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At least 109 records · Page 6Linked to original sources
PubMed2005

Basic principles of noninvasive blood pressure measurement in infants.

Correct measurement of blood pressure in infants is essential because blood pressure is an important indicator of cardiovascular status. This article provides a review of the fundamental principles of blood pressure measurement. Formulas to estimate mean arterial pressure are discussed along with an overview of pulse pressure. The advantages, challenges, and accuracy of the widely used oscillometric method of noninvasive blood pressure measurement are discussed. A step-by-step guide to noninvasive blood pressure measurement is outlined along with pragmatic strategies to ensure appropriate technique, thereby improving accuracy.

Age Factors↗
PubMed2002

Standardized Uptake Values in 2-Deoxy-2-[18F]Fluoro-D-Glucose with Positron Emission Tomography. Clinical Significance of Iterative Reconstruction and Segmented Attenuation Compared with Conventional Filtered Back Projection and Measured Attenuation Correction.

PURPOSE: To evaluate the clinical significance of differences in 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography (FDG-PET) lymph node standardized uptake values (SUV) in human immunodeficiency virus (HIV) infection using iterative reconstruction with segmented attenuation correction (IR SAC) compared to filtered back-projection with measured attenuation correction (FBP MAC). PROCEDURES: Seven patients with HIV infection and multiple focal lymph node abnormalities were investigated with whole-body FDG-PET. Mean and maximum SUVs from lymph node regions of interest (n = 961) were compared for quantitative differences between reconstruction techniques. RESULTS: IR MAC resulted in significantly lower mean SUV [0.06; 95% (confidence interval (CI)) = 0.04-0.07] and maximum SUV (0.82; 95% CI = 0.77-0.88) values compared to FBP MAC. With IR, segmentation of attenuation correction (AC) resulted in significantly higher mean SUV (0.12; 95% CI = 0.11-0.13) and maximum SUV (0.21; 95% CI = 0.18-0.23) values compared to IR MAC. The overall effect of both IR and SAC was a slight but significant increase in mean SUV (0.06; 95% CI = 0.06-0.08; bias = 2.1%) and a significant decrease in maximum SUV (0.62; 95% CI = 0.56-0.67) compared to FBP MAC. CONCLUSIONS: With our reconstruction parameters, significant differences in mean and maximum SUV values were observed. The magnitude of the mean SUV difference, however, was small. IR SAC is a promising method to accurately quantify standardized uptake values for clinical use.

Journal Article↗
PubMed2000

Measurement error correction using validation data: a review of methods and their applicability in case-control studies.

Measurement error is a serious problem in the analysis of epidemiological data. In the past 20 years, a large number of methods for the correction of measurement error have been developed. While at the beginning mostly methods for cohort studies were considered, recently more attention has been paid to case-control studies. Although a variety of methods have been proposed, they are very rarely used in practice. To stimulate their use and further development, this article provides a comprehensive overview on methods developed for multivariable regression analysis of epidemiologic studies with validation data sets. The methods are systematically classified with respect to the underlying theory. An assessment of prerequisites, assumptions and performance of the available methods is given. Particular attention is paid to applicability to case-control studies and need for further research and development is pointed out.

Bias↗
PubMed2006

A multivariate method for measurement error correction using pairs of concentration biomarkers.

PURPOSE: Measurement error is a pervasive problem in behavioral epidemiology, and available methods of correction all have generally untenable assumptions. We propose a multivariate method with more realistic assumptions. METHODS: The method uses two concentration biomarkers for each nutritional variable of interest and structural equation modeling. This produces corrected estimates of the effects on an outcome variable of changing the true exposure variables by one standard deviation, a standardized regression calibration. However, hypothesis testing in original units is preserved. The main assumptions are that certain error correlations between dietary estimates and biomarkers or between biomarkers be close to zero. RESULTS: Two illustrative models used simulated data with the covariance structure of a real data set. The corrections produced often were very substantial. A sensitivity analysis allowed error correlations to depart from zero over a modest range. Root mean square biases show the advantage of the corrected approach. Relatively large calibration studies are needed for adequate precision. CONCLUSIONS: As long as concentration biomarkers are selected carefully, error-corrected multivariate hypothesis testing and standardized effect estimation is possible. With the deviations from assumptions that were tested, the corrected method usually produces much less biased results than an uncorrected analysis.

Bias↗
PubMed2006

Prolonged ventricular repolarization measured by corrected QT interval (QTc) in subclinical hyperthyroidism.

