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Results for “Measuring algorithm”

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At least 397 records · Page 22Linked to original sources

PubMed1993

Ultrasonic measurements of breathing rate in rats and computer assisted analysis.

PURPOSE: An ultrasound breathing rate measurement technique and a computer analysis algorithm have been developed to reduce the amount of time needed to collect and analyze animal breathing rate data, as well as to improve the testing environment. The system is not airtight, therefore, acclimatization and collection time is not limited, and the technique makes use of a top loading apparatus to facilitate animal entry. METHODS AND MATERIALS: Breathing rate is measured using two ultrasound transducers housed directly above the rat thorax in the plexiglass jig. The breathing rate signal is stored and evaluated by computer. The ultrasound technique was tested using a loud speaker driven by a signal generator, over a range of 30 to 450 cycles/min. In addition, the ultrasonic breathing rate method was used to record the breathing rate response of Sprague Dawley rats, treated with graded single doses of radiation, over a period of 170 days. RESULTS: For the loud speaker tests, the measured frequency agreed with that of the input signal with a maximum deviation of 1%. For the animal irradiations, all breathing rate data were analyzed by both user and computer selection of regular breathing. The techniques gave the same results at the 95% confidence limit. Using the computer program to assess the traces, 240 breathing rates can be determined per hour, from previously measured data. CONCLUSION: A new technique for measuring breathing rate has been developed and enhances both the collection and analysis of data.

Algorithms↗

PubMed1996

[Detection of rapid eye movement with rapidly adapting neuronal fuzzy systems in imprecise REM syntax].

Both living beings and artificial neuronal networks are capable of 'learning' and behavioural adaptation. But also the fuzzy program designed to detect rapid eye movements (REM) during sleep and described here, can be provided with a self-learning option that provides important information about REM sleep. The algorithm computes REM on the basis of horizontal and vertical EOG. EEG, EMG and actiography signals are employed to optimize the method and eliminate artefacts. In a second step, the fuzzy system learns to detect REM with the aid of a sample data set and a minimal set of syntax rules. From sample data and the actions and reactions of visual scorers, the program extracts additional rules and information, which are then used to build a complete fuzzy structure. Thereafter, the REM detection program optimizes the fuzzy logic structure, independently of visual monitoring, on its own. A direct comparison of the results of the algorithm in a 10-night analysis with those of two experienced visual scorers revealed a better than 95% agreement. Re-analysis with the algorithm showed a 100% concurrence. Complete visual measurement of the eye movements occurring in a single night requires several hours; this compares with only 15 minutes required by the algorithm.

Algorithms↗

PubMed1983

A computerized timing algorithm for determination of pulmonary tissue volume.

We developed a computerized method to measure pulmonary tissue volume (Vt) and capillary blood flow (Qc) that requires only a single interface for measurement of a soluble and an insoluble gas. The method uses a timing algorithm that replaces either a marker gas (C18O) or a volume signal. Gas concentrations are stored in digitized form. The data analysis consists of three parts: 1) initial and end-tidal samples found by using minima and maxima; 2) a timing algorithm derived from the end-tidal dead space method (ETDS, J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 782-795, 1978); and 3) calculations of Vt and Qc, also by the ETDS method. Both the timing and Vt and Qc agree well with the hand-calculated values, but the coefficient of variation of Vt is slightly improved (6 vs. 7% manually). We conclude that our computerized method is equivalent to the manual ETDS method, but it is faster and more accurate; in addition, it has the advantage of requiring only one interface without the use of expensive gases.

Capillaries↗

PubMedDate not supplied

Recent advances in the estimation of population exposure to mobile source pollutants.

