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Results for “Measuring algorithm”

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At least 1,621 records · Page 90Linked to original sources

PubMed2002

A blind comparison of four non-invasive twelve-lead electrocardiogram algorithms for predicting susceptibility to ventricular tachycardia.

INTRODUCTION: To reduce QT measurement error, a new method was tested in which high-gain, high-speed, simultaneous 12-lead electrocardiographic (ECG) recordings were obtained during a single cardiac cycle. To increase its predictive power, the utility of combining QTD with the QRS duration for predicting susceptibility to ventricular tachyarrhythmia (VT) was analyzed. METHODS AND RESULTS: A total of 113 patients referred for electrophysiological study underwent baseline simultaneous 12-lead ECG followed by electrophysiological study to determine VT inducibility. Twenty-six patients had inducible VT while 87 patients did not. QT intervals and the width of QRS complex were measured from a single cardiac cycle with high-gain (8 times normal) and high-speed (100 mm/second) 12-lead ECG recordings. This method resulted in 100% QT interval identification throughout all 12 leads for every patient. Receiver-operator characteristic curves (ROC) and the areas under the ROC curves (AUC) were used to quantitatively analyze the performance of four ECG variables (QTD3, QTD12, QTD12 + QRS and QTD3 + QRS). All four ECG variables were significantly increased in the patients with inducible VT as compared to those without inducible VT. The QTD3 algorithm was less useful than QTD12 in predicting inducible VT; however, the addition of QRS duration to all QTD algorithms enhanced VT detection. CONCLUSION: 1) QRS duration has an incremental benefit in the detection of VT when combined with QTD; 2) QTD12 + QRS duration provided the highest predictive power among the four tested algorithms; 3) high-gain, high-speed 12-lead ECG recordings reduced QT measurement error.

Aged↗

PubMed1991

Volume rendering and connectivity algorithms for MR angiography.

Several display algorithms for three-dimensional angiographic data are evaluated. The mathematical analysis assumes additive Gaussian noise to predict the background distribution function for maximum intensity projection, sum projection, and connectivity display methods. In the maximum intensity projection method the mean noise level increases with the number of voxels in the ray, while in the sum projection the noise distribution width increases with the projection thickness, but the mean level remains constant. Comparisons of maximum intensity projection, sum projection, and connectivity algorithms applied to an MR angiogram of the circle of Willis are made. Measurements of the noise distribution are in agreement with the analysis. Algorithms combining connectivity with maximum intensity and sum projection are also evaluated. In these methods, a projection image is created using only the voxels marked by connectivity, typically with a 6% threshold of the data. Fine vessels are resolved and background noise is reduced in agreement with the analysis.

Algorithms↗

PubMedDate not supplied

Identification algorithm for systemic arterial parameters with application to total artificial heart control.

A new algorithm for estimating systemic arterial parameters from systolic pressure and flow measurements at the root of the aorta is developed and tested through a systems identification approach. The resulting procedure has direct application to a total artificial heart (TAH) control system currently under development. Identification models, representing the systemic arterial system, are developed from existing work in the area of cardiovascular modeling. The resistive and compliance components of these models are physically significant, representing overall hydraulic properties of the systemic arterial system. A unique method of parameterizing the identification models is designed which operates on the basis of aortic pressure and flow measurements taken exclusively during systole. The estimator is a modified recursive least squares algorithm which utilizes covariance modification to track time-varying parameters and a dead-zone to improve the robustness. Performance of the estimation algorithm was tested on data generated by a higher-order distributed model of the systemic arterial bed using normal canine parameters. Results from model-to-model experiments verify the consistency of the estimates and the ability of the estimator to converge quickly and track dynamically varying parameters.

Adaptation, Physiological↗

PubMed2003

Application of remote sensing techniques for monitoring the thermal pollution of cooling-water discharge from nuclear power plant.

This article introduces a practical method to investigate thermal pollution in coastal water from satellite data. The intensity and distribution areas of thermal pollution by the heated effluent discharge from the nuclear power plant on Daya Bay, southern China were investigated by using Landsat-5 Thematic Mapper (TM) thermal band data from 1994 to 2001. A local algorithm was developed, based on sea-truth data of water surface temperature measured when the satellite passed over the study area. The local algorithm was then applied to estimate water temperature from TM data. It shows that the remote sensing technique provides an effective means to quantitatively monitor the intensity of thermal pollution and to retrieve a very detailed distribution pattern of thermal pollution in coastal waters. The remotely-sensed results of the thermal pollution can be used for environmental management of coastal waters.

