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Results for “Measuring algorithm”

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PubMed1998

[Evaluation of the Swedish Interactive Thresholding Algorithm, a new thresholding algorithm, of the Humphrey field analyzer in normal subjects].

The Swedish Interactive Thresholding Algorithm (SITA) is a new thresholding algorithm that aims to obtain the same quality of visual fields in a shorter examination time than with the conventional up-and-down method. We investigated the correlation between thresholds measured with the SITA algorithm and those with the conventional up-and-down method in 47 eyes of 47 normal subjects. In each test point, thresholds with the SITA accurate and with the SITA fast showed significant correlation with those of the conventional method (r = 0.693, p < 0.0001 and r = 0.689, p < 0.0001, respectively). The mean deviation (MD) in the conventional method and the difference between MD values of the conventional method and SITA accurate and SITA fast were significantly correlated (r = -0.442, p < 0.006 and r = -0.509, p < 0.00092, respectively). The examination times of the SITA accurate and SITA fast were 48% and 27% of the conventional method. Although the new thresholding algorithm enables us to perform perimetric examination with relatively high accuracy, further investigations should be conducted before we apply it to glaucoma cases.

Algorithms↗

PubMed2003

Uniqueness and reconstruction in magnetic resonance-electrical impedance tomography (MR-EIT).

Magnetic resonance-electrical impedance tomography (MR-EIT) was first proposed in 1992. Since then various reconstruction algorithms have been suggested and applied. These algorithms use peripheral voltage measurements and internal current density measurements in different combinations. In this study the problem of MR-EIT is treated as a hyperbolic system of first-order partial differential equations, and three numerical methods are proposed for its solution. This approach is not utilized in any of the algorithms proposed earlier. The numerical solution methods are integration along equipotential surfaces (method of characteristics), integration on a Cartesian grid, and inversion of a system matrix derived by a finite difference formulation. It is shown that if some uniqueness conditions are satisfied, then using at least two injected current patterns, resistivity can be reconstructed apart from a multiplicative constant. This constant can then be identified using a single voltage measurement. The methods proposed are direct, non-iterative, and valid and feasible for 3D reconstructions. They can also be used to easily obtain slice and field-of-view images from a 3D object. 2D simulations are made to illustrate the performance of the algorithms.

Algorithms↗

PubMed2000

An adaptive system for active noise reduction.

An adaptive system for active noise reduction in an acoustic duct is presented. The system is based on a modification of a least mean square (LMS) algorithm called filtered-U with on-line error path modelling. The system was assembled and examined on a laboratory test stand in the Laboratory of Active Noise Reduction Methods of the Central Institute for Labour Protection (Warsaw, Poland). The structure of the test stand, the block structure of the active noise reduction system, the basic assumption concerning the applied adaptive algorithm, and examples of measured effectiveness of the system for various kinds of noise are presented.

Acoustics↗

PubMed2004

"Spectral implementation" for creating a labeled pseudo-pure state and the Bernstein-Vazirani algorithm in a four-qubit nuclear magnetic resonance quantum processor.

A quantum circuit is introduced to describe the preparation of a labeled pseudo-pure state by multiplet-component excitation scheme which has been experimentally implemented on a 4-qubit nuclear magnetic resonance quantum processor. Meanwhile, we theoretically analyze and numerically investigate the low-power selective single-pulse implementation of a controlled-rotation gate, which manifests its validity in our experiment. Based on the labeled pseudo-pure state prepared, a 3-qubit Bernstein-Vazirani algorithm has been experimentally demonstrated by spectral implementation. The "answers" of the computations are identified from the split peak positions in the spectra of the observer spin, which are equivalent to projective measurements required by the algorithms.

Journal Article↗

PubMed1998

Multimodality evaluation of pressure relief surfaces.

Multimodality evaluation of six different support surfaces was performed measuring interface pressure, transcutaneous oxygen tension, and blood flow in pressure ulcer-prone areas on healthy subjects. Interface pressure was measured with a flexible force-sensing resistor array. The interface pressure distribution patterns of 10 healthy male volunteers were measured in the supine and lateral positions using a pressure sensor (force sensing resistor) array. Transcutaneous oxygen (TcPO2) and laser Doppler flowmeter probes were placed over the sacrum, the right trochanter, and the right ischium. Data were recorded for 15 minutes each with the subject in the supine and lateral decubitus positions. Statistically significant differences (p < 0.05) between the various surfaces could be observed for blood flow and pressure measurements, especially in the lateral position over the trochanter and for the TcPO2 measurements in the supine position over the sacrum. We conclude that measuring interface pressure, transcutaneous oxygen tension, and blood flow allows a more thorough evaluation of the physiologic effects of special support surfaces than any single technique. Future studies on patients will assess algorithms for using these measurement techniques to predict the efficacy of various support surfaces in minimizing pressure ulceration.

