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Results for “Measuring algorithm”

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At least 1,027 records · Page 57Linked to original sources

PubMed1997

Comparison of methods of measuring pulmonary artery pressure.

BACKGROUND: Pulmonary artery waveforms fluctuate because of changes in intrathoracic pressure caused by respirations. Monitoring system algorithms determine digital displays of pressure measurements on the basis of recognition, analysis, and comparison of consecutive waveforms. OBJECTIVE: To compare three methods of measuring pulmonary artery pressure during mechanical ventilation and spontaneous breathing in cardiac surgery patients with stable hemodynamics. METHODS: Pulmonary artery pressure was measured during mechanical ventilation after cardiac surgery in 53 patients; 37 of the patients were studied again after extubation. Three monitoring methods were compared: graphic strip recording, the "stop cursor" (monitor screen freezing) method, and digital-display recording. Difference scores were calculated between the methods and analyzed for frequency and direction. RESULTS: All comparisons showed differences of at least +/-3 mm Hg in measurements obtained with the three methods. During mechanical ventilation, the digital and graphic measurements of systolic pressure varied most often; 57% (30/53) of the comparisons had difference scores of at least +/-3 mm Hg. The cursor and graphic measurements of diastolic pressures varied least often; 6% (3/53) of the comparisons had difference scores of at least +/-3 mm Hg. As expected, the digital method most often gave higher results than the graphic method. During spontaneous breathing, measurements of systolic pressure varied more often (38% to 53%) than did measurements of diastolic pressure (12% to 37%). Unexpectedly, for systolic pressures, the difference between digital and graphic measurements was 3 mm Hg or more 30% (11/37) of the time, and the difference between cursor and graphic measurements was 3 mm Hg or more 53% (17/32) of the time. CONCLUSIONS: Because of physiological and technical influences, measurements of systolic and diastolic pressures in the pulmonary artery made with the digital and cursor methods were not as reliable as measurements made with the graphic method. The findings support continued use of the graphic method for accurate measurements of pulmonary artery pressure.

Adult↗

PubMedDate not supplied

A new look at displacement factor and point of measurement corrections in ionization chamber dosimetry.

A new technique is presented for determination of the effective point of measurement when cavity ionization chambers are used to measure the absorbed dose due to ionizing radiation in a dense medium. An algorithm is derived relating the effective point of measurement to the displacement correction factor. This algorithm relates variations of the displacement factor to the radiation field gradient. The technique is applied to derive the magnitudes of the corrections for several chambers in a p(66)Be(49) neutron therapy beam.

Mathematics↗

PubMed2004

Local, three-dimensional strain measurements within largely deformed extracellular matrix constructs.

The ability to create extracellular matrix (ECM) constructs that are mechanically and biochemically similar to those found in vivo and to understand how their properties affect cellular responses will drive the next generation of tissue engineering strategies. To date, many mechanisms by which cells biochemically communicate with the ECM are known. However the mechanisms by which mechanical information is transmitted between cells and their ECM remain to be elucidated. "Self-assembled" collagen matrices provide an in vitro-model system to study the mechanical behavior of ECM. To begin to understand how the ECM and the cells interact mechanically, the three-dimensional (3D) mechanical properties of the ECM must be quantified at the micro-(local) level in addition to information measured at the macro-(global) level. Here we describe an incremental digital volume correlation (IDVC) algorithm to quantify large (>0.05) 3D mechanical strains in the microstructure of 3D collagen matrices in response to applied mechanical loads. Strain measurements from the IDVC algorithm rely on 3D confocal images acquired from collagen matrices under applied mechanical loads. The accuracy and the precision of the IDVC algorithm was verified by comparing both image volumes collected in succession when no deformation was applied to the ECM (zero strain) and image volumes to which simulated deformations were applied in both ID and 3D (simulated strains). Results indicate that the IDVC algorithm can accurately and precisely determine the 3D strain state inside largely deformed collagen ECMs. Finally, the usefulness of the algorithm was demonstrated by measuring the microlevel 3D strain response of a collagen ECM loaded in tension.

Anisotropy↗

PubMed2004

Estimating mutual information using B-spline functions--an improved similarity measure for analysing gene expression data.