Algorithms↗

PubMed2006

Ultrasonic concentration measurement of aqueous solutions using PLS regression.

This work demonstrates the use of a multivariate statistical technique called partial least squares (PLS) to extract material related data by analyzing spectra of ultrasonic pulses. We show how PLS can be used to estimate the concentration of sodium chloride in an aqueous solution. The paper describes the use of PLS and discusses pre-processing of ultrasonic data, the PLS algorithm as well as model validation. The measured concentrations are compared to reference values. The influence of disturbances and parameter changes is highlighted. The proposed method is easily adaptable to similar applications and permits a cost-saving implementation using existing and approved hardware.

Algorithms↗

PubMed2003

Monte Carlo modeling of an integrating sphere reflectometer.

The Monte Carlo method has been applied to numerical modeling of an integrating sphere designed for hemispherical-directional reflectance factor measurements. It is shown that a conventional algorithm of backward ray tracing used for estimation of characteristics of the radiation field at a given point has slow convergence for small source-to-sphere-diameter ratios. A newly developed algorithm that substantially improves the convergence by calculation of direct source-induced irradiation for every point of diffuse reflection of rays traced is described. The method developed is applied to an integrating sphere reflectometer for the visible and infrared spectral ranges. Parametric studies of hemispherical radiance distributions for radiation incident onto the sample center were performed. The deviations of measured sample reflectance from the actual reflectance as a result of various factors were computed. The accuracy of the results, adequacy of the reflectance model, and other important aspects of the algorithm implementation are discussed.

Journal Article↗

PubMed2004

Design of adaptive treatment margins for non-negligible measurement uncertainty: application to ultrasound-guided prostate radiation therapy.

Daily imaging during the course of a fractionated radiotherapy treatment has the potential for frequent intervention and therefore effective adaptation of the treatment to the individual patient. The treatment information gained from such images can be analysed and updated daily to obtain a set of patient individualized parameters. However, in many situations, the uncertainty with which these parameters are estimated cannot be neglected. In this work this methodology is applied to the adaptive estimation of setup errors, the derivation of a daily optimal pre-treatment correction strategy, and the daily update of the treatment margins after application of these corrections. For this purpose a dataset of 19 prostate cancer patients was analysed retrospectively. The position of the prostate was measured daily with an optically guided 3D ultrasound localization system. The measurement uncertainty of this system is approximately 2 mm. The algorithm finds the most likely position of the target maximizing an a posteriori probability given the set of measurements. These estimates are used for the optimal corrections applied to the target volume. The results show that the application of the optimal correction strategy allows a reduction in the treatment margins in a systematic way with increasing progression of the treatment. This is not the case using corrections based only on the measured values that do not take the measurement uncertainty into account.

Algorithms↗

PubMed2005

Spatial resolution improvement of 3D EIT images by the shrinking sLORETA-FOCUSS algorithm.

This paper describes the use of the shrinking sLORETA-FOCUSS algorithm to improve the spatial resolution of three-dimensional (3D) EIT images. Conventional EIT yields inaccurate, low spatial resolution images, due to noise, the low sensitivity of boundary voltages to inner conductivity perturbations and a limited number of boundary voltage measurements. The focal underdetermined system solver (FOCUSS) algorithm produces a localized energy solution based on the weighted minimum-norm least-squares (MNLS) solution. It was successfully applied for the spatial resolution improvement of EIT images of simulated and tank data for a 2D homogeneous circular disc. However, due to the fact that a 3D mesh system contains many more elements, much more memory is required to store the weighting matrix. In order to extend the work to 3D, the shrinking-FOCUSS method is utilized to shrink the solution space as well as the weighting matrix in each iteration step. The solution of the standardized low resolution electromagnetic tomography algorithm (sLORETA) is adopted as the initial estimate of the shrinking-FOCUSS. The effectiveness is verified by implementing the new algorithm on tank data for a three-dimensional homogeneous sphere.

Algorithms↗

PubMed2005

Information-theoretic approach to network modularity.