The U.S. Environmental Protection Agency (EPA) has developed several computer-based exposure models applicable to pollutants which are directly or indirectly linked to mobile sources. Probabilistic versions of the National Ambient Air Quality Standards (NAAQS) Exposure Model (pNEM) have been used to estimate the exposures of urban populations to carbon monoxide and ozone. An enhanced version of the Hazardous Air Pollutant Exposure Model (HAPEM-MS) has been used to develop city-specific estimates of exposure to benzene and other volatile organic compounds emitted by mobile sources. These models are similar in that each contains algorithms that simulate microenvironmental pollutant levels, time/activity patterns, and commuting patterns. The pNEM models also provide estimates of equivalent ventilation rate (EVR), defined as ventilation rate divided by body surface area. This paper summarizes the methods and results of selected research projects conducted since 1991 with the goal of improving pNEM, HAPEM-MS, and similar exposure models applicable to mobile source pollutants. The studies include: (1) the development of an improved algorithm for estimating EVR, (2) a field study to measure ozone levels near roadways and inside vehicles, (3) the development of an algorithm for estimating school commuting patterns, and (4) the construction of a comprehensive database containing time/activity data from ten activity diary studies.

Adult↗

PubMedDate not supplied

A useful algorithm for calculating central ray TAR and TMR values.

An algorithm utilizing a two-dimensional polynomial power functions least squares fit has been applied to the calculations of TAR in the case of CO-60 teletherapy and TMR in the case of an 8MV LS75/10 linear accelerator giving less than +/- 1/2% errors respectively between calculated and measured values. The TAR and TMR algorithms are used as subroutines in pocket sized and table top programmable calculators or computers and thus provide rapid calculation of treatment time or monitor units as well as given dose.

Cobalt Radioisotopes↗

PubMed1996

A new single-fibre laser Doppler flowmeter based on digital signal processing.

A new laser Doppler flowmeter, based on a personal computer with a digital signal processor for detecting the blood perfusion in skeletal muscle, was designed and evaluated. An infrared laser diode (750 nm) fed a single optical fibre, 400 microns in diameter, which was introduced into the muscle. A PC equipped with a digital processing unit was used for emulation of the laser Doppler algorithm and for presentation of the measurement results. The Doppler signal power spectral density and corresponding flow values were visualized on the computer screen continuously in real-time, and could also be saved on the hard disk for off-line analyses. The graphic-user interface supported by Labwindows software made the system easy to use. It is possible to alter in the software the signal processing and the ways in which the signals and results are presented. The new system was evaluated by using a flow model as well as a mechanical model. The model studies showed linear relationships between particle velocity and flow in the range of 0-5 mm s-1. The system was also tested in measurements of the blood flow in the brachioradial muscle, and was found to have advantages over our previously used systems.

Algorithms↗

PubMed1994

Quantification of global and regional renal blood flow with electron beam computed tomography.

Alterations in renal blood flow distribution may occur in a variety of pathophysiologic situations; however, quantification of global and regional renal blood flows has been limited because of the lack of reliable, noninvasive techniques. To determine the feasibility of flow measurements with electron-beam computed tomography (EBCT), six anesthetized dogs were scanned by EBCT during basal conditions, after renal vasodilation, and at recovery. Flow (mL/min/cm3 tissue) was calculated from EBCT-derived time-density curves using three different algorithms and compared with simultaneously obtained electromagnetic flow (EMF) probe measurements after indexing to EBCT-derived renal volume. EBCT-determined flow correlated well with EMF measurements regardless of the algorithm used. An algorithm using the area under the time-density curve was concluded to be the most suitable for calculation of renal blood flow; it correlated with EMF as EBCT flow = 44.5 + 1.05 EMF (r = 0.885, SEE = 31.2 mL/min, P < .0001). Consistent overestimation of flow by EBCT resulted probably from retention of contrast media in the renal parenchyma. EMF showed an increase of 20 +/- 10% in renal blood flow after vasodilation. EBCT-derived global, cortical, and medullary flows increased by 33.8 +/- 10.3%, 24.8 +/- 17.8%, and 99.0 +/- 73.8%, respectively. In conclusion, EBCT was found feasible for credible quantitation of renal blood flow in the physiologic range studied.

Algorithms↗

PubMed1994

Accelerated learning by active example selection.

Much previous work on training multilayer neural networks has attempted to speed up the backpropagation algorithm using more sophisticated weight modification rules, whereby all the given training examples are used in a random or predetermined sequence. In this paper we investigate an alternative approach in which the learning proceeds on an increasing number of selected training examples, starting with a small training set. We derive a measure of criticality of examples and present an incremental learning algorithm that uses this measure to select a critical subset of given examples for solving the particular task. Our experimental results suggest that the method can significantly improve training speed and generalization performance in many real applications of neural networks. This method can be used in conjunction with other variations of gradient descent algorithms.

