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Results for “Correction factor”

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At least 73 records · Page 4Linked to original sources

PubMed1992

[Rectal temperature-time of death nomogram: dependence of corrective factors of body weight in significant thermal insulating conditions].

98 test coolings were made under various cooling conditions (moving air, two types of both clothing and covering) on dummies of real masses of 1, 3.3, 9.9, 24.5 and 33.4 kg resp. which cool under standard conditions (unclothed, uncovered, still air) like human bodies of 14, 33, 41, 83 and 104 kg resp. The results provide evidence on a nonlinear dependence of corrective factors of body weight upon the body weight. The dynamics of the dependence increases with the thickness of thermic isolation. Transferred to the use of the nomogram method on bodies, cooling conditions requiring corrective factors known by experience between 0.75 (moving air) and 1.3 (rather thin clothing/covering) can be used as in the past independent on the body weight. Only in higher corrective factors for thicker clothing/covering according to experience the dependence of corrective factors on the body weight must be taken into account in bodies of a very high or low body weight. Beside a simplified table a formula for computing is also given for that purpose.

Body Temperature Regulation↗

PubMedDate not supplied

Energy dependence of correction factors for the Victoreen Model 666 Portable Radiographic Health Survey System.

The energy dependence for each of three models of Victoreen 666 ionization chambers is characterized through an examination of the correction factors determined over the diagnostic x-ray range (0.4-4.9 mm A1 HVL) for many samples of each model. The results of an analysis of variance performed for each chamber model on the correction factors are reported as mean correction factors for the x-ray beams evaluated, with a relative standard error of less than 0.6% in all cases. Energy-dependence curves for the three chamber models are given, and their use is described.

Calibration↗

PubMed2002

Photon quality correction factors for ionization chambers in an epithermal neutron beam.

Photon quality correction factors (kQy) for ionization chamber photon dosimetry in an epithermal neutron beam were determined according to a modified absorbed dose to water formalism which was extended to mixed radiation fields. We have studied two commercially available ionization chambers in the epithermal neutron beam optimized for BNCT at the facility at Studsvik, Sweden. One of the chambers is nominally neutron insensitive; a magnesium-walled detector flushed with pure argon gas (denoted by Mg/Ar). The second chamber has approximately the same sensitivity for neutrons and photons; it is considered a 'tissue equivalent' detector, with A-150 walls flushed with methane-based tissue-equivalent gas (denoted by TE/TE). The kQy-factors in epithermal neutron beams have previously been assumed to be equal to unity or estimated from measurements in clinical accelerator produced photon beams. In this work the kQy-factors have been determined from absorbed dose calculations using cavity theory together with Monte Carlo derived electron fluences obtained with the MCNP4c system for water and PMMA phantoms. The calculated quality correction factors differ substantially from unity, being in the order of 10% for the Mg/Ar detector at shallow phantom depths, and between 2 and 4% for other depths and for the TE/TE chamber.

Boron Neutron Capture Therapy↗

PubMed2000

Air-braked cycle ergometers: validity of the correction factor for barometric pressure.

Barometric pressure exerts by far the greatest influence of the three environmental factors (barometric pressure, temperature and humidity) on power outputs from air-braked ergometers. The barometric pressure correction factor for power outputs from air-braked ergometers is in widespread use but apparently has never been empirically validated. Our experiment validated this correction factor by calibrating two air-braked cycle ergometers in a hypobaric chamber using a dynamic calibration rig. The results showed that if the power output correction for changes in air resistance at barometric pressures corresponding to altitudes of 38, 600, 1,200 and 1,800 m above mean sea level were applied, then the coefficients of variation were 0.8-1.9% over the range of 160-1,597 W. The overall mean error was 3.0 % but this included up to 0.73 % for the propagated error that was associated with errors in the measurement of: a) temperature b) relative humidity c) barometric pressure d) force, distance and angular velocity by the dynamic calibration rig. The overall mean error therefore approximated the +/- 2.0% of true load that was specified by the Laboratory Standards Assistance Scheme of the Australian Sports Commission. The validity of the correction factor for barometric pressure on power output was therefore demonstrated over the altitude range of 38-1,800 m.