UNLABELLED: Overt hyperthyroidism and hypothyroidism exert a major effect on cardiac function and on ECG. The influence of subclinical hyperthyroidism on the circulatory system is still under debate. Few studies examined the effect of thyroid hormones on ventricular repolarization measured by corrected QT interval (QTc). Longer QTc is associated with increased risk of arrhythmia and cardiac mortality. The aim of this study was to examine the influence of subclinical hyperthyroidism on ventricular repolarization measured by corrected QTc in a standard 12-lead electrocardiogram. The examined group consisted of thirty-two patients with subclinical hyperthyroidism; the controls were thirty-nine healthy individuals. In the group with subclinical hyperthyroidism, we observed a significant increase in heart rate (80.3 +/- 10.59 vs. 73.7 +/- 11.37 bpm, p < 0.05). The mean corrected QTc was 0.434 +/- 0.0207 seconds and 0.414 +/- 0.0208 in the examined groups and in controls, respectively (p < 0.001). QTc did not correlate with free thyroxin concentrations (p = 0.5084). CONCLUSION: Corrected QT intervals were significantly longer in patients with subclinical hyperthyroidism.

Arrhythmias, Cardiac↗
PubMed2000

End-tidal carbon monoxide measurements in women with pregnancy-induced hypertension and preeclampsia.

OBJECTIVE: We sought to compare the end-tidal carbon monoxide breath levels in pregnant women with and without pregnancy-induced hypertension and preeclampsia. STUDY DESIGN: We prospectively performed end-tidal carbon monoxide measurements corrected for ambient carbon monoxide in nonsmoking women during late gestation (>31 weeks). The study group included 22 women with pregnancy-induced hypertension or symptoms of preeclampsia and a control group of 20 normotensive pregnant women. RESULTS: The carbon monoxide measurements corrected for ambient carbon monoxide (mean +/- SD) were significantly lower (P <.01) in the hypertensive group than in the control group (1.17 +/- 0.35 vs 1.70 +/- 0.54 ppm). The study group had a significantly higher number of low (<1.2 ppm) end-tidal carbon monoxide measurements corrected for ambient carbon monoxide (13 [59.1%] vs 1 [5.0%]; P <.001). The end-tidal carbon monoxide measurements corrected for ambient carbon monoxide remained significantly lower in comparison with those found in the control group when the study group was divided into women with pregnancy-induced hypertension only (n = 11) and those with preeclampsia (n = 11) (1.19 +/- 0.37 ppm; P <.01; and 1.15 +/- 0.41 ppm; P <.01; respectively). CONCLUSIONS: Our findings suggest that carbon monoxide formation may be significantly lower in women with pregnancy-induced hypertension and preeclampsia. These data suggest that carbon monoxide could have a contributory role in the apparent paradox of the seemingly protective effect of smoking to decrease the risk of preeclampsia.

Adult↗
PubMedDate not supplied

Comparison of calculated and measured heterogeneity correction factors for 125I, 137Cs, and 192Ir brachytherapy sources near localized heterogeneities.

The influence of tissue and applicator heterogeneities on brachytherapy dose distributions is not well understood, despite widespread use of shielded applicators in intracavitary therapy. Heterogeneity correction factors (HCF) have been measured using a silicon diode detector arising from bounded heterogeneities consisting of lead, steel, titanium, silver, aluminum, and air cylinders near brachytherapy sources of 125I, 137Cs, and 192Ir. In addition, transverse-axis dose distributions for the three sources in homogeneous water were measured for distances of 0.2 to 16.0 cm. For each point of measurement, relative diode readings were simulated by a Monte Carlo photon transport code utilizing accurate models of the source internal structure, the experimental measure geometry and the source-strength calibration geometry. Comparison of measured and calculated HCF's reveals excellent agreement (1%-3% average) over a wide range of materials, diameters, and thicknesses. In addition, Monte Carlo simulation not only accurately reproduced the relative transverse-axis dose distributions in homogeneous medium, but was able to predict the variation of diode response with photon energy with an accuracy of 3% over the range of 30-662 keV. Our measurements demonstrate that HCF's vary by as much as 60%-100% with distance and heterogeneity diameter for a fixed thickness. Finally, silicon diode measurements of HCF (denied as reading with heterogeneity/reading in homogeneous medium) is shown to lead to errors of 5%-30% for 137Cs and 192Ir sources in the presence of high-atomic number shielding materials. This paper concludes, that Monte Carlo simulation is a powerful, convenient and accurate tool for investigating the long-neglected area of brachytherapy heterogeneity corrections.

