SEARCH · PubMed Health

Results for “Correction factor”

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 145 records · Page 8Linked to original sources

PubMed1981

Correction factor for thermodilution determination of cardiac output in children.

The authors determined the correction factor (Ct) for three sizes of commonly available central venous catheters. These catheters are used as the injectate catheter when a 2.5 Fr transthoracic thermistor is used to determine cardiac output by thermodilution. The valves for Ct were highly reproducible. These determinations can be used conveniently in children to determine cardiac output by thermodilution.

Age Factors↗

PubMed2006

Quantification of triacylglycerols in butterfat by gas chromatography-electron impact mass spectrometry using molar correction factors for [M-RCOO]+ ions.

A quantitative electron impact GC-MS method using molar correction factors (MCFs) for [M-RCOO]+ ions has been developed for determination of molecular species of triacylglycerols (TAGs). MCFs were determined by linear calibration for 226 ions of 104 TAG species with good reproducibility: on the average, coefficient of determination was 0.975 +/- 0.043 and 0.963 +/- 0.115 for saturated and unsaturated TAGs, respectively. The MCFs of the sn-1(3) regioisomers of short-chain TAGs were lower than those of sn-2 isomers indicating ca. 2-3-fold higher cleavage of butyroyl and caproyl groups from the primary positions than from the secondary position. The method enabled quantification of 139 and 135 individual TAG species of butterfat (BF) and interesterified butterfat, respectively, including several regioisomers of short-chain TAGs. The most abundant molecular species of the even-numbered TAGs in BF were butyroylpalmitoyloleoylglycerol (5.05 mol%), butyroyldipalmitoylglycerol (4.75 mol%), and palmitoyldioleoylglycerol (3.32 mol%). The method provides an alternative for elucidation of nutritional and technological properties of relatively saturated TAG mixtures.

Butter↗

PubMed2002

Determination of the Kwall correction factor for a cylindrical ionization chamber to measure air-kerma in 60Co gamma beams.

The factor Kwall to correct for photon attenuation and scatter in the wall of ionization chambers for 60Co air-kerma measurement has been traditionally determined by a procedure based on a linear extrapolation of the chamber current to zero wall thickness. Monte Carlo calculations by Rogers and Bielajew (1990 Phys. Med. Biol. 35 1065-78) provided evidence, mostly for chambers of cylindrical and spherical geometry, of appreciable deviations between the calculated values of Kwall and those obtained by the traditional extrapolation procedure. In the present work an experimental method other than the traditional extrapolation procedure was used to determine the Kwall factor. In this method the dependence of the ionization current in a cylindrical chamber was analysed as a function of an effective wall thickness in place of the physical (radial) wall thickness traditionally considered in this type of measurement. To this end the chamber wall was ideally divided into distinct regions and for each region an effective thickness to which the chamber current correlates was determined. A Monte Carlo calculation of attenuation and scatter effects in the different regions of the chamber wall was also made to compare calculation to measurement results. The Kwall values experimentally determined in this work agree within 0.2% with the Monte Carlo calculation. The agreement between these independent methods and the appreciable deviation (up to about 1%) between the results of both these methods and those obtained by the traditional extrapolation procedure support the conclusion that the two independent methods providing comparable results are correct and the traditional extrapolation procedure is likely to be wrong. The numerical results of the present study refer to a cylindrical cavity chamber like that adopted as the Italian national air-kerma standard at INMRI-ENEA (Italy). The method used in this study applies, however, to any other chamber of the same type.

Calibration↗

PubMed2001

Sensitivity and specificity of WAIS-III/WMS-III demographically corrected factor scores in neuropsychological assessment.

This study explored the neurodiagnostic utility of 6 factor scores identified by recent exploratory and confirmatory factor analyses of the WAIS-III and WMS-III: Verbal Comprehension, Perceptual Organization, Processing Speed, Working Memory, Auditory Memory and Visual Memory. Factor scores were corrected for age. education, sex and ethnicity to minimize their influences on diagnostic accuracy. Cut-offs at 1, 1.5 and 2 standard deviations (SDs) below the standardization sample mean were applied to data from the overlapping test normative samples (N = 1073) and 6 clinical samples described in the WAIS-III/WMS-III Technical Manual (N = 126). The analyses suggest that a I SD cut-off yields the most balanced levels of sensitivity and specificity; more strict (1.5 or 2 SD) cut-offs generally result in trading modest gains in specificity for larger losses in sensitivity. Finally, using combinations of WAIS-III/WMS-III factors together as test batteries, we explored the sensitivity and specificity implications of varying diagnostic decision rules (e.g.,1 vs. 2 impaired factors = "impairment"). For most of the disorders considered here, even a small (e.g., 3 factor) WAIS-III/WMS-III battery provides quite good overall diagnostic accuracy.

