SEARCH · PubMed Health

Results for “Measuring algorithm”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources

PubMed1988

Variceal hemorrhage.

Figure 2 is the algorithm followed in our institution for management of acute variceal hemorrhage. A small percentage of patients who present with active variceal hemorrhage will stop bleeding after gastric lavage alone. However, most patients require an intravenous vasopressin infusion at a dose of 0.4 units per minute, preferably combined with intravenous administration of nitroglycerin. Although glypressin and somatostatin may be associated with fewer side effects than vasopressin, the superiority of these drugs remains to be determined. Whether pharmacologic therapy succeeds or fails, most patients then proceed to endoscopic sclerotherapy. Sclerotherapy may be used as a temporizing measure in preparation for elective surgery or as a long-term, definitive treatment for prevention of recurrent hemorrhage. Balloon tamponade is reserved for patients who are bleeding too rapidly for effective sclerotherapy and for sclerotherapy failures in preparation for emergency surgery. Because recurrent hemorrhage frequently occurs after balloon deflation, a more definitive treatment (surgery or endoscopic sclerotherapy) should be planned for all patients who undergo balloon tamponade. Because operative risk is unacceptably high for patients with hepatic functional decompensation secondary to variceal hemorrhage, we believe that a policy of routine emergency surgery is unwise. Rather, emergency surgical intervention is reserved for the relatively small number of patients (15 to 25 per cent) who continue to bleed after nonoperative options have failed. Shunt surgery should be considered early in the course of patients with bleeding secondary to gastric varices and portal hypertensive gastropathy, both of which respond poorly to nonoperative measures.

Algorithms↗

PubMed1992

In vivo dosimetry during pelvic treatment.

High precision in vivo entrance and exit dose measurements have been performed with p-type diodes on patients during 8 MV X-ray irradiation of the pelvis, to investigate the accuracy of dose calculations in this region. Based on phantom measurements the accuracy of the p-type diode measuring system itself, i.e. the agreement with ionisation chamber dose measurements, was shown to be better than 0.7% while the reproducibility in the dose determination was 1.1%, 1.5% and 1.6% (1 S.D.) at the entrance point, isocentre and exit point, respectively, for the wedged lateral fields. Patient movement and the uncertainty in the diode position increased these values to 1.7%, 1.5% and 3.1% (1 S.D.) for dose determinations on patients. From the entrance and exit in vivo dose values the dose actually delivered to the isocentre was determined. For the anterior-posterior beams a good correspondence for most patients was observed at the entrance and exit point and at the isocentre between the in vivo and calculated dose values. For the wedged lateral beams a systematic deviation of about 3% was observed. In addition to the in vivo dose measurements phantom dose measurements have been performed to quantify the accuracy of the dose calculation algorithms including the computation of the number of monitor units. These measurements also served to quantify the effects of the actual patient on the dose delivery. The measurements showed that accurate calculation of the dose requires a separation of the head and phantom scatter contribution of the output of the treatment machine. The dependence of the wedge factor on field size, depth and source-skin-distance has also to be considered for accurate dose calculations. The effect of the patient on the dose calculation is mainly related to the actual electron densities of fat and bone structures compared to water: neglecting these densities in the dose computation could yield deviations up to 8.5% for the exit point in wedged beams. Based on these results, improvements in the dose calculation algorithms and monitor unit calculation including the use of the actual electron densities will be implemented in the treatment planning procedure.

Algorithms↗

PubMed1995

Effects of solutes on optical properties of biological materials: models, cells, and tissues.

