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Results for “Error minimization”

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At least 793 records · Page 44Linked to original sources

PubMed2006

Inverse analysis of constitutive models: biological soft tissues.

The paper describes a procedure for estimating the material parameters of biological soft tissue by fitting model prediction to experimental load-deformation data. This procedure minimizes the error between data and theoretical model prediction through systematically adjusting the parameters in the latter. The procedure uses commercially available software and is not specific to any particular model; nevertheless, for illustration purposes, we employ a six parameter fibril-reinforced poroelastic cartilage model. We are able to estimate any and all of these parameters by the procedure. Convergence of the parameters and convergence of the arbitrary initial stress relaxation to the data was demonstrated in all cases. Though we illustrate the optimization procedure here for unconfined compression only, it can be adapted easily to other experimental configurations such as confined compression, indentation and tensile test. Furthermore, the procedure can be applied in other areas of biomechanics where material parameters need to be extracted from experimental data.

Biomechanical Phenomena↗

PubMed2005

Capillary electrophoresis of glutathione to monitor oxidative stress and response to antioxidant treatments in an animal model.

Glutathione plays a central role in metabolism and antioxidant defence. Several factors can influence the analytical efficiency and rapidity of the quantitative determination of glutathione. Procedures in sample pre-treatment have been compared in order to minimize analytical errors. Capillary electrophoresis has been chosen as a more adequate technique for obtaining a rapid and simple method for glutathione and glutathione disulfide determination in the blood and liver of the rat. The methods, once optimised, have been validated and applied for monitoring the oxidative stress in an animal model, such as the rat made diabetic by streptozotocin injection, when the animals are treated with antioxidants and compared with the corresponding controls.

Animals↗

PubMed2005

Contamination by larger particles of two almost-uniform latices: analysis by combined dynamic light scattering and turbidimetry.

Multiangle dynamic light scattering (MDLS) and turbidimetry (T) were applied (both individually and combined) for determining the contamination by larger particles of two almost-uniform polystyrene (PS) latices. Latex 1 was synthesized in our laboratories, and it contained a main population diameter of 340 nm together with a small fraction of larger particles. This latex was used as the base material for producing an immunoassay kit. Latex 2 was obtained by a simple blend of two uniform PS standards. The proposed data treatment calculates the diameter and number fraction of the large particles contamination assuming that the PSDs are bimodal. The calculation involves minimizing the errors between the measurements and their theoretical predictions. When analyzed by combined MDLS-T, the contamination of Latex 1 involved number fraction 0.6% and particle diameter 865 nm. The T average diameter is a function of the measurement wavelength, and the highest deviations of this average to an increasing contamination by large particles were always observed at the higher wavelengths. The DLS average diameter is a function of the measurement angle, but in this case it is impossible to determine a priori the angle of observation that provides the largest deviation of this average diameter to an increasing contamination.

Journal Article↗

PubMed2005

Medical education in critical care.

Patient safety is garnering increasing attention in our health care system, and with a possible trend toward increasing patient adverse events in academic hospitals (CMAJ. 2004;170:1678-86), medical education needs to reevaluate resident training. Within critical care, teaching of trainees in a manner that minimizes medical errors and ensures competency when managing critically ill patients is now a priority. This article addresses 4 areas that are receiving increasing attention in medical education and are relevant to training in the critical care environment: evidence-based medicine, communication, evaluation, and simulation.

Clinical Competence↗

PubMed2004

A posture optimization algorithm for model-based motion capture of movement sequences.

