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Results for “Measuring algorithm”

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PubMed1999

Psychological stress in the workplace and menstrual function.

The relation between psychological stress at work and menstrual function was examined for 276 healthy, working, premenopausal women who participated in the California Women's Reproductive Health Study in 1990-1991. Subjects collected daily urine samples and completed a daily diary for an average of five menstrual cycles. Metabolites of estrogen and progesterone were measured in the urine, and computer algorithms were developed to characterize each cycle as ovulatory or anovulatory and to select a probable day of ovulation. A telephone interview collected information about psychological stress at work as well as other occupational, demographic, lifestyle, and environmental factors. Logistic regression was used to model stressful work and risk of anovulation (> or = 36 days without ovulating) and measures of within-woman cycle variability. Repeated measures analyses were performed on other menstrual cycle parameters. Stressful work (high demand in combination with low control) was not strongly related to an increased risk for anovulation or cycle variability or to any of the following cycle endpoints: short luteal phase (< or = 10 days), long follicular phase (> or = 24 days), long menses (> or = 8 days), or long cycle (> or = 36 days). However, women in stressful jobs had a more than doubled risk for short cycle length (< or = 24 days) compared with women not working in stressful jobs (adjusted odds ratio = 2.24, 95% confidence interval 1.09-4.59).

Adolescent↗

PubMed2003

An image analysis-based approach for automated counting of cancer cell nuclei in tissue sections.

BACKGROUND: Semiquantitative evaluation and manual cell counting are the commonly used procedures to assess positive staining of molecular markers in tissue sections. Manual counting is also a laborious task in which consistent objectivity is difficult to achieve. Recently, image analysis has been explored, but the studies reported were limited to histological images acquired at high magnification and containing uniformly stained cells. METHODS: The analyzed material consisted of histological sections from different squamous cell cancers that had stained for proliferation using Ki-67 and cyclin A detection. The first step of the method was based on detecting the overall number of cells irrespective to their stain, using second-order edge detection methodology. Then proliferating cells were located using principal component analysis (PCA) of the color image, combined with histogram thresholding. RESULTS: The algorithms' performances were validated on tissue section images encountered in routine clinical practice by comparison with objective measures of performance and manual cell identification. The algorithms correlated closely with manual counting of all cells (r(2) = 0.96-0.97) and stained cells (4-7% cell count error). CONCLUSIONS: Cell counting in complex large-scale histological images could be applied in routine practice using edge and color information. The proposed technique provides several benefits, such as speed of analysis, consistency, and automation. Moreover, it is faster than human observation and could replace the laborious task of manual cell counting.

Algorithms↗

PubMed1998

Star length distribution: a volume-based concept for the characterization of structural anisotropy.

Determination and quantification of anisotropy is of great interest in research fields dealing with physical structures or surface textures. In this paper, a volume-based method is presented, which essentially determines the mean object length in a certain direction for a typical point within a structure or texture. The mean object lengths for all orientations together form the so-called star length distribution (SLD). The validity and the accuracy of the SLD method are investigated, and illustrated by applying it to trabecular bone. By using a line sampling algorithm, the relation with other anisotropy measures could be studied analytically. Preliminary tests suggest that with SLD a more exact description of the mechanical properties of porous structures may be obtained than with other anisotropy measures. However, due to possible secondary orientations that become apparent with SLD, a fabric tensor must be of rank higher than two in order to properly describe an orthogonal structure mathematically.

Adolescent↗

PubMed2003

Reduction of interference in oscillometric arterial blood pressure measurement using fuzzy logic.

In oscillometry, oscillation amplitudes (OAs) embedded in the cuff pressure are drastically affected by a variety of artifacts and cardiovascular diseases, leading to inaccurate arterial blood pressure (ABP) measurement. The purpose of this paper is to improve the accuracy in the arterial pressure measurement by reducing interference in the OAs using a recursive weighted regression algorithm (RWRA). This method includes a fuzzy logic discriminator (FLD) and a recursive regression algorithm. The FLD is used to reduce the effect of artifacts caused by measurement motion disturbance or cardiovascular diseases, and to determine the truthfulness of the oscillation pulse. According to the truth degree, the relationship between the cuff pressure and OA is reconstructed using the regression algorithm. Because the regression method must utilize inverse matrix operation, which will be difficult to implement in an automatic or ambulatory monitor, the recursive regression method is proposed to solve this problem. To test the performance of this RWRA, 47 subjects underwent the ABP measurement using both the auscultation and the oscillometry combined with the RWRA. It was found that the average difference between the pooled blood pressures measured by the auscultation and those by the oscillometry combined with the RWRA was found to be only 4.9 mmHg. Clinical results demonstrated that the proposed RWRA is more robust than the traditional curve fitting algorithm (TCFA). We conclude that the proposed RWRA can be applied to effectively improve the accuracy of the oscillometric blood pressure measurement.

