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At least 1,567 records · Page 87Linked to original sources
PubMed1993

Computerised linking of medical records: methodological guidelines.

OBJECTIVES: To report on the development of computer assisted methods for linking medical records and record abstracts. DESIGN: The methods include file blocking, to put records in an order which makes searching efficient; matching, which is the process of comparing records to determine whether they do or do not relate to the same person; linkage, which is the process of assembling correctly matched records into a time sequenced composite record for the individual; and validation checks and corrections, in which any inconsistencies between different records for the same person are identified and corrected. SETTING: The dataset comprising the Oxford record linkage study which includes hospital inpatient records and vital records. RESULTS AND CONCLUSIONS: Probability matching, using an array of identifiers, achieves much higher levels of correct matching than is generally achievable by exact character by character comparisons. The increasing use of information technology to store data about health and health care means that there is increasing scope to link records for research and for patient care. Sophisticated methods to achieve this on a large scale are now available.

England↗
PubMed2003

Comparison of pathologist-detected and automated computer-assisted image analysis detected sentinel lymph node micrometastases in breast cancer.

Sentinel lymph node biopsy has stimulated interest in identification of micrometastatic disease in lymph nodes, but identifying small clusters of tumor cells or single tumor cells in lymph nodes can be tedious and inaccurate. The optimal method of detecting micrometastases in sentinel nodes has not been established. Detection is dependent on node sectioning strategy and the ability to locate and confirm tumor cells on histologic sections. Immunohistochemical techniques have greatly enhanced detection in histologic sections; however, comparison of detection methodology has not been undertaken. Automated computer-assisted detection of candidate tumor cells may have the potential to significantly assist the pathologist. This study compares computer-assisted micrometastasis detection with routine detection by a pathologist. Cytokeratin-stained sentinel lymph node sections from 100 patients at the University of Vermont were evaluated by automated computer-assisted cell detection. Based on original routine light microscopy screening, 20 cases that were positive and 80 cases that were negative for micrometastases were selected. One-level (43 cases) or two-level (54 cases) cytokeratin-stained sections were examined per lymph node block. All 100 patients had previously been classified as node negative by using routine hematoxylin and eosin stained sections. Technical staining problems precluded computer-assisted cell detection scanning in three cases. Computer-assisted cell detection detected 19 of 20 (95.0%; 95% confidence interval, 75-100%) cases positive by routine light microscopy. Micrometastases missed by computer-assisted cell detection were caused by cells outside the instrument's scanning region. Computer-assisted cell detection detected additional micrometastases, undetected by light microscopy, in 8 of 77 (10.4%; 95% confidence interval, 5-20%) cases. The computer-assisted cell detection-positive, light microscopy-missed detection rate was similar for cases with one (3 of 30; 10.0%) or two (5 of 47; 10.6%) cytokeratin sections. Metastases detected by routine light microscopy tended to be larger (0.01-0.50 mm) than did metastases detected only by computer-assisted cell detection (0.01-0.03 mm). In a selected series of patients, automated computer-assisted cell detection identified more micrometastases than were identified by routine light microscopy screening of cytokeratin-stained sections. Computer-assisted detection of events that are limited in number or size may be more reliable than detection by a pathologist using routine light microscopy. Factors such as human fatigue, incomplete section screening, and variable staining contribute to missing metastases by routine light microscopy screening. Metastases identified exclusively by computer-assisted cell detection tend to be extremely small, and the clinical significance of their identification is currently unknown.

Breast Neoplasms↗
PubMed1991

Computer vision.

The field of computer vision is devoted to discovering algorithms, data representations, and computer architectures that embody the principles underlying visual capabilities. This article describes how the field of computer (and robot) vision has evolved, particularly over the past 20 years, and introduces its central methodological paradigms.

Algorithms↗
PubMed1992

Application of computer-based experimental design to optimization of processing conditions for perfluorocarbon emulsion.