We have developed and evaluated a new optical motion capture approach that is suitable for a wide range of studies in neuroethology and motor control. Based on the stochastic search algorithm of Simulated Annealing (SA), it utilizes a kinematic body model that includes joint angle constraints to reconstruct posture from an arbitrary number of views. Rather than tracking marker trajectories in time, the algorithm minimizes an error function that compares predicted model projections to the recorded views. Thus, each video-frame is analyzed independently from other frames, enabling the system to recover from incorrectly analyzed postures. The system works with standard computer and video equipment. Its accuracy is evaluated using videos of animated locust leg movements, recorded by two orthogonal views. The resulting joint angle RMS errors range between 0.7 degrees and 4.9 degrees, limited by the pixel resolution of the digital video. 3D-movement reconstruction is possible even from a single view. In a real experimental application, stick insect walking sequences are analyzed with leg joint angle deviations between 0.5 degrees and 3.0 degrees. This robust and accurate performance is reached in spite of marker fusions and occlusions, simply by exploiting the natural constraints imposed by a kinematic chain and a known experimental setup.

Algorithms↗

PubMed2005

Detection of construction errors in ex vivo coronary artery anastomoses by 13-MHz epicardial ultrasonography.

OBJECTIVE: Intraoperative detection of suboptimal coronary anastomoses allows revision before chest closure. We evaluated an epicardial 13-MHz ultrasound minitransducer as a means to detect three different coronary anastomosis construction errors. METHODS: In total, 120 internal thoracic artery-to-coronary artery anastomoses were constructed correctly (n = 60) or incorrectly (n = 60) with one technical error: suture crossover, purse-string or deep toe stitch (n = 20 each). Anastomoses were performed on ex vivo pressure-perfused porcine (96 anastomoses) and human hearts (24 anastomoses). Two blinded observers scanned and scored the anastomoses with epicardial ultrasonography. In 24 human and 24 porcine anastomoses, angiograms were made of 24 correct and 24 incorrect anastomoses and scored by two other blinded observers. Angioscopy and cast injection served as a reference. RESULTS: Overall, 119 of 120 anastomoses were accurately scored as correct or incorrect within a median of 67 seconds (8-381 seconds) by both observers (sensitivity 0.98, specificity 1.00, kappa 1.00 (1.00, 1.00, and 1.00 in angiography subset, respectively). One deep toe stitch that induced outflow corner stenosis was spotted by both observers but regarded as insignificant and thus inaccurately scored as correct. In 5 anastomoses, unintended irregularities were detected. By angiography, anastomoses were accurately scored with a sensitivity of 0.75 and a specificity of 0.81 ( P < .001 vs ultrasonography) and kappa of 0.54. Angioscopy and cast confirmed ultrasonographic findings and did not reveal irregularities other than detected by ultrasonography. CONCLUSION: Ex vivo epicardial 13-MHz ultrasonography allowed rapid and accurate evaluation of coronary anastomoses and detected technical construction errors with higher sensitivity and specificity than angiography.

Angioscopy↗

PubMed2005

Correction of systematic setup errors in prostate radiation therapy: how many images to perform?

The purpose of this study was to develop an evidence-based off-line setup correction protocol for systematic errors in prostate radiation therapy. Daily orthogonal electronic portal images were acquired from 30 patients. Field displacements were measured in the medial-lateral (ML), superior-inferior (SI), and anterior-posterior (AP) directions for each treatment fraction. The off-line protocol corrects the mean field displacement found from n consecutive images, starting at a particular fraction of treatment, with a fixed tolerance level. Simulations were performed with the measured data to determine (1) how many images (n) should be averaged to determine the systematic error; (2) on which treatment fraction should the protocol be initiated; and (3) what tolerance level should be applied to determine whether the patient position should be corrected. Uncorrected systematic errors in the ML, SI, and AP directions were (mean position +/- 1 standard deviation [SD]): -0.7 +/- 2.2 mm, -1.5 +/- 1.3 mm, and 1.4 +/- 2.6 mm, respectively. Random errors (1 SD and range) were 1.9 mm (1.3 - 3.3), 1.5 mm (0. - 4.1), and 1.8 mm (1.0-2.6), respectively. A correction based on a single image taken on the first fraction actually increased the systematic errors in the ML and SI directions compared with no correction. More accurate correction of systematic errors was achieved with increasing number of images averaged, with only small benefit after 5 images. With fewer images averaged, delaying the start of the protocol resulted in more accurate correction because of the influence of unrepresentative positions at early fractions. The number of corrections made on patients with small (< 2 mm) systematic errors was minimized for tolerance values of 2 mm and n > or = 5 images averaged. The optimal off-line setup correction protocol would be to shift the patient by the mean displacement of the first 5 portal images of a radical course of radiation therapy. A small tolerance level should be utilized with 2 mm giving good accuracy with minimal unnecessary shifts.