Perturbations of scattering background for absorbance measurements by photon diffusion techniques complicate algorithms used for determining the concentration of blood and the saturation of hemoglobin in tissues. In order to better define these perturbations, we have undertaken a study of the effect of solutes, some of physiological importance, upon the scattering of three types of model systems: a lipid vessel suspension (Intralipid), a cell suspension (Baker's yeast), and a tissue (perfused liver). A simple formula relates absorbancy change to proportional changes of the input/output separation rho and the square root of mu a and mu's in relation to a relevant model system. Thus, absorbance changes at 850 nm slopes and intercepts are measured as a function of rho; the absorption and reduced scattering coefficient, mu a and mu's, are calculated. We studied each of these cases as a function of the perturbation induced by low-molecular-weight polyhydroxy solutes, generally sugars (mannitol, fructose, sucrose, and glucose), alcohols (propanediol and methanol), and electrolytes (sodium and potassium chloride). Dilatometric studies indicate volume changes of the solvent system and afford correction factors. The slopes are approximately +/- 0.5 x 10(-4) OD/mM solute per centimeter separation of input/output per percent scatter (yeast or Intralipid) and indicate possible physiological detection of solutes in tissues in the millimolar range. The large optical effects of temperature upon the solute effect on model systems and of osmotic and perfusion pressures on the perfused liver further complicate the possibility of quantitative in vivo studies of these solutes.

Animals↗

PubMed1989

A reliable potentiometric measurement of ionized calcium and pH on the ICA2 Radiometer in clinical practice.

A second generation analyser for potentiometric measurement of ionized calcium and pH (ICA2 Radiometer, Copenhagen) was tested with respect to analytical performance in two different laboratories. Newly-developed aqueous buffered solutions were used at different Ca2+ concentrations as well as biological specimens prepared from human subjects. The overall precision of ICA2 was very good: CV = 0.0-0.4% for within-run and 0.4-1.7% for day-to-day precision with protein-free solutions and CV = 0.3-0.9% for within-run precision on biological specimens. The adjusted value of Ca2+ to pH 7.40 is an analytical advantage for which the calculation is correct but the assumption made for this algorithm may limit its clinical relevance. Measurements were comparable on ICA2 when performed on either whole blood, serum or plasma. Pre-analytical conditions should be observed such as the choice of anticoagulant and anaerobic conditions. Such a reliable and accurate instrument may promote the use of ionized calcium measurement in daily clinical practice.

Calcium↗

PubMed1984

Diffraction tomography using arbitrary transmitter and receiver surfaces.

The theory of diffraction tomography for two-dimensional objects within the Born approximation is presented for cases where the scattered field is measured over arbitrarily shaped boundaries surrounding the object. Reconstruction algorithms are presented for both plane wave (parallel beam) and cylindrical wave (fan beam) insonification. Special attention is devoted to cases where the measurement and source boundaries are either lines or circles. The theory and algorithms presented are shown to be readily extended to the case of three-dimensional objects.

Filtration↗

PubMed1994

The choice of approach in surgery for acoustic neuromas (vestibular schwannomas).

The advantages and disadvantages of the different surgical approaches for surgery of vestibular schwannomas are described, as well as the problems in evaluating the outcome of the treatment, regarding especially the evaluation of facial nerve function and hearing capacity. The eclectic Copenhagen treatment algorithm is outlined: 1) All tumors measuring 25 mm or more on MRI are operated via the translabyrinthine approach. 2) All patients with PTA poorer than 30 dB, and SDS poorer than 70% are operated via the translabyrinthine approach. 3) Tumors less than 10mm extrameatally, and PTA better than 30 dB and SDS better than 70% are removed via the middle fossa route. 4) Tumors measuring 10-25 mm and PTA better than 30 dB and SDS better than 70% are operated via the suboccipital route. Finally some consequences of postponing surgical treatment is described, demonstrating that 74% of 127 tumors continued to grow with a mean of 3.4 mm increased tumor diameter per year, and that 75% of patients, who were candidates for hearing preservation surgery lost the candidature in the observation period.

Algorithms↗

PubMed1988

DESIGN: computerized optimization of experimental design for estimating Kd and Bmax in ligand binding experiments. I. Homologous and heterologous binding to one or two classes of sites.

We have developed a versatile computer program for optimization of ligand binding experiments (e.g., radioreceptor assay system for hormones, drugs, etc.). This optimization algorithm is based on an overall measure of precision of the parameter estimates (D-optimality). The program DESIGN uses an exact mathematical model of the equilibrium ligand binding system with up to two ligands binding to any number of classes of binding sites. The program produces a minimal list of the optimal ligand concentrations for use in the binding experiment. This potentially reduces the time and cost necessary to perform a binding experiment. The program allows comparison of any proposed experimental design with the D-optimal design or with assay protocols in current use. The level of nonspecific binding is regarded as an unknown parameter of the system, along with the affinity constant (Kd) and binding capacity (Bmax). Selected parameters can be fixed at constant values and thereby excluded from the optimization algorithm. Emphasis may be placed on improving the precision of a single parameter or on improving the precision of all the parameters simultaneously. We present optimal designs for several of the more commonly used assay protocols (saturation binding with a single labeled ligand, competition or displacement curve, one or two classes of binding sites), and evaluate the robustness of these designs to changes in parameter values of the underlying models. We also derive the theoretical D-optimal design for the saturation binding experiment with a homogeneous receptor class.

