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Results for “Measuring algorithm”

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At least 1,099 records · Page 61Linked to original sources

PubMed1988

Improved algorithms for automatic bone histomorphometry on a numerized image analysis system.

Quantitative histological methods have proved to be the most effective methods in bone disease research. Faster and more accurate techniques are currently needed. We have developed a simple digitized image analysis system which allows accurate measurements of trabecular bone mass. The algorithm is based on the 'four-connected sets' mathematical theory. Given a numerized image displayed by a CCD camera, the algorithm recognizes all possible four-connected sets and provides area measurements. The first procedure automatically eliminates small, irrelevant profiles (wrinkles, cell nuclei, etc.) while larger profiles are erased interactively. The second procedure similarly erases the artefactual defects within the trabeculae (artefactual cracks or empty osteocytic lacunae). The method was shown to be very accurate and time-saving.

Algorithms↗

PubMed1998

A commercial IMRT treatment-planning dose-calculation algorithm.

PURPOSE: The dose-calculation algorithm for a commercial arc-based intensity modulated radiation therapy (IMRT) treatment-planning and delivery system (Peacock, NOMOS Corporation) is described. METHODS AND MATERIALS: The IMRT delivery system uses a dynamically controlled multileaf collimator with 40 leaves that project on our accelerator to either 1.0 x 0.84 cm2 or 1.0 x 1.68 cm2 at isocenter arranged in two banks of 20 leaves each. The dose-calculation algorithm uses tissue-phantom ratios derived from percent depth dose measurements, measured relative output data, and single leaf profiles. Some compromises are made in the algorithm terms to enable more straightforward dosimetry measurements and to reduce dose computation times. The dose calculation algorithm is presented, and consequences of the approximations are investigated using previously published 4 MV photon beam data. RESULTS: Most of the approximations lead to dose errors of a few percent. However, the use of depth-invariant single-leaf profiles results in errors as large as 9% for 4 MV fixed beams. CONCLUSIONS: Large dosimetric errors are possible for small fixed fields using this algorithm. However, the algorithm is designed for tomotherapy dose delivery, where doses are delivered from multiple directions and depths. Investigations of the algorithm in more clinically relevant conditions have been conducted and show that the algorithm accuracy is 1.3% and therefore is clinically acceptable for tomotherapy.

Algorithms↗

PubMed2001

Stages of Change Assessments in Alcohol Problems: Agreement Across Self- and Clinician-Reports.

A number of self-report scales and "algorithms" have been developed to measure stage of change in alcohol problems. These methods rely on client self-reports, but an alternative approach is to use clinician judgments. The purpose of this investigation was to compare approaches including a newly developed Readiness to Change Questionnaire - Clinician Version (RCQ-CV). Clients being assessed for alcohol treatment (N = 64) completed SOCRATES, the Readiness to Change Questionnaire (RCQ), a social desirability scale, and a stage of change algorithm. Clinicians completed the RCQ-CV and provided a simple assessment of stage of change. The agreement among the alternative methods was generally good with the continuous measures, including agreement between scales, between clients and clinicians, and between experienced clinicians and trainees. Agreement among categorical stage assignments was poor. The RCQ-CV shows promise as a clinical and research tool.

Journal Article↗

PubMed2004

Correcting confocal acquisition to optimize imaging of fluorescence resonance energy transfer by sensitized emission.

Imaging of fluorescence resonance energy transfer (FRET) between suitable fluorophores is increasingly being used to study cellular processes with high spatiotemporal resolution. The genetically encoded Cyan (CFP) and Yellow (YFP) variants of Green Fluorescent Protein have become the most popular donor and acceptor pair in cell biology. FRET between these fluorophores can be imaged by detecting sensitized emission. This technique, for which CFP is excited and transfer is detected as emission of YFP, is sensitive, fast, and straightforward, provided that proper corrections are made. In this study, the detection of sensitized emission between CFP and YFP by confocal microscopy is optimized. It is shown that this FRET pair is best excited at 430 nm. We identify major sources of error and variability in confocal FRET acquisition including chromatic aberrations and instability of the excitation sources. We demonstrate that a novel correction algorithm that employs online corrective measurements yields reliable estimates of FRET efficiency, and it is also shown how the effect of other error sources can be minimized.

Algorithms↗

PubMed1996

[Detection and diagnosis of small ocular misalignment with the Purkinje reflex pattern method].