Dose Fractionation, Radiation↗

PubMed2006

How initiation factors maximize the accuracy of tRNA selection in initiation of bacterial protein synthesis.

During initiation of bacterial protein synthesis, messenger RNA and fMet-tRNAfMet bind to the 30S ribosomal subunit together with initiation factors IF1, IF2, and IF3. Docking of the 30S preinitiation complex to the 50S ribosomal subunit results in a peptidyl-transfer competent 70S ribosome. Initiation with an elongator tRNA may lead to frameshift and an aberrant N-terminal sequence in the nascent protein. We show how the occurrence of initiation errors is minimized by (1) recognition of the formyl group by the synergistic action of IF2 and IF1, (2) uniform destabilization of the binding of all tRNAs to the 30S subunit by IF3, and (3) an optimal distance between the Shine-Dalgarno sequence and the initiator codon. We suggest why IF1 is essential for E. coli, discuss the role of the G-C base pairs in the anticodon stem of some tRNAs, and clarify gene expression changes with varying IF3 concentration in the living cell.

Bacterial Proteins↗

PubMed2004

Integrated wavelet processing and spatial statistical testing of fMRI data.

We introduce an integrated framework for detecting brain activity from fMRI data, which is based on a spatial discrete wavelet transform. Unlike the standard wavelet-based approach for fMRI analysis, we apply the suitable statistical test procedure in the spatial domain. For a desired significance level, this scheme has one remaining degree of freedom, characterizing the wavelet processing, which is optimized according to the principle of minimal approximation error. This allows us to determine the threshold values in a way that does not depend on data. While developing our framework, we make only conservative assumptions. Consequently, the detection of activation is based on strong evidence. We have implemented this framework as a toolbox (WSPM) for the SPM2 software, taking advantage of multiple options and functions of SPM such as the setup of the linear model and the use of the hemodynamic response function. We show by experimental results that our method is able to detect activation patterns; the results are comparable to those obtained by SPM even though statistical assumptions are more conservative.

Attention↗

PubMed2006

Synthesizing average 3D anatomical shapes.

Average shape estimates are often used to characterize normal morphological variation and discriminate dysmorphology in populations. The purpose of this paper is to estimate "average" or the most representative shapes in populations by using high-resolution medical images as input. The "average" shape is computed from high-dimensional spatial transformations used to co-register each subject in the population rather than the image intensities. Inverse consistent image registration is used to help minimize correspondence errors and produce better population average estimates. Testing the method was done using a population of adult MR brain scans from 22 individuals with no know structural abnormalities. Population averages were computed using the spatial transformation method and local changes in morphology were mapped. Results suggest that this method is a feasible means for robust estimation of population average shape. It is also shown that using inverse consistent transformations produces average shape estimates with less error compared to those produced with transformations with nontrivial inverse consistent errors.

Adult↗

PubMed2006

Responses of collicular fixation neurons to gaze shift perturbations in head-unrestrained monkey reveal gaze feedback control.

A prominent hypothesis in motor control is that endpoint errors are minimized because motor commands are updated in real time via internal feedback loops. We investigated in monkey whether orienting saccadic gaze shifts made in the dark with coordinated eye-head movements are controlled by feedback. We recorded from superior colliculus fixation neurons (SCFNs) that fired tonically during fixation and were silent during gaze shifts. When we briefly (<or=700 ms) interrupted gaze shifts by transiently braking head movements, SCFNs fired steadily during brake-induced gaze immobility, and their mean frequency was inversely related to the remaining distance between current gaze position and the target. After head release, a corrective gaze saccade brought gaze on the unseen goal, and SCFN firing frequency peaked. The results support gaze feedback control and show that the SC is part of a network that encodes, during orientation, the distance between eye and target, irrespective of gaze trajectory characteristics.