Blood Gas Monitoring, Transcutaneous↗

PubMed2004

An evaluation of anesthesia patient satisfaction instruments.

The purpose of this study was to systematically review the instruments used to obtain anesthesia-specific patient satisfaction data and to determine the degree to which each instrument controlled for measurement error bias, such as poor survey design. By using an assessment and evaluation tool developed for the present study that held proven internal reliability and construct validity, we analyzed and scored each instrument according to the presence or absence of measurement error in survey design. We found that a paucity of anesthesia-specific patient satisfaction studies exists and that patient satisfaction studies dealing with anesthesia care were erratically defined, nonstandardized, and imprecise regarding intent and method. Moreover, the simple rating forms used in most of the reviewed studies were inadequate to achieve the goal of measuring the quality of anesthesia care. One instrument, the Iowa Satisfaction With Anesthesia Scale (ISAS), developed by Dexter et al (1997), was the first found to inculcate scientifically accepted psychometric item construction algorithms, an indicator of measurement reliability. Although the ISAS holds substantial potential for future application in this realm, we recommend that it be refined further and that the search for a superlative instrument to obtain anesthesia-specific patient satisfaction continue.

Evaluation Studies as Topic↗

PubMed1998

Diagnostic strategies in myocardial infarction using myoglobin measurement.

Determination of myoglobin, a low molecular weight haeme protein (17.8 kDa), present in both cardiac and skeletal muscle, is an old test with new perspectives. Advantages and disadvantages of myoglobin determination are well known; recent availability of rapid and accurate methods for the assay of this protein has greatly enhanced interest in the clinical utilization of the test. However, since myoglobin is present in both skeletal and cardiac muscle, any damage to these muscle types results in its release in blood and, consequently, high levels of the protein are observed in conditions unrelated to acute myocardial infarction (AMI). New strategies for myoglobin measurement may resolve this limitation. These strategies include both the combined measurement of myoglobin and a skeletal specific marker (carbonic anhydrase III) or a cardiac specific marker (troponin I or T), as well as myoglobin evaluation on serial samples. In particular. the diagnostic algorithm based on combined measurement of myoglobin and troponins significantly improves diagnostic efficiency in laboratory assessment of suspected AMI patients. However, further efforts are necessary to improve the standardization of present methods for myoglobin measurement: the significant disagreement demonstrated between some commercially available assays should be carefully considered in clinical practice.

Biomarkers↗

PubMed2001

Kalman filter detection of blinks in video-oculography: applications for VVOR measurement during locomotion.

A Kalman filter algorithm was implemented for automatic detection of blink artifacts in video-oculography (VOG) data, and a cubic spline used to patch the eliminated data. The algorithm was tested by randomly introducing artificial blinks into eye movement data and computing the errors introduced by the patches. We also computed visual vestibulo-ocular reflex (VVOR) gain and phase in healthy and vestibulopathic subjects during a locomotor task, before and after blink removal, to demonstrate the interpretive importance of eliminating blink artifacts. The error introduced by the patched data was small (0.50+/-0.32 degrees ) and within the resolution of head angle measurements. Comparison of gain and phase shift before and after removing blinks revealed that even when calculated values are within expected limits, coherence of the VVOR signal was significantly (p=0.003) lower prior to blink removal (0.51+/-0.37) compared to that after blink removal (0.92+/-0.08). Comparison of VVOR calculations between healthy and vestibulopathic subjects (after removal of blinks) revealed that vestibulopathic subjects had significantly decreased gains (p=0.018) and increased phase shifts (p=0.009): these results agree with data reported in literature. We conclude that the Kalman filter detection and cubic spline patching algorithms are useful tools for VOG and should enable reliable VVOR measurements during unconstrained, ecologically meaningful locomotor activities.

Adult↗

PubMed2006

Subdimension-based similarity measure for DNA microarray data clustering.

Microarray data analysis is useful for understanding biological processes. A number of clustering algorithms have been used to achieve this task. However, the performance of these methods can be significantly degraded due to the presence of nonsignificant conditions. In this paper, we propose a robust clustering algorithm based on a similarity measure. The key concept of the proposed similarity measure is to measure the similarity between two data points by their subdimensions. For example, assume that x1, x2, and x3 are ten-dimensional data vectors. The data point x3 is said to be closer to x1 than x2 if more than half of the dimensions of x1 and x3 are closer to x1 than x2. Thus, if two patterns are very similar except for a small amount of features, this measure will preserve the similarity. We have performed eight experiments to test the robustness of the proposed method, including three synthetic data sets, three real world data sets, and two microarray data sets. We also have compared the proposed method with four different clustering algorithms. Experimental results show that the proposed method yields better results than existing clustering algorithms.