Altitude↗

PubMed2002

Fluence correction factors in plastic phantoms for clinical proton beams.

In recent codes of practice for reference dosimetry in clinical proton beams using ionization chambers, it is recommended to perform the measurement in a water phantom. However, in situations where the positioning accuracy is very critical, it could be more convenient to perform the measurement in a plastic phantom. In proton beams, a similar approach as in electron beams could be applied by introducing fluence correction factors in order to account for the differences in particle fluence distributions at equivalent depths in plastic and water. In this work, fluence correction factors as a function of depth were determined for proton beams with different energies using the Monte Carlo code PTRAN for PMMA and polystyrene with reference to water. The influence of non-elastic nuclear interaction cross sections was investigated. It was found that differences in proton fluence distributions are almost entirely due to differences in non-elastic nuclear interaction cross sections between the plastic materials and water. For proton beams with energies lower than 100 MeV, for which the contributions from non-elastic interactions become small compared to the total dose, the fluence corrections are smaller than 1%. For beams with energies above 200 MeV, depending on the cross sections dataset for non-elastic nuclear interactions, fluence corrections of 2-5% were found at the largest depths. The results could, with an acceptable accuracy, be represented as a correction per cm penetration of the beam, yielding values between 0.06% and 0.15% per cm for PMMA and 0.06% to 0.20% per cm for polystyrene. Experimental information on these correction factors was obtained from depth dose measurements in PMMA and water. The experiments were performed in 75 MeV and 191 MeV non-modulated and range-modulated proton beams. From the experiments, values ranging from 0.03% to 0.15% per cm were obtained. A decisive answer about which dataset for non-elastic nuclear interactions would result in a better representation of the measurements could not be given. We conclude that below 100 MeV, dosimetry could be performed in plastic phantoms without a dramatic loss of accuracy. On the other hand, in clinical high-energy proton beams, where accurate positioning in water is in general not an issue, substantial correction factors would be required for converting dose measurements in a plastic phantom to absorbed dose to water. It is therefore not advisable to perform absorbed dose measurements nor to measure depth dose distributions in a plastic phantom in high-energy proton beams.

Calibration↗

PubMed1985

Determination of correction factors of 3H-beta-self-absorption for quantitative evaluation of grain number in autoradiographic studies. Interferometric studies of different cell types in the mouse brain.

Deparaffinized and Feulgen-stained sagittal sections of the mouse brain were studied interferometrically in order to measure optical path differences of euchromatin and heterochromatin of various cell types. Furthermore, the ratio eu-: heterochromatin of each cell type was determined. From these data mass densities of karyoplasm and, finally, correction factors of 3H-beta-self-absorption were calculated for comparing grain numbers of different cell types in quantitative autoradiographic studies after application of tritium-labelled substances. Remarkable differences of correction factors up to a factor of 2.18 were found. Furthermore, the actual section thickness was determined interferometrically. A reduction to about 0.60 of the microtome setting was measured in two different areas of the brain. Using mass densities together with actual section thickness correction factors for a thickness of 1 micron were calculated. This was done also for cell types outside the brain the data of which were taken from literature. Thus, differences in correction factors up to about a factor of 4 were found pointing out the importance of considering 3H-beta-self-absorption in quantitative autoradiographic studies.

Animals↗

PubMed1997

[Determination of dimethyl ether correction factors in gas chromatography with TCD and FID].

Dimethyl ether (DME) correction factors in gas chromatography with thermal conductivity detector (TCD) and flame ionization detector (FID) by using H2 as carrier gas were determined in this work. The homemade DME gas was quantitatively absorbed in ice-cold water. With ethanol as standard, the aqueous mixture was injected into a gas chromatograph, equipped with serially-connected TCD and FID. The weight correction factors of DME based on methanol were 0.86 and 0.55 for TCD and FID respectively. The result for TCD was also confirmed by calculation based on the stoichiometrical transformation of methanol into DME in reaction gas chromatography.

English Abstract↗

PubMed2005

Is the correction factor used in the breath test assessment of gastric emptying appropriate for use in infants?