Action Potentials↗

PubMed2004

SINEs of speciation: tracking lineages with retroposons.

The value of short interspersed elements (SINEs) for diagnosing common ancestry is being expanded to examine the differential sorting of lineages through the course of speciation events. Because most SINEs are neutral markers of identical descent, are not precisely excised from the genome and have a known ancestral condition, they are advantageous for reconciling gene trees and species trees with minimal phylogenetic error. A population perspective on SINE evolution combined with coalescence theory provides a context for investigating the phenomenon of ancestral polymorphism and its role in producing incongruent SINE insertion patterns among multiple loci. Studies of human Alu repeats demonstrate the value of young polymorphic SINEs for assessing human genomic diversity and tracking ancient demographics of human populations, whereas incongruent insertion patterns revealed by older fixed SINE loci, such as those in African cichlid fishes, contain information that might help identify ancient radiations that are otherwise obscured by accumulated mutations in sequence data. Here, we review the utility of retroposons for inferring common ancestry, discuss limits to the method, and clarify confusion by providing examples from the literature that illustrate how discordant multi-locus insertion patterns of retroelements can indicate lineage-sorting events that should not be misinterpreted as phylogenetic noise.

Journal Article↗

PubMed2005

Curvature affects Doppler investigation of vessels: implications for clinical practice.

In clinical practice, blood velocity estimations from Doppler examination of curved vascular segments are normally different from those of nearby straight segments. The observed "accelerations," sometimes considered as a sort of stochastic disturbances, can actually be related to very specific physical effects due to vessel curvature (i.e., the development of nonaxial velocity [NAV] components) and the spreading of the axial velocity direction in the Doppler sample volume with respect to the insonation axis. The relevant phenomena and their dependence on the radius of curvature of the vessels and on the insonation angle are investigated with a beam-vessel geometry as close as possible to clinical setting, with the simplifying assumptions of steady flow, mild vessel curvature, uniform ultrasonic beam and complete vessel insonation. The insonation angles that minimize the errors are provided on the basis of the study results.

Algorithms↗

PubMed2005

Computational analyses for illusory transformations in the optic flow field and heading perception in the presence of moving objects.

When we see a stimulus of a radial flow field (the target flow) overlapped with a lateral flow field or another radial flow field, the focus of expansion (FOE) of the target radial flow appears to be shifted in a direction. Royden and Conti [(2003). A model using MT-like motion-opponent operators explains an illusory transformation in the optic flow field. Vision Research, 43, 2811-2826] argued that local motion subtraction is crucial for explanation of this phenomenon. The flow field which causes the illusory displacement of FOE was computationally analyzed. It was shown that the flow field is approximately a rigid-motion flow; the flow can be generated by simulating a situation where an observer moves toward a stationary scene. The heading direction for the observer corresponds to the perceived position of the FOE of the radial flow pattern. It implies that any algorithms which assume rigidity of the scene and recover veridical heading explain the bias in perceived FOE. There is no need for local motion subtraction in order to explain the phenomena. Furthermore, the flow for an observer's translation in the presence of objects moving laterally or in depth was computationally analyzed. It was found that algorithms which minimizes standard error functions with less weights to the independently moving objects show similar biases in recovered heading to the bias of human observers. It implies that local motion subtraction is not necessary for explanation of the bias in perceived heading due to an object moving laterally or in depth, contrary to the argument of Royden [(2002). Computing heading in the presence of moving objects: a model that uses motion-opponent operators. Vision Research, 42, 3043-3058].

Algorithms↗

PubMed1979

The roles of Gallium-67 scintigraphy, ultrasonography, and computed tomography in the detection of abdominal abscesses.