Adolescent↗

PubMed1991

Measurements of ultrasonic fields with optical diffraction tomography.

This article describes a light diffraction technique that allows a measurement of ultrasonic pressure and phase in the cross-section of an ultrasonic beam. The light diffraction measurements are based on the Raman-Nath model of ultrasonic continuous-wave light diffraction. The diffracted light intensity can be expressed as an integration of sound pressure along the light path. This integration is analogous to the integration of the absorption coefficient in x-ray tomography. Tomography algorithms can be employed on the light measurement data to calculate the pressure and phase in a measuring plane perpendicular to the ultrasound propagation vector. The reconstruction of the measurement plane is done with an implementation of an algebraic reconstruction technique (ART). Satisfactory results are obtained with 10 projections. The measurement method is applicable up to Raman-Nath parameter values of 2.3. The experimental results are compared to miniature PVDF hydrophone measurements.

Algorithms↗

PubMed2005

Accuracy evaluation of a new glucometer with automated hematocrit measurement and correction.

BACKGROUND: Blood glucose meters are widely used in point of care testing, however, many studies have shown inaccuracies in the glucose measurement due to a number of factors. The present study evaluated the accuracy of a new glucometer capable of simultaneous measurement of patient's hematocrit with algorithmic adjustment of glucose result. This meter was compared with a reference method and 2 other existing meters widely used in the market. METHODS: Venous whole blood samples from healthy volunteers were pooled and reconstituted to produce 5 different hematocrit (30-60%) concentrations. Each hematocrit specimen was spiked to produce 4 different glucose (50-500 mg/dl) concentrations. RESULTS: Hematocrit measured by the new meter correlated well with the reference method. Mean percentage error differences, compared to the reference method, showed obvious differences between existing meters across the wide hematocrit range at various glucose concentrations. The new meter showed a steady and consistent glucose concentrations compared to the reference method. CONCLUSION: The new glucometer, which simultaneously measures hematocrit and performs automated correction for the hematocrit effect, provides a glucose result with improved accuracy. Its measurement of hematocrit from the same blood sample will eliminate the need for additional collection of blood or measurement using another method.

Blood Glucose↗

PubMedDate not supplied

Echocardiographic design of a multicenter investigation of free-living elderly subjects: the Cardiovascular Health Study.

The Framingham study has shown by M-mode echocardiography that left ventricular hypertrophy is a powerful, independent predictor for the development of coronary heart disease and that increased left atrial dimension has been associated with an increased risk of stroke. No previous population-based study has evaluated the risk factor correlates and predictive value for coronary heart disease and stroke of two-dimensional and Doppler, as well as M-mode, echocardiography. The Cardiovascular Health Study is a multi-year prospective epidemiologic study of 5201 men and women older than 65 recruited from four geographic sites in the United States. The main objectives of incorporating echocardiography were to determine whether echocardiographic indices, or changes in these indices, are (1) correlated with traditional risk factors for coronary heart disease and stroke; and (2) independent predictors of morbidity and mortality for coronary heart disease and stroke. Echocardiographic measurements of interest include those related to global and segmental left ventricular systolic and diastolic structure and function and left atrial size. For each subject, a baseline echocardiogram was recorded in super-VHS tape using a standard protocol and equipment. All studies were sent to a reading center where images were digitized and measurements were made using customized computer algorithms. Calculated data and images were stored on optical disks to facilitate retrieval and future comparisons in longitudinal studies. A second echocardiogram is scheduled in year 7, with a goal of determining whether changes in cardiac anatomy or function over a 5-year period are important predictors of morbidity or mortality from coronary heart disease and stroke. Quality control measures included standardized training of echocardiography technicians and readers, technician observation by a trained echocardiographer, periodic blind duplicate readings with reader review sessions, phantom studies, and quality control adults.

Allied Health Personnel↗

PubMed2002

Endoscopic therapy in the management of hepatobiliary hydatid disease.