OBJECTIVES: The gastric emptying breath test (GEBT) is now routinely used in many centers. Validation studies in adults have shown that although there is a linear correlation between the GEBT and scintigraphy, the GEBT overestimates gastric half emptying time (GEt1/2) by a constant of approximately 60 minutes because of postgastric processing. It is therefore conventional to apply a "correction factor" to the GEBT result. Because = no similar validation studies have been performed in infants, the aim of this study was to directly characterize the postgastric processing of 13C octanoic acid in infants to assess the suitability of the standard correction factor for use in infants. METHODS: The pattern of breath 13CO2 excretion after separate infusion of 13C octanoic acid into either the stomach or the duodenum was measured in 13 healthy preterm infants (6 male, 7 female). The raw 13CO2 half excretion time after intragastric (GEt1/2 raw) and intraduodenal (DEt1/2 raw) administration of C octanoic acid was calculated, and the difference between GEt1/2 raw and DEt1/2 raw (i.e., GEt1/2 raw - DEt1/2 raw) was directly compared with GEt1/2 corrected, derived by applying the standard correction factor to GEt1/2 raw. RESULTS: Values for GEt1/2 raw - DEt1/2 raw correlated significantly with GEt1/2 corrected. CONCLUSION: Our results show that the standard correction factor is appropriate for performing the GEBT in preterm infants.

Area Under Curve↗

PubMedDate not supplied

Interspecies scaling of inhalational anesthetic potency minimum alveolar concentration (MAC): application of a correction factor for the prediction of MAC in humans.

The objective of this study was to predict minimum alveolar concentration (MAC) of inhalational anesthetics in humans from animal data. The MAC of 10 anesthetics was obtained from the literature. At least three animal species (excluding humans) were used in the scaling. Interspecies scaling of MAC was performed in two ways: (1) using the traditional allometric approach, the MAC of each drug was plotted against the body weight of the species on a log-log scale, and MAC in humans was predicted from the resultant equation; and (2) MAC in each species was multiplied by a correction factor obtained by adjusting the lung weight of the species based on per kg body weight. The product of the correction factor and the MAC was then plotted against body weight as described in the traditional approach. Predicted MAC values in humans from animal data using simple allometry produced comparatively more error than the prediction made by incorporating the correction factor into the scaling. The results of this study indicate that MAC may not be predicted in humans from animal data using simple allometry; however, applying a correction factor may significantly improve the prediction of MAC in humans from animal data.

Anesthetics, Inhalation↗

PubMed2004

Variation in barometric pressure in Melbourne does not significantly affect the BTPS correction factor.

The conventional BTPS (body temperature and pressure, saturated with water vapour) correction factor varies with ambient barometric pressure (P(B)) and many lung function laboratories measure P(B) daily. The aim was to investigate whether a fixed value for P(B) could replace daily measurements. P(B) was measured daily over a 12-month period. The highest and lowest values in Melbourne in the last century were also recorded from data published by the Bureau of Meteorology. Using these P(B) values, the BTPS factor was determined for a range of spirometer temperatures and compared to the BTPS factors obtained using a fixed ambient pressure of 101.3 kPa. The mean (SD) P(B) measured over the 12-month period was 102.2 kPa (0.64) with a range of 99.9-103.6 kPa. The level of disagreement between the BTPS factor calculated using a P(B) of 101.3 kPa instead of the measured value was greater at lower temperatures. Over the extremes of P(B) during the last century (98.0-104.3 kPa) the use of a standard pressure (101.3 kPa) produced an error in the BTPS factor of </= 0.16%. Daily variations in P(B) do not significantly affect the magnitude of the conventional BTPS correction factor and a fixed value, such as 101.3 kPa at sea level, can be used with little error.

Atmospheric Pressure↗

PubMedDate not supplied

Energy dependence of correction factors for two models of Keithley diagnostic ion chambers.

The energy dependence for each of two models of ionization chambers compatible with the Keithley model 35020 Digital Dosimeter, is determined by measurement of the exposure correction factors determined over the diagnostic x-ray range (0.4--4.9 mm AL HVL) for several for several samples of each model. The results of an analysis of variance performed by model on the correction factors are reported as mean correction factors for the x-ray beams evaluated, with a relative standard error of less than 1% for both cases. Energy-dependence curves for the two chamber models are given, and their use is described.

