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PubMed1993

Determining the volume of prostatic carcinoma: value of MR imaging with an external-array coil.

OBJECTIVE: The size of prostatic carcinomas, as determined by estimations of the tumor volume, has a direct correlation with the histologic grade and stage. Therefore, accurate information about tumor volume can play an important role in determining appropriate treatment and establishing a patient's prognosis. Accordingly, we performed a study to assess the accuracy of MR imaging with external-array coils and the fast spin-echo technique for determining tumor volume in patients with prostatic cancer. SUBJECTS AND METHODS: In a prospective study, 20 patients with biopsy-proved prostatic cancer had MR imaging before radical prostatectomy. A 1.5-T system, a prototype external-array coil, and fast spin-echo technique were used to obtain axial T2-weighted (4000/120 [TR/TE]) MR images throughout the prostate and seminal vesicles. Contiguous 5-mm sections were obtained with a 256 x 256 or 256 x 192 matrix, 24-cm field of view, four excitations, and fat suppression. The volumes of cancer obtained with MR imaging and surgical specimens were determined independently. The areas of tumor were determined from individual axial sections by summing and multiplying by the section thickness. RESULTS: Seventeen of the 20 cancers were detected on MR images. A significant correlation between the volume of the tumor as determined with MR imaging and measurements of the specimens was observed (r = .81, p < .001). Four transition zone tumors were detected as zones of rather homogeneous decreased intensity. One important source of error for volumes determined with MR images was a limitation in the histologic specificity of MR imaging for the delineation of cancer; in some cases benign changes or normal prostates were interpreted as cancer. Another limitation was the presence of changes after biopsy that concealed portions of 10 of the 17 tumors visualized. CONCLUSION: The accuracy of the MR technique used was not sufficient for reliable prediction of tumor volume. The lack of specificity of T2-weighted MR imaging for cancer detection and the presence of changes caused by biopsy were major sources of error.

Aged↗
PubMed2006

[Analysis of films by X-ray fluorescence spectrometry].

As a quantitative method of film sample, the X-ray fluorescence (XRF) technique has been used extensively because it is non-destructive, fast and accurate. Moreover it could determine the concentration and thickness of film sample simultaneously. A review was given of the study on the quantitative method of films by X-ray fluorescence spectrometry, in which the theoretical calculation of fluorescence intensity, the matrix effects and the methods for their correction, the sources of errors, the software for quantitative analysis, and the application of the method were summarized and discussed. New development and application of films characterization by X-ray fluorescence spectrometry were also expected. Because the similar calibration specimen for film sample is difficult to prepare and the fundamental parameter method could quantitatively analyze film samples even if only the pure element specimen is employed, the fundamental parameter method is studied extensively. The fundamental parameter method was introduced mainly in the present article, including the fundamental parameter equations to calculate the theoretical intensity of fluorescence, the source of error in calculation, and the software for analysis.

English Abstract↗
PubMed1997

Athletic injury reporting. Development of universal systems.

There are numerous athletic injury reporting systems currently in place. In order for our understanding of athletic injury epidemiology to advance, we must be able to compare data from divergent sources. This paper provides a review of existing athletic injury reporting systems in North America. The epidemiological designs employed in these systems are outlined, along with a description of the strengths and weaknesses of each approach to reporting. The differences between the case-series and cohort methods are delineated and the importance of injury definition, sources of error, denominator data and exposure estimation are discussed within this context. Four recommendations are then offered to assist in moving toward more universal systems for athletic injury reporting. First, comparability of data between systems should be maximised through clear indication of the reporting system design and the methods of data collection. Secondly, an exact definition should be given as to what constitutes a reportable event ('injury'). Thirdly, whenever possible, outcome information should be collected on each reported event so that an injury definition may be applied at the time of data analysis. Lastly, any limitations or sources of error should be acknowledged.

Athletic Injuries↗
PubMed2005

Uncertainty assessment of VOC emissions from paint in The Netherlands using the NUSAP system.

