SEARCH · PubMed Health

Results for “Measuring algorithm”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources

PubMedDate not supplied

Classification of in vivo autofluorescence spectra using support vector machines.

An algorithm based on support vector machines (SVM), the most recent advance in pattern recognition, is presented for use in classifying light-induced autofluorescence collected from cancerous and normal tissues. The in vivo autofluorescence spectra used for development and evaluation of SVM diagnostic algorithms were measured from 85 nasopharyngeal carcinoma (NPC) lesions and 131 normal tissue sites from 59 subjects during routine nasal endoscopy. Leave-one-out cross-validation was used to evaluate the performance of the algorithms. An overall diagnostic accuracy of 96%, a sensitivity of 94%, and a specificity of 97% for discriminating nasopharyngeal carcinomas from normal tissues were achieved using a linear SVM algorithm. A diagnostic accuracy of 98%, a sensitivity of 95%, and a specificity of 99% for detecting NPC were achieved with a nonlinear SVM algorithm. In a comparison with previously developed algorithms using the same dataset and the principal component analysis (PCA) technique, the SVM algorithms produced better diagnostic accuracy in all instances. In addition, we investigated a method combining PCA and SVM techniques for reducing the complexity of the SVM algorithms.

Algorithms↗

PubMed2004

Three-dimensional point spread function measurement of cone-beam computed tomography system by iterative edge-blurring algorithm.

With separability assumed, we decompose a three-dimensional point spread function (3D PSF) into two-dimensional (2D) PSFs and further into one-dimensional (ID) PSFs. Based on the observation of the location invariance of a step edge under convolution, we propose a rectification procedure to automatically establish the step-edge function from a blurred edge profile. The ID PSF is modelled as a single-parameter Gaussian function, which is determined by iteratively blurring a step-edge function into a spread edge profile. A plastic solid ball (diameter approximately 6 mm) is used to provide double-edged rectangular functions along scanlines passing through the ball centre, and correspondingly, the reconstructed digital volume provides the blurred rectangular profiles. Experimenting with a cone-beam computed tomography system, we demonstrate the iterative edge-blurring algorithm for PSF measurement. By repositioning the ball phantom in the object support space, we measure the system's spatial variance in terms of full-width-at-half-maximum (FWHM) of the local PSFs. Specifically, we obtained the FWHMs for three specific locations at (0, 0, -40 mm), (0, 0, 0) and (0, 0, 40 mm), which are given by 0.92 +/- 0.10 mm, 0.65 +/- 0.08 mm and 0.93 +/- 0.10 mm, respectively.

Algorithms↗

PubMed1994

Development and evaluation of tracking algorithms for cardiac wall motion analysis using phase velocity MR imaging.

Phase velocity magnetic resonance imaging (MRI) has shown considerable potential for tracking distinct regions of the myocardium throughout the cardiac cycle. Phase contrast MR imaging produces multiple images, each phase encoded for velocity in a different direction, in which individual pixels depict the local motion of the tissue. In this work we present in detail three algorithms for tracking motion based on these images. Both simulated and phantom data are used to examine some of the problems encountered in practice in tracking points based on velocity maps. Solutions to these problems are offered when possible. The impact of noise and low order phase errors in the data on each of the three tracking approaches is examined. In addition, problems due to tissue expansion and contraction, to 2D versus 3D tracking, and to round off errors from motion which is small relative to pixel size or slice thickness, are considered. An example using data obtained in vivo is included to demonstrate the efficacy of the best of the three tracking algorithms in measuring left ventricular circumferential shortening preinfarct and postinfarct in a canine model.

Algorithms↗

PubMed2003

WSARE: What's Strange About Recent Events?