Adult↗

PubMed1995

Calorimetric determination of the absorbed dose-to-water beam quality correction factor kQ for high-energy photon beams.

A method has been developed for measuring photon beam quality correction factors kQ using direct transfer with a water calorimeter. kQ values were measured for beam qualities varying between 6 and 23 MV for a Capintec PR-06 and a PTW W30001 cylindrical ionization chamber. Measured values were intercompared with published sets of computed kQ values and agreement was found to be within measurement uncertainty (1%, one standard deviation).

Biophysical Phenomena↗

PubMed2006

Wall correction factors, Pwall, for thimble ionization chambers.

The EGSnrc Monte Carlo user-code CSnrc is used to calculate wall correction factors, Pwall, for thimble ionization chambers in photon and electron beams. CSnrc calculated values of Pwall give closer agreement with previous experimental results than do the values from the standard formalism used in current dosimetry protocols. A set of Pwall values, computed at the reference depth in water, is presented for several commonly used thimble chambers. These values differ from the commonly used values by up to 0.8% for megavoltage photon beams, particularly for nominal beam energies below 6 MV. The sleeve effect, which is not currently taken into account by the TG-51 dosimetry protocol, is computed to be up to 0.3% and is in some cases larger than the Pwal1 correction itself. In electron beams, where dosimetry protocols assume a wall correction of unity, CSnrc calculations show Pwall values of up to 0.6% at the reference depth, depending on the wall material. Pwall is shown to be sensitive to the depth of measurement, varying by 2.5% for a graphite-walled cylindrical Farmer-like chamber between a depth of 0.5 cm and R50 in a 6 MeV electron beam.

Algorithms↗

PubMed2005

Reliability of a new correcting factor in calculating intraocular lens power after refractive corneal surgery.

PURPOSE: To test the reliability of a corneal radius correcting factor (R factor) in calculating intraocular lens (IOL) power in eyes that developed cataract after refractive surgery and compare it with the clinical history (CHM) and double-K (DKM) methods. SETTING: Department of Ophthalmology, Second University of Naples, Naples, Italy. METHODS: Nineteen eyes from the literature that underwent cataract extraction and IOL implantation after refractive surgery were used to compare actual postoperative and expected refractive errors utilizing the R factor, CHM, and DKM. Intraocular lens powers were calculated with 3 formulas: SRK/T, Hoffer Q and Holladay 1. The differences were evaluated with the Wilcoxon test and Spearman correlation. RESULTS: With the R factor SRK/T and Holladay 1 formulas gave the best results; 16 (84.2%) and 17 (89.5%) eyes were within +/-2 diopters (D) of emmetropia. With CHM, the best results were obtained using the SRK/T and Holladay 1 formulas; with both formulas 12 (63.2%) eyes were within +/-2 D of emmetropia. With DKM, the best results were obtained using SRK/T and Holladay 1 formulas; with both formulas 10 eyes (52.63%) were in the range of +/-2 D from emmetropia. CONCLUSIONS: The R factor can be used with the SRK/T or Holladay 1 formula because this method seems comparable or superior to DKM and CHM.

Cataract Extraction↗

PubMed1994

[Variation in blood pressure values in a pediatric population assigned to a primary care team by applying a correction factor according to brachial perimeter].

OBJECTIVE: To quantitative changes in blood pressure values and in hypertension diagnosis after applying a correction factor (CF) according to brachial perimeter. MATERIALS AND METHODS: A sample of 164 male and female children, aged 11-14 years from a population attended at our Health Institution was studied. Blood pressure and brachial perimeter at the right arm were determined in all children and the CF was applied according to brachial perimeter. RESULTS: Mean brachial perimeter was 23.8 cm, with a higher value in males (p < 0.05); a significant increase in blood pressure values was observed both for the overall sample and for both sexes taken separately; prevalence of hypertension increased significantly after correction of sample and for males, not for females. CONCLUSIONS: For an appropriate blood pressure measurement it is essential to correctly fit the cuff bladder size to the brachial perimeter; when it is not possible the CF should be applied.

