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Results for “Measuring algorithm”

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At least 217 records · Page 12Linked to original sources

PubMed1983

Automated radioautographic grain counting. Correction for grain overlap.

An algorithm is described for the calculation of radioautographic cell grain count from measurements of total cell nuclear area and total grain area. This algorithm provides a statistical correction for grain overlap that is based on the solution to the occupancy problem in probability theory. This method permits the use of automated grain counting over a wide range of grain counts per cell, and extends the useful dynamic range of radioautographic grain counting to well over 200 grains/cell.

Autoradiography↗

PubMed1989

Tracking time-varying properties of the systemic vascular bed.

The problem of tracking changes in viscoelastic properties of the systemic arterial bed is considered and a recursive estimation procedure, belonging to the class of output-error algorithms with adjustable compensator, is developed and discussed. By means of computer simulations, suitable values are determined for the key design variable which controls the tradeoff between tracking ability and noise sensitivity of the algorithm. In this way, the algorithm allows on-line estimation of arterial compliance, peripheral resistance, and characteristic impedance on the basis of aortic pressure and flow signals. Furthermore, the results obtained from data numerically simulated, as well as measured on a mock circulatory system, demonstrate that the dominant arterial time-constant can be tracked by the algorithm using only measurements of the aortic pressure during diastole.

Algorithms↗

PubMed1992

6R instrumented spatial linkages for anatomical joint motion measurement--Part 2: Calibration.

The six-revolute-joint instrumented spatial linkage (6R ISL) is often the measurement system of choice for monitoring motion of anatomical joints. However, due to tolerances of the linkage parameters, the system may not be as accurate as desired. A calibration algorithm and associated calibration device have been developed to refine the initial measurements of the ISL's mechanical and electrical parameters so that the measurement of six-degree-of-freedom motion will be most accurate within the workspace of the anatomical joint. The algorithm adjusts the magnitudes of selected linkage parameters to reduce the squared differences between the six known and calculated anatomical position parameters at all the calibration positions. Weighting is permitted so as to obtain a linkage parameter set that is specialized for measuring certain anatomical position parameters. Output of the algorithm includes estimates of the measuring system accuracy. For a particular knee-motion-measuring ISL and calibration device, several interdependent design parameter relationships have been identified. These interdependent relationships are due to the configuration of the ISL and calibration device, the number of calibration positions, and the limited resolution of the devices that monitor the position of the linkage joints. It is shown that if interdependence is not eliminated, then the resulting ISL parameter set will not be accurate in measuring motion outside of the calibration positions, even though these positions are within the ISL workspace.

Algorithms↗

PubMedDate not supplied

A maximum likelihood method for region-of-interest evaluation in emission tomography.

A maximum likelihood (ML) estimation method, called the ML-ROI algorithm, is presented for the calculation of region-of-interest (ROI) values from emission tomography scans. The EM algorithm is used to directly estimate ROI values from tomographic projection data given the location, size, and shape of all ROIs. The algorithm requires for the specification of a detailed model of the physical factors contributing to projection measurements including resolution and attenuation. The ML-ROI algorithm also provides an estimate of the variability of the ROI estimator (covariance matrix). The algorithm was tested with simulation and phantom data and compared with ROI estimation strategies using filtered backprojection (FBP) images. The ML-ROI estimates were unbiased, i.e., the partial volume effect was eliminated. Except for regions smaller than the detector resolution, the variability of the ML estimates was comparable to or less than the biased FBP estimators. Computation time for the ML-ROI algorithm was between 5 and 10 s/iteration. An evaluation of the sensitivity of the algorithm to misdefinition of the location and size of the ROIs was also performed.

Humans↗

PubMed1988

Quantitative regional curvature analysis: a prospective evaluation of ventricular shape and wall motion measurements.