BACKGROUND: The information theoretic concept of mutual information provides a general framework to evaluate dependencies between variables. In the context of the clustering of genes with similar patterns of expression it has been suggested as a general quantity of similarity to extend commonly used linear measures. Since mutual information is defined in terms of discrete variables, its application to continuous data requires the use of binning procedures, which can lead to significant numerical errors for datasets of small or moderate size. RESULTS: In this work, we propose a method for the numerical estimation of mutual information from continuous data. We investigate the characteristic properties arising from the application of our algorithm and show that our approach outperforms commonly used algorithms: The significance, as a measure of the power of distinction from random correlation, is significantly increased. This concept is subsequently illustrated on two large-scale gene expression datasets and the results are compared to those obtained using other similarity measures.A C++ source code of our algorithm is available for non-commercial use from kloska@scienion.de upon request. CONCLUSION: The utilisation of mutual information as similarity measure enables the detection of non-linear correlations in gene expression datasets. Frequently applied linear correlation measures, which are often used on an ad-hoc basis without further justification, are thereby extended.

Algorithms↗

PubMed2002

Confocal DNA cytometry: a contour-based segmentation algorithm for automated three-dimensional image segmentation.

BACKGROUND: Confocal laser scanning microscopy (CLSM) presents the opportunity to perform three-dimensional (3D) DNA content measurements on intact cells in thick histological sections. So far, these measurements have been performed manually, which is quite time-consuming. METHODS: In this study, an intuitive contour-based segmentation algorithm for automatic 3D CLSM image cytometry of nuclei in thick histological sections is presented. To evaluate the segmentation algorithm, we measured the DNA content and volume of human liver and breast cancer nuclei in 3D CLSM images. RESULTS: A high percentage of nuclei could be segmented fully automatically (e.g., human liver, 92%). Comparison with (time-consuming) interactive measurements on the same CLSM images showed that the results were well correlated (liver, r = 1.00; breast, r = 0.92). CONCLUSIONS: Automatic 3D CLSM image cytometry enables measurement of volume and DNA content of large numbers of nuclei in thick histological sections within an acceptable time. This makes large-scale studies feasible, whereby the advantages of CLSM can be exploited fully. The intuitive modular segmentation algorithm presented in this study detects and separates overlapping objects, also in two-dimensional (2D) space. Therefore, this algorithm may also be suitable for other applications.

Algorithms↗

PubMed2000

[Kirlian photography: accidental or person-specific pattern?].

OBJECTIVE: Is the corona electrography of Kirlian photography an accidental pattern or an individual specific discharge pattern? PATIENTS: 30 patients of the Stauferklinik Schwäbisch Gmünd, suffering from a great variety of diseases. STUDY DESIGN: At intervals of 10-15 min 10 Kirlian photos each of all fingers and toes were taken from each patient. Out of this material, from 8 patients 4 Kirlian photos each with evident similarity of the discharge radiographs of 3 fingers were selected. These images were scanned for mathematical procedures, and heuristic measurements of the histograms were evaluated by a genetic algorithm. RESULTS: Three pattern groups showed different heuristic measurements: accidental pattern 0.28 +/- 0.01, Kirlian pattern in general 0.3 +/- 0.02, and Kirlian pattern of the same person 0.44 +/- 0.05. CONCLUSIONS: The mathematical objectivation of the Kirlian photographs confirm the visual impression of strong similarity. Because of the lack of anatomical irregularities and since, due to new positioning, physical and chemical surface characteristics were changed in the single Kirlian photographs, the identification of the basic pattern stresses the existence of an individual discharge pattern and thus of an individual electromagnetic field.

Complementary Therapies↗

PubMed2003

Soft learning vector quantization.

Learning vector quantization (LVQ) is a popular class of adaptive nearest prototype classifiers for multiclass classification, but learning algorithms from this family have so far been proposed on heuristic grounds. Here, we take a more principled approach and derive two variants of LVQ using a gaussian mixture ansatz. We propose an objective function based on a likelihood ratio and derive a learning rule using gradient descent. The new approach provides a way to extend the algorithms of the LVQ family to different distance measure and allows for the design of "soft" LVQ algorithms. Benchmark results show that the new methods lead to better classification performance than LVQ 2.1. An additional benefit of the new method is that model assumptions are made explicit, so that the method can be adapted more easily to different kinds of problems.

Costs and Cost Analysis↗

PubMed2005

A statistical analysis of RNA folding algorithms through thermodynamic parameter perturbation.