Biometry↗
PubMed1997

[The evaluative cycle of the process of an overall geriatric evaluation program at a health center].

OBJECTIVE: To improve the procedures in an Elderly Persons' Care programme. DESIGN: A complete evaluative cycle of the care process, with an analysis phase and a phase to implement corrective measures. SETTING: Primary care. Ortuella (Bizkaia) Health Centre. PATIENTS AND PARTICIPANTS: Data on the first 50% on the list of residents over 75 in Ortuella were analysed in this evaluation (n = 249). Residents in elderly people's homes, people passing through and who had recently moved were excluded. In the re-evaluation all those still to be evaluated were analysed once corrective measures had been implemented (n = 81). INTERVENTIONS: After analysis of the first phase, corrective measures were applied, and both the coverage and the correct performance of activities generated in the development of the programme were re-evaluated. MEASUREMENTS AND MAIN RESULTS: There was similar coverage (72.3 to 66.7%). There was improvement in registration (76.9 to 90.7%), long-treatment card (60 to 85.7%), medicines (42.9 to 75%) and nutritional habits (46.1 to 57.1%). Action taken on visual (93.1 to 75%) and hearing (76 to 71.4%) pathologies deteriorated. CONCLUSIONS: The programme's procedures improved with simple corrective measures (a session concerning proper recording of the history and how to follow the protocol; professionals who controlled registration and coverage). A proper record was important.

Aged↗
PubMed1989

Measured attenuation correction methods.

Accurate attenuation correction is a prerequisite for the determination of exact local radioactivity concentrations in positron emission tomography. Attenuation correction factors range from 4-5 in brain studies to 50-100 in whole body measurements. This report gives an overview of the different methods of determining the attenuation correction factors by transmission measurements using an external positron emitting source. The long-lived generator nuclide 68Ge/68Ga is commonly used for this purpose. The additional patient dose from the transmission source is usually a small fraction of the dose due to the subsequent emission measurement. Ring-shaped transmission sources as well as rotating point or line sources are employed in modern positron tomographs. By masking a rotating line or point source, random and scattered events in the transmission scans can be effectively suppressed. The problems of measured attenuation correction are discussed: transmission/emission mismatch, random and scattered event contamination, counting statistics, transmission/emission scatter compensation, transmission scan after administration of activity to the patient. By using a double masking technique simultaneous emission and transmission scans become feasible.

Humans↗
PubMed1992

Use and limitations of dual measurements in correcting for nondifferential exposure misclassification.

Recently, several authors have encouraged the use of dual measurement strategies to correct for bias due to nondifferential misclassification in epidemiologic research. Among these, latent class techniques, which give unbiased results if both measurements are independent conditional on the true value, have become most popular. In practice, however, measurement errors are usually more likely to be positively correlated, and hence reliability studies cannot replace studies of validity. I offer here a quantitative illustration and a comparison of the performance of latent class approaches and other dual response strategies in situations of positive error covariance. I conclude that, except under very special circumstances, dual measurement strategies are likely to remove only part, if any, of the effect attenuation due to nondifferential exposure misclassification. Under certain conditions, it may make sense, however, to estimate a "minimum" effect of the exposure on the basis of the strongest association found in various dual and single measurement strategies.

Bias↗
PubMed1989

Scatter fraction: measurement and correction.

The concept of scatter in Positron Emission Tomography is reviewed regarding origin and influence on data. Different ways to measure and correct for scatter are discussed.

Scattering, Radiation↗
PubMedDate not supplied

Intraoperative force measurements during correction of scoliosis.

Intraoperative forces applied to the spine were measured during the routine application of Harrington instrumentation for correction of scoliosis. This was accomplished by instrumenting the outrigger and distractor with strain gauges. Measurements were obtained in 16 patients undergoing their first operative procedure for scoliosis. Outrigger forces employed by two surgeons unapprised of the force data were not significantly different. Outrigger forces were significantly different for adolescent and adult groups of idiopathic scoliotics. Unusually low initial outrigger forces appeared to correlate with lower final correction obtained. In addition, in several cases transient distractor forces were observed that exceeded average levels at which bone failure is postulated to occur.

Adolescent↗
PubMedDate not supplied

[Usefulness of the measurement of corrected QT (QTc) for the diagnosis of diabetic neuropathy of the autonomic cardiovascular system].