To overcome the assumptions and approximations mandated by the use of traditional wall motion methodologies, a method was recently developed for measuring ventricular shape based on quantitative curvature analysis of ventricular outlines. This study was designed to assess prospectively the performance of this algorithm, to compare it to traditional wall motion measurements (centerline method), and to determine the comparative degree to which each method mimicked the interpretation of wall motion by clinical observers. Semiquantitative visual grading of regional function in 52 patients was performed by four independent observers on two occasions. Anterior, apical, or inferior segments were judged to be normal (0 points) or abnormal (1 point) based on viewing nonrealigned, end-diastolic and end-systolic ventricular silhouettes from cineventriculograms obtained in the 30-degree right anterior oblique projection. Each segment was assigned a collated score ranging from 0 (all observers felt the region was normal on both readings) to 8 (all observers felt the region was abnormal on both readings). Quantitative regional curvature analysis and wall motion analysis (centerline method) were performed. Quantitative shape and wall motion scores correlated equally well with the semiquantitative visual scores. When a visual score of greater than or equal to 4 was used to designate an abnormal segment, both quantitative approaches demonstrated comparable sensitivity, specificity, and concordance rates. Both methods achieved optimal performance when maximum and minimum deviations from normal were recorded. Under these circumstances, the shape analysis demonstrated a greater concordance with the clinical diagnosis than did wall motion analysis (99% vs-93%, p less than 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed1990

[Computer-assisted selection of therapeutic measures in ischemic heart disease and arterial hypertension during mass screening of a rural population].

Expert assessments of 537 case histories of patients with various coronary heart diseases made it possible to derive an algorithm for automatic choice of therapeutic and prophylactic measures. This approach was tested within the framework of the automatic system "Cardioscreening". It was shown that there was a good correlation between the automatic choice of therapeutic and prophylactic actions and the strategy of a skilled cardiologist.

Algorithms↗

PubMed1992

A linear scale for measuring vagal tone in man.

1. Different levels of parasympathetic control of the heart were measured using ratios of the longest to the shortest intervals between R-waves in the ECGs (R-R) recorded during a deep breathing exercise in the supine position (respiratory sinus arrhythmia). The mean of absolute differences in consecutive R-R intervals was also measured in the supine position during quiet breathing (beat-to-beat variation), in six healthy volunteers, after cumulative doses of atropine (0.1-2.0 mg 70 kg-1, i.v.). 2. Full atropinization was observed at 2.0 mg 70 kg-1 where the respiratory sinus arrhythmia decreased by 97%, and the beat-to-beat variation dropped by 94%. There was no further drop in both indices at doses above 2.0 mg 70 kg-1. The different levels of parasympathetic control of the heart were directly proportional to the equivalent levels of respiratory sinus arrhythmia or beat-to-beat variation. 3. A universal linear vagal scale was calculated for use with these non-invasive indices to assess the levels of parasympathetic control of the heart. Zero in this scale would represent no activities in the cardiac vagus nerve. 4. It was concluded that vagal tone could be selectively measured in an intact person using these simplified and fast algorithms for quantifying respiratory sinus arrhythmia or beat-to-beat variation. A linear scale for measuring the vagal tone was possible. This linear scale was called the linear vagal scale (LVS).

Adult↗

PubMed1989

A generalised algorithm for spectral reconstruction in Compton spectroscopy with corrections for coherent scattering.

Reconstruction of primary-photon energy spectra from pulse-height distributions obtained in a Compton spectrometer has earlier been performed under the assumption that coherent scattering in the scatterer is negligible. This holds for most clinical x-ray units operated in the range 40-150 kV. In mammography, and to some extent in dental radiography, the relatively high frequency of low-energy photons (less than 30 keV) in the primary beam makes it necessary to extend the algorithms to allow for significant contribution of coherent scattering. This extension is performed as a perturbation calculation to the algorithms developed earlier in which a modified Klein-Nishina scattering cross section was taken as the total scattering cross section. Comparison with energy spectra measured in the primary beam indicates that the Compton spectrometer with the extended algorithm is an excellent instrument for measuring energy spectra with energies down to a few keV.

Algorithms↗

PubMed1992

Models of the actin monomer and filament from fluorescence resonance-energy transfer.