Computational RNA secondary structure prediction is rather well established. However, such prediction algorithms always depend on a large number of experimentally measured parameters. Here, we study how sensitive structure prediction algorithms are to changes in these parameters. We found already that for changes corresponding to the actual experimental error to which these parameters have been determined, 30% of the structure are falsely predicted whereas the ground state structure is preserved under parameter perturbation in only 5% of all the cases. We establish that base-pairing probabilities calculated in a thermal ensemble are viable although not a perfect measure for the reliability of the prediction of individual structure elements. Here, a new measure of stability using parameter perturbation is proposed, and its limitations are discussed.

Algorithms↗

PubMed2000

[What methods are available to assess quality of life of patients fitted with a pacemaker?].

Quality of life (QOL) measurements are one of the main determinants for indication and technologic choice in permanent cardiac pacing. QOL measurements are obtained using questionnaire application. Questionnaire for QOL has to be reliable, comprehensive, sensitive and specific. Pacing mode and pacemakers algorithms have been evaluated by QOL measurements: VVI vs DDD, DDD vs VVIR, AAI vs DDD, fall back, algorithm.... Survival data and costs are also relevant aspects of cardiac pacing evaluation.

Humans↗

PubMed2000

Automated surface and volume measurement of fused cells.

OBJECTIVE: To design and evaluate an algorithm to automatically calculate membrane area, volume and derived values from grey scale microscopic images of pairs of spheroid fused cells, especially human erythrocytes. STUDY DESIGN: Pairs of fused cells ("doublets") were identified by their high optical contrast, which resulted from their unhemolysed state. Global thresholding and noise-removing algorithms were applied to the image and resulted in a binary, "8"-shaped contour. The contour was used as a base for the calculation of a two-dimensional weighted distance histogram, the hilltops of which could be identified as center points of the contour's spheres. This allowed calculation of the distance of both center points and of the spheres' radii. With these three values, calculation of membrane area, volume and other derived values of the doublets became possible. High-speed time series were created based on consecutive images of the postfusion swelling and hemoglobin ejection from erythrocyte doublets at different temperatures. RESULTS: The influence of observation temperature on the dynamics of electrofused erythrocytes was measured with the algorithms given, and results were in agreement with physical changes in cell plasma viscosity. Images taken by optical and electron microscopy were in agreement with the two-spheres model of a doublet. The algorithm was not affected by fragmented contours. CONCLUSION: The velocity of hemoglobin ejection from electrofused erythrocytes and the relative change in static membrane area increase with temperature. The algorithm delivered reliable geometric values of fused cell configurations.

Algorithms↗

PubMed2006

Evaluation of right and left ventricular function by quantitative blood-pool SPECT (QBS): comparison with conventional methods and quantitative gated SPECT (QGS).

Though quantitative ECG-gated blood-pool SPECT (QBS) has become a popular tool in research settings, more verification is necessary for its utilization in clinical medicine. To evaluate the reliability of the measurements of left and right ventricular functions with QBS, we performed QBS, as well as first-pass pool (FPP) and ECG-gated blood-pool (GBP) studies on planar images in 41 patients and 8 healthy volunteers. Quantitative ECG-gated myocardial perfusion SPECT (QGS) was also performed in 30 of 49 subjects. First, we assessed the reproducibility of the measurements of left and right ventricular ejection fraction (LVEF, RVEF) and left and right ventricular end-diastolic volume (LVEDV, RVEDV) with QBS. Second, LVEF and RVEF obtained from QBS were compared with those from FPP and GBP, respectively. Third, LVEF and LVEDV obtained from QBS were compared with those from QGS, respectively. The intra- and inter-observer reproducibilities were excellent for LVEF, LVEDV, RVEF and RVEDV measured with QBS (r = 0.88 to 0.96, p < 0.01), while the biases in the measurements of RVEF and RVEDV were relatively large. LVEF obtained from QBS correlated significantly with those from FPP and GBP, while RVEF from QBS did not. LVEF and LVEDV obtained from QBS were significantly correlated with those from QGS, but the regression lines were not close to the lines of identity. In conclusion, the measurements of LVEF and LVEDV with QBS have good reproducibility and are useful clinically, while those of RVEF and RVEDV are less useful compared with LVEF and LVEDV. The algorithm of QBS for the measurements of RVEF and RVEDV remains to be improved.

