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At least 55 records · Page 3Linked to original sources
PubMed1996

[Change of calibration method for enzyme assay in clinical biochemistry using automatic analyzer--comparison of calibration methods using K factor and human standard serum].

Enzyme activities in serum from experimental animals had been assayed by HITACHI 7150 Automatic Analyzer using K factors for calibration. Because K factor is derived from a molar extinction coefficient and, reagent and sample volumes for each assay system, it is a constant value in usual assay. As an alternative calibration method, a human standard serum, which is commercially available and well-controlled, is presently used in the same assay system because of some difficulties in supply. Four serum enzymes of human, rat, dog and monkey sera were determined by the above two methods. All values calibrated by human standard serum were approx. 10% higher than that using K factors. These small differences are allowable because data calibrated by human standard serum can be compared with previous data given by K factors.

Animals↗
PubMed2003

Reflectance-based calibration of SeaWiFS. I. Calibration coefficients.

We present a calibration approach for the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) based on the reflectance properties of the instrument's onboard diffuser. This technique uses SeaWiFS as a reflectometer, measuring the reflected solar irradiance from the Earth and from the onboard diffuser. Because the Sun is the common source of light for both measurements, the ratio of the SeaWiFS-measured radiances from the Earth and the diffuser provide the ratio for the reflectances of the two samples. The reflectance characterization of the onboard diffuser is the calibration reference for this approach. Knowledge of the value of the solar irradiance is not required for these measurements because it falls out of the ratio. Knowledge of the absolute calibration coefficient for the SeaWiFS measurements of each of the two samples is not required either. Instead, the result of the ratioing technique is based on the linearity of the instrument's response to the intensity of the input light. The calibration requires knowledge, however, of the reflectance of the onboard diffuser at the start of the SeaWiFS mission and the response of the instrument bands, in digital numbers, for measurements of the diffuser at that time.

Journal Article↗
PubMed1991

Calibration is the key to immunoassay but the ideal calibrator is unattainable.

Unlike assays for ions and small molecules protein and peptide measurements depend entirely on comparison of a test sample with a calibrator. Owing to the innate molecular heterogeneity of proteins it is frequently impossible to ensure that the calibrator is identical to the test and this may give rise to dissimilar behaviour in assays. Despite these fundamental limitations it is clear that internationally agreed calibrators are essential and properly used greatly improve homogeneity of reporting of protein values in biological fluids. Unfortunately, only international units can be ascribed to these materials with confidence and the use of mass values which are not internationally agreed has jeopardized the value of international calibrants.

Antibodies↗
PubMed1985

Calibration bias and imprecision for automated hematology analyzers. An evaluation of significance of short-term bias resulting from calibration of an analyzer with S Cal.

A Coulter S + IV analyzer was used both before and after recalibration with S Cal to analyze a series of patient blood specimens and stabilized control specimens. A statistically significant bias was introduced as compared with results on the same analyzer calibrated to fresh whole blood, but the degree of bias did not appear to approach medical significance when compared with two external theoretical models for determining acceptable bias in hematology analysis. Long-term bias accumulation on analyzers calibrated to control or stabilized calibration material remains a problem that must be addressed by further study.

Autoanalysis↗
PubMed1998

Characterisation, calibration and comparison by international collaborative study of international standards for the calibration of therapeutic preparations of FSH.

