss in signal-to-noise ratio (S/N) at TR = 20 s, sufficient to eliminate spectral distortions caused by saturation, compared with TR = 1 s (47-65%) can be overcome by using one-dimensional (1D)-phase encoding with a small number of phase-encode steps. The liver spectra obtained by 1D-CSI with 4-step phase-encoding (spatial resolution 10 cm) have the highest S/N and, after multiplication of the PDE signal by a factor of 1.4, closely reflect the liver metabolite levels. It is concluded that clinical 31P MR studies of liver function can be performed without T1-weighting and that the current practice to compromise the MRS quantification of lever metabolites with uncertainties caused by (differential changes in) T1-weighting is not warranted.

Humans↗
PubMed2000

Methods for ELNES-quantification: characterization of the degree of inversion of Mg-Al-spinels

The energy loss near-edge structures in electron energy-loss spectra contain information about bonding characteristics, the electronic structure and coordinations of the excited atoms. We have calculated sets of reference spectra for the normal and for the inverse Mg-Al-spinel using a full multiple scattering approach. By a quantitative comparison of these reference spectra with experimental data ELNES-quantification becomes possible. We characterized the degree of inversion lambda by the analysis of the relative peak-intensities and the relative peak-positions within 35 eV beyond the edge onset. The results demonstrate that by using the provided methods ELNES-quantification will become possible when uncertainties in the experiment are reduced and a better fit of the simulations to the experiment is achieved.

Journal Article↗
PubMed2000

Direct in situ measurements of labile inorganic and organically bound metal species in synthetic solutions and natural waters using diffusive gradients in thin films.

The emerging technique of DGT (diffusive gradients in thin films) is shown to be capable of performing new speciation measurements in situ in natural waters. In DGT, metals are bound to a resin layer after passing through a well-defined diffusion layer. Cd was measured in solutions containing glycine, EDTA, and fulvic (FA) and humic acids (HA) by atomic absorption spectroscopy (AAS), anodic stripping voltammetry (ASV), and DGT. DGT measured similar labile fractions to ASV, with detailed differences being consistent with a thicker diffusion layer allowing more dissociation of labile complexes and a slower diffusion of FA and HA complexes through the gel. When single measurements are made in complex solutions with DGT, precise quantification is impossible due to uncertainties concerning the distribution of species with different diffusion coefficients. A new procedure was proposed based on the advantage of DGT of being able to control the pore size of the diffusive gel layer. Small (inorganic) species diffuse freely through all gels but larger FA and HA (organic) complexes diffuse less freely in more constrained gels. When measurements were made on known solutions of Cu and FA or HA, it was possible to quantify the inorganic and organic species separately. They agreed well with predictions made using the WHAM speciation code. Multiple DGT units were also deployed in situ in a stream with high dissolved organic carbon (14.6 mg/L). The systematic differences between the devices with different gel compositions enabled determination, for the first time, of the in situ concentrations of both labile inorganic and organic species in natural water. A single DGT device with a constrained gel can be used to quantify inorganic species directly, providing absolute accuracy is not required. This ability of DGT to measure well-defined fractions of metals in situ using a simple device gives it considerable potential as a regulatory tool. A direct speciation measurement may be preferable to modeling approaches which require diverse input data that are difficult to determine.

Benzopyrans↗
PubMedDate not supplied

Processing biological images from very low light emissions.

As opposed to strong light signals (> 10(8) photons mm-2 s-1), the construction of images from object sources with low level signals (< 10(2) photons mm-2 s-1) involves a probabilistic transfer- or point-spread function. The resulting images carry considerable uncertainty or spread, restricting resolution and quantification. In this paper we propose various strategies how to reconstruct object characteristics from very low light emissions by unfolding the imaging equation. Further, calibration techniques which help to associate light emissions with the decomposition of luminogenic substrates in a spatially selective way will be discussed.

Animals↗
PubMed2002

The sequestration switch: removing industrial CO2 by direct ocean absorption.

This review paper considers direct injection of industrial CO2 emissions into the mid-water oceanic column below 500 m depth. Such a process is a potential candidate for switching atmospheric carbon emissions directly to long term sequestration, thereby relieving the intermediate atmospheric burden. Given sufficient research justification, the argument is that harmful impact in both the Atmosphere and the biologically rich upper marine layer could be reduced. The paper aims to estimate the role that active intervention, through direct ocean CO2 storage, could play and to outline further research and assessment for the strategy to be a viable option for climate change mitigation. The attractiveness of direct ocean injection lies in its bypassing of the Atmosphere and upper marine region, its relative permanence, its practicability using existing technologies and its quantification. The difficulties relate to the uncertainty of some fundamental scientific issues, such as plume dynamics, lowered pH of the exposed waters and associated ecological impact, the significant energy penalty associated with the necessary engineering plant and the uncertain costs. Moreover, there are considerable uncertainties regarding related international marine law. Development of the process would require acceptance of the evidence for climate change, strict requirements for large industrial consumers of fossil fuel to reduce CO2 emissions into the Atmosphere and scientific evidence for the overall beneficial impact of ocean sequestration.