Evaluation Studies as Topic↗

PubMed1993

Dose conversion and wall correction factors for Fricke dosimetry in high-energy photon beams: analytical model and Monte Carlo calculations.

This paper presents the dose conversion and wall correction factors for Fricke dosimetry in high-energy photon beams calculated using both an analytical general cavity model and Monte Carlo techniques. The conversion factor is calculated as the ratio of the absorbed dose in water to that in the Fricke dosimeter solution with a water-walled vessel. The wall correction factor accounts for the change in the absorbed dose to the dosimeter solution caused by the inhomogeneous dosimeter wall material. A usercode based on the EGS4 Monte Carlo system, with the application of a correlated sampling variance reduction technique, has been employed in the calculations of these factors and the parameters used in the cavity model. Good agreement has been achieved between the predictions of the model and that obtained by direct Monte Carlo simulation and also with other workers' experiments. It is shown that Fricke dosimeters in common use cannot be considered to be 'large' detectors and therefore 'general cavity theory' should be applied in converting the dose to water. It is confirmed that plastic dosimeter vessels have a negligible wall effect. The wall correction factor for a 1 mm thick Pyrex-walled vessel varies with incident photon energy from 1.001 +/- 0.001 for a 60Co beam to 0.983 +/- 0.001 for a 24 MV (TPR(10)20 = 0.80) photon beam. This implies that previous Fricke measurements with glass-walled vessels should be re-evaluated.

Ferrous Compounds↗

PubMedDate not supplied

Energy dependence of correction factors for some low-energy direct-reading pocket dosimeters.

The energy dependence for each of five models of low-energy direct-reading pocket dosimeters was characterized through an examination of the exposure correction factors determined over the diagnostic x-ray range (0.4-4.1-mm Al HVL) for many samples of each model. The results of an analysis of variance performed by model on the correction factors are reported as mean correction factors for the x-ray beams evaluated, the relative standard error being less than 0.8% in all cases. Energy-dependence curves for the dosimeter models are given, and their use is described.

Radiography↗

PubMed1997

The biological effectiveness of intermittent irradiation as a function of overall treatment time: development of correction factors for linac-based stereotactic radiotherapy.

PURPOSE: Continuous irradiation of relatively short duration as administered in gamma-ray stereotactic radiosurgery (SRS) is biologically not equivalent to the more protracted intermittent exposures during accelerator-based radiosurgery with multiple arcs. Accelerator-based SRS and fractionated stereotactic radiotherapy (SRT) is currently performed with a high degree of variability in equipment and techniques resulting in highly variable treatment delivery times. The present work is designed to quantify the effects of radiation delivery times on biological effectiveness. For this, the intermittent radiation delivery schemes, typical for linac-based SRS/SRT, have been simulated in vitro to derive biological correction factors. METHODS AND MATERIALS: The experiments were carried out using U-87MG human glioma cells in suspension at 37 degrees C irradiated with 6 MV X-rays to clinically relevant doses ranging from 6 to 18 Gy, delivered over total irradiation times from 16 min to 3 h. The resulting cell survival data was used to calculate dose correction factors to compensate for wide variations in dose delivery times. RESULTS: At each total dose level, cell survival increased with increasing total irradiation time. The increase in survival was more pronounced at higher dose levels. At a total dose of 12 Gy, cell survival increased by a factor of 4.7 when irradiation time was increased from 16 to 112 min. Dose correction factors were calculated to allow biologically equivalent irradiations over the range of exposure times. Cells irradiated with corrected total doses of 11.5 Gy delivered incrementally in 16 min up to 13.3 Gy in 112 min were found to exhibit the same survival within the experimental limits of accuracy. CONCLUSIONS: For a given total dose, variations in dose delivery time typical of SRS/SRT techniques will result in significant changes in cell survival. In the dose range studied, an isoeffect dose correction factor of 2 to 3 cGy/min was shown to compensate for the change in delivery time for U-87 MG human gloma cells in vitro.

Brain Neoplasms↗

PubMedDate not supplied

Energy dependence of correction factors for some Victoreen Model 570 Condensor R-Meter medium-energy chambers.