We demonstrate an innovative approach to uncertainty assessment known as the NUSAP system, to assess qualitative and quantitative uncertainty for the case of emissions of volatile organic compounds (VOC) from paint in The Netherlands. Using expert elicitation, we identified key sources of error, critical assumptions, and bias in the monitoring process. We assessed pedigree and probabilistic uncertainty of all input quantities. We used four pedigree criteria to assess the strength of the knowledge base: proxy representation, empirical basis, methodological rigour and degree of validation. Using Monte Carlo analysis, we assessed sensitivity and propagation of uncertainty. Results for sensitivity and pedigree were combined in a 'NUSAP Diagnostic Diagram', which effectively highlighted the assumption for VOC percentage of imported paint as the weakest spot in the monitoring of VOC emissions. We conclude that NUSAP facilitates systematic scrutinization of method and underlying assumptions and structures creative thinking on sources of error and bias. It provides a means to prioritise uncertainties and focus research efforts on the potentially most problematic parameters and assumptions, at the same time identifying specific weaknesses in the knowledge base. With NUSAP, nuances of meaning about quantities can be conveyed concisely and clearly, to a degree that is not possible with statistic methods only.

Air Pollutants↗
PubMed1993

An examination of the reliability of the radiochemical assay for monoamine oxidases A and B.

The radiochemical assay for MAO A has been compared with the polarographic and alcohol dehydrogenase-coupled assays, using 5-hydroxytryptamine (5-HT) and tyramine and the homogeneous human liver enzyme expressed in yeast, and rat liver mitochondria. Despite efforts to measure true initial rates and to avoid known sources of error in the radiochemical procedure, significantly higher rates (Vmax) and lower Km values for the substrate were obtained with the polarographic than with the radiochemical method for 5-HT and tyramine, using either highly purified enzyme or mitochondria. The rate of tyramine oxidation measured by the polarographic method and the coupled assay agreed well, however. Consequently, for kinetic and inhibition studies we recommend the polarographic method for MAO A substrates. Comparison of the radiochemical, polarographic, spectrophotometric, and coupled assays for MAO B from beef liver (mitochondria and homogeneous enzyme) showed polarography to be the method of choice on all substrates tested, although, if all known sources of error are carefully controlled, the radiochemical assay gives the same Vmax and Km values. We also report that with each substrate studied the apparent Km is much lower when mitochondria are used than when the highly purified, virtually lipid-free preparations of MAO A are studied.

Animals↗
PubMed2000

Xenon CT cerebral blood flow in patients with head injury: influence of pulmonary trauma on the input function.

The noninvasive xenon-enhanced CT (Xe CT) cerebral blood flow (CBF) method has been used in patients with severe traumatic brain injury (TBI) to identify the blood-flow thresholds for the development of irreversible ischaemia or infarction following severe TBI. Quantitative regional CBF (rCBF) estimates are based on the assumption of identity between the end-tidal xenon concentration curve, used as the input function, and the arterial xenon concentration curve, being the true input function to the brain. Accordingly, rCBF data addressing the issue of ischaemia should be viewed in relation to possible deviations between the end-tidal and arterial xenon concentration curves. To evaluate this possible source of error, we studied five patients with severe TBI (Glasgow coma score < or =7) who also had pulmonary trauma. CBF was studied with the Xe CT CBF method and flow rates were determined by fitting the Kety equation to each CT voxel using either the end-tidal or the arterial xenon curve as input function. In all patients rCBF estimates were lower using the end-tidal xenon curve than with the arterial xenon curve; the mean underestimation was 20.3% in gray metter and 17.3 % in white matter. The deviation between the end-tidal and arterial xenon concentration curves should be considered as a source of error when defining critical flow values according to the flow thresholds of tissue viability.

Adult↗
PubMed1991

Clinical decision making of critical care nurses managing computer-simulated tachydysrhythmias.