Exploiting recent developments in information theory, we propose, illustrate, and validate a principled information-theoretic algorithm for module discovery and the resulting measure of network modularity. This measure is an order parameter (a dimensionless number between 0 and 1). Comparison is made with other approaches to module discovery and to quantifying network modularity (using Monte Carlo generated Erdös-like modular networks). Finally, the network information bottleneck (NIB) algorithm is applied to a number of real world networks, including the "social" network of co-authors at the 2004 APS March Meeting.

Algorithms↗

PubMed1999

An On-line agglomerative clustering method for nonstationary data.

An on-line agglomerative clustering algorithm for nonstationary data is described. Three issues are addressed. The first regards the temporal aspects of the data. The clustering of stationary data by the proposed algorithm is comparable to the other popular algorithms tested (batch and on-line). The second issue addressed is the number of clusters required to represent the data. The algorithm provides an efficient framework to determine the natural number of clusters given the scale of the problem. Finally, the proposed algorithm implicitly minimizes the local distortion, a measure that takes into account clusters with relatively small mass. In contrast, most existing on-line clustering methods assume stationarity of the data. When used to cluster nonstationary data, these methods fail to generate a good representation. Moreover, most current algorithms are computationally intensive when determining the correct number of clusters. These algorithms tend to neglect clusters of small mass due to their minimization of the global distortion (Energy).

Algorithms↗

PubMed1997

[The i-STAT analyzer. A new, hand-held device for the bedside determination of hematocrit, blood gases, and electrolytes].

UNLABELLED: Exact and quick measurements of basic laboratory parameters are important in selected patients in the perioperative period. Depending on the capabilities of a hospital's central laboratory, the anaesthesiologist may only obtain such laboratory tests after unacceptable delays. This problem may be overcome by a new bedside measurement device that has become available from i-STAT Corporation, Princeton, USA. The hand-held, battery-driven analyser accepts blood specimens that are injected into a disposable cartridge (EG7+) and measures acidity, blood gas tensions, haematocrit, and electrolytes. The aim of this study was to determine the accuracy of such measurements by comparing them with measurements obtained by conventional laboratory test methods. METHODS: Heparinised arterial blood specimens were collected in duplicate from 49 surgical patients. Measurements of ionised calcium (Ca), sodium (Na), potassium (K), pH, pCO2, pO2, base excess (BE), haematocrit (Hct), and haemoglobin (Hb) obtained by the i-STAT analyser were compared with measurements from the calibrated analysers ABL 615 and EML 100 (Radiometer, Copenhagen). Because the i-STAT analyser calculates the Hb concentration from a conductometrically measured Hct, 19 blood specimens were centrifuged in order to compare test results with conventionally obtained Hct and Hb values. As the Hct test sensitivity with the i-STAT changes with diluted blood due to its low albumin concentration, Hct and Hb measurements during cardio-pulmonary bypass (CPB) must be corrected by activating an analyser-implemented correction algorithm (Hct/CPB and Hb/CPB). Correlation analysis was performed between conventional measurements and i-STAT values (Ca, Na, K, Hct, pCO2, pO2), between values that the i-STAT analyser derives (Hb, HCO3, BE) and conventionally obtained results, and between normal and CPB-corrected Hct and Hb values. Accuracy was judged according to the national quality standard, which requires test results to lie within the 95% confidence interval of conventional tests. RESULTS: Each blood specimen was analysed: erroneous results or technical failures did not occur. Measurement of one set of i-STAT values required 2.5 min. Correlation coefficients (r) between conventional and i-STAT results were: 0.85 for CA, 1.0 for K; 0.86 for Na; 0.99 for pH; 0.98 for pCO2; 0.99 for pO2; 0.93 for HCO3; 0.93 for BE; 0.46 for Hb values not corrected for CPB and 0.95 for CPB-corrected Hb; and 0.74 for Hct values not corrected for CPB and 0.98 for CPB-corrected Hct. The correlation coefficient for Hct between centrifuged and CPB-uncorrected i-STAT values was 0.81 and that for CPB-corrected values was 0.98. National accuracy requirements were not met for tests of: Ca (by 0.02 mmol/l); pH (by 0.01); pO2 including hyperoxic values (by 26.7 mmHg, but were met for pO2 values < 200 mmHg); Hb (by 1.6 g/dl); Hb/CPB (by 0.8 g/dl); and Hct (by 6.5%, but were met for Hct/CPB values). All other tests fulfilled the required standards. CONCLUSION: This analyser is easy to use, reliable, and portable, and therefore suitable for the operating room, for analyses during emergencies, on peripheral wards, for preclinical screening, or at times when availability of lab tests is time-consuming or limited. The test accuracy for electrolytes, blood gases, and Hb is high enough to justify routine use of the i-STAT analyser in clinical practice. That the nationally required quality standards for Ca, pH, and Hb were not met is not of importance because the measured deviation was too small to have clinical relevance. When analysing diluted blood with a low Hct and low oncotic pressure, it is important to activate the analyser's correction algorithm "CPB", because the obtained results will then comply with the required accuracy.

