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Results for “Error minimization”

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PubMed2002

Optimized pulse parameters for reducing quantitation errors due to saturation factor changes in magnetic resonance spectroscopy.

We present an analysis of the effects of chemical exchange and changes in T(1) on metabolite quantitation for heart, skeletal muscle, and brain using the one-pulse experiment for a sample which is subject to temporal variation. We use an optimization algorithm to calculate interpulse delay times, TRs, and flip angles, theta, resulting in maximal root-mean-squared signal-to-noise per unit time (S/N) for all exchanging species under 5 and 10% constraints on quantitation errors. The optimization yields TR and theta pairs giving signal-to-noise per unit time close or superior to typical literature values. Additional simulations were performed to demonstrate explicitly the dependence of the quantitation errors on pulse parameters and variations in the properties of the sample, such as may occur after an intervention. We find that (i) correction for partial saturation in accordance with the usual analysis neglecting variations in metabolite concentrations and rate constants may readily result in quantitation errors of 15% or more; the exact degree of error depends upon the details of the system under consideration; (ii) if T(1)'s vary as well, significantly larger quantitation errors may occur; and (iii) optimal values of pulse parameters may minimize errors in quantitation with minimal S/N loss.

Adenosine Triphosphate↗

PubMed2026

The genetic code at the balance point of error and demand.

The origin and organizing principles of the genetic code remain central problems in molecular evolution. The low probability of the natural codon-to-amino acid mapping arising by chance has spurred the hypothesis that its structure is optimized for robustness to mutations and translational errors. For the construction of effective molecular machines, the repertoire of encoded amino acids must also be diverse enough in physicochemical features. Here, we examine whether the standard genetic code can be understood as a near-optimal solution balancing these two objectives: minimizing error load and aligning codon assignments with the naturally occurring amino acid composition. Using simulated annealing, we explore this trade-off across a broad range of parameters. We find that the standard genetic code resides near an optimum in the fitness landscape of possible genetic codes. The degeneracy of the code plays a dual role, minimizing mistranslation errors while matching codon multiplicity to amino acid usage frequencies. As a result, uniform codon usage alone is sufficient to recover the empirical amino acid composition, without any additional bias. It is a highly effective solution that balances fidelity against resource availability constraints. A comparative analysis of natural variants also reveals a functional decoupling: error robustness acts as a rigid global constraint determined by code topology, whereas compositional alignment serves as a more flexible variable that adapts to lineage-specific demands. These results support a multi-objective optimization framework in which the genetic code reflects a balance between translational fidelity and proteomic demand.

Genetic Code↗

PubMed2001

Infrared patient positioning for stereotactic radiosurgery of extracranial tumors.

We report on a novel, non-invasive patient positioning system for radiosurgery of extracranial tumors. The system consisted of infrared cameras and reflective markers attached to the skin. Because localization accuracy is critical in radiosurgery, we performed a theoretical analysis of the accuracy of the system. A computer simulation program modeled errors in marker position, and was used to predict errors in targeting and study methods for minimizing errors. The use of redundant markers improved the overall accuracy of targeting. Experimental data was collected using a rigid torso phantom and correlated with theoretical results. The accuracy of the infrared system was compared with existing systems.

Computer Simulation↗

PubMed1998

Error rates in clinical radiotherapy.

PURPOSE: Error rates in clinical oncology are undergoing increasing scrutiny. The purpose of this study was to understand error frequency, error patterns, underlying causal links, consequences, and possible prevention strategies in clinical radiotherapy. PATIENTS AND METHODS: Treatment information, self-reported error documentation, and retrospective analyses of electronic treatment verification transcripts for 1,925 consecutive patients treated with a total of 93,332 individual radiotherapy fields were reviewed and analyzed. RESULTS: A total of 59 separate errors that affected 168 individual treatment fields were detected, which yielded a crude radiation delivery error rate of 0.18%. All 59 errors were judged to be level I (negligible chance of adverse medical outcome) with the most common error category being a minor treatment field block misplacement. A comprehensive quality assurance program and an electronic record-and-verify linear accelerator interlock system seem to have prevented the occurrence of many additional errors. However, nine of the 59 errors were directly related to the use of this system and generally involved the transposition of similar numbers within series of treatment coordinate data-sets. Overall, radiotherapy error rates favorably compare with reported error rates for pharmaceutical administration in large tertiary care hospitals. CONCLUSION: When modern automated error-minimization methods are used along with nonpunitive error reporting systems, clinical radiotherapy seems to be highly safe. Formal error analysis studies may allow the rational design of prevention strategies that are attuned to the frequency, seriousness, and antecedent causes of many classes of potential radiotherapy errors.