BACKGROUND: Application test for an automatic classification strategy for ocular alignment data for the detection of ocular misalignment in strabismic patients. METHODS: Photographic Purkinje Reflection Pattern Evaluation was used a) with a handheld device for the detection and measurement of ocular misalignments in near fixation (group 1, n = 64 strabismic patients) and b) with a stationary device for the detection and measurement of ocular misalignments in near fixation (group 2, n = 38 patients) and in distance fixation (group 3, n = 36 patients). The orthoptic diagnoses were mostly primary and secondary microtropia with manifest angles of strabismus from naught or 0.25 degrees to 3-4 degrees, with maximum angles up to 6-9 degrees. The ocular alignment data were classified using the computer based strabismus index procedure. This strategy relies on thresholds derived from means and standard deviations in orthotropic control populations. In this way the data sets were classified automatically as "no referral" or "referral". In addition, an automatic diagnosis of the type of misalignment was given and the results were compared to the orthoptic gold standard. RESULTS: The sensitivity for the detection of a manifest ocular misalignment was a ca. 80% in group 1 and 2, and 90% in group 3, with specificities from 90% to 100%. All manifest angles of strabismus larger than 1 degree were correctly classified as "referral". There was good agreement between the diagnoses of the type of misalignment in most cases. Discrepancies were observed with very small ocular misalignments or with incomplete data sets, or they could be explained by a switch of fixation. The amount of the misalignment varied markedly as compared to the orthoptic measurement in a number of cases. CONCLUSIONS: The examination allows for a detection of small manifest ocular misalignments with a very high sensitivity. The deviated eye and the type of the misalignment in the primary position are evaluated automatically by a data base computer algorithm. The differences between the measured angles of strabismus indicate that the photographic examination conditions and the orthoptic simultaneous prism and cover test conditions are not exactly alike. Purkinje Reflection Pattern Evaluation represents a step towards an examiner-independent measurement of the angle of strabismus.

Adolescent↗

PubMed1997

Calculation of LDL-cholesterol by using apolipoprotein B for classification of nonchylomicronemic dyslipemia.

In this paper we propose a calculation of LDL-cholesterol (LDL-C) not affected by hypertriglyceridemia by using lipid quantities directly measured in total serum. We also propose an algorithm for the classification of nonchylomicronemic dyslipemias. Plasma apolipoproteins (apo) A-I, B, total cholesterol (TC), triglycerides (TG), and cholesterol of lipoproteins were measured in a group of 38 normolipemic and 120 dyslipemic patients (42 phenotype IIa, 38 IIb, and 40 IV) classified according to TG and LDL-C values. Discriminant analysis was applied to obtain the best classification with the lowest number of quantities directly measured from total serum (TC, TG, and apo B), and multiple regression analysis was performed to find an equation to calculate LDL-C from these quantities. Apo B seems to be a useful discriminator between normolipemic and phenotype IIa patients, by using a cutoff value of 1.35 g/L obtained by ROC curve analysis. The proposed algorithm, based on lipid quantities measured by easily automated methods, is shown to be a good alternative for the classification of nonhyperchylomicronemic dyslipemia. LDL-C calculated from TC, TG, and apo B proved a better estimate of true LDL-C than the estimate obtained with Friedewald's formula.

Algorithms↗

PubMedDate not supplied

Experimental resolution measurement in critical dimension scanning electron microscope metrology.

By applying the basic principles of metrology we discuss how to define the standards that any experimental method to measure resolution has to obey. Our results clearly indicate the need to apply a calibration procedure when designing algorithms to estimate resolution to satisfy accuracy requirements. Similarly, the precision of an algorithm has to be clearly specified. We compare here the performances of a variety of commonly used implementations of published methods, with that of an algorithm based on an approach known to be reliable. Our results confirm that when an algorithm is designed with the clear intent of satisfying metrology requirements, it demonstrates excellent accuracy, precision, and lack of sensitivity to the noise level, as is desirable. As a consequence, the algorithm will have the ability to measure accurately the point spread function convoluted in the image, thus paving the way for quantitative deconvolution techniques.

Journal Article↗

PubMed1995

Performance comparison of several published tissue near-infrared spectroscopy algorithms.

We have collected multiwavelength near-infrared (NIR) attenuation spectra on human forearm muscle, the adult rat head, and newborn piglet head to compare the changes in chromophore concentration derived from these data using published algorithms from four groups. We find differences between the results from the algorithms on each data set, particularly in their estimation of cytochrome oxidase (cyt-aa3) redox changes. We also find some differences when applying the same algorithm to the three data sets, suggesting possible difficulties in transferring algorithms between different physiological systems (e.g., Kurth, C. D., Steven, J. M., Benaron, D., and Chance, B. (1993) J. Clin. Monit. 9, 163-170). We have also compared the algorithms using simulated data generated using measured hemoglobin absorption spectra and a diffusion model for light transport in tissue. We find that while the algorithms from three groups are in broad agreement, that published by Piantadosi (Piantadosi, C. A. (1993) Methods Toxicol. 2, 107-126) produces significantly different results for cyt-aa3 and HbO2. Either the hemoglobin spectra used to produce the simulated data are inaccurate or the modeling is incorrect, or this algorithm is erroneous.