Adolescent↗

PubMed1997

Comparison of parametrization methods of the collimator scatter correction factor for open rectangular fields of 6-25 MV photon beams.

PURPOSE: To facilitate the use of the collimator scatter correction factor, Sc, parametrization methods that relate Sc to the field size by fitting were investigated. MATERIALS AND METHODS: Sc was measured with a mini-phantom for five types of dual photon energy accelerators with energies varying between 6 and 25 MV. Using these Sc-data six methods of parametrizing Sc for square fields were compared, including a third-order polynomial of the natural logarithm of the field size normalized to the field size of 10 cm2. Also five methods of determining Sc for rectangular fields were considered, including one which determines the equivalent field size by extending Sterling's method. RESULTS: The deviations between measured and calculated Sc-values were determined for all photon beams and methods investigated in this study. The resulting deviations of the most accurate method varied between 0.07 and 0.42% for square fields and between 0.26 and 0.79% for rectangular fields. A recommendation is given as to how to limit the number of fields for which Sc should be measured in order to be able to accurately predict it for an arbitrary field size.

Mathematical Computing↗

PubMed2006

Wall correction factors, Pwall, for parallel-plate ionization chambers.

The EGSnrc Monte Carlo user-code CSnrc is used to calculate wall correction factors, Pwall,, for parallel-plate ionization chambers in photon and electron beams. A set of Pwall values, computed at the reference depth in water, is presented for several commonly used parallel-plate chambers. These values differ from the standard assumption of unity used by dosimetry protocols by up to 1.7% for clinical electron beams. Calculations also show that Pwall is strongly dependent on the depth of measurement and can vary by as much as 6% for a 6 MeV beam in moving from a depth of dref to a depth of R50. In photon beams, where there is limited information available regarding Pwall for parallel-plate chambers, CSnrc calculations show Pwall values of up to 2.4% at the reference depth over a range of photon energies. The Pwall values for photon beams are in good agreement with previous estimates of the wall correction but have much lower statistical uncertainties and cover a wider range of photon beam energies.

Algorithms↗

PubMedDate not supplied

Replacement correction factors for electron measurements with a parallel-plate chamber.

The AAPM Task Group dosimetry protocol is ambiguous regarding the replacement correction factors Prepl to be applied to electron measurements with parallel-plate chambers. By intercomparison with a cylindrical chamber whose Prepl values at dmax may be calculated from Task Group 21, the Prepl values for a PTW/Markus parallel-plate chamber have been determined in the range of mean incident energies of 5-11 MeV. The Prepl values for this chamber are found to differ significantly from unity, if one assumes that the cylindrical chamber values are valid.

Electrons↗

PubMed1980

Age correction factor in noise-induced hearing loss: a quantitative model.

This paper considers the factors of presbyacusis and noise exposure in relation to permanent hearing loss and provides a quantitative model from which an age correction factor in occupational hearing loss may be derived. The rationale for a presbyacusis correction is provided in terms of physiological and audiometric data. The additivity hypothesis is considered and constraints on this approach are presented. A quantitative model for assessing the age component in occupational hearing loss is then derived from empirical functions. The model is based on the concept of a variable ratio for partitioning the effects of presbyacusis and noise exposure. Consideration is given to the application of the model in medico-legal cases of occupational hearing loss in which the degree of hearing impairment must be assessed.

Aging↗

PubMed2026

A correction factor for bridging compaction simulator and different roller compactors.

Roller compaction (RC) is an important dry granulation technique. Since pilot and commercial scale roller compactors, which operate continuously on a large scale, usually require kilograms of material per run, formulation and process development directly on such roller compactors is not practical. In contrast, a compaction simulator (CS) can produce ribblets, also known as "slugs", using only a few grams of material with sinusoidal displacement profile replicating the motion of a specific point on the roll surface. Thus, it is possible to develop RC formulation and process in laboratory using a CS-based material-sparing approach. However, because of the inherently different configurations for applying pressure between die compression and roll compression, translating uniaxial pressure from CS experiments to roll pressure during RC is often unreliable, leading to significant uncertainties in the critical quality attributes of ribbons, such as ribbon solid fraction (or porosity) and mechanical strength. The objective of this study was to identify a correction factor (Kp = uniaxial die compression pressure/roll pressure), by correlating the compressibility profiles from CS and a roller compactor of interest, to enable more reliable process translation from CS to roller compactor. In this study, a Kp value of 0.5 was determined for Alexanderwerk WP120 and validated for Gerteis Mini-Pactor and Bepex Pharmapactor. This value may serve as a starting point for translating the optimal compaction pressure identified based on CS investigation to common roller compactors, requiring only minor adjustments to attain optimal RC process parameters (i.e., roll force and roll gap) for a chosen roller compactor.

