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Results for “Measuring algorithm”

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At least 181 records · Page 10Linked to original sources

PubMed1990

A modified algorithm of the single pool urea kinetic model.

Urea Kt/V, calculated according to the variable volume single pool urea kinetic model (UKM), has been accepted as the yardstick reflecting the adequacy of haemodialysis therapy. However, the classical algorithm of UKM requires great care in dialyser urea clearance (K) measurement in order to avoid major inaccuracies in estimating the urea distribution volume (V). Thus, we suggest a modified algorithm of UKM which avoids the measurement of K. It assumes an arbitrary V value and then calculates kinetically K as a function of the assumed V value. The rationale of the modified algorithm can be derived from the knowledge that the classical algorithm imposes a proportionality ration between K and V: given a particular set of data, a change in the attributed value of K leads to a proportional change in the calculated V value, so that the ratio K/V remains nearly constant. Aims of the study were (1) to validate the modified algorithm by comparing the resulting Kt/V and normalised protein catabolic rate (NPCR) values with the homologous ones obtained using the classical algorithm in a group of 33 patients on thrice-weekly haemodialysis; plasma water urea concentrations were used with the classical algorithm (CApw) and the modified algorithm (MApw); and (2) to verify the possibility of using plasma urea concentrations with the modified algorithm (MAp) instead of the more rigorous plasma water concentrations. NPCR (g/kg per day) was 1.33 +/- 0.05 in CApw, 1.29 +/- 0.05 in MApw and 1.28 +/- 0.04 in MAp. Kt/V was 1.27 +/- 0.03 in CApw, 1.25 +/- 0.03 in MApw and 1.26 +/- 0.03 in MAp.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMedDate not supplied

A restricted angular scattering model for electron penetration in dense media.

A restricted angular scattering model for electron penetration in dense media is presented. In the model, the Fermi-Eyges transport equation is modified through the addition of an extra term which may be interpreted as representing an apparent force opposing the scattering of electrons into wider angles. The introduction of this extra term allows the modeling of the measured saturation in the mean square angular spread of electrons with depth. The restricted scattering model retains the Gaussian features of the Fermi-Eyges model and, therefore, may be readily incorporated into existing dose computation algorithms. Good agreement is obtained with measured angular electron distribution data for a point monodirectional beam over a wide range of incident electron energies (5-20 MeV) and scattering media (atomic numbers of 6 to 82). Also, a comparison of the restricted scattering model predictions with measurements of the lateral pencil beam spread shows an improvement over the predictions of Fermi-Eyges model close to the end of the electron range. Broad beam profiles were generated using both the Fermi-Eyges and restricted scattering models. A comparison of predicted and measured beam profiles shows that the restricted scattering model is a significant improvement over the Fermi-Eyges model for the prediction of beam penumbra shape in homogeneous media.

Aluminum↗

PubMed1991

Estimation of time-varying respiratory mechanical parameters by recursive least squares.

Continuous estimation of time-varying respiratory mechanical parameters is required to fully characterize the time course of bronchoconstriction. To achieve such estimation, we developed an estimator that uses the recursive linear least-squares algorithm to fit the equation Ptr = RV + EV + K to measurements of tracheal pressure (Ptr) and flow (V). The volume (V) is obtained by numerical integration of V. The estimator has a finite memory with length into the past at each point in time that varies inversely with the difference between the current measurement of Ptr and that predicted by the model, to allow the algorithm to track rapidly varying parameters (R, E, and K). V usually exhibits significant drift and must be corrected. Of the several correction methods investigated, subtraction of the recursively weighted average of V before integration to V was found to perform best. The estimator was tested on simulated noisy data where it successfully followed a fivefold increase in R and a twofold increase in E occurring over 10 s. Three dogs and two cats were anesthetized, paralyzed, tracheostomized, and challenged with a bolus of methacholine (approximately 13 mg/kg iv). Increases of 3- to 10-fold were observed in R and 2- to 3-fold in E, beginning within 10-40 s after the bolus injection. In some animals we found that the increase in E occurred more slowly than that in R, which the V signal suggested was due to dynamic hyperinflation of the lungs. These results demonstrate that our recursive estimator is able to track rapid changes in respiratory mechanical parameters during bronchoconstrictor challenge.

