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Results for “Measuring algorithm”

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At least 505 records · Page 28Linked to original sources

PubMed1994

Bedside assessment of intravascular volume status in patients undergoing coronary bypass surgery.

BACKGROUND: Management of intravascular volume is crucial in patients after cardiopulmonary bypass as myocardial dysfunction is common. The purpose of this study was to validate a novel bedside technique for real-time assessment of intravascular volumes. METHODS: Eleven patients undergoing cardiopulmonary bypass were studied. In addition to standard monitors, a fiberoptic thermistor catheter was placed in the descending aorta and central venous injections of 10 ml ice-cold indocyanine green dye were performed. Total blood volume was measured by a standard in vitro technique. Circulating and central blood volume were calculated by using cardiac output, mean transit times, and a newly developed recursive convolution algorithm that models recirculation. Measurements were performed after induction of anesthesia and at 1, 6, and 24 h after surgery. RESULTS: A two-compartment model of the circulation was required for adequate fit of the data. We found a significant correlation between total and circulating blood volumes (r = 0.87). One hour after surgery, central blood volume was decreased by 10% (P < 0.05). At 6 and 24 h after surgery, circulating blood volumes were significantly increased by 29% and 20%, respectively (P < 0.01), although central blood volume was similar to control values. Before surgery stroke volume index correlated with circulating blood volume (r = 0.87) but not with pulmonary capillary wedge and central venous pressures. CONCLUSIONS: This study shows that bedside determinations of intravascular blood volumes are feasible and that these measurements are more indicative of intravascular volume status than are either pulmonary capillary wedge or central venous pressures in the post-cardiopulmonary bypass period. Our data also demonstrate that despite a normal central blood volume both circulating and total blood volume are significantly increased in the immediate post-cardiopulmonary bypass period.

Aged↗

PubMed1986

Morphological measurement of the SEP using a dynamic time warping algorithm.

A dynamic time warping technique was created to align the components of digitally high-pass (300 Hz-2500 Hz) filtered somatosensory evoked potentials evoked by median nerve stimulation recorded with a bipolar cephalic montage. A cost function was assigned related to the amount of warping necessary to match a standard wave derived from 24 normal subjects. Its value ranged from 0.525 to 2.456 (mean 1.305 +/- 0.501). This contrasted with a mean of 5.089 +/- 4.277 (range 0.701-13.972) derived from 25 patients with definite (n = 24) or possible (n = 1) multiple sclerosis chosen on the basis of having few or no clinical abnormalities at the time of testing. Fourteen (56%) of the patients had cost functions that were 3 or more S.D.s above the normal mean as compared to 3 (12%) having prolonged latency of the N19 peak. When used in combination, the cost function and latency yielded 60% abnormalities; 5 times higher than latency measurement alone.

Adult↗

PubMed2000

The clinical value of assessing left ventricular function from gated SPECT perfusion studies.

Gated myocardial perfusion SPECT is a technique that is rapidly becoming widespread in the nuclear cardiology arena, and it currently accounts for a majority of all perfusion SPECT acquisitions performed in the USA. Its main advantage is that of providing important incremental clinical information over SPECT perfusion assessment alone, at essentially no extra cost. With respect to the diagnosis of cardiac disease, gated SPECT has been demonstrated to improve specificity by helping identify attenuation artifacts in patients with suspected coronary artery disease, and is also key in identifying patients with non-ischemic cardiomyopathies. In prognostic assessment, gated SPECT-derived measurements of ejection fraction achieve substantial incremental stratification of patients at risk for cardiac death or myocardial infarction, compared to perfusion scores, and volume measurements further improve risk stratification. New quantitative algorithms allow the fast, accurate and reproducible measurement of parameters of global cardiac function (ejection fraction, end-systolic and end-diastolic volume) as well as regional cardiac function (myocardial wall motion and thickening), all of which have been validated against a wide variety of gold standards.

Coronary Disease↗

PubMed2003

Development of an evidence-based algorithm for the management of cervical cancer.