The purposes of this study were to describe the clinical decision making of critical care nurses managing computer-simulated tachydysrhythmias and to assess the major sources of error related to the management of two tachydysrhythmias: atrial flutter and ventricular tachycardia. In this descriptive study, 142 critical care nurses each completed four computerized clinical simulations (two atrial flutter and two ventricular tachycardia). Simulation performance was measured by proficiency score (comparison with expert performance), patient outcome (cure or die), and amount of data collected before the first intervention. Mean proficiency scores were 51% for atrial flutter and 35% for ventricular tachycardia. Thirteen percent of the atrial flutter and 35% of the ventricular tachycardia simulations ended in patient death. Failure to recognize ventricular tachycardia and unfamiliarity with second- and third-line treatments were major sources of error. Medication errors were the cause of death in 87% of the simulations ending in patient death. These results document the need for emphasis on dysrhythmia management in the critical care curriculum.

Arrhythmias, Cardiac↗
PubMed1993

Whole body irradiation does not affect induction of new bone development.

The effect of whole body irradiation given either beforehand to the donor or after implantation to the recipient rats on the inductive capacity of decalcified bone grafts was studied. In examining the effect of advance whole body irradiation of the donor animal, the grafts were harvested five days after the irradiation, non-irradiated rats serving as control donors. Error! Reference source not found-irradiation with doses of 800, 950 or 1100 rad was used. The grafts, implanted either alone or in composite form in the muscle pouches of non-irradiated rats of an inbred strain, were removed four weeks after implantation and examined by measuring 45Ca uptake, ash weight and area of radio-opacity in roentgenographs. There were no differences in bone-inductive capacity between the grafts obtained after total body irradiation and the control grafts. In the other part of the study, decalcified bone grafts were implanted in the abdominal muscle pouches of the recipient rats, which were exposed to Error! Reference source not found.-radiation of 800 rad on either the second, 10th or 21st day after implantation. Four weeks after implantation the grafts were removed and examined. No differences in new bone formation were found between the groups subjected to irradiation at different times or between these and the non-irradiated controls. It is concluded that donor whole body irradiation of 800-1100 rad in rat has no significant effect on the properties of new bone developed in allogeneic decalcified bone grafts, neither does recipient 800 rad irradiation administered after implantation affect the bone induction activity.

Animals↗
PubMed1998

Evaluation of dual-tip micromanometers during 21-day implantation in goats.

Investigative research efforts using a cardiovascular model required the determination of central circulatory haemodynamic and arterial system parameters for the evaluation of cardiovascular performance. These calculations required continuous beat-to-beat measurement of pressure within the four chambers of the heart and great vessels. Sensitivity and offset drift, longevity, and sources of error for eight 3F dual-tipped micromanometers were determined during 21 days of implantation in goats. Subjects were instrumented with pairs of chronically implanted fluid-filled access catheters in the left and right ventricles, through which dual-tipped (test) micromanometers were chronically inserted and single-tip (standard) micromanometers were acutely inserted. Acutely inserted sensors were calibrated daily and measured pressures were compared in vivo to the chronically inserted sensors. Comparison of the pre- and post-gain calibration of the chronically inserted sensors showed a mean sensitivity drift of 1.0 +/- 0.4% (99% confidence, n = 9 sensors) and mean offset drift of 5.0 +/- 1.5 mmHg (99% confidence, n = 9 sensors). Potential sources of error for these drifts were identified, and included measurement system inaccuracies, temperature drift, hydrostatic column gradients, and dynamic pressure changes. Based upon these findings, we determined that these micromanometers may be chronically inserted in high-pressure chambers for up to 17 days with an acceptable error, but should be limited to acute (hours) insertions in low-pressure applications.

Animals↗
PubMed1985

Fluid filled oculoplethysmography and carotid artery disease: imperfect but useful.