Algorithms↗

PubMed2005

Analysis of discrete and continuous distributions of ventilatory time constants from dynamic computed tomography.

In this study, an algorithm was developed to measure the distribution of pulmonary time constants (TCs) from dynamic computed tomography (CT) data sets during a sudden airway pressure step up. Simulations with synthetic data were performed to test the methodology as well as the influence of experimental noise. Furthermore the algorithm was applied to in vivo data. In five pigs sudden changes in airway pressure were imposed during dynamic CT acquisition in healthy lungs and in a saline lavage ARDS model. The fractional gas content in the imaged slice (FGC) was calculated by density measurements for each CT image. Temporal variations of the FGC were analysed assuming a model with a continuous distribution of exponentially decaying time constants. The simulations proved the feasibility of the method. The influence of experimental noise could be well evaluated. Analysis of the in vivo data showed that in healthy lungs ventilation processes can be more likely characterized by discrete TCs whereas in ARDS lungs continuous distributions of TCs are observed. The temporal behaviour of lung inflation and deflation can be characterized objectively using the described new methodology. This study indicates that continuous distributions of TCs reflect lung ventilation mechanics more accurately compared to discrete TCs.

Algorithms↗

PubMed1988

Wideband external pulse recording during cuff deflation: a new technique for evaluation of the arterial pressure pulse and measurement of blood pressure.

Analysis of the external brachial pulse recorded during standard blood pressure cuff deflation with use of a transducer with a wide frequency response has revealed a reproducible pattern with three distinct components that we have labeled K1, K2, and K3. K1 is a low-amplitude, low-frequency signal that is present with cuff pressures above systolic pressure. K2 is a triphasic signal appearing at systolic pressure and disappearing at diastolic pressure, which approximately corresponds to the audible Korotkoff sound. K3 appears with cuff pressure between systolic and diastolic pressure and continues to be present below diastolic pressure. Intra-arterial pressure recordings made with a high-fidelity Millar catheter-tip manometer revealed K2 and K3 analogs. K3 resembles the intra-arterial pressure waveform and when calibrated according to the pulse pressure, noninvasive dK3/dt determinations correlated well with intra-arterial dP/dt measurements. The appearance/disappearance property of K2 was designated as the "K2 algorithm" and represents a new, objective noninvasive method for measurement of blood pressure. The K2 algorithm compares favorably with intra-arterial measurements, is more accurate than the auscultatory technique, and may be especially useful in clinical situations in which the auscultatory technique does not work well.

Adolescent↗

PubMed2005

Monte Carlo- versus pencil-beam-/collapsed-cone-dose calculation in a heterogeneous multi-layer phantom.

The aim of this work was to evaluate the accuracy of dose predicted in heterogeneous media by a pencil beam (PB), a collapsed cone (CC) and a Monte Carlo (MC) algorithm. For this purpose, a simple multi-layer phantom composed of Styrofoam and white polystyrene was irradiated with 10 x 10 cm2 as well as 20 x 20 cm2 open 6 MV photon fields. The beam axis was aligned parallel to the layers and various field offsets were applied. Thereby, the amount of lateral scatter was controlled. Dose measurements were performed with an ionization chamber positioned both in the central layer of white polystyrene and the adjacent layers of Styrofoam. It was found that, in white polystyrene, both MC and CC calculations agreed satisfactorily with the measurements whereas the PB algorithm calculated 12% higher doses on average. By studying off-axis dose profiles the observed differences in the calculation results increased dramatically for the three algorithms. In the regions of low density CC calculated 10% (8%) lower doses for the 10 x 10 cm2 (20 x 20 cm2) fields than MC. The MC data on the other hand agreed well with the measurements, presuming that proper replacement correction for the ionization chamber embedded in Styrofoam was performed. PB results evidently did not account for the scattering geometry and were therefore not really comparable. Our investigations showed that the PB algorithm generates very large errors for the dose in the vicinity of interfaces and within low-density regions. We also found that for the used CC algorithm large deviations for the absolute dose (dose/monitor unit) occur in regions of electronic disequilibrium. The performance might be improved by better adapted parameters. Therefore, we recommend a careful investigation of the accuracy for dose calculations in heterogeneous media for each beam data set and algorithm.