Binding Sites↗

PubMed1983

Automated radioautographic grain counting. Correction for grain overlap.

An algorithm is described for the calculation of radioautographic cell grain count from measurements of total cell nuclear area and total grain area. This algorithm provides a statistical correction for grain overlap that is based on the solution to the occupancy problem in probability theory. This method permits the use of automated grain counting over a wide range of grain counts per cell, and extends the useful dynamic range of radioautographic grain counting to well over 200 grains/cell.

Autoradiography↗

PubMed1989

Tracking time-varying properties of the systemic vascular bed.

The problem of tracking changes in viscoelastic properties of the systemic arterial bed is considered and a recursive estimation procedure, belonging to the class of output-error algorithms with adjustable compensator, is developed and discussed. By means of computer simulations, suitable values are determined for the key design variable which controls the tradeoff between tracking ability and noise sensitivity of the algorithm. In this way, the algorithm allows on-line estimation of arterial compliance, peripheral resistance, and characteristic impedance on the basis of aortic pressure and flow signals. Furthermore, the results obtained from data numerically simulated, as well as measured on a mock circulatory system, demonstrate that the dominant arterial time-constant can be tracked by the algorithm using only measurements of the aortic pressure during diastole.

Algorithms↗

PubMed1992

6R instrumented spatial linkages for anatomical joint motion measurement--Part 2: Calibration.

The six-revolute-joint instrumented spatial linkage (6R ISL) is often the measurement system of choice for monitoring motion of anatomical joints. However, due to tolerances of the linkage parameters, the system may not be as accurate as desired. A calibration algorithm and associated calibration device have been developed to refine the initial measurements of the ISL's mechanical and electrical parameters so that the measurement of six-degree-of-freedom motion will be most accurate within the workspace of the anatomical joint. The algorithm adjusts the magnitudes of selected linkage parameters to reduce the squared differences between the six known and calculated anatomical position parameters at all the calibration positions. Weighting is permitted so as to obtain a linkage parameter set that is specialized for measuring certain anatomical position parameters. Output of the algorithm includes estimates of the measuring system accuracy. For a particular knee-motion-measuring ISL and calibration device, several interdependent design parameter relationships have been identified. These interdependent relationships are due to the configuration of the ISL and calibration device, the number of calibration positions, and the limited resolution of the devices that monitor the position of the linkage joints. It is shown that if interdependence is not eliminated, then the resulting ISL parameter set will not be accurate in measuring motion outside of the calibration positions, even though these positions are within the ISL workspace.

Algorithms↗

PubMedDate not supplied

A maximum likelihood method for region-of-interest evaluation in emission tomography.

A maximum likelihood (ML) estimation method, called the ML-ROI algorithm, is presented for the calculation of region-of-interest (ROI) values from emission tomography scans. The EM algorithm is used to directly estimate ROI values from tomographic projection data given the location, size, and shape of all ROIs. The algorithm requires for the specification of a detailed model of the physical factors contributing to projection measurements including resolution and attenuation. The ML-ROI algorithm also provides an estimate of the variability of the ROI estimator (covariance matrix). The algorithm was tested with simulation and phantom data and compared with ROI estimation strategies using filtered backprojection (FBP) images. The ML-ROI estimates were unbiased, i.e., the partial volume effect was eliminated. Except for regions smaller than the detector resolution, the variability of the ML estimates was comparable to or less than the biased FBP estimators. Computation time for the ML-ROI algorithm was between 5 and 10 s/iteration. An evaluation of the sensitivity of the algorithm to misdefinition of the location and size of the ROIs was also performed.