Algorithms↗

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↗

PubMed1983

[Concept of the mean stopping power and the mean electron energy in electron dosimetry].

In consideration of the variations of the values E,Er,EH and Ew of the energy spectrum of electrons at the measuring point in case of a given energy on the surface Eo and in the depth t of a phantom with a low Z-number, the authors present the practical realisation of a conception allowing to determine by one single conversion curve Sw,1 (Er) the energy-dose of rapid electrons in water Dw, at least within the spectrum of Eo = 5 to 42 MeV and Er = 2.2 to 42 MeV, from the cavity ion dose Jc measured absolutely or by means of a calibrated electron chamber. Sw,1 (Er) is the relative unrestricted mass collision stopping power as a function of the mean rest energy Er at the measuring point. Er can be calculated in a simple manner from Eo and t and coincides almost perfectly with the most probable energy Ew of measured electron spectra. The authors present an algorithm for the calculation of the true mean electron energy E from Eo and t with a good coincidence with the values of measured electron spectra. It is shown that, contrary to the curve with one parameter Sw,1 (Er), a relation of Sw,1 to E leads to a series of curves with two parameters Sw,1 (Eo, t). The method using a relation of Sw,1 to Er which offers the advantage of a simple practical application and good precision is presented as "conception of the mean stopping power in electron dosimetry".

Electrons↗

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↗

PubMedDate not supplied

MR quantification of cerebral ventricular volume using a semiautomated algorithm.

PURPOSE: A semiautomated border identification algorithm, insensitive to user bias, is evaluated for accuracy and speed in the measurement of ventricular volumes from three-dimensional MR images. METHODS: A three-dimensional gradient-echo technique was implemented on a Signa clinical imaging system. Data from phantoms and patients were analyzed for volume using a segmentation algorithm designed with: 1) correction for partial volume averaging; 2) insensitivity to user bias; and 3) speed. Accuracy, precision, and intra- and interobserver variability were determined. RESULTS: Average error for phantom studies was 4% to 6%, or 1 to 2 cc across the volumes, which ranged from normal to mild hydrocephalus (< 60 cc). Patient studies showed intra- and interobserver error of 2.3% and 7.8%, respectively. The correction for partial volume averaging resulted in a threefold decrease in error. Data were acquired and reconstructed within 7 minutes. Experienced radiologists required less than 15 minutes to perform each analysis. CONCLUSIONS: This algorithm allows accurate measurement of ventricular volumes in an efficient, minimally supervised manner.

Adult↗

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↗

PubMed1997

A simple electrocardiographic algorithm for detecting ventricular tachycardia.

The purpose of this study was to determine whether a simple ECG algorithm could be developed for predicting susceptibility to ventricular tachyarrhythmias (VT) as defined by sustained spontaneous or inducible VT. Two different QT dispersion algorithms were determined by the difference between the longest and shortest QT interval measured in three orthogonal leads (I, aVF, V1; QTD3), and at least 11 of 12 leads (QTD12) from the 12-lead ECG. These QT dispersion algorithms were investigated (with and without the QRS duration from the 12-lead ECG) and compared to the signal-averaged ECG (SAECG) in order to determine their sensitivity and specificity for detecting VT. Only patients who underwent SAECG and were referred for programmed electrical stimulation were included in this study. A positive SAECG was defined by filtered QRS duration > 114 ms, and/or low amplitude signal duration > 38 ms, and/or root mean square voltage in the last 40 ms of < 20 microV. Sixty patients were enrolled in this study with a mean age of 63 +/- 2 years. Fifty-five percent of the patients had coronary artery disease. A simple ECG algorithm consisting of the sum of QTD3 plus the QRS duration had a sensitivity and specificity of 90% and 63%, respectively, wheras the SAECG had a sensitivity and specificity of 60% and 63%, respectively (P = 0.022). We conclude that a simple ECG algorithm is more sensitive than the SAECG for predicting VT. This algorithm combines two easily measured variables obtained from the 12-lead ECG, and can easily be performed without expensive computer equipment.

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↗