Therapeutic preparations of FSH, used primarily for treatment of infertility, are calibrated by in vivo bioassay against international standards (IS) derived from different sources deemed appropriate to their use according to pharmacopoeial monographs. Menotrophins, which have been used for several decades to treat infertility, have been calibrated against the IS for urinary FSH and LH (ISU) but are now being replaced by highly purified urinary FSH or rDNA-derived FSH (rFSH). The aim of this study was to evaluate two preparations of human rFSH and one preparation of highly purified urinary FSH as candidate WHO IS for bioassay in an international collaborative study by 27 laboratories in 12 countries, and to characterise them in a range of in vitro bioassays and immunoassays. The biological activity of the three candidate standards was confirmed by all laboratories using all assays contributed to the study. Dose-response relationships by in vivo bioassay for any of the candidate standards did not differ significantly from that for the ISU. Dose-response relationships obtained in in vitro bioassays and immunoassays were also broadly similar among these preparations although dose-response lines for some preparations appeared to be non-parallel in some immunoassays. For each of the three candidate IS, estimates of the relative potency in terms of ISU by in vivo bioassay did not differ significantly between laboratories. In contrast estimates by immunoassays and in vitro bioassays showed significant differences between laboratories. Estimates of relative potency of the highly purified candidate IS materials in terms of one another exhibited less inter-laboratory variability than estimates in term of ISU. Each of the candidate standards showed adequate stability to serve as an IS. On the basis of the results of this study rFSH (code 92/642) was established as the first IS for FSH, human, recombinant for bioassay with an assigned unitage of 138 IU per ampoule and urinary FSH (code 92/512) was established as the first IS for FSH, human, urinary (urofollitropin) for bioassay with an assigned unitage of 121 IU per ampoule, based on their respective calibration by in vivo bioassay in terms of ISU. These assignments of unitage maintain continuity of unitage for preparations in therapeutic use and also appear to be consistent with one another.

Biological Assay↗
PubMedDate not supplied

A chamber and electrometer calibration factor as determined by each of the five AAPM accredited dosimetry calibration laboratories.

The same calibration grade ionization chamber and electrometer were sequentially sent to all five currently AAPM Accredited Dosimetry Calibration Laboratories (ADCL). A Cesium-137 based check device was utilized to ensure chamber and electrometer factor constancy and showed a maximum deviation of 0.32% (typically less than 0.1%) over the 227 days needed to complete the intercomparison. The chamber and electrometer calibration factor provided by each of the five ADCLs were analyzed for consistency. The maximum percent difference in reported chamber factor between all five ADCLs was 1.40%. The reported electrometer factor had a maximum discrepancy of only 0.50%. System (chamber plus electrometer) factors as provided by three of the five ADCLs had a maximum discrepancy of 1.51%.

Humans↗
PubMed1991

Calibration of retinal image size with distance in the Mongolian gerbil: rapid adjustment of calibrations in different contexts.

Mongolian gerbils were trained to jump from one platform to another across a gap whose size varied randomly from trial to trial. In test sessions, probe landing platforms differing in width from those used in training were used, and the distance that the animals jumped was measured. The first experiment demonstrated that the gerbils learned to calibrate the retinal image size of the landing platform with its distance and that they could learn more than one calibration at a time. The second experiment provided evidence that such calibrations are rapidly adjusted to environmental contingencies. These findings suggest that retinal image size might be a useful distance cue for gerbils in a variety of ecological contexts.

Animals↗
PubMed2006

Flow rate calibration. III. The use of stabilized biostandards to calibrate the flow rate and calculate absolute CD4+ T-cell counts.

BACKGROUND: We have previously reported a flow rate calibration method for the determination of absolute CD4(+) T-lymphocyte counts that removes the need for the addition of latex beads to each sample. However, a limitation with this approach is that a calibration factor (CF) needs to be applied to adjust for differences in viscosity between latex bead suspensions and biological specimens. We have also demonstrated the value of using stabilized whole blood samples in external quality assessment (EQA) studies; such samples have a stable absolute lymphocyte count for over 1 year, at 4 degrees C. It was successfully demonstrated that this material can be used as a flow rate biocalibration (FRB) material for use as a flow cytometric control to provide a sample with a known CD4(+) T-lymphocyte count. Such material has advantages over latex bead technology as it can act as a full process control as well as having the same matrix and viscosity characteristics as the test material, thus removing the need for a CF. METHODS: In this study, we have analyzed 268 consecutive normal, abnormal, and HIV(+) samples using FRB, incorporating the PanLeucoGating approach and compared this to the MultiSet method, defined as the predicate. RESULTS: Percentage similarity statistics revealed the following: 0-3,000 CD4(+) cells/mul mean percentage difference (MPD; bias) 1.2%, 95% CI of 5.6-8%; 0-200 CD4(+) cells/microl MPD of 1.25%, 95% CI of 11.63-14.13%; 201-500 CD4(+) cells/microl MPD of 1%, 95% CI of 4.6-6.6%. DISCUSSION: This study demonstrates that stabilized whole blood can be used for FRB. It has the advantage of being a full process control, in addition to costing less than latex beads with highly comparable results. As bench top flow cytometers are extremely stable, this is a low cost and robust alternative to bead based methods for generating absolute CD4 counts.