Adult↗

PubMed1994

Improved iterative image reconstruction using variable projection binning and abbreviated convolution.

Noise propagation in iterative reconstruction can be reduced by exact data projection. This can be done by area-weighted projection using the convolution method. Large arrays have to be convolved in order to achieve satisfactory image quality. Two procedures are described which improve the convolution method used so far. Variable binning helps to reduce the size of the convolution arrays without loss of image quality. Computation time is further reduced by abbreviated convolution. The effects of the procedures are illustrated by means of phantom measurements.

Algorithms↗

PubMed1997

A self organizing map approach to image quality.

A block-wise vector quantization of images was carried out by using different types of self organizing maps. The quality of the coded images was estimated by human observers with the result that good image quality assumes a balance of two types of image blocks, namely flat regions and edges. On the basis of these types of blocks a segmentation error model was derived which enables to estimate the quality of a distorted image in comparison with an original. In this model the segmentation of errors was done block-wise by a classification into those types found as important for image quality. An error metric was formed by a non-linear combination of segmented components over space and classes which for a large set of images and distortions shows better conformity with the quality estimates of human observers than standard technical measures.

Algorithms↗

PubMed2006

An intuitive visualisation of intercomparison results applied to the KCDB.

A simple and intuitive graphical method is presented for producing a summary overview of experimental results of a common measurand, e.g. in the frame of an intercomparison. The PomPlots display (relative) deviations of individual results from the consensus value on the horizontal axis and (relative) uncertainties on the vertical axis. The z-scores, z=1, 2 and 3, are represented by diagonal lines, creating the aspect of a pyramidal structure. The most accurate and precise measurement results should be situated close to the top of the pyramid. The plots are used to visualise data from the BIPM key comparison database on primary radioactivity measurements.

Algorithms↗

PubMed2005

Piecewise affine registration of biological images for volume reconstruction.

This manuscript tackles the reconstruction of 3-D volumes via mono-modal registration of series of 2-D biological images (histological sections, autoradiographs, cryosections, etc.). The process of acquiring these images typically induces composite transformations that we model as a number of rigid or affine local transformations embedded in an elastic one. We propose a registration approach closely derived from this model. Given a pair of input images, we first compute a dense similarity field between them with a block matching algorithm. We use as a similarity measure an extension of the classical correlation coefficient that improves the consistency of the field. A hierarchical clustering algorithm then automatically partitions the field into a number of classes from which we extract independent pairs of sub-images. Our clustering algorithm relies on the Earth mover's distribution metric and is additionally guided by robust least-square estimation of the transformations associated with each cluster. Finally, the pairs of sub-images are, independently, affinely registered and a hybrid affine/non-linear interpolation scheme is used to compose the output registered image. We investigate the behavior of our approach on several batches of histological data and discuss its sensitivity to parameters and noise.

Algorithms↗

PubMed2003

The use of a Monte Carlo method to calculate the average solid angle subtended by a detector to source in a non-parallel plane.

In a previous scientific note, a short computer program for a personal computer was described that calculated the average solid angle subtended by a circular or rectangular detector window to a circular or rectangular source in a parallel plane by a Monte Carlo method. This note describes the development of the program for conditions where the detector window is not parallel to the plane of the source, and in particular looks at a method of analysing orientations that relates straightforwardly to practical measurement.

Algorithms↗

PubMed2004

The ENEA criticality accident dosimetry system: a contribution to the 2002 international intercomparison at the SILENE reactor.

The present paper summarises the activity carried out at the ENEA Radiation Protection Institute for updating the methodologies employed for the evaluation of the neutron and photon dose to the exposed workers in case of a criticality accident, in the framework of the 'International Intercomparison of Criticality Accident Dosimetry Systems' (Silène reactor, IRSN-CEA-Valduc June 2002). The evaluation of the neutron spectra and the neutron dosimetric quantities relies on activation detectors and on unfolding algorithms. Thermoluminescent detectors are employed for the gamma dose measurement. The work is aimed at accurately characterising the measurement system and, at the same time, testing the algorithms. Useful spectral information were included, based on Monte Carlo simulations, to take into account the potential accident scenarios of practical interest. All along this exercise intercomparison a particular attention was devoted to the 'traceability' of all the experimental and computational parameters and therefore, aimed at an easy treatment by the user.

Algorithms↗

PubMed1995

Colour Doppler myocardial imaging: potential applications in acquired and congenital heart disease.