Adult↗

PubMed2001

Adrenal sparing surgery during radical nephrectomy in patients with renal cell cancer: a new algorithm.

PURPOSE: Ipsilateral adrenalectomy is usually performed during radical nephrectomy because of renal cell cancer. Because renal tumors are detected more often in the earlier stages due to widespread use of ultrasound and computerized tomography, we define a subset of patients who would be eligible for adrenal sparing surgery. In a retrospective analysis we evaluated whether parameters obtained preoperatively are able to predict adrenal metastasis. MATERIALS AND METHODS: A total of 866 consecutive patients who underwent nephrectomy and ipsilateral adrenalectomy from 1983 to 1999 were evaluated. Preoperative parameters, including tumor size, location, clinical stage, number of tumors, and patient age and sex, were retrospectively compared with the histological results. Univariate and multivariate analyses were performed. RESULTS: A total of 27 (3.1%) adrenal metastases were noted in the 866 patients, and 63% were on the left side and 37% on the right side. Mean tumor size was 10 cm. with versus 6 cm. without adrenal involvement. Of the 27 patients 21 had multiple metastases at diagnosis and only 6 (0.7% of all 866) presented with solitary ipsilateral adrenal metastasis. Univariate and multivariate analyses revealed tumor size and M stage as best preoperative predictors of adrenal involvement. CONCLUSIONS: Adrenal sparing surgery is possible, and we suggest a new algorithm. If maximum tumor size measured by computerized tomography is less than 8 cm. and staging examination does not show organ or lymph node metastases, adrenalectomy is not necessary because of oncological reasons. This algorithm has to be validated by a prospective analysis.

Adolescent↗

PubMed1992

Maximal dynamic range electrotactile stimulation waveforms.

A new method to measure the dynamic range of electrotactile (electrocutaneous) stimulation uses both steepest ascent (gradient) and one-variable-at-a-time methods to determine the waveform variables that maximize the subjective magnitude (intensity) of the electrotactile percept at the maximal current without discomfort for balanced-biphasic pulse bursts presented at a 15-Hz rate. The magnitude at the maximal current without discomfort is maximized by the following waveform (range tested in parentheses): number of pulses/burst = 6 (1-20), pulse repetition rate within a burst = 350 Hz (200-1500), and phase width = 150 microseconds (40-350). The interphase interval (separation between positive and negative phases in a biphasic pulse) does not affect dynamic range from 0-500 microseconds. The number of pulses/burst has a large effect on the perceived dynamic range when this is measured using a subjective-magnitude-based algorithm, whereas it has little effect on the traditional dynamic range measure, i.e., (maximal current without discomfort)/(sensation threshold current). The perceived stimulus magnitude at the maximal current without discomfort is approximately twice as strong with 6 pulses/burst as it is with 1 pulse/burst (a frequently-used waveform).

Bias↗

PubMed1999

Do management algorithms improve chest pain triage?

OBJECTIVE: To audit the use of management algorithms for chest pain in an emergency department. DESIGN AND SETTING: Prospective study of all patients with chest pain presenting to the emergency department of an urban teaching hospital between 12 January and 4 May 1997. Staff were asked to complete a standardised admission form that incorporated the risk stratification algorithms for managing patients with suspected acute coronary syndrome. MAIN OUTCOME MEASURES: Compliance with the use of management algorithms; concordance with a cardiologist's review of the triage grouping and admission/discharge decision; and major cardiovascular events over four months. RESULTS: Emergency department staff documented the triage group in 223 of 503 cases (45%). Concordance with the group assigned by a cardiologist was 70% (kappa = 0.73; SE kappa = 0.04). When the management algorithm was applied correctly, 92% of triage decisions were correct (95% confidence interval [CI], 87%-96%). The triage decision was less often correct when risk stratification was not done (78% [73%-83%], P < 0.001), overestimated (77% [66%-88%], P < 0.01), or underestimated (50% [18%-82%], P < 0.001). The proportion of patients free of major cardiovascular events at four-month follow-up was 50% for those with myocardial infarction with ST-segment elevation, 47% for those with a high short-term risk of an adverse cardiac event, 82% for those with intermediate risk, and 99% for those with a low risk or non-coronary chest pain (P < 0.001). CONCLUSIONS: Use of management algorithms by emergency staff was poor. When used, triage decisions were more likely to be correct. Subsequent outcome confirms that the NHMRC risk stratification algorithms are useful for prognostic stratification of patients with suspected acute coronary syndrome.