Algorithms↗
PubMed2007

Backside calibration potentiometry: ion activity measurements with selective supported liquid membranes by calibrating from the inner side of the membrane.

In direct potentiometry, the magnitude of the measured potentials is used to determine the composition of the sample. While this places rather formidable demands on the required reproducibility of the associated potential measurements, typically on the order of microvolts, in vitro clinical analyses of blood samples are today successfully performed with direct potentiometry using ion-selective electrodes (ISEs). Unfortunately, most other analytical situations do not permit the sensor to be recalibrated every few minutes, as in environmental monitoring or in vivo measurements, and direct potentiometry is often bound to fail as an accurate method in these circumstances. This paper introduces a novel direction for potentiometric sensing, termed backside calibration potentiometry. Chemical asymmetries across thin supported liquid ISE membranes are assessed by determining the direction of potential drift upon changing the stirring rate on either side of the membrane. Disappearance of this drift indicates the disappearance of concentration gradients across the membrane and is used to determine the sample composition if the solution composition at the backside of the membrane and the interfering ion concentration in the sample are known. For practical determinations, the concentration of either the primary or the interfering ion is varied in the reference solution until the stirring effect disappears. The procedure is demonstrated with a Ca2+-selective membrane using Ba2+ as the dominant interfering ion. Another example includes the determination of Pb2+ in environmental samples where the pH is adjusted to a known level. At pH 4.0, H+ turns out to be the dominant interfering ion. The practical applicability of the method is shown with different environmental water samples, for which the results obtained with the novel method are compared with those obtained by traditional calibration using standard additions. The limitations of the novel method in terms of accuracy and applicable concentration ranges are discussed.

Barium↗
PubMedDate not supplied

A proposal for the calibration of plane-parallel ion chambers by accredited dosimetry calibration laboratories.

A procedure is described by which the AAPM-accredited dosimetry calibration laboratories could offer calibrations of plane-parallel ionization chambers for radiotherapy dosimetry applications, by comparison with a cylindrical ion chamber in a phantom irradiated by 60Co gamma rays. Ngas can thus be determined for the plane-parallel chamber under uniform conditions of photon scatter, and without the need for an electron fluence correction.

Calibration↗
PubMed1994

The Canadian National Calibration Reference Centre for In-Vivo Monitoring: thyroid monitoring. Part III: A basic calibration procedure for thyroid monitoring.

This article is the third of a five-part series covering various aspects of occupational thyroid monitoring. This article introduces the basic concepts required to understand the procedure for determining the counting efficiency of a thyroid detector. The B.R.M.D. thyroid-neck phantom is used as the calibration source. A procedure for personnel monitoring is also discussed and the concept of Minimum Detectable Activity (MDA) is introduced. The last two articles in this series discuss energy calibration, counting system optimization based on a single-channel analyzer and placement error minimization.

Calibration↗
PubMedDate not supplied

NPL secondary standard radionuclide calibrator. Syringe calibration factors for radionuclides used in nuclear medicine. National Physical Laboratory.

The measurement of the activity of a radiopharmaceutical administration to a patient is normally achieved via the use of a radionuclide calibrator. Although these radionuclides are normally measured initially in a standard glass vial, an aliquot of the solution is then usually withdrawn into a syringe prior to the administration. Both for general quality assurance good practice and for additional guarantees for patient safety, a confirmatory measurement of the syringe is almost obligatory Because of the different geometries and elemental compositions between plastic syringes and glass vials, the calibration factors for syringes may well be significantly different from those for the glass containers. The magnitude of these differences depends on the energies of the emitted photons. A variety of syringes typically used in hospital administrations, and covering a range of volumes and manufacturers, were obtained. The results obtained were compared to those for glass vials and show the large errors that can be produced by ignoring these differences in container format.

Glass↗
PubMedDate not supplied

Calibration in water versus calibration in air for cobalt-60 gamma rays.