We have developed algorithms for combining fluorescence resonance-energy transfer (FRET) efficiency measurements into structural models which predict the relative positions of the chemical groups used in FRET. We used these algorithms to construct models of the actin monomer and filament derived solely from FRET measurements based on seven distinct loci. We found a mirror-image pair of monomer models which best fit the FRET data. One of these models agrees well with the atomic-resolution crystal structure recently published by Kabsch et al. in Heidelberg [Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F. & Holmes, K. C. (1990) Nature 347, 37-44]. The root-mean-square deviation between this FRET model and the crystal structure was about 0.9 nm. Other macromolecular models assembled from FRET measurements are likely to have a similar resolution. The largest discrepancy was for the Cys10 locus which deviated 1.44 nm from the crystal position. We discuss the limitations of the FRET method that may have contributed to this discrepancy, and conclude that the Cys10 FRET data have probably located Cys10 incorrectly in the FRET monomer model. Using the FRET monomer models, we found three orientations in the filament which best fit the intermonomer FRET data. These orientations differ substantially from the atomic-resolution filament model proposed by the Heidelberg group [Holmes, K., Popp, D., Gebhard, W. & Kabsch, W. (1990) Nature 347, 44-49], largely because of the discrepancies in the Cys10 data. These data should probably be excluded from the analysis; however, this would leave too few measurements to assemble a filament model. In the near future, we hope to obtain additional FRET measurements to other actin loci so that the filament modelling can be done without the Cys10 data.

Actins↗

PubMed1988

On estimating the number density of random scatterers from backscattered acoustic signals.

When an acoustic pulse interacts with an inhomogeneous, attenuating medium, the backscattered signals exhibit random fluctuations which are correlated with the physical properties of the medium. This paper proposes a robust model for characterizing the statistical nature of these backscattered signals. This model takes into account frequency-dependent attenuation, spatially varying media statistics, arbitrary beam geometries, and arbitrary pulse shapes. Based on this model, statistical estimation schemes are proposed for estimating both the attenuation coefficient and scatterer number density of the medium. Using appropriate simplifying assumptions, it is shown that this model is consistent with attenuation estimation algorithms currently used for ultrasonic tissue characterization. A statistical approach for estimating the number density of scatterers is described and its theoretical performance is evaluated. The algorithm for estimating the scatterer number density incorporates measurements of both the statistical moments of the backscattered signals and the point spread function of the acoustic system. The number density algorithm has been applied to simulated waveforms, waveforms obtained from ultrasonic phantoms with known number densities, and in vitro mammalian tissues. There is an excellent agreement between theoretical, simulation, and experimental results. The application of this technique to ultrasonic tissue characterization is also discussed.

Algorithms↗

PubMed1988

Semi-automated analysis of manually reconstructed tracks of progressively motile human spermatozoa.

Several alternative algorithms for computer-assisted derivation of measurements of movement characteristics from manually reconstructed tracks of progressively motile human spermatozoa were compared. Fifty tracks were reconstructed at 30 Hz from video recordings and analysed using traditional manual methods and by four combinations of computer algorithms. The best algorithm set was identified ('Videomot.mdpt') and the values for the curvilinear, average path and linear velocities (VCVL, VAVE and VLIN respectively), the amplitude of lateral displacement of the sperm head about the axis of progression (AH) and the number of times the sperm head crossed the average path (the 'beat/cross frequency', BXF) obtained using it were compared to those obtained by manual analysis. There was a considerable time saving when the computer-assisted method was used and the values it gave for the various movement characteristics showed good correspondence with those obtained manually. In addition, repeated data entry and analysis was found to be highly reproducible. When the tracks were re-plotted at 6 Hz (as used by the multiple-exposure photomicrography method for sperm motility analysis) insufficient information remained in the tracks for reliable determination of anything other than VLIN. We conclude that the Videomot.mdpt program provides reliable values for the movement characteristics of progressively motile human spermatozoa, and believe it will be of great value in the validation of commercial systems providing automated sperm movement analysis and in laboratories which do not have access to such costly equipment.

Algorithms↗

PubMed1984

On the construction of functional maps in positron emission tomography.

A linear algorithm for the rapid calculation of local rate constants is proposed. The method is applicable to the three-compartment models currently used in the analysis of positron camera measurements with [11C]methionine, [11C]deoxyglucose, and [11C]glucose. The same technique can also be used for the regional measurement of local blood flow with the aid of a freely diffusible tracer. The algorithm was applied to measurements on humans with [11C]glucose. As a comparison, the same data were also analyzed with a standard nonlinear technique. Good agreement between the two methods was obtained.