The energy dependence of each of six models of medium-energy Victoreen 570 Condenser R-Meter chambers was determined by measurement of the exposure correction factors over the diagnostic x-ray beam-quality range (0.4-4.1 mm A1 HVL) for several samples of each model. The results of an analysis of variance performed by model on the correction factors are reported as mean correction factors for the x-ray beams evaluated, with a relative standard error less than 0.8% in all cases. Energy-dependence curves for the six chamber models are given; their use is described.

Calibration↗

PubMedDate not supplied

The effect of scattered radiation in 60Co beams on wall correction factors for ionization chambers.

The Awall correction factors used in dosimetry protocols are obtained by Monte Carlo methods that assume 60Co beams equivalent to 1.25-MeV radiation. Real 60Co beams contain lower energy components; in addition, Awall is defined differently by different authors. In the present work, Awall as defined by Rogers, Bielajew, and Nahum (1985) has been calculated by Monte Carlo methods at several energies, for a graphite cavity chamber, using the revised stopping-power data of Seltzer and Berger (1982). It is concluded that the true value of Awall for chambers designed for use in 60Co beams will not move more than 0.1% below the value calculated for 1.25-MeV photons.

Cobalt Radioisotopes↗

PubMed1993

An unbiased correction factor for cell counts in histological sections.

It is common procedure to correct raw counts of cells (or nuclei or other such particles) in histological sections by multiplying them by a 'correction factor', to allow for sectioned particles being counted more than once. However, the derivation of the standard formulae assumes that the particles to be counted are of uniform size. Therefore, these formulae may be biased in practical situations. Here, a more general correction factor (C) not depending on this restrictive assumption is derived: C = sigma i = 1 m T/(T - h(i))/sigma i = 1 m (T - R - S + h(i))/(T - h(i)) where T is section thickness, h(i) is the height of particle i measured perpendicular to the section plane, R and S are the heights, assumed constant, of the upper and lower 'lost caps', and the summation is performed over m (about 20) particles sampled randomly from among those lying wholly within individual sections. It is proposed that h(i) be measured by a differential focusing method; the formula will then be valid for particles of variable shape as well as size.

Bias↗

PubMed2000

Photon fluence perturbation correction factors for solid state detectors irradiated in kilovoltage photon beams.

Dose perturbation correction factors, gamma(p), for LiF, CaF2 and Li2B4O7 solid state detectors have been determined using the EGS4 Monte Carlo code. Each detector was simulated in the form of a disc of diameter 3.61 mm and thickness 1 mm irradiated in a clinical kilovoltage photon beam at a depth of 1 cm in a water phantom. The perturbation correction factor gamma(p) is defined as the deviation of the absorbed dose ratio from the average mass energy absorption coefficient ratio of water to the detector material, (mu(en)/rho)med,det, which is evaluated assuming that the photon fluence spectrum in the medium and in the detector material are identical. We define another mass energy absorption coefficient ratio, (kappa(en)/rho)med,det, which is evaluated using the actual photon fluence spectrum in the medium and detector for LiF and CaF2 rather than assuming they are identical. (kappa(en)/rho)med,det predicts the average absorbed dose ratio of the medium to the detector material within 0.3%. When the difference in atomic number between the cavity and the phantom material is large then their photon fluence spectra will differ substantially resulting in a difference between (kappa(en)/rho)med,det and (mu(en)/rho)med,det. The value of gamma(p) calculated using (mu(en)/rho)med,det is up to 27% greater than unity for a cavity of CaF2 in 50 kV x-rays. When the atomic number of the medium and detector are similar, their photon fluence spectra are similar, and the difference between (kappa(en)/rho)med,det and (mu(en)/rho)med,det is small. For instance their difference for LiF is less than 2%. The average mass energy absorption coefficient ratio, (mu(en)(E)/rho)w,LiF, evaluated using the mean or representative energy, E, is up to 8% different from (mu(en)/rho)w,LiF. For calcium fluoride the difference between (mu(en)/rho)w,CaF2 and (mu(en)(E)/rho)w,CaF2 is up to 42% in the energy range studied.

Models, Theoretical↗