Hydatid disease constitutes a serious public health problem throughout the world, especially in endemic areas, despite the use of various kinds of preventive measures. Currently, there are three treatment options for hepatic hydatid disease including surgery, PAIR (puncture, aspiration, injection, and re-aspiration), and chemotherapy with benzimidazole compounds. Each of these therapeutic modalities has limitations depending on the individual case. The authors review the use of diagnostic and therapeutic endoscopic retrograde cholangiopancreatography (ERCP) in the management of hepatobiliary hydatid disease (HHD) to clarify its place in the treatment algorithm among surgical, medical, and percutaneous measures. ERCP in the preoperative period: (1) defines the cystobiliary relationship to help in surgery planning, (2) permits evaluation for acute conditions like cholangitis and obstruction so that subsequent surgery can be performed on an elective basis, (3) may give permanent cure specifically in cases of frank intrabiliary rupture if evacuation of biliary tract and cystic cavity is manageable, and (4) when combined with preoperative endoscopic sphincterotomy may decrease the incidence of the development of postoperative external fistula. ERCP in the postoperative period: (1) can help to clarify the causes of ongoing or recurrent symptoms or laboratory abnormalities, (2) may help to resolve the obstruction or cholangitis due to residual material in biliary ducts, (3) may provide the chance to manage postoperative external biliary fistulae, and (4) may be a realistic solution for secondary biliary strictures. Considering the current literature and adding this experience, the authors propose a new treatment algorithm in HHD including medical, surgical, PAIR, and ERCP-related therapies. To illustrate the algorithm, a case is presented of a patient who had a persistent external biliary fistula in the postoperative period and was managed successfully by endoscopic approach.

Adult↗

PubMed1998

Approximate Statistical Tests for Comparing Supervised Classification Learning Algorithms.

This article reviews five approximate statistical tests for determining whether one learning algorithm outperforms another on a particular learning task. These tests are compared experimentally to determine their probability of incorrectly detecting a difference when no difference exists (type I error). Two widely used statistical tests are shown to have high probability of type I error in certain situations and should never be used: a test for difference of two proportions and a paired-differences t test based on taking several random train-test splits. A third test, a paired-differences t test based on 10-fold cross-validation, exhibits somewhat elevated probability of type I error. A fourth test, McNemar's test, is shown to have low type I error. The fifth test is a new test, 5 x 2 cv, based on five iterations of twofold cross-validation. Experiments show that this test also has acceptable type I error. The article also measures the power (ability to detect algorithm differences when they do exist) of these tests. The cross-validated t test is the most powerful. The 5 x 2 cv test is shown to be slightly more powerful than McNemar's test. The choice of the best test is determined by the computational cost of running the learning algorithm. For algorithms that can be executed only once, McNemar's test is the only test with acceptable type I error. For algorithms that can be executed 10 times, the 5 x 2 cv test is recommended, because it is slightly more powerful and because it directly measures variation due to the choice of training set.

Journal Article↗

PubMed1996

Algorithms for robust nonlinear regression with heteroscedastic errors.

Nonlinear regression algorithms were compared by Monte-Carlo simulations when the measurement error was dependent on the measured values (heteroscedasticity) and possibly contaminated with outliers. The tested leastsquares (LSQ) algorithms either required user-supplied weights to accommodate heteroscedasticity or the weights were estimated within the procedures. Robust versions of the LSQ algorithms, namely robust iteratively reweighted (IRR) and least absolute value (LAV) regressions, were also considered. The comparisons were based on the efficiency of the estimated parameters and their resistance to outliers. Based on these criteria, among the tested LSQ algorithms, extended least squares (ELSQ) was found to be the most reliable. The IRR versions of these algorithms were slightly more efficient than the LAV versions when there were no outliers but they provided weaker protection to outliers than the LAV variants.

Algorithms↗

PubMed2005

[Dysphonia: current methods of evaluation].

OBJECTIVES: The aim of this review article was to provide an update on current techniques for evaluation of dysphonia in routine clinical practice. MATERIALS AND METHODS: Recent medical and other scientific literature was reviewed and pertinent current theories concerning the physiology of laryngeal function described. RESULTS: Perceptual voice quality evaluation by a professional jury of listeners is still considered to be the most reliable and complete means of evaluating pathologic voice, even though it is difficult to perform in routine and the results lack reproducibility. The objective evaluation of the vocal fundamental frequency and its variations and the spectral characteristics of voice has the advantage of being simple to perform, reproducible and quantifiable. However, automatic measurements need to be analyzed with precaution for severe dysphonia, the computer algorithms being designed for voices retaining a certain periodicity. Aerodynamic measurements are quantifiable and reproducible and provide information as to the quality of laryngeal function as a transducer of aerodynamic energy into acoustic energy. Videostroboscopy and electroglottography provide information as to the quality of the laryngeal vibrations, the source of sound production. CONCLUSIONS: All of these types of analysis are complementary, informing as to different aspects of vocal quality and laryngeal function. No one measurement alone can diagnose or characterize dysphonia.