Humans↗

PubMed2003

Signal detection via residence times statistics: noise-mediated minimization of the measurement error.

We study the problem of detecting a small dc signal by quantifying its effect on the mean difference DeltaT in residence times in the stable steady states of a bistable dynamical measurement device, in the presence of a noise floor and a known time-sinusoidal bias signal. Errors in the measurement process occur due to a finite observation time that is present in most practical scenarios. The error is found to have a nonmonotonic dependence on the noise intensity; at a critical noise intensity, the error is minimized. This phenomenon, reminiscent of the well-known stochastic resonance effect, can also be obtained by adjusting the device tuning parameters for a given noise floor. The effect appears to be most pronounced for subthreshold bias signals in the strongly nonlinear response regime.

Journal Article↗

PubMedDate not supplied

Medical errors: computers are no panacea.

Increased patient loads, time pressures, and heightened public awareness of medical errors are forcing many physicians and clinical administrators to consider acquiring computerized physician order entry (CPOE) systems and clinical information systems. The recent revelation that CPOE systems can facilitate medical errors, however, is a call to physicians to remain vigilant despite the new technologies. By attending to specific data-capture and data-access errors associated with clinical information systems, physicians can minimize errors associated with clinical information systems and maximize the potential benefits to their patients.

Computer Security↗

PubMed2002

Interruptions improve choice performance in gray jays: prolonged information processing versus minimization of costly errors.

Under the assumption that selection favors minimization of costly errors, erroneous choice may be common when its fitness cost is low. According to an adaptive-choice model, this cost depends on the rate at which an animal encounters the choice: the higher this rate, the smaller the cost of choosing a less valuable option. Errors should thus be more common when interruptions to foraging are shorter. A previous experiment supported this prediction: gray jays, Perisoreus canadensis, were more error prone when subjected to shorter delays to access to food rewards. This pattern, though, is also predicted by an attentional-constraints model. Because the subjects were able to inspect the rewards during delays, their improved performance when subjected to longer delays could have been a byproduct of the experimentally prolonged opportunity for information processing. To evaluate this possibility, a follow-up experiment manipulated both delay to access and whether rewards could be inspected during delays. Depriving jays of the opportunity to inspect rewards (using opaque lids) induced only a small, nonsignificant increase in error rate. This effect was independent of length of delay and so the jays' improved performance when subjected to longer delays was not simply a byproduct of prolonged information processing. More definitively, even when the jays were prevented from inspecting rewards during delays, their performance improved when subjected to longer delays. The findings are thus consistent with the adaptive-choice model.

Animals↗

PubMed1993

Picogram detection of stable dye-DNA intercalation complexes with two-color laser-excited confocal fluorescence gel scanner.