Brain↗

PubMed1979

Automated scene analysis of CT scans.

Since the advent of computed tomography, there has been an increasing realization that CT scans contain quantitative as well as qualitative information useful in the diagnostic process. Often however, the use of this information is impeded by the tedious manual outlining of the areas of interest in the scan. To alleviate this problem, we have developed a scene segmentation algorithm which will automatically delineate areas of interest in a CT scan. This procedure uses known information about the expected objects in the scan in conjuction with an algorithm to label those objects. The resultant scene segmentation divides the scan into four anatomical areas: skull, normal brain, high density lesions and CSF. After an area of interest is interactively selected by the clinician, volume, density or other quantitative measures may be computed. Limitations of the algorithm and its clinical applications are discussed.

Absorptiometry, Photon↗

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↗

PubMed1989

A program package for self-assessment and examination in biochemistry.

A BASIC program has been developed for self-evaluation and testing of an individual's knowledge of main categories in biochemistry. The computer tests permit sequential or random distribution of items, random distribution of answers in each item at each new run, effective feedback control with the student, use of a program clock to determine different time allowance, precise and quick analysis and grading of student's answer thus saving the time and labour of examiners. Editing, deleting and appending of new items is easily achieved. Information is obtained for verifying the quality of the test itself. Examination versions of tests in ten categories have been combined into an annual computer test in biochemistry.

Algorithms↗

PubMed1986

Simulation of the spatial distribution of muscle fibres in human muscles.

A composite muscle cross section model was simulated on a VAX 780 computer. The various motor unit territories in the cross section area were circular, partially overlapping each other. The radii of the territories of the motor units, their centres, and the number of muscle fibres in each motor unit were treated as random variables. Two different models were generated, one with a uniform distribution of the fibres in the motor unit territories, and the other with a normal distribution of the fibres. An algorithm for simulation of fibre density measurements was written, and the effects of varying the parameters of the model on fibre density measurements were investigated. The results of the computer simulation were in agreement with analytical and laboratory findings.

Computers↗

PubMed2026

Prediction of antimicrobial minimum inhibitory concentration from bacterial genomes using a scalable and interpretable machine learning approach.

Although machine learning models can predict antimicrobial susceptibility from bacterial whole genome sequencing (WGS), state-of-the-art approaches are computationally demanding or dependent on knowledge of genetic resistance determinants. Here, we describe an efficient data-driven approach to predicting minimum inhibitory concentration (MIC) by progressively extending and refining predictive genome segments, independent of prior knowledge of resistance determinants. Resultant models had high interpretability - known and potentially novel resistance determinants were captured. Using 762 clinical E. coli strains, 71.6% of predictions were within one dilution of the measured MIC. Models trained with this algorithm generalised better onto external data (F1 score = 0.85) compared with alternative models trained on annotated resistance determinants (F1 = 0.82) or k-mer counts (F1 = 0.74). Computational demands were low (RAM usage 23.6GB vs 38.8GB for k-mer model). These advantages represent an important advance in predicting antimicrobial susceptibility from WGS, with potential applications for clinical diagnostics, drug development, and surveillance.

Journal Article↗

PubMed1977

An acoustic-perceptual method for the quantitative evaluation of hypernasality.

A computer implementation is proposed as a method for assessing the quality of an individual's speech from a perceptual and communicative point of view. The input to this procedure is a standardized set of speech samples (vowels and selected consonants) designed to permit an evaluation of the speaker's phonology. The output is a numerical specification of the functional adequacy of the target values of the phonetic segments under analysis. The computer program consists of three parts: a simulated auditory analyzer, the output of which is a spectral representation of each test item; an algorithm that computes a psychoacoustically based measure of distinctiveness or perceptual distance for each pair of test spectra, and a routine for comparing, in terms of this measure, the test items with the corresponding reference items drawn from a population of normal speakers or a recording made before patient intervention.

Acoustics↗