In the United States it is common practice to calibrate Cobalt-60 teletherapy machines "in air," despite recommendations by the International Commission on Radiation Units and Measurements (ICRU) and other organizations that calibration be accomplished by measurement at 5-cm depth in a water phantom. A comparison has been made between the results of ionization measurements in air at 80.5-cm distance from the source and in water at 80-cm source-skin distance (SSD) for the determination of absorbed dose at three depth (5, 10, and 15 cm) for each of three fields sizes (6 X 6, 10 X 10, and 20 X 20 cm2), for a total of 42 Cobalt-60 machines. The mean of the ratio, absorbed dose from in-water measurements to absorbed dose at the same depth calculated from in-air measurements, ranged frt 5-cm depth for a 20 X 20-cm2 field size. Reasons for the differences are offered, and compliance with ICRU recommendations is suggested.

Air↗
PubMed1994

[A simple method for measurement of cerebral blood flow using 123I-IMP SPECT with calibrated standard input function by one point blood sampling; validation of calibration by one point venous blood sampling as a substitute for arterial blood sampling].

In a simplified method for measurement of cerebral blood flow using one 123I-IMP SPECT scan and one point arterial blood sampling (Autoradiography method), input function is obtained by calibrating a standard input function by one point arterial blood sampling. A purpose of this study is validation of calibration by one point venous blood sampling as a substitute for one point arterial blood sampling. After intravenous infusion of 123I-IMP, frequent arterial and venous blood sampling were simultaneously performed on 12 patients of CNS disease without any heart and lung disease and 5 normal volunteers. The radioactivity ratio of venous whole blood which obtained from cutaneous cubital vein to arterial whole blood were 0.76 +/- 0.08, 0.80 +/- 0.05, 0.81 +/- 0.06, 0.83 +/- 0.11 at 10, 20, 30, 50 min after 123I-IMP infusion, respectively. The venous blood radioactivities were always 20% lower than those of arterial blood radioactivity during 50 min. However, the ratio which obtained from cutaneous dorsal hand vein to artery were 0.93 +/- 0.02, 0.94 +/- 0.05, 0.98 +/- 0.04, 0.98 +/- 0.03, at 10, 20, 30, 50 min after 123I-IMP infusion, respectively. The venous blood radioactivity was consistent with artery. These indicate that arterio-venous difference of radioactivity in a peripheral cutaneous vein like a dorsal hand vein is minimal due to arteriovenous shunt in palm. Therefore, a substitution by blood sampling from cutaneous dorsal hand vein for artery will be possible. Optimized time for venous blood sampling evaluated by error analysis was 20 min after 123I-IMP infusion, which is 10 min later than that of arterial blood sampling.

Amphetamines↗
PubMed2006

Monte Carlo calculations of calibration and geometry correction factors of a radionuclide calibrator.

The activity of radioactive pharmaceuticals administered to patients in nuclear medicine is usually determined using well-type high-pressure ionization chambers. For the Bqmeter chamber (Consortium BQM, Czech Republic) a Monte Carlo model was created using the MCNP4C2 code. Basic chamber characteristics for two sample containers of various geometry (a vial and an ampoule) were calculated and compared with measurements. As the pharmaceuticals are often measured in various syringes, the chamber response for samples in syringes was also studied.

Algorithms↗
PubMed2000

EOG correction: comparing different calibration methods, and determining the number of epochs required in a calibration average.

OBJECTIVE: A form of EOG correction called the 'aligned-artifact average' (AAA) method has been advanced by the authors. In contrast to many previous methods, this used a correction coefficient (B), based on an average of eye movements rather than raw data, to remove eye movement related contamination from the EEG. The first part of this study was aimed at determining whether a variation of this procedure that is more easily implemented would produce a similar correction. The second part was designed to determine the number of epochs needed in an average to correct adequately. METHODS: Subjects performed a series of eye movement tasks whilst EEG and EOG data were recorded. Data were manipulated according to either the AAA or an alternate new ERP method (NERP) and the resultant Bs were compared in part A. In part B, averages were created from varying numbers of epochs, and the resultant r(2)-values were compared. RESULTS: The AAA and NERP methods produced the same Bs, and averages with at least 40 epochs were required for adequate B estimation for both VEOG and HEOG. CONCLUSION: There is no difference between the AAA and NERP methods and thus it is acceptable to use the more easily implemented NERP method for EOG correction. It is recommended that when applying this procedure, at least 40 epochs should be used to make up the averages from which to calculate correction coefficients.

Adolescent↗