This article presents an algorithm for performing early detection of disease outbreaks by searching a database of emergency department cases for anomalous patterns. Traditional techniques for anomaly detection are unsatisfactory for this problem because they identify individual data points that are rare due to particular combinations of features. Thus, these traditional algorithms discover isolated outliers of particularly strange events, such as someone accidentally shooting their ear, that are not indicative of a new outbreak. Instead, we would like to detect groups with specific characteristics that have a recent pattern of illness that is anomalous relative to historical patterns. We propose using an anomaly detection algorithm that would characterize each anomalous pattern with a rule. The significance of each rule would be carefully evaluated using the Fisher exact test and a randomization test. In this study, we compared our algorithm with a standard detection algorithm by measuring the number of false positives and the timeliness of detection. Simulated data, produced by a simulator that creates the effects of an epidemic on a city, were used for evaluation. The results indicate that our algorithm has significantly better detection times for common significance thresholds while having a slightly higher false positive rate.

Algorithms↗

PubMed2004

Fitness threshold accepting over extremal optimization ranks.

We treat the problem of selecting the next degree of freedom for update in an extremal optimization algorithm designed to find the ground state of a system with a complex energy landscape. We show that there exists a best distribution for selecting the next degree of freedom in order to optimize any linear function of the state probabilities, e.g., the expected number of visits to the ground state. We dub the class of algorithms using this best distribution in conjunction with extremal optimization fitness threshold accepting. In addition, we construct an extended random walk and use it to show that fitness threshold accepting is optimal also for several other measures of algorithm performance, such as maximizing the expected probability of seeing the ground state and minimizing the expected value of the lowest energy seen.

Journal Article↗

PubMed2001

The use of cross-correlation analysis between high-frequency ultrasound images to measure longitudinal median nerve movement.

Impaired nerve movement can lead to nerve injury (e.g., carpal tunnel syndrome). A noninvasive method to measure nerve movement in longitudinal section would enable an extensive analysis of nerve entrapment syndromes. A method has been developed using cross-correlation between successive high-frequency ultrasound (US) images to measure longitudinal movement of nerve and muscle. Control "phantom" experiments demonstrated the accuracy and reliability of this method at velocities of 1-10 mm/s. Increasing the frame interval between the compared frames enabled the accurate calculation of slower velocities. The correlation algorithm successfully measured relative movement when the US transducer was moved 1-3 mm over the surface of the forearm. Median nerve movement was repeatedly measured in the forearm during 30 degrees passive wrist extension in three subjects (range 2.63-4.12 mm) and index finger extension in seven subjects (range 1.59-4.48 mm). Median nerve movement values were consistent with those from cadaver studies.

Adult↗

PubMed1986

Multicompartmental analysis of tracer clearance and its application to cerebral blood flow measurement.

A new algorithm for computing cerebral blood flow is shown to overcome compartmental slippage and unstability problems associated with the conventional bicompartmental analysis. The tracer clearance curve is decomposed into a nonnegative linear combination of predetermined flow components. A weighted average of flows above (below) a fixed threshold yields the gray (white) matter flow. The accuracy and the stability of the new algorithm are analyzed by Monte-Carlo simulations, determining the effect of factors such as random error in tracer concentration, gray-white flow difference, tissue content of gray matter, and end-fit time. While the new algorithm requires 50-100% more CPU time and memory space than the bicompartmental method, its accuracy and stability is superior, especially as the conditions of the measurement deteriorate. The results suggest that more than twofold error reduction in measuring the blood flow in pathological brain tissue is possible.

Aged↗

PubMed1996

Comparison of different mathematical algorithms to correct DNA-histograms obtained by measurements on thin liver tissue sections.