Drug Compounding↗

PubMed1989

Measured inhomogeneity correction factors for lung in electron beam treatments of the chest wall.

A set of clinically relevant measurements of percentage depth dose and inhomogeneity correction factors for electron beam irradiation of the chest wall and underlying lung is given. Electron beam nominal energies of 9, 12, 15, and 18 MeV and lung densities of 0.22 g/cm3 and 0.404 g/cm3 are considered. This data can serve in treatment planning to indicate the penetration of the beam into the lung and serve as a comparison for calculation algorithms which are used to calculate electron dose absorption in heterogeneous phantoms.

Algorithms↗

PubMed1995

A method of obtaining the Awall correction factor of an ionization chamber in a 60Co gamma-ray beam using tissue-air ratio data.

A method is reported that evaluates the wall correction factor (Awall)water of an ionization chamber using measured data. The method needs a revised type of tissue-air ratio (TARcav) that should be measured with the ionization chamber. An experimental study has been carried out for 60Co gamma-rays using zero-area TARcav data extrapolated from non-zero-area TARcav data using the extrapolation method developed by Bjärngard and Petti. Using this technique, it is found that the value of (Awall)water for an ionization chamber has a deviation of -0.1% to -0.4% as compared with the Monte Carlo results. An experimental study has also been carried out using a published set of 60Co traditional tissue-air ratio (TAR) data assuming TARcav = TAR.

Air↗

PubMed1985

Molar absorptivity and the blank correction factor.

In photometry, where both the product formed and one or several reactants absorb light at the same wavelength, the absorbance of the "blank" of the sample at the end of the reaction may be less than that measured at the beginning of the reaction, because of consumption of reactant(s). The blank correction factor for the determined result with one light-absorbing reagent is epsilon P / (epsilon P - epsilon R), where epsilon R and epsilon P are the molar absorptivities of the reagent and the product, respectively. We derived a factor for the case when more than one reagent absorbs light at the same wavelength as the measured product. This factor is independent of the concentration of reagent(s) and can correct the determined result or absorbance for the consumption of light-absorbing reagent(s) during the reaction.

Biuret Reaction↗

PubMed2006

Cephalometric correction factors for bite opening--a dry skull study.

The lateral cephalometric radiograph supplies the clinician with valuable information regarding the facial skeletal morphology of the patient, provided that it is taken correctly. These radiographs should be taken while the patient is occluding in maximum intercuspation, failing which the exposure is often repeated, leading to an increase in patient radiation dose as well as added cost in time and materials. This study investigated the relationship between limited bite opening and selected cephalometric variables. Thirty-one dry skulls were used and five splints were constructed for each skull giving increments of bite opening from 0 to 5 mm. Six lateral radiographs per skull were taken at each increment of bite opening. The radiographs were traced and the points plotted using a reflex metrograph. A linear relationship was found between bite opening and SNB, ANB, SN-mandibular plane, and SN-Y-axis angles. Errors in digitization, superimposition, and landmark identification were determined and found to be acceptable. Regression analysis produced a highly significant (P < 0.001) gradient for each of these angular relationships, allowing a set of correction factors to be produced, which can be applied to bite openings up to 5 mm.

Cephalometry↗

PubMedDate not supplied

Compensation for beam intensity fluctuation in determination of P(ion) the ion-recombination correction factor for ionization chambers, by the two-voltage technique.

We have developed a method of compensation for fluctuations in beam intensity that may occur during measurement of Pion, the ion-recombination correction factor, by the two-voltage technique. The method requires signals proportional to beam intensity during measurement. We used a parallel-plate ionization chamber, whose Pion was known, and a vacuum chamber to obtain signals that were proportional to the beam intensity. Experiments were conducted using pulsed proton beam providing doses that ranged from 0.16 to 0.01 cGy/pulse. The value of Pion of a thimble ionization chamber was measured. With these measurements, the validity of the method which we proposed for pulsed beam was verified experimentally.

Particle Accelerators↗