Adult↗

PubMed2005

Analysis and prediction of baculovirus promoter sequences.

Consensus patterns of baculovirus sequences upstream from the translational initiation sites have been analyzed and a web tool, Local Alignment Promoter Predictor (LAPP), for the prediction of baculovirus promoter sequences has also been developed. Potential consensus sequences, i.e., TCATTGT, TCTTGTA, CTCGTAA, TCCATTT and TCATT plus TCGT in approximately 30 bp spacing context, have been found in baculovirus promoter regions, in addition to well-characterized late and early promoter elements G/T/ATAAG and TATAA, which is accompanied about 30-bp downstream by a transcriptional initiation sequence CAGT or CATT. Promoter prediction is performed by a dynamic programming algorithm based on maximal segment pair measure with scores above some cutoff against each sequence in a refined promoter database. The algorithm was able to discriminate between promoter and non-promoter sequences in a test set of baculovirus sequences with prediction specificity and sensitivity superior to that using five other eukaryotic promoter recognition programs available on the Internet. A web server that implements the LAPP with continually updated promoter database is freely available at http://life.zsu.edu.cn/LAPP/.

Algorithms↗

PubMed2002

The diagnosis and management of postoperative chylous ascites.

PURPOSE: Postoperative chylous ascites is a rare complication of retroperitoneal and mediastinal surgery that represents a difficult management problem due to the serious mechanical, nutritional and immunological consequences of the constant loss of protein and lymphocytes. We reviewed the topic of postoperative chylous ascites with special emphasis on the relevant diagnostic and imaging modalities. We propose a novel management algorithm. MATERIALS AND METHODS: We performed a MEDLINE search of the literature on chylous ascites using chyloperitoneum as the subject heading and chylous ascites as an additional key word. The search yielded 651 articles. We focused on 102 series, collective reviews and mainly case reports related to the issue of postoperative chylous ascites. RESULTS: We propose a novel algorithm based on a step-up approach aimed at promoting decreased lymph production and flow as well as maintaining nutritional balance. The management algorithm integrates repeat palliative paracentesis, dietary measures, total parenteral nutrition therapy, peritoneovenous shunting and surgical closure of the lymphoperitoneal fistula. Due to the remarkable effectiveness of somatostatin therapy for the closure of lymphatic fistula somatostatin therapy should be attempted with or without total parenteral nutrition early in the course of treatment of chylous ascites before any invasive steps are taken. CONCLUSIONS: Various management modalities may be used successfully to treat chylous ascites. Therefore, treatment should be individualized and adjusted to the severity of lymphatic leakage and its consequences. The outcome mostly depends on the underlying pathological condition. Thus, in the absence of malignant or congenital underlying pathology the prognosis in cases of postoperative chylous ascites is good with the majority responding to conservative measures.

Adult↗

PubMed2002

Signal evaluation for high-speed confocal measurements.

The confocal-detection principle is open especially for use in medical applications. For inspection systems applications for technical objects in reflection confocal setups are of growing importance. For such applications the confocal measurements need to have a very short measuring time. A fast detection system is needed and to satisfy this requirement only a small number of height levels are measured and a fast-evaluation algorithm is used. Drawbacks of the reduction of height levels are a greater influence of noise and additional systematic errors on the measured heights. Study the effects of the reduction are calculated, different evaluation algorithms are analyzed, and the optimization of the parameters is discussed.

Journal Article↗

PubMed2002

Generalized analysis of experimental data for interrelated biological measurements.

Important biological mechanisms, such as signal transduction and gene expression, are mediated by numerous interacting multifunctional molecules, whose expression and activation are tightly regulated in space and time in response to stimuli. In order to describe the network of functional inter-relationships that govern such mechanisms, we use simple algorithms to interpret multiple variable measurements, identify the prominent participants, evaluate their interactions and obtain a 'functional fingerprint' of cell behaviour. Dynamic measurements of responses yield hierarchical information about causal relations in the underlying pathway. As a proof of principles we apply this approach to phosphorylation assays in protein gels, probing hormone and insulin signalling.

Algorithms↗