Several mathematical algorithms have been published so far to correct histograms obtained from DNA-measurements on thin sections. All these methods require knowledge of the thickness of the section currently under investigation. As the problem of determining the actual section thickness has recently been solved, the different methods for recalculation can be compared under strictly controlled conditions. For histogram recalculation, the algorithms published by Bins, McCready, Bacus, Rigaut and Haroske are applied on a series of rat liver tissue sections with increasing section thicknesses. The histograms are compared to that of measurements of a single cell preparation of the same tissue block. Our results suggest that DNA-measurements on thin paraffin sections are possible if the actual section thickness is known. Correct ploidy equivalents throughout the whole spectrum of section thicknesses investigated are calculated using the formulas of McCready and Haroske. This is also the case using the correction method of Bins in very thin sections. The algorithms of Bacus and Rigaut do not lead to reliable results. Recalculated histograms show some differences to those obtained by DNA-measurements of single cell preparations. The histograms show broader CVs of the peaks and lymphocytes as internal ploidy standard are not useful in the majority of the algorithms. Nevertheless the promising results of this study legitimize efforts to establish standards for the interpretation of recalculated histograms in the near future. The broader applicability to tumour sections remains unproven. Therefore, further investigation are necessary using more heterogeneous tissue including aneuploid tumour cell populations.

Algorithms↗

PubMed2006

Laboratory measurements of spectral reflection from ice clouds of various habits.

Spectral light from 550 to 650 nm reflected from the surface of an ice cloud produced in a temperature-controlled column is measured at seven different angles between 16.7 degrees and 29.9 degrees . Cloud optical depth (tau) is determined from the extinction of a 670 nm laser and is corrected for forward scattering using a Monte Carlo ray-tracing algorithm. Reflection measurements are compared to expectations from a plane-parallel radiative transfer model with input parameters based on the measured tau and a phase function for the observed ice crystal types. The plane-parallel radiative transfer model can be used to interpret the measured reflection for tau less than about 0.4 for this particular experiment, ideal for providing a validation data set to assist with the development of satellite bidirectional remote sensing.

Journal Article↗

PubMed2001

Fast Monte Carlo algorithm for site or bond percolation.

We describe in detail an efficient algorithm for studying site or bond percolation on any lattice. The algorithm can measure an observable quantity in a percolation system for all values of the site or bond occupation probability from zero to one in an amount of time that scales linearly with the size of the system. We demonstrate our algorithm by using it to investigate a number of issues in percolation theory, including the position of the percolation transition for site percolation on the square lattice, the stretched exponential behavior of spanning probabilities away from the critical point, and the size of the giant component for site percolation on random graphs.

Journal Article↗

PubMed2001

Reproducibility of an automatic quantitation of regional myocardial wall motion and systolic thickening on gated 99mTc-sestamibi myocardial SPECT.

UNLABELLED: We investigated the reproducibility of an automatic quantitative algorithm for measuring regional myocardial wall motion and systolic thickening. METHODS: 99mTc-sestamibi gated myocardial SPECT with dipyridamole stress was performed twice consecutively on 31 patients with known or suspected coronary artery disease, with the patients in the same position for each scan. With AutoQUANT software, segmental wall motion and systolic thickening were quantified automatically and expressed in millimeters and percentage increase, respectively, for 20 segments. Afterward, the correlation and agreement between repeated measurements were investigated, and the influences of wall location, perfusion grade, and partitioning of the myocardium on reproducibility were evaluated by ANOVA and t testing. RESULTS: High correlations (r = 0.95 for wall motion and 0.88 for systolic thickening) and good agreements (weighted kappa = 0.81 and 0.71, respectively) were obtained from repeated measurements on consecutive gated SPECT. Changes in wall location and perfusion grade did not cause significant differences between repeated measurements (P > 0.05 in ANOVA and t testing), but a change in partitioning did. On Bland-Altman analysis, 2 SDs for repeated wall motion and for systolic thickening were 2.0 mm and 20%, respectively. CONCLUSION: The automatic quantitative algorithm for myocardial SPECT provided by AutoQUANT software has good reproducibility under diverse conditions. A change of motion > 2.0 mm or a change of systolic thickening > 20% can be regarded as significant during a follow-up study using this software.

Adult↗

PubMed2004

A knowledge-based framework for image enhancement in aviation security.