Electrodiagnosis↗

PubMed2004

An intelligent case-adjustment algorithm for the automated design of population-based quality auditing protocols.

We develop a method and algorithm for deciding the optimal approach to creating quality-auditing protocols for guideline-based clinical performance measures. An important element of the audit protocol design problem is deciding which guide-line elements to audit. Specifically, the problem is how and when to aggregate individual patient case-specific guideline elements into population-based quality measures. The key statistical issue involved is the trade-off between increased reliability with more general population-based quality measures versus increased validity from individually case-adjusted but more restricted measures done at a greater audit cost. Our intelligent algorithm for auditing protocol design is based on hierarchically modeling incrementally case-adjusted quality constraints. We select quality constraints to measure using an optimization criterion based on statistical generalizability coefficients. We present results of the approach from a deployed decision support system for a hypertension guideline.

Algorithms↗

PubMed2002

A new method to identify multiple sources of oscillatory activity from magnetoencephalographic data.

Identifying the sources of oscillatory activity in the human brain is a challenging problem in current magnetoencephalography (MEG) and electroencephalography (EEG) research. The fluctuations in phase and amplitude of cortical oscillations preclude signal averaging over successive sections of the data without a priori assumptions. In addition, several sources at different locations often produce oscillatory activity at similar frequencies. For example, spontaneous oscillatory activity in the 8- to 13-Hz band is produced simultaneously at least in the posterior parts of the brain and bilaterally in the sensorimotor cortices. The previous approaches of identifying sources of oscillatory activity by dipole modeling of bandpass filtered data are quite laborious and require that multiple criteria are defined by an experienced user. In this work we introduce a convenient method for source localization using minimum current estimates in the frequency domain. Individual current estimates are calculated for the Fourier transforms of successive sections of continuous data. These current estimates are then averaged. The algorithm was tested on simulated and measured MEG data and compared with conventional dipole modeling. The main advantage of the proposed method is that it provides an efficient approach for simultaneous estimation of multiple sources of oscillatory activity in the same frequency band.

Algorithms↗

PubMed2003

Cardiovascular risk factors and estimated risk for CAD in a randomized trial comparing calcineurin inhibitors in renal transplantation.

Cardiovascular morbidity and mortality is high in patients following renal transplantation. The present analysis assessed major cardiovascular risk factors and estimated the risk of coronary artery disease in the largest present-day comparative trial of tacrolimus vs. microemulsified cyclosporine A. In this 6-month study, 557 patients were randomly allocated to therapy with tacrolimus (n = 286) or cyclosporine A (n = 271) concomitantly with azathioprine and corticosteroids. The primary endpoint was the incidence of and time to acute rejection. Blood pressure, serum cholesterol, HDL cholesterol, triglycerides, and blood glucose were measured at baseline, and at months 1, 3, and 6. Ten-year risk of coronary heart disease was estimated according to the Framingham risk algorithm. Tacrolimus resulted in significantly lower summary measures (time-weighted average) of serum cholesterol (p = 0.0004) and mean arterial blood pressure (p = 0.0156), but in a higher summary measure of blood glucose (p = 0.0028) than cyclosporine. The summary measure of serum triglycerides was not different between treatment groups (p = 0.368). The mean 10-year coronary artery disease risk estimate was significantly lowered in men (p = 0.0032) treated with tacrolimus, but was unchanged in women. Tacrolimus and cyclosporine A microemulsion exert a compound-specific impact on cardiovascular risk factors and appear to affect the predicted rate of cardiovascular morbidity in different manners.

Calcineurin Inhibitors↗

PubMed2004

Optimal selection of SNP markers for disease association studies.