Airway Resistance↗

PubMed1986

Optimal detection of the progression of coronary artery disease: comparison of methods suitable for risk factor intervention trials.

To assess the best method of quantitating progression of coronary disease, we studied four measurements in 114 coronary segments from 35 medically treated patients from whom angiograms were obtained 5 years apart. Only stenoses of less than 70% that were visualized in nearly identical projections on both angiograms were evaluated. Vessel edges were measured by use of catheter calibration and an automated computer algorithm yielding two "absolute dimensions" (mean and minimum diameters) and two measurements (percent stenosis and atheroma area) that required a "normal reference" diameter. The coefficient of variation for repeated segment measurements was less for mean and minimum diameter than for percent stenosis and area of atheroma. The best measure of progression of coronary disease as determined by t test comparison of different methods was the change in mean diameter over time (6.7 +/- 14.1% decrease), whether calculated on a per coronary segment or per patient basis (p less than .001). Based on this measurement and its standard deviation of progression of coronary disease in this patient subset with relatively benign disease, it is estimated that 470 patients per group would be required for an interventional study to demonstrate a 33% reduction in disease progression (207 patients for 50% reduction) at a 95% confidence level and 90% power.

Cardiac Catheterization↗

PubMed1990

Comparative analysis of arterial oxygen saturations during exercise by pulse oximetry, photometric measurements, and calculation procedures.

Pulse oximetry allows non-invasive monitoring of arterial oxygen saturation (SO2). To study the validity of pulse oximetry, comparative measurements were performed. During exhaustion limited exercise SO2-values measured by pulse oximetry (SO2puls), calculated SO2-values (algorithms of Kelman, Severinghaus, and Siggaard-Andersen--SO2calc), and as "golden standard" photometric measured SO2-values (SO2meas) were compared. Fourteen triathletes performed a stepwise cycling exercise test in the supine position. SO2calc was determined on the basis of capillary actual blood gas values. SO2puls was measured continuously with a finger probe attached to the second finger. The SO2puls- and SO2calc-values differed from the SO2meas-values (p less than 0.05); however, the differences were of no clinical relevance. Performing linear regression analysis, only SO2puls correlated significantly (r = 0.47, p less than 0.001) with SO2meas. Pulse oximetry is able to replace invasive measurements of arterial oxygen saturation in athletes. It is superior to SO2-calculations and permits reliable, valid and non-invasive continuous monitoring of SO2.

Adult↗

PubMedDate not supplied

Response force titration for the assessment of the neuromuscular toxicity of 2,5-hexanedione in rats.

A silent, non-moving glass lever combined with strain gauges and mounted in an operant chamber measured the vertical isometric force exerted by the forepaw of rats. Every weekday the rats were subjected to a force titration schedule consisting of a sequence of discrete trials signalled by a lever light. The required force, above which a water reinforcement is delivered, was regulated by a generalized bisection algorithm. A stable force level which the rat was able to attain at 50% of the trials was quickly reached in each session by this algorithm. This technique was used to measure the neuromuscular performance decrement due to repeated 2,5-hexanedione treatment (250 and 500 mg/kg/day per os). The results were compared with fore- and hindlimb grip strength measurements on the same animals. This experiment showed that the force titration technique is able to distinguish between motivational and true force decrements, a distinction which cannot be made by the grip strength technique.

Analysis of Variance↗

PubMed1987

An algorithmic approach to diagnosis of hypoglycemia.