Response surface methodology was applied during process optimization of a parenteral emulsion formulation containing perfluorocarbon (PFC). E-Chip, a computer software program, was used to design and analyze the optimization experiments. The levels of eight process variables of interest were varied: pre-emulsification temperature and mixing time, mixer speed, generator type, rate of PFC addition, homogenization temperature, pressure and number of passes. Dependent variables evaluated included emulsion median diameter, viscosity and percent unemulsified PFC. A predictive model describing the relationship between the dependent and process variables was developed. Median diameter of the emulsion was affected significantly by homogenization temperature and pressure, and marginally by the rate of addition of the PFC. Viscosity was not influenced by any of the process variables. Percent unemulsified PFC was slightly influenced by the number of homogenization passes. The model was then used to set optimum process conditions.

Blood Substitutes↗
PubMed2000

Synthesis of bioprocesses using physical properties data.

The aim of this article is to illustrate and evaluate a synthesis procedure which has been extended to tackle bioprocesses. Physical property information is used to screen candidate units thereby reducing the size of the synthesis problem. In this way, only units which exploit large property differences between components in a stream are selected. This is important for bioprocesses because of the large number of components and wide range of unit operations which are available. The screening technique and bioprocess-unit-design methodologies have been incorporated within an implicit enumeration algorithm which was developed for chemical process synthesis and is implemented in Java programming language. An important advantage is the ability of the bioprocess synthesis software to generate a ranked list of flowsheets which may subsequently be analyzed in more detail. Two case studies are used to evaluate the bioprocess-synthesis technique. The first system involves a product which is secreted from the host organism. The second has significantly different characteristics in that the product is intracellular and forms inclusion bodies. The latter case study, in particular, is a large synthesis problem with 12 unit operations and 20 contaminant compounds. The results show that the synthesis methodology identifies a set of economically optimal flowsheets in a reasonable computational time which demonstrates its ability to deal with large synthesis problems. Using the synthesis methodology we can generate bioprocesses which are optimal in a system-wide, rather than unit-by-unit, sense.

Algorithms↗
PubMed1993

Determination of the optimized individual kinetic constants of the aminolysis reaction in basic medium of beta-lactam antibiotics by a numerical computational method.

The individual kinetic constants of the aminolysis reaction in basic medium of several beta-lactam compounds (6-aminopenicillanic acid, carbenicillin, 7-aminocephalosporanic acid, and cephalothin) are determined and improved by application of a computational method KINBETA. The method uses a modified version of the AGDC optimization algorithm adapted to the reaction system. Initial estimates of the constants for this reaction, obtained from the conventional methodology reported in the literature, were used. The computational method applied is self-consistent and affords both a considerable saving in experimental time and more reliable and exact results.

Anti-Bacterial Agents↗
PubMed1998

The teaching of computer programming and digital image processing in radiography.

The increased use of digital processing techniques in Medical Radiations imaging modalities, along with the rapid advance in information technology has resulted in a significant change in the delivery of radiographic teaching programs. This paper details a methodology used to concurrently educate radiographers in both computer programming and image processing. The students learn to program in visual basic applications (VBA), and the programming skills are contextualised by requiring the students to write a digital subtraction angiography (DSA) package. Program code generation and image presentation interface is undertaken by the spreadsheet Microsoft Excel. The user-friendly nature of this common interface enables all students to readily begin program creation. The teaching of programming and image processing skills by this method may be readily generalised to other vocational fields where digital image manipulation is a professional requirement.

Angiography, Digital Subtraction↗
PubMed1995

Simulations of Levothyroxine Bioavailability Using a Single-Dose Study Protocol.

Computation of oral levothyroxine bioavailability parameters is hampered due to a long pharmacokinetic half-life and the secretion of endogenous levothyroxine hormone. To overcome these difficulties, Berg and Mayor (J Clin Pharmacol 1992; 32: 1135--1140) suggested the use of a single, supraphysiologic levothyroxine oral dosage protocol and measurement of levothyroxine area under the serum concentration versus time curves (AUC) for 48 h after dose administration. Since this protocol is a nonstandard methodology, simulations were performed to assess potential errors associated with the proposed method. The pharmacokinetic simulations indicate a potential methodological error of about 1% in AUC computations. However, for patients with extremely short levothyroxine half-lives (<2--3 days), larger errors in AUC values are possible.