Genetic association studies with population samples hold the promise of uncovering the susceptibility genes underlying the heritability of complex or common disease. Most association studies rely on the use of surrogate markers, single-nucleotide polymorphism (SNP) being the most suitable due to their abundance and ease of scoring. SNP marker selection is aimed to increase the chances that at least one typed SNP would be in linkage disequilibrium (LD) with the disease causative variant, while at the same time controlling the cost of the study in terms of the number of markers genotyped and samples. Empirical studies reporting block-like segments in the genome with high LD and low haplotype diversity have motivated a marker selection strategy whereby subsets of SNPs that 'tag' the common haplotypes of a region are picked for genotyping, avoiding typing redundant SNPs. Based on these initial observations, a plethora of 'tagging' algorithms for selecting minimum informative subsets of SNPs has recently appeared in the literature. These differ mostly in two major aspects: the quality or correlation measure used to define tagging and the algorithm used for the minimization of the final number of tagging SNPs. In this review we describe the available tagging algorithms utilizing a 3-step unifying framework, point out their methodological and conceptual differences, and make an assessment of their assumptions, performance, and scalability.

Algorithms↗

PubMed2004

Tridimensional animated brain mapping from conventional paper-ink EEG recordings.

One of the most powerful functional evaluations of the electrical activity of the brain is the EEG imaging, but wide clinical use is limited by its costs. It is also of clinical, academic and scientific interest to obtain brain electrical maps from old paper/ink, patient recordings. The aim of the present study was the development of a computer system designed to obtain bidimensional and tridimensional maps, continuous movie map display and mosaic presentation from conventional paper/ink EEG recordings. The wave amplitude was manually measured with a translucent template from conventional 8- to 16-channel EEG paper recordings using 10-20 monopolar montage for one or both hemispheres. The computer system allows the selection of the number and location of electrodes, input of amplitude values, and the map display mode. The electrical brain field was generated from amplitude measurements by a spherical splines interpolation algorithm on a conventional Pentium-based computer. The interpolated surface was represented on a semi-sphere modeled skull. The EEG maps displayed with pseudo-color or gray scales can be rotated, zoomed in or zoomed out and/or printed for clinical reports. Movie animation or mosaic display of space-temporal EEG voltage changes were generated by processing sequential amplitude measurements. This system represents a cost-effective method for EEG mapping from conventional paper/Ink EEG equipments.

Brain Mapping↗

PubMed2007

Characteristics and value of directed algorithms in high content screening.

High content screening requires image processing algorithms that can accurately and robustly analyze large image numbers without requiring human intervention. Thus, a suite of algorithms that are directed by an understanding of the biology being studied was developed for the optimized automated acquisition and quantitation of cellular images. Two categories of directed algorithms were developed: Developer Tools for assay development and Specific Algorithms for turnkey screening of specific biological situations. The same basic sequence of analysis steps are used in these directed algorithms: 1. Primary object identification. 2. Measurement of primary object properties. 3. Identification and measurements of associated targets. 4. Analysis of raw measurements for specific biological problems. The detailed application of these steps is guided by the biology being studied and the expected phenotypic changes. Most cell biological problems to be analyzed using high content screening can be categorized by either the phenotype of the problem or labeling pattern, or by a standard biological response behavior of the cells. This enables application of directed algorithms optimized for these categories. Examples of the use of directed algorithms for specific categories are discussed, as well as the detailed analysis steps for a specific directed algorithm.

Algorithms↗

PubMed1994

A simulation of emission and transmission noise propagation in cardiac SPECT imaging with nonuniform attenuation correction.

Transmission computed tomography provides information needed for nonuniform attenuation correction of cardiac single photon emission computed tomography (SPECT). Nonuniform attenuation correction is accomplished using an iterative ML-EM algorithm and a projection-backprojection operation that incorporates attenuation factors measured from the reconstructed transmission map. The precision and accuracy of the attenuation corrected emission reconstruction is a function of emission and transmission statistics. This paper presents an error propagation analysis that uses a mathematical cardiac chest phantom to simulate various combinations of total emission counts C and transmission flux I0 under ideal imaging conditions (without geometric response distortion and without scatter). The spatial average, spatial variance, and accuracy measures for a 4 x 4 pixel region in the heart are tabulated after 30 iterations of the ML-EM algorithm. The confidence intervals for these measures were determined from 1000 realizations of reconstructions from projections randomly generated with the same transmission and emission statistics. It can be shown empirically from the simulation results that the spatial %rms uncertainty for the simulated cardiac region has a simple expression: %rms2 = K1/C+K2/I0(2)+B2 where K1 and K2 are least-square estimates based on the simulation results, and B is the measured spatial %rms uncertainty for the simulation at infinite statistics. For a transmission incident flux of 1500 events per projection bin of 0.712 cm and typical clinical emission events totaling 1 x 10(5), the spatial %rms uncertainty is approximately 14%. At clinical transmission and emission statistics, the statistical noise in the simulated attenuation-corrected reconstructions are dominated by the emission statistics.

Algorithms↗