Fluid filled oculoplethysmography (OPG) is a widely used method of assessing carotid stenosis but it has limitations in the detection of bilateral internal carotid artery lesions and of external carotid artery stenoses. In this study, 157 consecutive patients having carotid angiography and fluid filled OPG were assessed to determine the accuracy of the technique and define the sources of error. Haemodynamically significant stenosis (HDS) was defined as at least 50% stenosis of the internal carotid artery (ICA). Only the most severely stenosed side of the 35 bilateral HDS lesions was detected owing to the poor reliability of ear pulse delays. Eye/eye delays alone detected the most severely stenosed side in 82 of 98 patients with an HDS stenosis of one or both ICAs for a sensitivity of 84% a specificity of 71% (41/59) and accuracy of 79% (81/157). The measurement of ear/ear pulse delays for external carotid artery (ECA) stenosis had a sensitivity of only 15% (5/34). Ear/eye pulse delays detected none of the 35 patients with bilateral HDS ICA stenosis. Bilateral equal HDS ICA stenoses were a significant source of error. Stenotic disease was present in the aortic arch and branches (five patients) or the carotid siphon (eight patients) and in seven cases it resulted in an incorrect localization on OPG. There was no diagnostic relationship between the severity of delay and the presence of total occlusion. Chronic local eye pathology was present in 13 patients and did not affect the results of the OPG. We have ceased to use ear pulse measurements for routine assessment but continue to use the eye/eye delays in conjunction with a carotid doppler imaging system.

Adult↗
PubMed1997

[Analysis of reject x-ray films as a quality assurance element in diagnostic radiology].

PURPOSE: Analysis of reject films from a large radiological department under the following aspects: How big is the waste of films? Where are the sources of error? What are the possible means of quality assurance? MATERIAL AND METHOD: During a total period of 9 months, separated into three quarters, 14,570 reject films were analysed and assigned to 4 categories ("positioning", "exposure", "reject films due to patients" and "others"). In addition they were classified according to the respective parts of the body. The influence of a "study effect" was quantified by the analysis before and after information of staff. RESULTS: The reject film rate in relation to all performed x-rays, was 9.0-13.2% of all the films taken during that period: of these, the failure rate (x-rays useless for diagnosis because of their bad quality) was between 54.2 and 57.5%. In this category, the main sources of error were positioning (55%) and exposure (34%). Surprisingly, the technical film waste amounted to 42.5-45.8% (not developed or preexposed films, x-rays of phantoms etc.). CONCLUSION: Wasted films due to errors occurring during taking, as well as technical film waste, are unavoidable. Their proportion in relation to the total number of films should not exceed 8%. The main approach to reducing cost must be to cut down technical film waste.

Humans↗
PubMed1975

Radioimmunological determination of human C-peptide in serum.

A routing radioimmunoassay for human C-peptide in serum is described. Antibodies against human C-peptide were raised by immunizing guinea pigs with human b-component. Nine out of 12 animals produced useful antibodies within 6 months. Insulin antibodies coupled to Sepharose were used to bind human proinsulin and insulin in the serum and after centrifugation C-peptide was determined in the supernatant. The detection limit of the assay (calculated as 2 SD from zero) was about 0.003 pmole of C-peptide (in 100 mul). The main sources of error were: (1) Normal and diabetic sera devoid of C-peptide gave a displacement of 125I-Tyr-C-peptide varying from 0 to 0.16 nM (6 different antisera). Only one antiserum (M 1181) showed no displacement, and the values of C-peptide determined with this antiserum in normal and diabetic sera were lower than the values determined with another antiserum, which gave a value of 0.07 nM in the sera free of C-peptide. It is suggested that displacement found with most antisera is due to substances in serum that are not related to C-peptide or proinsulin. (2) Serial dilutions of pancreatic extracts and sera may yield dilution curves slightly different to those of the synthetic standard. Possible explanations are discussed. These sources of error can be eliminated or reduced by the proper selection of antisera. Fasting sera from 15 normals, 8 maturity-onset diabetics and 10 insulin-requiring diabetics showed the following concentrations of C-peptide: (M 1181) 0.35 +/- 0.09, 0.74 +/- 0.51 and 0.21 +/- 0.14 (nM, mean +/- SD). One hour after 1.75 g/kg oral glucose the values increased to 2.24 +/- 0.71, 2.34 +/- 0.24 nM.

Animals↗
PubMed1980

Thiocyanate as a marker of saliva in gastric juice?