An algorithm has been devised to facilitate the diagnostic approach to the causes of hypoglycemia. This systematic approach enables the physician to reach the final diagnosis in a logical way without subjecting the child to unnecessary and possibly hazardous investigations. The algorithm is based on the following measurements as required by each patient: concentrations of blood glucose, lactate, ketone bodies, and glucose-regulating hormones. These measurements are performed with the patient in the fasting state and after loading tests (glycerol and galactose) as needed. If indicated, an enzymatic test is performed to establish the final diagnosis. Eighteen children aged 1 month to 7 years who had persistent or recurrent hypoglycemia have been examined according to this algorithm. The correct diagnosis was arrived at in 17 patients. The diagnosis was not reached in one neonate who had glucose-6-phosphatase deficiency and initially did not have lactic acidosis; once lactic acidosis developed, his illness fitted perfectly into the algorithm.

Algorithms↗

PubMed1992

Accuracy and precision of the CellForm-Human automated sperm morphometry instrument.

OBJECTIVE: To evaluate the accuracy and precision of the CellForm-Human (CFH) automated sperm morphometry instrument (Motion Analysis Corp., Santa Rosa, CA). SETTING: Clinical and research andrology and in vitro fertilization laboratories. PATIENTS: Individuals undergoing semen evaluation and infertility work-up. RESULTS: Coefficients of variation for repeated measures of the same sperm were 1%. Coefficients of variation of normal sperm measurements were 7.4% to 12.8%, depending on the measure. Of the objects recognized as sperm by the instrument, 6.8% were debris; hence, the sperm recognition algorithms need improvement. Mean values for all CFH measures of normal sperm from specimens clinically classified as having predominantly normal, tapered, or amorphous sperm were not different; hence, the morphometry of normal sperm from normal specimens was similar to normal sperm from specimens with two different abnormalities. The instrument classified sperm as abnormal if their length or width fell outside a critical range of values recommended by the World Health Organization. Using this method, manual and CFH classification agreed unambiguously 60% of the time. When disagreement occurred, length or width marginally exceeded the range by no more than 0.1 microns. In these cases, the technician classified sperm as normal 25% of the time and classified them as abnormal 6% of the time. Because this disagreement between methods is well below the resolution of manual methods, the overall accuracy of CFH was 91% for cell type classification. CONCLUSION: At its present stage of development, the CFH instrument exceeds the accuracy and precision of most manual approaches. With improvements in sperm recognition and type classification algorithms, it could significantly improve the reliability of morphology assays in clinical and research laboratories.

Equipment Design↗

PubMed1989

Peak flow records in asthma: evaluation of an algorithm for interpretation of patterns.

The clinical value of serial measurements of peak expiratory flow (PEF) in asthma is well established, but the analysis of the PEF records is not standardized. We developed an algorithm for interpretation of PEF, based upon the characteristic features of chronic airflow limitation, and retrospectively analysed the PEF of fifty outpatients affected by non-seasonal asthma. For each patient we correlated the developed indices of evolution of PEF with, respectively, the severity of asthma (evaluated in terms of consumption of drugs), forced expiratory volume in one second and with the trend of the indices over several months. The developed indices were well correlated with the severity score and to a lesser extent to other investigated parameters. These results seem to provide a useful approach to a computerized evaluation of the results of PEF monitoring.

Adolescent↗

PubMed1991

Measurements of ultrasonic fields with optical diffraction tomography.

This article describes a light diffraction technique that allows a measurement of ultrasonic pressure and phase in the cross-section of an ultrasonic beam. The light diffraction measurements are based on the Raman-Nath model of ultrasonic continuous-wave light diffraction. The diffracted light intensity can be expressed as an integration of sound pressure along the light path. This integration is analogous to the integration of the absorption coefficient in x-ray tomography. Tomography algorithms can be employed on the light measurement data to calculate the pressure and phase in a measuring plane perpendicular to the ultrasound propagation vector. The reconstruction of the measurement plane is done with an implementation of an algebraic reconstruction technique (ART). Satisfactory results are obtained with 10 projections. The measurement method is applicable up to Raman-Nath parameter values of 2.3. The experimental results are compared to miniature PVDF hydrophone measurements.