Journal Article↗
PubMed1985

Bayesian estimation and prediction of clearance in high-dose methotrexate infusions.

Much attention has been paid to the problem of estimating the pharmacokinetic parameters of individual patients in order to optimize dosage choices. Individual kinetics determined by test-dose bolus injection are a basis for predicting drug concentrations after high-dose methotrexate infusion and for computing appropriate dosages. Simplifications may be attempted, even allowing the test-dose to be omitted by using Bayesian estimation rather than likelihood estimation. To individualize pharmacokinetic parameters, Bayesian estimation combines information about population characteristics and those of individuals based on few measured plasma levels during high-dose infusion. Application of this procedure to methotrexate reveals interesting predictive performances and ability to handle variation due to intraindividual time variability without using test doses. The methodology promises to be more efficient in computing dosages in order to avoid toxic levels and will be less expensive in routine clinical use.

Aged↗
PubMed2005

Conformational and electronic properties of a microperoxidase in aqueous solution: a computational study.

A theoretical study of the conformational properties of a small heme peptide in aqueous solution is carried out by classical, long-timescale molecular dynamics simulations. The electronic properties of this species, that is, the relative energies of its excited electronic states and the redox potential, are reproduced and related to the conformational behavior using the perturbed matrix method and basic statistical mechanics. Our results show an interesting coupling between the conformational transitions and the electronic properties. These investigations, beyond the biophysically relevant results addressing the long-standing question of the actual role of the enzyme structure on the enzyme activity, are also of some methodological interest since they offer a further computational perspective for including the electronic degrees of freedom into the modeling of rather complex molecular systems.

Biophysics↗
PubMed2002

Evaluation of protective shielding thickness for diagnostic radiology rooms: theory and computer simulation.

This work presents the development and evaluation using modern techniques to calculate radiation protection barriers in clinical radiographic facilities. Our methodology uses realistic primary and scattered spectra. The primary spectra were computer simulated using a waveform generalization and a semiempirical model (the Tucker-Barnes-Chakraborty model). The scattered spectra were obtained from published data. An analytical function was used to produce attenuation curves from polychromatic radiation for specified kVp, waveform, and filtration. The results of this analytical function are given in ambient dose equivalent units. The attenuation curves were obtained by application of Archer's model to computer simulation data. The parameters for the best fit to the model using primary and secondary radiation data from different radiographic procedures were determined. They resulted in an optimized model for shielding calculation for any radiographic room. The shielding costs were about 50% lower than those calculated using the traditional method based on Report No. 49 of the National Council on Radiation Protection and Measurements.

Calibration↗
PubMed1999

Group sequential procedures for repeated events data with frailty.

In this article we consider the design aspects of group sequential trials with recurrent study endpoints, where the subjects are from a heterogeneous population. The usual procedures of sequential analysis based on the "independent increments" property are no longer valid due to the heterogeneity of the study subjects, as pointed out by Cook and Lawless. We focus on the aspect of study planning and consider a special model (Poisson process with frailty) to investigate the effects of frailty (or subject heterogeneity). We prescribe the valid procedures and provide convenient tables for computing stopping boundaries and sample sizes. The methodology is illustrated through an example of an animal experiment with recurrent tumors, using procedures such as group sequential tests and repeated confidence intervals. Minimal cost analysis is considered for determining the optimal combination of study duration and sample size.

Animals↗
PubMed2026

The Role of Artificial Intelligence Combined With Digital Cholangioscopy for Indeterminant and Malignant Biliary Strictures: A Systematic Review and Meta-analysis.