Absorption↗
PubMed1993

The evaluation and interpretation of cervical cytology: application of the likelihood ratio concept.

The Papanicolaou smear (Pap test), used for the detection and prevention of neoplastic lesions of the cervix, is known to have both false negative and false positive results. Proper handling of the diagnostic uncertainty resulting from these errors demands quantification of flaws. Traditionally, sensitivity, specificity and predictive values are used for that aim. In this study another approach is advocated, namely the use of the likelihood ratio. For cervical cytology this ratio is the quotient of the probability of a Pap class within the diseased population to the probability of that same Pap class within the non-diseased group. This approach enables the characterization of each Pap class separately, and is therefore much better for clinical interpretation of the result. It is also a superior approach for quality assessment.

Female↗
PubMedDate not supplied

The representation of uncertainty in medical expert systems.

The development of the rule-based expert system has provided important new techniques for the representation of knowledge. However, continued use of this representational scheme has highlighted some of its deficiencies. In particular, many within scientific and non-scientific fields attempting to use the rule-base design to describe natural phenomena often find it difficult to represent the complexities of the world as 'absolute' rules. For this reason, many investigators acknowledge the need to add an uncertainty mechanism to the rule-base construct. Such a facility would allow the quantification of accuracy or strength of association within individual rules Although agreement exists on the need for an uncertainty representation facility, the debate concerning the most appropriate methodology is far from resolved. The purpose of this paper is to provide a review and commentary on the current state of debate over the five most popular candidate uncertainty models: symbolic representation, MYCIN certainty factors, Bayesian, Dempster-Shafer and fuzzy set logic. The advantages and disadvantages of each uncertainty calculi will be presented and assessed with respect to their applicability to the medical expert systems domain.

Bayes Theorem↗
PubMed1977

Improved method for the analysis of estrogenic steroids in pregnancy urine by high-performance liquid chromatography.

The use of microparticulate packing materials and large injection volumes gives significant improvements in the analysis of complex samples, such as urine extracts by high-performance liquid chromatography. Lower detection limits and improved accuracy can now be attained. In addition, the combined use of adsorption and reversed-phase chromatography leads to reduced uncertainty in peak identification and gives more reliable quantification.

Chromatography, High Pressure Liquid↗
PubMed1995

A Monte Carlo investigation of dual-energy-window scatter correction for volume-of-interest quantification in 99Tcm SPECT.

Using Monte Carlo simulation of 99Tcm single-photon-emission computed tomography (SPECT), we investigate the effects of tissue-background activity, tumour location, patient size, uncertainty of energy windows, and definition of tumour region on the accuracy of quantification. The dual-energy-window method of correction for Compton scattering is employed and the multiplier which yields correct activity for the VI as a whole calculated. The model is usually a sphere containing radioactive water located within a cylinder filled with a more dilute solution of radioactivity. Two simulation codes are employed. Reconstruction is by ML-EM algorithm with attenuation compensation. The scatter multiplier depends only slightly on the sphere location or the cylinder diameter. It also depends little on whether correction is before or after reconstruction. At low background level, it changes with VOI size, but not at higher background. For a geometrical VOI, it is 1.25 at zero background, decreases sharply to 0.56 for equal concentrations, and is 0.44 when the background concentration is very large. Quantification is accurate (less than 9% error) if the test background is reasonably close to that used in setting the universal scatter-multiplier value, or if the test backgrounds are always large and so is the universal-value background, but not if the test backgrounds cover a large range of values including zero. Results largely agree with those from experiment after the experimental data with background is re-evaluated with prejudice.

Humans↗
PubMed1994

Risk of premenopausal breast cancer and use of electric blankets.