Algorithms↗

PubMed2005

A tabu search algorithm for post-processing multiple sequence alignment.

Tabu search is a meta-heuristic approach that is proven to be useful in solving combinatorial optimization problems. We implement the adaptive memory features of tabu search to refine a multiple sequence alignment. Adaptive memory helps the search process to avoid local optima and explores the solution space economically and effectively without getting trapped into cycles. The algorithm is further enhanced by introducing extended tabu search features such as intensification and diversification. The neighborhoods of a solution are generated stochastically and a consistency-based objective function is employed to measure its quality. The algorithm is tested with the datasets from BAliBASE benchmarking database. We have observed through experiments that tabu search is able to improve the quality of multiple alignments generated by other software such as ClustalW and T-Coffee. The source code of our algorithm is available at http://www.bii.a-star.edu.sg/~tariq/tabu/.

Algorithms↗

PubMed2005

Segmentation algorithm for DNA sequences.

A new measure, to quantify the difference between two probability distributions, called the quadratic divergence, has been proposed. Based on the quadratic divergence, a new segmentation algorithm to partition a given genome or DNA sequence into compositionally distinct domains is put forward. The new algorithm has been applied to segment the 24 human chromosome sequences, and the boundaries of isochores for each chromosome were obtained. Compared with the results obtained by using the entropic segmentation algorithm based on the Jensen-Shannon divergence, both algorithms resulted in all identical coordinates of segmentation points. An explanation of the equivalence of the two segmentation algorithms is presented. The new algorithm has a number of advantages. Particularly, it is much simpler and faster than the entropy-based method. Therefore, the new algorithm is more suitable for analyzing long genome sequences, such as human and other newly sequenced eukaryotic genome sequences.

Algorithms↗

PubMed2005

Combined tag tracking and strain reconstruction from tagged cardiac MR images without user-defined myocardial contours.

PURPOSE: To develop an unsupervised method for measuring quantitative three-dimensional regional strain in the left ventricular wall from tagged cardiac MR images. MATERIALS AND METHODS: A total of 10 normal human volunteers and eight patients with myocardial infarction were imaged using a parallel tagged imaging protocol. Each study was analyzed using the combined tag tracking and strain reconstruction (COTTER) algorithm. In contrast to existing techniques, which first track tag lines independently in each slice, then reconstruct myocardial deformation, the COTTER algorithm fits a three-dimensional cardiac deformation model directly to the image data. This approach ensures that tag line positions identified in the image data are consistent from slice to slice. A total of 10 imaging studies (six normals, four patients) were used to optimize parameters of the COTTER algorithm. RESULTS: In the remaining eight imaging studies, the root-mean-square difference between tags tracked by COTTER and user-supervised analysis was 0.66 pixels at end-systole. The correlation coefficient between circumferential shortening strains at end-systole computed by COTTER and user-supervised analysis was 0.84 (P < 0.005) at the midwall. CONCLUSION: The COTTER algorithm can compute accurate measurements of three-dimensional regional strain without user supervision.

Algorithms↗

PubMed2006

Commentary on the British Thoracic Society guidelines for the investigation of unilateral pleural effusion in adults.

The publication of guidelines for the investigation of unilateral pleural effusion in adults by the British Thoracic Society has focused attention on this subject which, although comprising only a small proportion of laboratory workload, is a fairly common clinical problem. We critically reviewed the guidance applicable to clinical biochemistry laboratories and found a number of deficiencies. In particular, the need for anaerobic sample collection for pH measurement and preservation of samples for glucose assay is not mentioned and health and safety issues related to the handling of potentially infected fluids are also not considered. There are discrepancies between recommendations in the text and in the accompanying diagnostic algorithm, which require clarification. Measurement of total protein is an essential first step in the analysis of pleural fluid and will usually distinguish transudates from exudates. Measurement of lactate dehydrogenase activity is only required when total protein results are equivocal. There are practical difficulties with measurement of fluid pH as recommended in the guidelines and there is little evidence that such measurements are valuable. Similarly, there is little evidence to support the recommendation for measurement of complement in suspected rheumatoid effusions, and the recommendation for amylase isoenzyme studies if acute pancreatitis is a possibility is not practical. The different nature of pleural fluid demands a good understanding of the handling of these samples, the limitations of the analytical methods and the subsequent result interpretation by laboratory staff. We propose a modified diagnostic algorithm reflecting our criticisms of the original. Dialogue between the laboratory and local clinicians, possibly with the production of local guidelines, informed by these recommendations, should help optimize diagnostic management of patients with pleural effusion.