Corrected QT interval was determined in diabetic patients and in a group of obese individuals with glucose intolerance. It was shown that the measurements of corrected QT (QTc) interval may be a reliable test in the diagnosis of the autonomic diabetic neuropathy. Its simplicity enables routine measurements in diabetic patients treated in out-patients clinics.

Adolescent↗
PubMed1994

JPCalc, a software package for calculating liquid junction potential corrections in patch-clamp, intracellular, epithelial and bilayer measurements and for correcting junction potential measurements.

The JPCalc program has been designed to graphically illustrate how junction potential contributions arise in various electrophysiological situations, to enable the magnitude and direction of those values to be readily calculated and to show clearly how the resultant appropriate corrections need to be applied to experimental measurements. In particular, the program covers the analysis of junction potential contributions and corrections in all the various different patch-clamp configurations (intact patches, inside-out patches, outside-out patches, whole-cell recording and perforated patches), intracellular recording, epithelial and bilayer measurements. It can also be used to correct experimental measurements designed to try to directly measure junction potentials and to compare both the magnitude and direction of such corrected measurements with their theoretical values. Although it is recommended that all of the above measurements be done with salt-filled electrodes or salt bridges, the program will allow the use of Ag/AgCl reference electrodes in direct contact with bathing solution in most situations. JPCalc also makes use of a library file of mobility and valency data for about 30 ions which can be extended by the user. In addition to its value in correcting electrical measurements, the program with its graphical displays may also be of value in focusing discussion about the contribution of junction potentials to such measurements and in helping to design experiments to either minimize their contribution or to measure their values. The JPCalc program, designed for IBM-compatible computers with color or monochrome monitors, can also be run on Macintosh computers with SoftPC emulation software.

Animals↗
PubMed2001

Measurement error correction in nutritional epidemiology based on individual foods, with application to the relation of diet to breast cancer.

Nutrient intake is often measured with error by commonly used dietary instruments such as the food frequency questionnaire (FFQ) or 24-hour recall. More accurate assessments of true intake are obtained by using weighed diet records, in which subjects record what they eat on a real-time basis, but these records are expensive to administer. Validation studies are often performed to relate "gold standard" intake to intake according to surrogate instruments and to correct relative risk estimates obtained in the main study for measurement error. Most measurement error correction methods use validation study data at the nutrient level. However, subjects almost always report intake at the food rather than the nutrient level. In addition, the validity of measurement of different foods can vary considerably; it is relatively high for some foods (e.g., beverages) but relatively low for others (e.g., meats, vegetables). This differential validity could be incorporated into measurement error methods and potentially improve on nutrient-based measurement error methods. In this paper, the authors discuss correction methods for food-based measurement error and apply them to study the relation between FFQ intake in 1980 and incident breast cancer in 1980-1994 among approximately 89,000 women in the Nurses' Health Study, in whom approximately 3,000 incident breast cancers were observed.

Adult↗
PubMed1997

Assessment of cognitive deterioration in individual patients following cardiac surgery: correcting for measurement error and practice effects.

Assessment of cognitive change in individual patients may be confounded by unreliability of test scores and effects of repeated testing. An index correcting for both problems is proposed and compared with change indices that do not or do not adequately deal with measurement error and practice effects. These indices were used to examine cognitive deterioration in a sample of 63 patients undergoing cardiac surgery. It was demonstrated that for test measures with a low reliability, failure to correct for measurement error resulted in overestimation of deterioration rates. For test measures with a high reliability, but showing substantial practice effects, failure to correct for practice effects resulted in underestimation of deterioration rates. With the proposed index, cognitive deterioration shortly after cardiac surgery was most frequently observed for attention and psychomotor speed, less frequently for verbal fluency, and only occasionally for learning and memory.

Aged↗
PubMed2000

An efficient algorithm for measurement and correction of chromatic aberrations in fluorescence microscopy.

Even the best optical microscopes available on the market exhibit chromatic aberrations to some extent. In some types of study, chromatic aberrations of current optics cannot be neglected and a software correction is highly desirable. This paper describes a novel method of chromatic aberration measurement and software correction using sub-resolution bead imaging and computer image analysis. The method is quick, precise and enables the determination of both longitudinal and lateral chromatic aberrations. Correction function can be computed in about half an hour, including image acquisition. Using this approach, chromatic aberrations can be reduced to 10-20 nm laterally and 10-60 nm axially depending on the type of optical set-up. The method is especially suitable for fluorescence microscopy, where a limited number of wavelengths are observed.

Journal Article↗