Blood Gas Analysis↗

PubMed2000

Feasibility of computer-assisted recognition of different dental hard tissues.

For pattern recognition, fuzzy set theory has been proven to be highly useful. The aim of the present investigation was to combine the fuzzy set with an ultrasonic scaler, to test its suitability for automatic detection of different tooth substances. An experienced operator placed the tip of a piezoceramic ultrasonic scaler on a tooth, thereby inducing oscillations in the contact area around the ultrasonic tip. Each surface showed a characteristic oscillatory behavior in the immediate vicinity of the tip. The oscillations were then re-transmitted to the scaler tip and recorded by the measurement of variations in current and voltage. Because the ultrasonic scaler is driven by piezoceramics, it can be used as both an oscillatory excitation and a sensor system. The data were processed with Fast Fourier transformation and analyzed by means of a fuzzy pattern recognition algorithm. Re-classification of the different measurements was carried out by the experienced operator's assessment. With a combination of six features (frequencies), re-classification was correct for 99% of all surfaces. The diagnostic reliability of the system was tested by the assessment of 50 teeth for which no learning data had previously been recorded. The unknown samples were correctly classified to 100%. The excellent results of these experiments suggest promising possibilities for the implementation of new diagnostic and therapeutic instruments in periodontology practice.

Algorithms↗

PubMed2000

Measurement variation among 12 electronic home blood pressure monitors.

Although there are AAMI and BHS standards for accuracy of electronic home electronic blood pressure monitors (HBPM), patient composition differences and differences in manufacturer's algorithm for calculation of the systolic and diastolic measurement may result in measurement differences between monitors. The aim of this study was the measurement of differences among HBPM. Paired comparisons were performed between the Omron 712c electronic home monitor and each of 12 other HBPM (Sunbeam 7654, Sunbeam 7623, Omron 711, Omron 432c, A&D-UA767, Lumiscope 1085M, Omron 725CIC, Assure A30, Lumiscope 1083N, Omron 815, Omron 605, and Assure BD-W20), in addition to comparison to the auscultatory method by trained observers. Measurements were made in normotensive subjects in an ambulatory setting. The main outcome measures were systolic and diastolic blood pressure measurements. All of the HBPM, except for the Sunbeam 7654 and the Assure A30/ BD-W20 (wrist) models, demonstrated small differences of <4/4 mm Hg for systolic/diastolic measurements with pulse measurement differences of <3 beats/min. These differences were less than the differences previously reported for office BP auscultation of 6/5-10 mm Hg for systolic/diastolic measurements. The Omron 712c, passing previous AAMI and BHS standards, measured the systolic reading within 2 mm Hg of auscultatory mercury or aneroid measurement and under-measured the diastolic by 6-9 mm Hg. Differences in the patient composition studied could account for the difference. The wrist and finger manometers performed clinically similar to the Omron 712c, except for the Assure BD-W20, which overmeasured the diastolic by 7 mm Hg. It is concluded that the small differences among the various HBPM, which are less than those in clinical office auscultation, should encourage greater use of electronic manometers in the office and at home.

Blood Pressure↗

PubMed2000

Basic study of the measurement of bone mineral content of cortical and cancellous bone of the mandible by computed tomography.