OBJECTIVE: To develop a description of the management of cervical cancer to support locally developed, regional guidelines and to identify the level of primary research evidence to support it. DESIGN: Development of a flow-charted algorithm, using regional guidelines and clinician consensus. A Medline literature search for primary research was done to validate the algorithm and selection of papers, to verify if they were valid according to pre-defined criteria and to compare algorithm management with an alternative. MAIN OUTCOME MEASURE: The highest level of evidence for algorithm management was based on the design of the supporting research. RESULTS: Twenty percent of the algorithm is supported by level I evidence (randomised controlled trials), 70% by level II evidence (cohort studies) and 10% by level IV evidence (expert opinion or case series). Level II evidence supports the management of Stage Ia, squamous cell carcinoma by cone biopsy or a simple hysterectomy. This level of evidence also applies to research on the management of Stages Ib-IIa, by radical hysterectomy and pelvic lymphadenectomy followed by radiotherapy, if the lymph nodes are positive. Radiotherapy to treat Stages IIb-IV cervical cancer is supported by level I evidence. The management of Stage I adenocarcinoma is supported by level II evidence. CONCLUSIONS: Evaluations of the effect of informing clinicians of the strengths of the proposed management are now required, as constructing evidence-based algorithms is worthwhile, only if they are likely to affect clinical practice.

Adenocarcinoma↗

PubMed1989

Automated determination of the magnitude and time delay ("phase") of the cardiac cycle dependent variation of myocardial ultrasonic integrated backscatter.

An algorithm for quantitative description of cardiac cycle dependent variation of integrated backscatter (cyclic variation) has been developed and is shown to be suitable for analysis of nonsinusoidal data typical of ultrasonic tissue characterization measurements from myocardium in vivo. The algorithm produces estimates of the magnitude of variation and of the time delay relative to the electrocardiographically recorded QRS-complex. To validate the algorithm, 246 integrated backscatter measurements were analyzed both manually and by the automated method. The magnitude and time delay estimates from the two methods correlated closely. With a separate set of data, the algorithm produced reasonable descriptions of the cyclic variation for 89 of 101 integrated backscatter measurements. Only modest computational power is required for effective implementation of this algorithm, facilitating inclusion of online automated analysis capabilities in quantitative ultrasonic tissue characterization systems.

Algorithms↗

PubMedDate not supplied

A method of calculating peripheral dose distributions of photon beams below 10 MV.

The radiation dose outside the radiotherapy treatment field can be of clinical concern and, therefore, a method of accurately predicting the peripheral doses received by tissues would be beneficial. This paper describes a semiempirical method developed for calculating the peripheral dose received at points outside the collimated field edge for incident photon beams with energies below neutron production thresholds (less than 10 MV). The dependence of the peripheral dose upon depth, distance, field shape and size, azimuthal angle about the central axis, external contour variations, and tissue heterogeneities are accounted for by this calculation. Predictions by this algorithm are compared with measurements and it is shown that the method is capable of reproducing the measured peripheral dose values usually to within the statistical uncertainties of the data.

Algorithms↗

PubMed2000

Three-dimensional optical measurement of instantaneous pressure.

Local perturbations in material density induced in a material by a compressional wave give rise to local perturbations in refractive index. Accurate, high-resolution, three-dimensional, optical measurements of an instantaneous refractive index perturbation in a homogeneous, optically transparent medium may be obtained from measurements of scattered optical intensity alone. The method of generalized projections allows incorporation of optical intensity measurements into an iterative algorithm for computing the phase of the interrogating optical pulse as the solution of a fixed point equation. The complex optical field amplitude, computed in this manner, is unique up to a constant unit magnitude complex coefficient. The three-dimensional refractive index distribution may be computed via the Fourier slice reconstruction algorithm from the optical phase data under the assumption of weak optical scattering. The refractive index perturbation is related to local instantaneous pressure under a linear, small-displacement model for the mechanical wave. A numerical simulation of the measurement experiment, phase recovery, and reconstruction process for a plane piston ultrasound transducer with a semicircular aperture and center frequency of 1.5 MHz is described and corresponds very well with experiment. Experimental data obtained using an 810-nm laser source are used to reconstruct the three-dimensional pressure field from two elements of a 2.5-MHz linear array. Comparison with a measurement obtained via a 500-microm needle hydrophone shows excellent agreement.

Acoustics↗

PubMed1998

An adaptive control algorithm for optimization of intensity modulated radiotherapy considering uncertainties in beam profiles, patient set-up and internal organ motion.