Algorithms↗

PubMedDate not supplied

Echocardiographic design of a multicenter investigation of free-living elderly subjects: the Cardiovascular Health Study.

The Framingham study has shown by M-mode echocardiography that left ventricular hypertrophy is a powerful, independent predictor for the development of coronary heart disease and that increased left atrial dimension has been associated with an increased risk of stroke. No previous population-based study has evaluated the risk factor correlates and predictive value for coronary heart disease and stroke of two-dimensional and Doppler, as well as M-mode, echocardiography. The Cardiovascular Health Study is a multi-year prospective epidemiologic study of 5201 men and women older than 65 recruited from four geographic sites in the United States. The main objectives of incorporating echocardiography were to determine whether echocardiographic indices, or changes in these indices, are (1) correlated with traditional risk factors for coronary heart disease and stroke; and (2) independent predictors of morbidity and mortality for coronary heart disease and stroke. Echocardiographic measurements of interest include those related to global and segmental left ventricular systolic and diastolic structure and function and left atrial size. For each subject, a baseline echocardiogram was recorded in super-VHS tape using a standard protocol and equipment. All studies were sent to a reading center where images were digitized and measurements were made using customized computer algorithms. Calculated data and images were stored on optical disks to facilitate retrieval and future comparisons in longitudinal studies. A second echocardiogram is scheduled in year 7, with a goal of determining whether changes in cardiac anatomy or function over a 5-year period are important predictors of morbidity or mortality from coronary heart disease and stroke. Quality control measures included standardized training of echocardiography technicians and readers, technician observation by a trained echocardiographer, periodic blind duplicate readings with reader review sessions, phantom studies, and quality control adults.

Allied Health Personnel↗

PubMedDate not supplied

3D PET using a conventional multislice tomograph without septa.

A conventional multislice positron emission tomography scanner was modified to operate without interplane septa to evaluate its performance in collecting and reconstructing data in a three-dimensional (3D) format, thereby significantly increasing system sensitivity. A 3D filtered backprojection algorithm was implemented and tested, using both computer simulations and phantom measurements. No artifacts were apparent in the test images, although the algorithm was shown to lead to a 11% degradation in transaxial resolution in the outer planes. Following septa removal, sensitivity was found to increase by a factor of 7 with an increase in scatter fraction from 16 to 41%. Axial resolution degraded from 6.9 to 7.7 mm full width at half maximum at the center of the field of view. The maximum count rate without septa was 2.4 x 10(5) cps, at a concentration of 0.4 microCi/ml, compared with 1.3 x 10(5) cps at 1.5 microCi/ml with septa. Brain studies were performed with volunteers using 18F-fluorodeoxyglucose, 18F-fluorodopa, and H2 15O to compare noise-equivalent count rates and qualitatively assess image quality over a wide range of imaging conditions.

Algorithms↗

PubMedDate not supplied

A geometric algorithm for medical image correlations.

An automatic image correlation algorithm is discussed for the cranial region which is based on the geometric properties of the second moment tensor associated with a volume. The second moment tensor of two identical volumes represented in two different coordinate frames is evaluated to obtain the set of translations, rotations, and anisotropic scaling operators which relate the two coordinate frames. The theory is presented along with a discussion of quantitative error analysis to measure the usefulness of such an algorithm in the clinical setting.

Algorithms↗

PubMed1990

Image analysis techniques for automatic evaluation of two-dimensional electrophoresis.

Techniques for automatic analysis of two-dimensional electrophoresis gels by computer-aided image analysis are described. Original gels or photographic films are scanned using a laser scanner and the files are transferred to a microcomputer. The program package first performs a compression and preevaluation of the files. Spot identification and quantification is performed by the chain code algorithm after appropriate zooming and cutting. Labeling facilitates spot identification and quantification in numerical and graphical (pseudocolor) representation on peripheral devices for camera ready output. Interpolation between measured basepoints is performed by cubic spline algorithms which are automatically switched on and off, depending on the need by the program. High speed analysis and graphic representation is achieved using fast Assembler language routines rather than high level languages. One-dimensional gels can be analyzed using the same software. Spot matching between parallel two-dimensional gels has not yet been implemented.