Electric blanket use, estimated to significantly increase background exposure to 60-Hz electromagnetic fields, has been hypothesized to increase breast cancer risk. From 1986 to 1991 in western New York State, the authors investigated the use of electric blankets as a risk factor for breast cancer in a case-control study of premenopausal women. A total of 290 premenopausal breast cancer cases and 289 age-matched randomly selected community controls were queried in regard to their use of electric blankets in the previous 10 years, including frequency of use in season and mode of use. After adjusting for age, education, and other risk factors, the odds ratio for use of an electric blanket at any time in the previous 10 years (40% of cases and 37% of controls) was 1.18 (95% confidence interval (CI) 0.83-1.68). Estimates of risk did not differ in a dose-response fashion for number of years of electric blanket use. The risk associated with daily use in season relative to nonuse was 1.27 (95% CI 0.86-1.88). The risk of breast cancer among those who reported use of the blanket through the night was 1.43 (95% CI 0.94-2.17). However, the risk for those who reported daily use in season, continuously throughout the night for the previous 10 years was 1.10 (95% CI 0.59-2.05). These findings do not support the hypothesis that electric blanket use is associated with an increased risk for breast cancer. Studies with improved measures of more highly exposed individuals with quantification of total electromagnetic field exposure might clarify the uncertainties regarding risk of breast cancer associated with such exposure.

Adult↗
PubMed2002

Probabilistic Boolean Networks: a rule-based uncertainty model for gene regulatory networks.

MOTIVATION: Our goal is to construct a model for genetic regulatory networks such that the model class: (i) incorporates rule-based dependencies between genes; (ii) allows the systematic study of global network dynamics; (iii) is able to cope with uncertainty, both in the data and the model selection; and (iv) permits the quantification of the relative influence and sensitivity of genes in their interactions with other genes. RESULTS: We introduce Probabilistic Boolean Networks (PBN) that share the appealing rule-based properties of Boolean networks, but are robust in the face of uncertainty. We show how the dynamics of these networks can be studied in the probabilistic context of Markov chains, with standard Boolean networks being special cases. Then, we discuss the relationship between PBNs and Bayesian networks--a family of graphical models that explicitly represent probabilistic relationships between variables. We show how probabilistic dependencies between a gene and its parent genes, constituting the basic building blocks of Bayesian networks, can be obtained from PBNs. Finally, we present methods for quantifying the influence of genes on other genes, within the context of PBNs. Examples illustrating the above concepts are presented throughout the paper.

Cell Cycle↗
PubMed2002

Determination of endocrine-disrupting pesticides and polychlorinated biphenyls in human serum by GC-ECD and GC-MS-MS and evaluation of contributions to the uncertainty of the results.

The chemicals endosulfan-alpha, endosulfan-beta, endosulfan sulfate, endosulfan ether, endosulfan lactone, PCB-21, PCB-48, PCB-61, and PCB-136 have been determined in 100 serum samples from women living in agricultural areas of Almería (Spain). The study includes a surgically treated breast cancer patient and a matching group of women with no sign of estrogenic-dependent disease. The determination was performed by gas chromatography with electron capture detection (GC-ECD) and tandem mass spectrometry (GC-MS-MS). Recovery, precision, linear range, detection limit (LOD), and quantification limit (LOQ) were calculated for each pesticide as was the expanded uncertainty (U). The method was evaluated for our laboratory and could be applied to subsequent results with relevant quality-control data. Comparison of the results was performed. The advantage of MS-MS over ECD for determination of endocrine-disrupting compounds in complex matrices is presented. The most commonly encountered pesticide was endosulfan-alpha. Endosulfan-beta and the PCB-48 congener were detected at concentrations lower than their LOQ. Endosulfan sulfate, endosulfan ether, endosulfan lactone, PCB-21, PCB-61 and PCB-136 were not found in any of the serum samples analysed.

Breast Neoplasms↗
PubMed2001

Monitoring of pesticides in drinking and related waters in NE Spain with a multiresidue SPE-GC-MS method including an estimation of the uncertainty of the analytical results.

A new method, developed in an EC project (SMT4-CT96-2142) for the determination of 22 pesticides in drinking and related waters, has been used to analyze source and drinking water samples in the area of Barcelona (NE Spain). The procedure includes solid-phase extraction of water and subsequent analysis by GC-MS using few selected ions (SIR) in order to increase their sensitivity. The method was subjected to intra and interlaboratory tests and met the requirements of the EC Directive in terms of accuracy, precision and detection limit (0.025 microg/l range in water samples). A detailed analysis of the uncertainty sources of this method is included, which allows to estimate expanded uncertainties in the 10-20% range. The dominant sources of uncertainty are the solid-phase extraction procedure and the chromatographic quantification. Two triazine compounds, simazine and atrazine, are the main pesticides detected in wells of the Llobregat river and in water of the Ter river, respectively.

Gas Chromatography-Mass Spectrometry↗