The main aim of this paper is to present a knowledge-based framework for automatically selecting the best image enhancement algorithm from several available on a per image basis in the context of X-ray images of airport luggage. The approach detailed involves a system that learns to map image features that represent its viewability to one or more chosen enhancement algorithms. Viewability measures have been developed to provide an automatic check on the quality of the enhanced image, i.e., is it really enhanced? The choice is based on ground-truth information generated by human X-ray screening experts. Such a system, for a new image, predicts the best-suited enhancement algorithm. Our research details the various characteristics of the knowledge-based system and shows extensive results on real images.

Algorithms↗

PubMed2005

Prospective motion correction of X-ray images for coronary interventions.

A method for prospective motion correction of X-ray imaging of the heart is presented. A 3D + t coronary model is reconstructed from a biplane coronary angiogram obtained during free breathing. The deformation field is parameterized by cardiac and respiratory phase, which enables the estimation of the state of the arteries at any phase of the cardiac-respiratory cycle. The motion of the three-dimensional (3-D) coronary model is projected onto the image planes and used to compute a dewarping function for motion correcting the images. The use of a 3-D coronary model facilitates motion correction of images acquired with the X-ray system at arbitrary orientations. The performance of the algorithm was measured by tracking the motion of selected left coronary landmarks using a template matching cross-correlation. In three patients, we motion corrected the same images used to construct their 3D + t coronary model. In this best case scenario, the algorithm reduced the motion of the landmarks by 84%-85%, from mean RMS displacements of 12.8-14.6 pixels to 2.1-2.2 pixels. Prospective motion correction was tested in five patients by building the coronary model from one dataset, and correcting a second dataset. The patient's cardiac and respiratory phase are monitored and used to calculate the appropriate correction parameters. The results showed a 48%-63% reduction in the motion of the landmarks, from a mean RMS displacement of 11.5-13.6 pixels to 4.4-7.1 pixels.

Algorithms↗

PubMed2004

Novel algorithm for improving accuracy of ultrasound measurement of residual urine volume according to bladder shape.

OBJECTIVES: To suggest a novel algorithm based on individually determined proportionality constants to improve the accuracy of noninvasively calculated residual urine volume using ultrasound bladder images. METHODS: The residual urine volume of 116 subjects was calculated from ultrasound images obtained using a conventional two-dimensional ultrasound device at two institutions. The proposed method uses individually determined proportionality constants for specific bladder shapes. The corresponding true residual volumes were determined by measuring the catheterized volume. The accuracy of our method was confirmed by comparing the mean and standard deviation of the fractional absolute error (FAE) versus true volume with values obtained using other methods, which rely on fixed constants. RESULTS: The calculated residual bladder volume of 116 patients correlated significantly (r = 0.94, P <0.001) and the differences from the true values were not statistically significant (P = 0.42). The mean FAE was 0.17 +/- 0.10. Subgroups divided by sex, postvoid residual urine volume (over and under 150 mL), and institution produced different results (mean FAE for men 0.15 +/- 0.11 and for women 0.18 +/- 0.12; mean FAE for greater than 150 mL, 0.16 +/- 0.11 and for less than 150 mL, 0.17 +/- 0.14; mean FAE for Seoul National University Hospital 0.15 +/- 0.10 and for Seoul National University Bundang Hospital 0.18 +/- 0.18). Our method provided better accuracy than other known formulas using a conventional two-dimensional ultrasound scanner. The latter multiply the product of the sagittal height and depth and transverse width by a fixed coefficient. CONCLUSIONS: Our method, based on individually determined proportionality constants, improved the accuracy of residual bladder volume determinations. The proposed algorithm can easily be implemented on a personal computer connected to a conventional ultrasound imaging unit.

Adult↗

PubMed1997

Human arm stiffness and equilibrium-point trajectory during multi-joint movement.