Doppler myocardial imaging (DMI) is a new ultrasound technique which has been developed to allow colour Doppler imaging of cardiac structures as opposed to blood pool imaging. This is achieved by changing the velocity, filtering and threshold parameters of the standard colour Doppler algorithms. DMI parameters which can be measured are regional tissue velocity, acceleration and reflected Doppler energy. In addition, concomitant changes in the pulsed Doppler algorithms allow interrogation of instantaneous peak velocities during the cardiac cycle in the myocardial region in which the sample volume is placed. In both adult acquired heart disease and congenital heart disease, these new ultrasound parameters may provide new information on myocardial contractile function, diastolic function, myocardial perfusion and myocardial structure. The relative lack of image quality by chest wall attenuation inherent in the Doppler technique means that the methodology is potentially superior to standard grey-scale two-dimensional imaging in boundary detection and may prove to be of value in providing a robust boundary detection algorithm for use in volume calculations and in three-dimensional reconstruction of ventricular function.

Arrhythmias, Cardiac↗

PubMed2004

Efficient particle transport simulation through beam modulating devices for Monte Carlo treatment planning.

For Monte Carlo treatment planning it is essential to model efficiently patient dependent beam modifying devices, e.g., Multi-Leaf Collimators (MLC). Therefore a Monte Carlo geometry tracking procedure is presented allowing the simulation of photon and electron transport through these devices within short calculation time. The tracking procedure is based on elemental regions, on surfaces (mainly planes) to separate the regions as well as on bit patterns and bit masks to identify the regions. Photon cross sections for photoelectric absorption, Compton scattering and pair production as well as electron stopping powers and ranges are provided by the Physical Reference Data of the National Institute of Standards and Technology (NIST). The tracking procedure is implemented in c + + with object-oriented design based on c + + class hierarchies and inheritance. Using the geometry technique, several MLC models are constructed. Some of them take into account tongue-and-groove effects as well as curved leaf ends. The models are integrated into the Monte Carlo dose calculation engine XVMC for treatment planning. The system is tested by comparing different MLC implementations and by verification with measurement.

Algorithms↗

PubMedDate not supplied

New vessel analysis tool for morphometric quantification and visualization of vessels in CT and MR imaging data sets.

Image processing algorithms and a prototypical research software tool have been developed for visualization and quantitative analysis of vessels in data sets from computed tomography and magnetic resonance imaging. The software is based on a sequence of processing steps, which are as follows: (a) vessel segmentation based on a region growing algorithm, (b) interactive "premasking" to optionally exclude interfering structures close to the vessels of interest, (c) distance transform-based skeletonization, (d) multiplanar reformation orthogonal to the vessel path, (e) identification of the lumen boundary on the orthogonal cross-section images, and (f) morphometric measurements. The development of the algorithmic components and the application user interface has been carried out in close cooperation with clinical users to achieve a high degree of usability and flexible support of work flow. The software has been successfully applied to the intracranial arteries, carotid arteries, and abdominal and thoracic aorta, as well as the renal, coronary, and peripheral arteries.

Algorithms↗

PubMed2006

Early experience from the application of a noninvasive magnetic resonance imaging-based measurement of intracranial pressure in hydrocephalus.

OBJECTIVE: The decision for surgical intervention in hydrocephalic patients presenting with symptoms suggesting raised intracranial pressure (ICP) is challenging because radiographic ventricular size often lacks the specificity to predict abnormal ICP. An early assessment of the potential clinical usefulness of a noninvasive magnetic resonance imaging-based measurement of ICP (MR-ICP) in symptomatic hydrocephalic patients is reported. METHODS: Twenty-seven symptomatic hydrocephalic patients (18 with shunts and 9 without shunts) underwent brain magnetic resonance imaging-based studies that included measurements of cerebrospinal fluid and blood flows to and from the cranial vault, from which measurements of ICP were derived using a previously described algorithm. The predictive values of the MR-ICP measurement were determined on the basis of whether or not the patient underwent a surgical treatment of a shunt placement or shunt revision within a 3-month period after the magnetic resonance imaging-based study. RESULTS: MR-ICP values in these patients spanned a much wider range than in healthy control subjects. However, the majority of the patients (20 out of 26 patients) had MR-ICP values within the normal range. The short-term follow-up of patients who had normal MR-ICP measurement reveals that only one of the 20 patients required surgery. Consequently, the MR-ICP measurement has a strong negative predictive value (95% for all patients and 100% for patients without a shunt). CONCLUSION: A finding of a normal MR-ICP value in hydrocephalic patients presenting with symptoms suggestive of abnormal ICP is a strong predictor for resolution of symptoms or stable outcome without surgical intervention.

Adult↗