OBJECTIVES: To develop an algorithm for automatic separation of cortical from cancellous bone in the mandible and for measuring mandibular bone mineral content (BMC). METHODS: A dried mandible was scanned together with a reference phantom by spiral CT. A new algorithm was developed specifically for the mandible and cross-sectional images reconstructed in the buccolingual plane. The cortical bone was extracted with a threshold of 80% of the peak height in the line-scan profile and the cancellous bone extracted separately. The volume and BMC were estimated. Images of cortical and cancellous bone were displayed in a plane approximating the orientation used for dental radiography and BMC expressed as aluminium-equivalents (Al-eqs). RESULTS: The ratio of cortical to cancellous bone by volume was 22:78, and the ratio of the BMC 60:40. Comparison of BMC from reconstructed CT with Al-eqs showed good correlation but was 1.5 times higher with CT. CONCLUSIONS: It is possible to separate cancellous from cortical bone automatically from CT images and to measure the BMC.

Absorptiometry, Photon↗

PubMed2006

New actigraph for long-term tremor recording.

A new method of movement analysis is validated, allowing an actigraph to discriminate tremor from other movements and store duration and intensity measures of both movement types. For algorithm optimization, wrist acceleration was recorded in nine controls and nine Parkinson's disease patients, while simultaneously rating their observed tremor minute by minute on item 20 of the Unified Parkinson's Disease Rating Scale. An optimization procedure to minimize false positives in controls while maximizing tremor detection in patients resulted in false positive tremor classification in 2.4% +/- 2.5% of the movement time of control subjects (range, 0%-7%), while providing tremor classification in 82.1% +/- 15.4% of the movement time in patients (range, 55%-100%), correlating r = 0.93 with their averaged observed tremor score. A second, generalizability study showed that application of the optimized algorithm resulted in accurate classification of 71% +/- 14% of the observed tremor time (range, 46%-90%) in another 9 patients and in a false positive classification in only 0.5% +/- 0.8% of the time in another 10 controls (range, 0%-2.4%). The commercial availability of this actigraph now for the first time makes it possible to investigate tremor fluctuations over several weeks. An example is given of how long-term monitoring can be of use in evaluation of symptom management.

Aged↗

PubMed2003

Bayesian analysis of structural equation models with dichotomous variables.

Structural equation modelling has been used extensively in the behavioural and social sciences for studying interrelationships among manifest and latent variables. Recently, its uses have been well recognized in medical research. This paper introduces a Bayesian approach to analysing general structural equation models with dichotomous variables. In the posterior analysis, the observed dichotomous data are augmented with the hypothetical missing values, which involve the latent variables in the model and the unobserved continuous measurements underlying the dichotomous data. An algorithm based on the Gibbs sampler is developed for drawing the parameters values and the hypothetical missing values from the joint posterior distributions. Useful statistics, such as the Bayesian estimates and their standard error estimates, and the highest posterior density intervals, can be obtained from the simulated observations. A posterior predictive p-value is used to test the goodness-of-fit of the posited model. The methodology is applied to a study of hypertensive patient non-adherence to medication.

Algorithms↗

PubMed1998

Evaluation of enhanced high-resolution laser Doppler imaging in an in vitro tube model with the aim of assessing blood flow in separate microvessels.

An enhanced high-resolution laser Doppler imaging (EHR-LDI) technique intended for visualization of separate microvessels was evaluated by use of in vitro flow models. In EHR-LDI, a laser beam focused to a half-power diameter less than 40 microm successively scans the tissue under study in steps of 25 microm. Spatial blood flow variations within microvascular structures of 1.5 x 1.5 mm are rendered by 64 x 64 measurement sites. Individual microvessel diameters could be estimated and an average difference of 11 microm compared to microscopic measurements was obtained. For the flow algorithm used, the LDI output signal was found to scale linearly with average velocity (0-3.5 mm/s) when a plastic tube of inner diameter 175 microm was perfused with human blood (correlation coefficient 0.99). The LDI output signal was further found insensitive to hematocrit variations in the range 16-44%. Due to the limited laser light penetration in blood, a reduction in the LDI output signal was observed as the inner tube diameters were successively changed from 280 to 1400 microm.

Animals↗

PubMed1997

Surgical treatment of sphincteric incontinence in women.

There are many surgical options to correct sphincteric incontinence. The choice should take account of clinical features, urodynamic data and operation characteristics. Success should be evaluated both subjectively and objectively and it is desirable to have at least a two year follow-up. It is necessary to be aware of the complications of each procedure. Where new techniques are described it is important to use objective outcome measures.

Algorithms↗