By using a newly designed high-performance manipulandum and a new estimation algorithm, we measured human multi-joint arm stiffness parameters during multi-joint point-to-point movements on a horizontal plane. This manipulandum allows us to apply a sufficient perturbation to subject's arm within a brief period during movement. Arm stiffness parameters were reliably estimated using a new algorithm, in which all unknown structural parameters could be estimated independent of arm posture (i.e., constant values under any arm posture). Arm stiffness during transverse movement was considerably greater than that during corresponding posture, but not during a longitudinal movement. Although the ratios of elbow, shoulder, and double-joint stiffness were varied in time, the orientation of stiffness ellipses during the movement did not change much. Equilibrium-point trajectories that were predicted from measured stiffness parameters and actual trajectories were slightly sinusoidally curved in Cartesian space and their velocity profiles were quite different from the velocity profiles of actual hand trajectories. This result contradicts the hypothesis that the brain does not take the dynamics into account in movement control depending on the neuromuscular servo mechanism; rather, it implies that the brain needs to acquire some internal models of controlled objects.

Adult↗

PubMed2005

Vibratory adaptation of cutaneous mechanoreceptive afferents.

The objective of this study was to investigate the effects of extended suprathreshold vibratory stimulation on the sensitivity of slowly adapting type 1 (SA1), rapidly adapting (RA), and Pacinian (PC) afferents. To that end, an algorithm was developed to track afferent absolute (I0) and entrainment (I1) thresholds as they change over time. We recorded afferent responses to periliminal vibratory test stimuli, which were interleaved with intense vibratory conditioning stimuli during the adaptation period of each experimental run. From these measurements, the algorithm allowed us to infer changes in the afferents' sensitivity. We investigated the stimulus parameters that affect adaptation by assessing the degree to which adaptation depends on the amplitude and frequency of the adapting stimulus. For all three afferent types, I0 and I1 increased with increasing adaptation frequency and amplitude. The degree of adaptation seems to be independent of the firing rate evoked in the afferent by the conditioning stimulus. In the analysis, we distinguished between additive adaptation (in which I0 and I1 shift equally) and multiplicative effects (in which the ratio I1/I0 remains constant). RA threshold shifts are almost perfectly additive. SA1 threshold shifts are close to additive and far from multiplicative (I1 threshold shifts are twice the I0 shifts). PC shifts are more difficult to classify. We used an integrate-and-fire model to study the possible neural mechanisms. A change in transducer gain predicts a multiplicative change in I0 and I1 and is thus ruled out as a mechanism underlying SA1 and RA adaptation. A change in the resting action potential threshold predicts equal, additive change in I0 and I1 and thus accounts well for RA adaptation. A change in the degree of refractoriness during the relative refractory period predicts an additional change in I1 such as that observed for SA1 fibers. We infer that adaptation is caused by an increase in spiking thresholds produced by ion flow through transducer channels in the receptor membrane. In a companion paper, we describe the time-course of vibratory adaptation and recovery for SA1, RA, and PC fibers.

Action Potentials↗

PubMed1977

Signal-processing techniques in a computerized hearing aid test system.

General background is given to describe the factors leading up to the implementation of a computerized hearing aid test system in a production environment. The digital measurement methods for determination of the required acoustal components such as fundamental, rms, distortion, etc., in the presence of noise are discussed. The use of the concept of the average cycle for repetitive signals is described with its advantages in a Fourier type system. An algorithm for measuring rms for nonrepetitive signals that trades off resolution for memory size is described. Features and advantages of computerized testing of hearing aids are listed.

Acoustics↗

PubMed2005

Sorting method to extend the dynamic range of the Shack-Hartmann wave-front sensor.

We propose a simple and powerful algorithm to extend the dynamic range of a Shack-Hartmann wave-front sensor. In a conventional Shack-Hartmann wave-front sensor the dynamic range is limited by the f-number of a lenslet, because the focal spot is required to remain in the area confined by the single lenslet. The sorting method proposed here eliminates such a limitation and extends the dynamic range by tagging each spot in a special sequence. Since the sorting method is a simple algorithm that does not change the measurement configuration, there is no requirement for extra hardware, multiple measurements, or complicated algorithms. We not only present the theory and a calculation example of the sorting method but also actually implement measurement of a highly aberrated wave front from nonrotational symmetric optics.

Algorithms↗