A new general beam optimization algorithm for inverse treatment planning is presented. It utilizes a new formulation of the probability to achieve complication-free tumour control. The new formulation explicitly describes the dependence of the treatment outcome on the incident fluence distribution, the patient geometry, the radiobiological properties of the patient and the fractionation schedule. In order to account for both measured and non-measured positioning uncertainties, the algorithm is based on a combination of dynamic and stochastic optimization techniques. Because of the difficulty in measuring all aspects of the intra- and interfractional variations in the patient geometry, such as internal organ displacements and deformations, these uncertainties are primarily accounted for in the treatment planning process by intensity modulation using stochastic optimization. The information about the deviations from the nominal fluence profiles and the nominal position of the patient relative to the beam that is obtained by portal imaging during treatment delivery, is used in a feedback loop to automatically adjust the profiles and the location of the patient for all subsequent treatments. Based on the treatment delivered in previous fractions, the algorithm furnishes optimal corrections for the remaining dose delivery both with regard to the fluence profile and its position relative to the patient. By dynamically refining the beam configuration from fraction to fraction, the algorithm generates an optimal sequence of treatments that very effectively reduces the influence of systematic and random set-up uncertainties to minimize and almost eliminate their overall effect on the treatment. Computer simulations have shown that the present algorithm leads to a significant increase in the probability of uncomplicated tumour control compared with the simple classical approach of adding fixed set-up margins to the internal target volume.

Algorithms↗

PubMedDate not supplied

[A device for studying respiratory mechanics by the forced oscillation technique].

A new compact device for measuring respiratory impedance is designed. Input respiratory impedance, an impedance of upper airways and respiratory impedance corrected for upper airways shunt can be measured in 2 minutes. The space-condition requirements are complied by integrating an oscillation generator, sensors, a mouthpiece with a screen and a reference resistor in the measuring head. The oscillation generator produces small-amplitude forced oscillations (with a tidal volume of about 1 ml) at frequencies f = 7, 10, 13, 16, and 19 Hz. Algorithms of calibration and measurement provide impedance calculation. For 55 different external impedances, complex transmission factors are measured for each of the five frequencies. The standard deviation of amount and phase of complex transmission factors are less than 5% and 0.06, respectively.

Humans↗

PubMed2002

Experimental evaluation of leaky least-mean-square algorithms for active noise reduction in communication headsets.

An adaptive leaky normalized least-mean-square (NLMS) algorithm has been developed to optimize stability and performance of active noise cancellation systems. The research addresses LMS filter performance issues related to insufficient excitation, nonstationary noise fields, and time-varying signal-to-noise ratio. The adaptive leaky NLMS algorithm is based on a Lyapunov tuning approach in which three candidate algorithms, each of which is a function of the instantaneous measured reference input, measurement noise variance, and filter length, are shown to provide varying degrees of tradeoff between stability and noise reduction performance. Each algorithm is evaluated experimentally for reduction of low frequency noise in communication headsets, and stability and noise reduction performance are compared with that of traditional NLMS and fixed-leakage NLMS algorithms. Acoustic measurements are made in a specially designed acoustic test cell which is based on the original work of Ryan et al. ["Enclosure for low frequency assessment of active noise reducing circumaural headsets and hearing protection," Can. Acoust. 21, 19-20 (1993)] and which provides a highly controlled and uniform acoustic environment. The stability and performance of the active noise reduction system, including a prototype communication headset, are investigated for a variety of noise sources ranging from stationary tonal noise to highly nonstationary measured F-16 aircraft noise over a 20 dB dynamic range. Results demonstrate significant improvements in stability of Lyapunov-tuned LMS algorithms over traditional leaky or nonleaky normalized algorithms, while providing noise reduction performance equivalent to that of the NLMS algorithm for idealized noise fields.

Journal Article↗

PubMed2000

Breast cancer: importance of spiculation in computer-aided detection.

PURPOSE: To determine the prevalence of spiculation in a large series of screening-detected breast cancers appearing as masses on mammograms and to assess the sensitivity of a computer-aided detection (CAD) algorithm that uses spiculation measures in the detection of such lesions. MATERIALS AND METHODS: Six hundred seventy-seven consecutive cases of breast cancers detected as masses on mammograms were independently reviewed by three radiologists who determined if the lesions were spiculated. All cancers were then analyzed by the CAD system. RESULTS: All three radiologists interpreted 375 (55%) of the 677 masses as being spiculated on at least one view. The CAD algorithm correctly marked 322 (86%) of the 375 clearly spiculated masses, with a mean of 0.24 additional mass mark per image. With a looser definition of spiculation, 585 (86%) of the 677 masses were called spiculated by at least one radiologist on one view. The algorithm correctly marked 464 (79%) of the 585 lesions that were spiculated or possibly spiculated. CONCLUSION: Spiculation was clearly present in a majority (55%) of consecutive screening-detected breast cancer masses found on mammograms in a large clinical trial. Incorporation of spiculation measures is, therefore, an important strategy in the detection of breast cancer with CAD. A present-generation CAD algorithm correctly identified a large proportion (86%) of spiculated breast cancers.