One source of error in gastric secretion studies is swallowed saliva. The possibility that salivary thiocyanate might be used to measure this contamination has been investigated. Thiocyanate concentration was measured in saliva and gastric juice collected simultaneously in 22 duodenal ulcer patients undergoing routine insulin and histamine secretion studies. On stimulation, despite the increase in the rate of gastric secretion this was not matched by an appropriate fall in the concentration of thiocyanate in gastric juice. Moreover, in one-third of the gastric juice specimens, the thiocyanate concentration was greater than in the simultaneous samples of saliva. Thus, contrary to what has been claimed, thiocyanate is present not only in saliva but also in gastric juice. Therefore it cannot be used as a marker of salivary contamination. An adequate marker of this source of error has not yet been found.

Duodenal Ulcer↗
PubMed2002

A stability analysis of a decentralized adaptive feedback active control system of sinusoidal sound in free space.

In some cases, the implementation of active control of sound in free space requires a large number of secondary sources and error sensors. In terms of control hardware, this may translate into considerable processing power requirement. A practical method to decrease processing power is to decentralize the control; that is, implement many single-input, single-output independent controllers operating simultaneously instead of a large multiple-input, multiple-output system. The main drawback of decentralized control is the risk of global instability. The purpose of this paper is to derive conditions under which globally stable control system behavior can be obtained in the case of adaptive feedback decentralized control for a sinusoidal disturbance. The main objective is to give practical conditions derived from the small gain theorem and the Nyquist criterion for the stability of the control system. These conditions only take into account the geometrical arrangement of the secondary sources and error sensors. This analysis involves a new parameter beta called "performance index," which is associated with both the convergence of the individual controllers and the global stability of the system. Simulation and experimental results are shown to illustrate the effectiveness of the developed analytical tools.

Feedback↗
PubMed2001

An accurate and precise methodology for routine determination of the false-negative rate of Papanicolaou smear screening.

BACKGROUND: Although the false-negative rate (FNR) is the most important quality control measure for Papanicolaou smear screening, accurate, precise, and feasible methods for determining this value are lacking. METHODS: The author undertook an analysis and review of the literature. RESULTS: The best estimates of the FNR using atypical squamous cells of undetermined significance (ASCUS) as a threshold range from 17% to 61%. Sources of error in the accuracy of this measure that must be accounted for include the FNR of the review method, differences in diagnostic thresholds between the original diagnostic method and the review method, and differences in diagnostic accuracy between the original diagnostic method and the review method. Statistically precise (valid to within 10%) measurement of this value in laboratories with an ASCUS+ rate of 7% can be made from interlaboratory rescreening of approximately 1200-1500 randomly selected normal and abnormal slides along with both laboratories rediagnosing without rescreening 300-400 benign cellular change and ASCUS slides to determine the difference in diagnostic threshold. Consensus for each slide is not required with this method. Changing the threshold to low grade squamous intraepithelial lesion (best estimate FNR, 14-58%) requires review of significantly more slides to achieve the same statistical level of precision. CONCLUSIONS: Detailed analysis of the sources of error in determining the FNR allow creation of methods that are relatively unbiased, feasible, and testable and whose accuracy and precision can be determined.

False Negative Reactions↗
PubMed2003

The importance of thermodynamic equilibrium for high throughput gene expression arrays.