Electrophoresis, Gel, Two-Dimensional↗

PubMed1989

Principles of morphometric grading.

Grading of the severity of lesions has increased in importance in histopathology. The simplest grading system has 2 grades. If there is variation in the measuring system, the grading will not be perfect, and there are also misgraded samples. We estimated the fraction of falsely graded cases by applying th NAG (Numerical Algorithm Group) Fortran Library. If all possible measurement values are equally probable the grades based on measurements within +/- 1 SD around the division line are false in 31.6% of cases. The corresponding figures for regions +/- 2 SD, +/- 3 SD, 1 to 2 SD, 1 to 3 SD, and 2 to 3 SD are 19.6, 13.3, 7.5, 4.2, and 0.8%, respectively. Detailed calculations were made which allowed accurate determination of the probability of a grade being false in different positions of the measurement scale. The results suggest that for diagnostic grading a borderline region should be defined (e.g. +/- 2 SD or +/- 3 SD around the division line).

Diagnostic Errors↗

PubMed1988

Jitter correction: a computer algorithm for reduction of the velocity recovery function artifact.

The measurement of neuromuscular jitter in single fiber electromyography may be artifactually raised by a component of interdischarge interval (IDI)-dependent jitter caused by the velocity recovery function (VRF) in muscle fibers. We have developed a computer algorithm for on-line mathematical correction for this artifact, thus improving the reliability of neuromuscular jitter estimates. The method, based on a modeling technique, was validated using intramuscular stimulation in order to either exclude an IDI-dependent component (using regular stimulation) or to include an IDI-dependent component (using pseudorandom stimulation). In 10 normal subjects the distribution of 106 corrected jitter values obtained using voluntary activity showed no difference from the measured values. This finding implies that previously published values for normal jitter are not likely to have been influenced by the VRF effect.

Action Potentials↗

PubMed1992

A new algorithm for the identification of multiple input Wiener systems.

Multiple-input Wiener systems consist of two or more linear dynamic elements, whose outputs are transformed by a multiple-input static non-linearity. Korenberg (1985) demonstrated that the linear elements of these systems can be estimated using either a first order input-output cross-covariance or a slice of the second, or higher, order input-output cross-covariance function. Korenberg's work used a multiple input LNL structure, in which the output of the static nonlinearity was then filtered by a linear dynamic system. In this paper we show that by restricting our study to the slightly simpler Wiener structure, it is possible to improve the linear subsystem estimates obtained from the measured cross-covariance functions. Three algorithms, which taken together can identify any multiple-input Wiener system, have been developed. We present the theory underlying these algorithms and detail their implementation. Simulation results are then presented which demonstrate that the algorithms are robust in the presence of output noise, and provide good estimates of the system dynamics under a wide set of conditions.

Algorithms↗

PubMed1990

Real-time tracking of parameters of lung mechanics: emphasis on algorithm tuning.

We consider the problem of tracking rapid changes in the viscous and elastic properties of the respiratory system by using mouth flow and transpulmonary pressure data measured during mechanical ventilation. A recursive least-squares algorithm with adjustable compensator is used for online estimation of an R-C model of the breathing mechanics. Specific simulation experiments are presented to provide guidelines to select suitable values for the key variable, which controls the compromise between tracking ability and noise sensitivity. The results obtained confirm the critical role of the optimum tuning in relation to the noise level. Experimental results obtained from data measured on mechanically-ventilated dogs, in which respiratory distress syndrome was intravenously induced by oleic acid, demonstrate that the tuned algorithm is able to track appropriately both the viscous and elastic properties of lung mechanics. Parameter estimates are consistent with those obtained by standard and robust offline algorithms and their time course is in qualitative agreement with known physiopathological behaviour.

Airway Resistance↗