The evaluation of patients with suspected abdominal abscesses begins with a history and careful physical examination. Gallium-67 (67Ga) scintigraphy, ultrasonography (US), and computed tomography (CT) are utilized only after other routine investigations have failed to localize the abscess. All three modalities are reliable for the detection of abdominal abscesses. The decision regarding which of these three diagnostic tests to use in a particular patient rests upon clinical considerations. If the patient has acute localizing signs and symptoms, 67Ga should not be used initially. In this type of patient, rapid diagnosis is best provided by either US or CT. Further radiologic investigation may be terminated if the CT or US findings are characteristic of an abscess. A 67Ga scan should be performed in a patient with acute localizing signs and symptoms if the initial CT or US is negative. In a patient with nonlocalizing signs and symptoms, 67Ga imaging should be employed as the first procedure since the entire body is easily surveyed. If the 67Ga images are abnormal, then CT or US should be utilized for further lesion characterization. This diagnostic approach will optimize the rapidity of patient evaluation and will minimize diagnostic errors.

Abdomen↗

PubMed1995

Variability of the relative afferent pupillary defect.

PURPOSE: Afferent asymmetry of visual function is detectable in both normal and pathologic conditions. With a computerized test, we assessed the variability in measuring afferent asymmetry of the pupillary light reflex, that is, the relative afferent pupillary defect. METHODS: In ten normal subjects, pupillary responses to an alternating light stimulus were recorded with computerized infrared pupillography. The relative afferent pupillary defect for each test was determined by using a new computer analysis. The 95% confidence interval of each determination of relative afferent pupillary defect was used to represent the short-term fluctuation in its measurement. To optimize the test for clinical use, we studied the influence of stimulus intensity, duration, and number on the variability of the relative afferent pupillary defect. RESULTS: When the relative afferent pupillary defect was based on only a few light alternations (stimulus pairs), there was excessive variability in its measurement (95% confidence interval > 0.5 log units). With approximately 200 stimulus pairs, the 95% confidence interval was reduced to less than 0.1 log unit (relative afferent pupillary defect +/- 0.05 log unit). Also, there was less variability when the dark interval between alternating light stimulation was less than one second. CONCLUSIONS: Computerized infrared pupillography can standardize the alternating light test and minimize the error in quantifying a relative afferent pupillary defect. A reproducible relative afferent pupillary defect measurement is desirable for defining afferent injury and following the course of disease.

Adult↗

PubMed1999

Cardiac sodium channel Markov model with temperature dependence and recovery from inactivation.

A Markov model of the cardiac sodium channel is presented. The model is similar to the CA1 hippocampal neuron sodium channel model developed by Kuo and Bean (1994. Neuron. 12:819-829) with the following modifications: 1) an additional open state is added; 2) open-inactivated transitions are made voltage-dependent; and 3) channel rate constants are exponential functions of enthalpy, entropy, and voltage and have explicit temperature dependence. Model parameters are determined using a simulated annealing algorithm to minimize the error between model responses and various experimental data sets. The model reproduces a wide range of experimental data including ionic currents, gating currents, tail currents, steady-state inactivation, recovery from inactivation, and open time distributions over a temperature range of 10 degrees C to 25 degrees C. The model also predicts measures of single channel activity such as first latency, probability of a null sweep, and probability of reopening.

Algorithms↗

PubMed1986

Evaluation of the Beckman ASTRA enzyme system.

We have evaluated the ASTRA enzyme analyzer. Six enzymes can be analyzed individually or as part of a larger profile of chemistry tests. The system can analyze all six enzymes at a rate of 35-40 specimens per hour. Within-run and day-to-day precision were comparable to that of other enzyme analyzers. A useful feature of the ASTRA enzyme analyzer permits the automatic reassay of specimens having activities that exceed certain defined limits. A comparison of methods for the ASTRA enzyme analyzer with those used on the SMA 12/60 and the ABA-100 showed good correlation with minimal random error.

Alanine Transaminase↗