BACKGROUND: Current endoscopic retrograde cholangiopancreatography (ERCP) and cholangioscopic-based diagnostic sampling for indeterminant biliary strictures remain suboptimal. Artificial intelligence (AI)-based algorithms by means of computer vision in machine learning have been applied to cholangioscopy in an effort to improve diagnostic yield. The aim of this study was to perform a systematic review and meta-analysis to evaluate the diagnostic performance of AI-based diagnostic performance of AI-associated cholangioscopic diagnosis of indeterminant or malignant biliary strictures. METHODS: Individualized searches were developed in accordance with PRISMA and MOOSE guidelines, and meta-analysis according to Cochrane Diagnostic Test Accuracy working group methodology. A bivariate model was used to compute pooled sensitivity and specificity, likelihood ratio, diagnostic odds ratio, and summary receiver operating characteristics curve (SROC). RESULTS: Five studies (n=675 lesions; a total of 2,685,674 cholangioscopic images) were included. All but one study analyzed a deep learning AI-based system using a convoluted neural network (CNN) with an average image processing speed of 30 to 60 frames per second. The pooled sensitivity and specificity were 95% (95% CI: 85-98) and 88% (95% CI: 76-94), with a diagnostic accuracy (SROC) of 97% (95% CI: 95-98). Sensitivity analysis of CNN studies (4 studies, 538 patients) demonstrated a pooled sensitivity, specificity, and accuracy (SROC) of 95% (95% CI: 82-99), 88% (95% CI: 72-95), and 97% (95% CI: 95-98), respectively. CONCLUSIONS: Artificial intelligence-based machine learning of cholangioscopy images appears to be a promising modality for the diagnosis of indeterminant and malignant biliary strictures.

Humans↗
PubMed2003

Accounting for nonignorable verification bias in assessment of diagnostic tests.

A "gold" standard test, providing definitive verification of disease status, may be quite invasive or expensive. Current technological advances provide less invasive, or less expensive, diagnostic tests. Ideally, a diagnostic test is evaluated by comparing it with a definitive gold standard test. However, the decision to perform the gold standard test to establish the presence or absence of disease is often influenced by the results of the diagnostic test, along with other measured, or not measured, risk factors. If only data from patients who received the gold standard test were used to assess the test performance, the commonly used measures of diagnostic test performance--sensitivity and specificity--are likely to be biased. Sensitivity would often be higher, and specificity would be lower, than the true values. This bias is called verification bias. Without adjustment for verification bias, one may possibly introduce into the medical practice a diagnostic test with apparent, but not truly, high sensitivity. In this article, verification bias is treated as a missing covariate problem. We propose a flexible modeling and computational framework for evaluating the performance of a diagnostic test, with adjustment for nonignorable verification bias. The presented computational method can be utilized with any software that can repetitively use a logistic regression module. The approach is likelihood-based, and allows use of categorical or continuous covariates. An explicit formula for the observed information matrix is presented, so that one can easily compute standard errors of estimated parameters. The methodology is illustrated with a cardiology data example. We perform a sensitivity analysis of the dependency of verification selection process on disease.

Aged↗
PubMed2004

Methods for applying the quantitative structure-activity relationship paradigm.

There are several Quantitative Structure-Activity Relationship (QSAR) methods to assist in the design of compounds for medicinal use. Owing to the different QSAR methodologies, deciding which QSAR method to use depends on the composition of system of interest and the desired results. The relationship between a compound's binding affinity/activity to its structural properties was first noted in the 1930s by Hammett and later refined by Hansch and Fujita in the mid-1960s. In 1988 Cramer and coworkers created Comparative Molecular Field Analysis (CoMFA) incorporating the three-dimensional (3D) aspects of the compounds, specifically the electrostatic fields of the compound, into the QSAR model. Hopfinger and coworkers included an additional dimension to 3D-QSAR methodology in 1997 that eliminated the question of "Which conformation to use in a QSAR study?", creating 4D-QSAR. In 1999 Chemical Computing Group Inc. (CCG) developed the Binary-QSAR methodology and added novel 3D-QSAR descriptors to the traditional QSAR model allowing the 3D properties of compounds to be incorporated into the traditional QSAR model. Recently CCG released Probabilistic Receptor Potentials to calculate the substrate's atomic preferences in the active site. These potentials are constructed by fitting analytical functions to experimental properties of the substrates using knowledge-based methods. An overview of these and other QSAR methods will be discussed along with an in-depth examination of the methodologies used to construct QSAR models. Also, included in this chapter is a case study of molecules used to create QSAR models utilizing different methodologies and QSAR programs.