Humans↗

PubMed1994

Sonographic evaluation of gallstone burden in humans.

A prospective blind study was performed to compare sonographic with postoperative findings of gallstone burden in 34 patients (10 males, 24 females; mean age 52 years). Gallstone size was assessed in single calculi (n = 15) by measuring the largest diameter by ultrasonography (US). The ellipsoid algorithm was used to estimate US volume for both single and multiple gallstones. After cholecystectomy, diameters were measured in single stones; stone volume was assessed by the ellipsoid formula (single stones) and fluid displacement (single and multiple stones). Stone volumes assessed by the ellipsoid formula and fluid displacement correlated closely (r = 0.98; p < 0.0001, n = 15). In the case of single gallstones, the mean length assessed by US was 25.3 +/- 3.2 mm and compared well with the value measured "in vitro" (24.8 +/- 3.1 mm). A highly significant and positive relationship existed between the sonographic size and the true stone size (r = 0.93; p < 0.0001, n = 15). Stone volumes assessed "in vivo" and by fluid displacement were comparable and correlated for both single (US: 6.6 +/- 1.3 vs fluid displacement: 5.8 +/- 1.4 ml; r = 0.79; p < 0.0005, n = 15) and multiple stones (US: 3.8 +/- 0.8 vs fluid displacement: 3.7 +/- 0.8 ml; r = 0.85; p < 0.0001, n = 19).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed1988

Quantitative regional curvature analysis: a prospective evaluation of ventricular shape and wall motion measurements.

To overcome the assumptions and approximations mandated by the use of traditional wall motion methodologies, a method was recently developed for measuring ventricular shape based on quantitative curvature analysis of ventricular outlines. This study was designed to assess prospectively the performance of this algorithm, to compare it to traditional wall motion measurements (centerline method), and to determine the comparative degree to which each method mimicked the interpretation of wall motion by clinical observers. Semiquantitative visual grading of regional function in 52 patients was performed by four independent observers on two occasions. Anterior, apical, or inferior segments were judged to be normal (0 points) or abnormal (1 point) based on viewing nonrealigned, end-diastolic and end-systolic ventricular silhouettes from cineventriculograms obtained in the 30-degree right anterior oblique projection. Each segment was assigned a collated score ranging from 0 (all observers felt the region was normal on both readings) to 8 (all observers felt the region was abnormal on both readings). Quantitative regional curvature analysis and wall motion analysis (centerline method) were performed. Quantitative shape and wall motion scores correlated equally well with the semiquantitative visual scores. When a visual score of greater than or equal to 4 was used to designate an abnormal segment, both quantitative approaches demonstrated comparable sensitivity, specificity, and concordance rates. Both methods achieved optimal performance when maximum and minimum deviations from normal were recorded. Under these circumstances, the shape analysis demonstrated a greater concordance with the clinical diagnosis than did wall motion analysis (99% vs-93%, p less than 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed1990

[Computer-assisted selection of therapeutic measures in ischemic heart disease and arterial hypertension during mass screening of a rural population].

Expert assessments of 537 case histories of patients with various coronary heart diseases made it possible to derive an algorithm for automatic choice of therapeutic and prophylactic measures. This approach was tested within the framework of the automatic system "Cardioscreening". It was shown that there was a good correlation between the automatic choice of therapeutic and prophylactic actions and the strategy of a skilled cardiologist.

Algorithms↗

PubMed1992

A linear scale for measuring vagal tone in man.

1. Different levels of parasympathetic control of the heart were measured using ratios of the longest to the shortest intervals between R-waves in the ECGs (R-R) recorded during a deep breathing exercise in the supine position (respiratory sinus arrhythmia). The mean of absolute differences in consecutive R-R intervals was also measured in the supine position during quiet breathing (beat-to-beat variation), in six healthy volunteers, after cumulative doses of atropine (0.1-2.0 mg 70 kg-1, i.v.). 2. Full atropinization was observed at 2.0 mg 70 kg-1 where the respiratory sinus arrhythmia decreased by 97%, and the beat-to-beat variation dropped by 94%. There was no further drop in both indices at doses above 2.0 mg 70 kg-1. The different levels of parasympathetic control of the heart were directly proportional to the equivalent levels of respiratory sinus arrhythmia or beat-to-beat variation. 3. A universal linear vagal scale was calculated for use with these non-invasive indices to assess the levels of parasympathetic control of the heart. Zero in this scale would represent no activities in the cardiac vagus nerve. 4. It was concluded that vagal tone could be selectively measured in an intact person using these simplified and fast algorithms for quantifying respiratory sinus arrhythmia or beat-to-beat variation. A linear scale for measuring the vagal tone was possible. This linear scale was called the linear vagal scale (LVS).