Algorithms↗

PubMed2003

Blind deblurring of spiral CT images.

To discriminate fine anatomical features in the inner ear, it has been desirable that spiral computed tomography (CT) may perform beyond their current resolution limits with the aid of digital image processing techniques. In this paper, we develop a blind deblurring approach to enhance image resolution retrospectively without complete knowledge of the underlying point spread function (PSF). An oblique CT image can be approximated as the convolution of an isotropic Gaussian PSF and the actual cross section. Practically, the parameter of the PSF is often unavailable. Hence, estimation of the parameter for the underlying PSF is crucially important for blind image deblurring. Based on the iterative deblurring theory, we formulate an edge-to-noise ratio (ENR) to characterize the image quality change due to deblurring. Our blind deblurring algorithm estimates the parameter of the PSF by maximizing the ENR, and deblurs images. In the phantom studies, the blind deblurring algorithm reduces image blurring by about 24%, according to our blurring residual measure. Also, the blind deblurring algorithm works well in patient studies. After fully automatic blind deblurring, the conspicuity of the submillimeter features of the cochlea is substantially improved.

Algorithms↗

PubMedDate not supplied

A method for approximating fractional power average relaxation times without inversion of multiexponential relaxation data.

A method is presented for approximating fractional power averages of relaxation times for data equispaced in log time, without the need to invert multiexponential relaxation data. This form of average permits giving emphasis to short or long times depending on the choice of the p value, thus giving the possibility of representing different specific properties of porous media. This method has been tested on a large number of nuclear magnetic resonance (NMR) relaxation measurements in porous samples. This new algorithm appears to be robust with respect to both measurement and computation, and its major advantage is that it does not depend on a particular inversion method. Moreover, it permits a very fast computation.

Algorithms↗

PubMed1991

Noninvasive measurement of transmural gradients in myocardial strain with MR imaging.

A method is presented for performing high-resolution strain measurements by using magnetic resonance (MR) tagging. Multispectral radiofrequency pulses are used to produce tagging grids from which strain estimates are obtained with a resolution of 2 mm. A tag detection algorithm is presented that measures the center of a tag line with a precision that ranges from 0.1 to 0.2 mm over the systolic interval. With this method, a transmural gradient in the strain of a normal dog heart was detected.

Animals↗

PubMed1995

Siggaard-Andersen algorithm-derived p50 parameters: perturbation by abnormal hemoglobin-oxygen affinity and acid-base disturbances.

The p50 and derived indexes, calculated by using the Siggaard-Andersen algorithm from a single measurement of arterial blood gas tensions and hemoglobin-oxygen saturation, are used to assess tissue oxygen availability in critical illness. We tested the accuracy of the Siggaard-Andersen p50 algorithm over a wide range of pathophysiologic conditions. Blood gases, cooximetry, and calculation of standard and in vivo p50 were performed at multiple saturations, CO2 tensions, and H+ concentrations on blood with normal (standard p50 of 26.1 and 26.7 mm Hg), increased (19.0 and 25.4), and reduced (33.9 and 38.2) hemoglobin-oxygen affinity, as well as on high-affinity blood from two patients with diabetic ketoacidosis (16.7 and 20.8). Log p50 in vivo/pH plots were constructed to determine the Bohr effect. Except in the normal affinity specimens (coefficient of variation < 1.7%), standard p50 values showed high variability (coefficient of variation > 5.9%), with saturation-linked bias and distortion of the Bohr effect. Standard p50 was overestimated by up to 11 mm Hg as saturation approached 97%. Although base deficit correction of the stored specimens (6.9 < pH < 7.1) restored the Bohr effect and improved the accuracy of standard p50 calculations (coefficient of variation = 4.4% and 2.9%), saturation-linked bias persisted. We conclude that Siggaard-Andersen p50 calculations may be misleading when there are disturbances of hemoglobin-oxygen affinity and acid-base balance, owing to changes in shape of the hemoglobin-dissociation curve. When metabolic acidosis occurs with high hemoglobin-oxygen affinity, as can occur in critical illness, indexes derived by the Siggaard-Andersen algorithm on arterial blood may greatly overestimate oxygen availability.

Acid-Base Imbalance↗

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↗