Algorithms↗
PubMed1993

A proposal for computer-based sleep/wake analysis.

The task group on Signal Analysis within the EC Concerted Action 'Methodology for the analysis of the sleep-wakefulness continuum' has proposed general guidelines for a computer-based sleep analyser that would not suffer from the most conspicuous limitations of manual standard scoring. The proposal specifies a standard format for digitized polygraphic recordings, a basic structure of the analyser, and a graphical output format for the analysis results. These analysis results include all sleep/wake related signal characteristics, an on/off REM sleep/wake process, and a continuous-scale NREM sleep/wake process, all with a time resolution of 1s. Several locally available sleep analysers were made to comply with these specifications and then applied to standardized digital polygraphic sleep recordings that were circulated among the laboratories. Analysis results were distributed, enabling evaluation of the local algorithms.

Journal Article↗
PubMed2000

Molecular electronic density fitting using elementary Jacobi rotations under atomic shell approximation

Fitted electron density functions constitute an important step in quantum similarity studies. This fact not only is presented in the published papers concerning quantum similarity measures (QSM), but also can be associated with the success of the developed fitting algorithms. As has been demonstrated in previous work, electronic density can be accurately fitted using the atomic shell approximation (ASA). This methodology expresses electron density functions as a linear combination of spherical functions, with the constraint that expansion coefficients must be positive definite, to preserve the statistical meaning of the density function as a probability distribution. Recently, an algorithm based on the elementary Jacobi rotations (EJR) technique was proven as an efficient electron density fitting procedure. In the preceding studies, the EJR algorithm was employed to fit atomic density functions, and subsequently molecular electron density was built in a promolecular way as a simple sum of atomic densities. Following previously established computational developments, in this paper the fitting methodology is applied to molecular systems. Although the promolecular approach is sufficiently accurate for quantum QSPR studies, some molecular properties, such as electrostatic potentials, cannot be described using such a level of approximation. The purpose of the present contribution is to demonstrate that using the promolecular ASA density function as the starting point, it is possible to fit ASA-type functions easily to the ab initio molecular electron density. A comparative study of promolecular and molecular ASA density functions for a large set of molecules using a fitted 6-311G atomic basis set is presented, and some application examples are also discussed.

Journal Article↗
PubMed1990

Characterization of the lipophilicity of natural and synthetic analogs of delta 9-tetrahydrocannabinol and its relationship to pharmacological potency.

delta 9-Tetrahydrocannabinol, the primary psychoactive constituent in marihuana, has been studied extensively for the last 20 years; however, the mechanisms responsible for cannabinoid activity in the central nervous system are not well understood. Although it is thought that lipophilicity plays an important role in the actions of cannabinoids, studies have not been conducted to determine whether a relationship exists between the lipophilicity and behavioral potency of cannabinoid analogs. Two procedures were used to obtain n-octanol/water partition coefficients (Po/w) of naturally occurring and synthetic cannabinoids: reverse-phase high-pressure liquid chromatographic estimation of Po/w and computer calculation of Po/w based on molecular structure. The Po/w value for delta 9-tetrahydrocannabinol obtained in this study, 9.44 x 10(6), is much greater than previously reported values obtained using shake-flask methodology, yet it is in agreement with the computer calculation based on molecular structure or molecular volume. The lipophilicity of the analogs determined in this study ranged from Po/w values of 3.92 x 10(2) to 1.93 x 10(11). All pharmacologically active cannabinoid compounds were extremely lipophilic (log Po/w values greater than 4.5). Several structural alterations were found to exert considerable influence on the lipophilicity of cannabinoid analogs. Increasing the length of the side chain in a homologous series of analogs results in an increase in lipophilicity of approximately 3-fold for each CH2 group added. Introduction of a single hydroxyl group decreased lipophilicity 3- to 40-fold, depending on the site of attachment. The behavioral potency of active analogs was not found to be correlated to lipophilicity. Therefore, data obtained in this study suggest that lipophilicity is a component, but not a primary determinant of pharmacological activity in the cannabinoids.

Animals↗