Adult↗

PubMed1996

Age-dependent influence on heart rate variability in salt-sensitive hypertensive subjects.

OBJECTIVE: The known association between systemic arterial hypertension in its initial stages and increased sympathetic nervous system drive prompted us to evaluate the influence of age on autonomic nervous system function in subjects with salt-sensitive arterial hypertension. DESIGN: In a randomized study, autonomic nervous system function was assessed by power spectral analysis of heart-rate variability calculated with an autoregressive algorithm in salt-sensitive hypertensives and controls at baseline and under sympathetic stress (passive head-up tilt). For 1 week before the study, all subjects kept to a diet supplying 120 mEq sodium. Sodium sensitivity was assessed by measuring and comparing arterial pressures after a 7-day controlled dietary sodium intake of 20 mEq per day after a 7-day period on 220 mEq sodium/day. SETTING: Geriatric division at the I Medical Clinic of the University of Rome "La Sapienza". PARTICIPANTS: Sixty-five patients with salt-sensitive hypertension (age range 19 to 89 years) and 64 age-matched normotensive controls, divided for data comparison into three age-groups: < 44 years; 44 to 64 years; and > or = 65 years. MEASUREMENTS: With an autoregressive algorithm in a power spectral analysis of heart rate variability, we detected four spectral frequency-domains: total power (0.0033 to 0.40 Hz), high-frequency power (0.16 to 0.40 Hz), low-frequency power (0.04 to 0.15 HZ) and very-low-frequency power (0.0033 to 0.04 Hz). To determine sodium sensitivity, for 1 week before the study all subjects kept to a diet supplying 120 mEq sodium. Sodium sensitivity was assessed by measuring and comparing arterial pressures after a 7-day controlled dietary intake of 20 mEq per day and after a 7-day period of 220 mEq sodium/day. RESULTS: Results were expressed as natural logarithms of power and normalized units. The hypertensive patients of all ages had significantly lower total power of heart rate variability than the normotensive controls (P < .05). At baseline, the youngest hypertensives had lower natural logarithms and low-frequency normalized units than controls (P < .001). After tilt, only their low-frequency normalized units exceeded those of controls (P < .001). The middle-aged hypertensive group had higher low-frequency normalized units than controls at baseline (P < .05) and after tilt (P < .001). At baseline and after tilt, the oldest hypertensives had lower low-frequency natural logarithms than controls (P < .05) and normalized units equal to those of controls. But the hypertensives of all ages were less able than controls (P < .001) to increase low-frequency power after head-up tilt. In the less than 44-year-old hypertensives, diastolic pressure correlated significantly with low-frequency power of heart rate variability, expressed in normalized units, at baseline (P < .05) and after head-tilt (P < .05). A significant inverse correlation was found between age and the natural logarithm of low-frequency power at baseline (r = -.682, P < .001) and after tilt (r = -.800; P < .001). Also, a significant inverse correlation was found to exist in normotensive subjects between the natural logarithm of low-frequency at baseline (r = -.595; P < .001) and after tilt (r = -.391; P < .001). The two regression line coefficients for age correlated significantly (P < .001) with the natural logarithm of low-power frequency after tilt. CONCLUSION: Whereas sodium chloride-sensitive hypertension appears to be associated with sympathetic hyperactivity in young and middle-aged subjects, in older people it is not. Sympathetic activity diminishes with age, declining faster in hypertensive subjects.

Adult↗

PubMed2005

Estimation of electrical conductivity distribution within the human head from magnetic flux density measurement.

We have developed a new algorithm for magnetic resonance electrical impedance tomography (MREIT), which uses only one component of the magnetic flux density to reconstruct the electrical conductivity distribution within the body. The radial basis function (RBF) network and simplex method are used in the present approach to estimate the conductivity distribution by minimizing the errors between the 'measured' and model-predicted magnetic flux densities. Computer simulations were conducted in a realistic-geometry head model to test the feasibility of the proposed approach. Single-variable and three-variable simulations were performed to estimate the brain-skull conductivity ratio and the conductivity values of the brain, skull and scalp layers. When SNR = 15 for magnetic flux density measurements with the target skull-to-brain conductivity ratio being 1/15, the relative error (RE) between the target and estimated conductivity was 0.0737 +/- 0.0746 in the single-variable simulations. In the three-variable simulations, the RE was 0.1676 +/- 0.0317. Effects of electrode position uncertainty were also assessed by computer simulations. The present promising results suggest the feasibility of estimating important conductivity values within the head from noninvasive magnetic flux density measurements.

Algorithms↗