Adult↗

PubMed1989

A generalised algorithm for spectral reconstruction in Compton spectroscopy with corrections for coherent scattering.

Reconstruction of primary-photon energy spectra from pulse-height distributions obtained in a Compton spectrometer has earlier been performed under the assumption that coherent scattering in the scatterer is negligible. This holds for most clinical x-ray units operated in the range 40-150 kV. In mammography, and to some extent in dental radiography, the relatively high frequency of low-energy photons (less than 30 keV) in the primary beam makes it necessary to extend the algorithms to allow for significant contribution of coherent scattering. This extension is performed as a perturbation calculation to the algorithms developed earlier in which a modified Klein-Nishina scattering cross section was taken as the total scattering cross section. Comparison with energy spectra measured in the primary beam indicates that the Compton spectrometer with the extended algorithm is an excellent instrument for measuring energy spectra with energies down to a few keV.

Algorithms↗

PubMed1992

Models of the actin monomer and filament from fluorescence resonance-energy transfer.

We have developed algorithms for combining fluorescence resonance-energy transfer (FRET) efficiency measurements into structural models which predict the relative positions of the chemical groups used in FRET. We used these algorithms to construct models of the actin monomer and filament derived solely from FRET measurements based on seven distinct loci. We found a mirror-image pair of monomer models which best fit the FRET data. One of these models agrees well with the atomic-resolution crystal structure recently published by Kabsch et al. in Heidelberg [Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F. & Holmes, K. C. (1990) Nature 347, 37-44]. The root-mean-square deviation between this FRET model and the crystal structure was about 0.9 nm. Other macromolecular models assembled from FRET measurements are likely to have a similar resolution. The largest discrepancy was for the Cys10 locus which deviated 1.44 nm from the crystal position. We discuss the limitations of the FRET method that may have contributed to this discrepancy, and conclude that the Cys10 FRET data have probably located Cys10 incorrectly in the FRET monomer model. Using the FRET monomer models, we found three orientations in the filament which best fit the intermonomer FRET data. These orientations differ substantially from the atomic-resolution filament model proposed by the Heidelberg group [Holmes, K., Popp, D., Gebhard, W. & Kabsch, W. (1990) Nature 347, 44-49], largely because of the discrepancies in the Cys10 data. These data should probably be excluded from the analysis; however, this would leave too few measurements to assemble a filament model. In the near future, we hope to obtain additional FRET measurements to other actin loci so that the filament modelling can be done without the Cys10 data.

Actins↗

PubMed1988

On estimating the number density of random scatterers from backscattered acoustic signals.

When an acoustic pulse interacts with an inhomogeneous, attenuating medium, the backscattered signals exhibit random fluctuations which are correlated with the physical properties of the medium. This paper proposes a robust model for characterizing the statistical nature of these backscattered signals. This model takes into account frequency-dependent attenuation, spatially varying media statistics, arbitrary beam geometries, and arbitrary pulse shapes. Based on this model, statistical estimation schemes are proposed for estimating both the attenuation coefficient and scatterer number density of the medium. Using appropriate simplifying assumptions, it is shown that this model is consistent with attenuation estimation algorithms currently used for ultrasonic tissue characterization. A statistical approach for estimating the number density of scatterers is described and its theoretical performance is evaluated. The algorithm for estimating the scatterer number density incorporates measurements of both the statistical moments of the backscattered signals and the point spread function of the acoustic system. The number density algorithm has been applied to simulated waveforms, waveforms obtained from ultrasonic phantoms with known number densities, and in vitro mammalian tissues. There is an excellent agreement between theoretical, simulation, and experimental results. The application of this technique to ultrasonic tissue characterization is also discussed.

Algorithms↗