We present an analysis of physical chemical constraints on the accuracy of DNA micro-arrays under equilibrium and nonequilibrium conditions. At the beginning of the article we describe an algorithm for choosing a probe set with high specificity for targeted genes under equilibrium conditions. The algorithm as well as existing methods is used to select probes from the full Saccharomyces cerevisiae genome, and these probe sets, along with a randomly selected set, are used to simulate array experiments and identify sources of error. Inasmuch as specificity and sensitivity are maximum at thermodynamic equilibrium, we are particularly interested in the factors that affect the approach to equilibrium. These are analyzed later in the article, where we develop and apply a rapidly executable method to simulate the kinetics of hybridization on a solid phase support. Although the difference between solution phase and solid phase hybridization is of little consequence for specificity and sensitivity when equilibrium is achieved, the kinetics of hybridization has a pronounced effect on both. We first use the model to estimate the effects of diffusion, crosshybridization, relaxation time, and target concentration on the hybridization kinetics, and then investigate the effects of the most important kinetic parameters on specificity. We find even when using probe sets that have high specificity at equilibrium that substantial crosshybridization is present under nonequilibrium conditions. Although those complexes that differ from perfect complementarity by more than a single base do not contribute to sources of error at equilibrium, they slow the approach to equilibrium dramatically and confound interpretation of the data when they dissociate on a time scale comparable to the time of the experiment. For the best probe set, our simulation shows that steady-state behavior is obtained in a relaxation time of approximately 12-15 h for experimental target concentrations approximately (10(-13) - 10(-14))M, but the time is greater for lower target concentrations in the range (10(-15)-10(-16))M. The result points to an asymmetry in the accuracy with which up- and downregulated genes are identified.

Algorithms↗
PubMed2004

Spearman's footrule as a measure of cDNA microarray reproducibility.

Replication is a crucial aspect of microarray experiments, due to various sources of errors that persist even after systematic effects are removed. It has been confirmed that replication in microarray studies is not equivalent to duplication, and hence it is not a waste of scientific resources. Replication and reproducibility are the most important issues for microarray application in genomics. However, little attention has been paid to the assessment of reproducibility among replicates. Here we develop, using Spearman's footrule, a new measure of the reproducibility of cDNA microarrays, which is based on how consistently a gene's relative rank is maintained in two replicates. The reproducibility measure, termed index.R, has an R2-type operational interpretation. Index.R assesses reproducibility at the initial stage of the microarray data analysis even before normalization is done. We first define three layers of replicates, biological, technical, and hybridizational, which refer to different biological units, different mRNAs from the same tissue, and separate cDNAs from a cDNA pool. As the replicate layer moves down to a lower level, the experiment has fewer sources of errors and thus is expected to be more reproducible. To validate the method we apply index.R to two sets of controlled cDNA microarray experiments, each of which has two or three layers of replicates. Index.R shows a uniform increase as the layer of the replicates moves into a more homogeneous environment. We also note that index.R has a larger jump size than Pearson's correlation or Spearman's rank correlation for each replicate layer move, and therefore, it has greater expandability as a measure in [0,1] than these two other measures.

Cell Line, Tumor↗
PubMed1989

Human serum LH inhibitor(s): behaviour and contribution to in vitro bioassay of LH using dispersed mouse Leydig cells.

The present study aimed at investigating the nature and causes of non-parallelism in testosterone responses to serial dilutions of peripheral serum and standard LH preparations in the mouse Leydig cell in vitro bioassay of LH. Immunoadsorption with monoclonal antibody to the beta-subunit of LH was used to obtain LH-free serum; the procedure removed more than 98% of the immunoassayable LH. When a constant amount of the LH-free serum was added to standard dilutions, the bioassay dose-response curves to serum dilutions, the standards became parallel, i.e. the well-known source of error of this assay system was eliminated. When standard curves prepared in medium and LH-free serum (final concentration 10%) were compared, no effect of the serum was found on basal cAMP and testosterone production. However, the LH-stimulated testosterone and cAMP production were suppressed by serum by a rather constant factor of 40%. Mild heating (60 degrees C, 15 min) or treatment with dextran-coated charcoal, but not other extraction, was able to eliminate the inhibitory activity of the LH-free serum. Binding studies demonstrated that [125I]HCG interaction with mouse Leydig cell homogenates was inhibited by LH-free serum in a fashion indicative of reduced LH receptor number, but not of reduced binding affinity. In conclusion, these data show that human serum contains LH inhibitor(s) which affect the LH-receptor interaction and LH stimulated testosterone production in mouse Leydig cell in vitro. The effect is marked in serum concentration over 1.5% and it shows only minor variation between individual sera. This source of error can be effectively removed from the LH in vitro bioassay by using LH-free serum for preparation of dilutions of LH standards.

Adsorption↗