The stable complexes between highly fluorescent, polyfunctional intercalators and dsDNA can be used to detect dsDNA in agarose gels at picogram levels and for multicolor detection of multiplexed dsDNA fragments. Development of additional DNA-binding fluorophores with appropriate spectroscopic properties will expand the range of applications. In principle, the DNA-dye intercalation complexes represent a more sensitive alternative to an established approach to fluorescent labeling and detection of restriction fragments by ligation to single-stranded short oligonucleotides labeled with different fluorochromes, followed by separation on denaturing polyacrylamide gels. The latter technique gives near single-base resolution up to 400 bases and the ability to quantitate fragment size up to 2000 bases, and has been successfully applied to cosmid mapping. Detection of DNA fragments as intercalation complexes requires that the separations be performed on agarose gels under nondenaturing conditions. Such conditions have been used for extensive mapping of yeast cosmids with postelectrophoresis staining with ethidium bromide. For the patterns on agarose gels, the magnitude of the "error window," which specifies how similar two fragments must be before the corresponding fragments in different digests are paired, was reported to be strongly size dependent. The error window was expanded by a factor of 1.3 for fragments from 400 to 600 bp, 1.2 for fragments from 600 to 800 bp, and 1.1 for fragments from 800 to 1000 bp. Moreover, it was necessary to introduce corrections for systematic differences between size estimates taken from two different gels. For the multiplexing procedure described here, the size estimates for fragments from 600 bp to over 23 kbp were in close agreement with actual sizes as determined from DNA sequence (Table I), and certainly within the error windows given above. The multiplexing procedure should also minimize errors introduced by gel-to-gel variations in mobility, because the standard and unknowns are always run in the same lanes. Kohara et al. established a physical map of almost the entire Escherichia coli chromosome by analysis of a large genomic library. In this case, partial restriction digests were used to generate patterns of fragments and the mapping was performed by agarose gel electrophoresis. The disadvantage of this approach is that fewer fragments are generated. However, this is compensated for by the fact that partial digests reveal the order of the fragments produced and thus greatly increase the amount of information relevant to the question of overlap between different DNA fragments.(ABSTRACT TRUNCATED AT 400 WORDS)

Benzothiazoles↗

PubMed2003

Sensory adaptation as Kalman filtering: theory and illustration with contrast adaptation.

Sensory adaptation allows biological systems to adjust to variations in the environment. A recent theoretical work postulated that the goal of adaptation is to minimize errors in the performance of particular tasks. The proposed minimization was Bayesian and required prior knowledge of the environment and of the limitations of the mechanisms processing the information. One problem with that formulation is that the environment changes in time and the theory did not specify how to know what the current state of the environment is. Here, we extend that theory to estimate optimally the environmental state from the temporal stream of responses. We show that such optimal estimation is a generalized form of Kalman filtering. An application of this new Kalman-filtering framework is worked out for retinal contrast adaptation. It is shown that this application can account for surprising features of the data. For example, it accounts for the differences in responses to increases and decreases of mean contrasts in the environment. In addition, it accounts for the two-phase decay of contrast gain when the mean contrast in the environment rises suddenly. The success of this and related theories suggest that sensory adaptation is a form of constrained biological optimization.

Adaptation, Physiological↗

PubMed1997

Quality and liability issues with the Papanicolaou smear: lessons from the science of error prevention.

The pathologists and cytologists who study Papanicolaou smears perform a highly successful cancer screening test in a low-prevalence population. This leads to a mathematically inevitable false-negative error rate even in the most competent professional hands. The US judicial system supports a public expectation of perfect performance by civil and, recently, criminal punishment of error. Lessons are sought from a considerable industrial experience with accident prevention for possible insights into process improvement that might mitigate the risk of false-negative errors. The elements that, by system analysis, contribute to accidents are reviewed, and the conditions that enhance the accident potential are outlined. The cognitive functions and aberrations that are involved in the operator component of error analysis are described. As a result of pathologists' activities in the systematic measurement of laboratory performance for the last half century, the College of American Pathologists' accreditation program and its derivative Clinical Laboratory Improvement Act requirements have already laid out the avenues of error minimalization. There are no lessons from the science of error prevention that can affect the public expectation of zero error in a screening test and the consequent punishment of cytology professionals. A thesis is offered that the problem is society's if its goal is eradication of cervical cancer mortality. A call is made for leadership by a prestigious, nonpathologist, national organization to make the public understand that the current cytology liability issue is primarily a threat to women and the public health. To initiate public dialogue, a mechanism is suggested to protect simultaneously a patient's right of access to the judicial system and the general availability of the Papanicolaou smear to reduce cervical cancer mortality and morbidity.

Diagnostic Errors↗

PubMed1993

Primary error detection and minimization (PEDMIN) strategies in social cognition: a reinterpretation of confirmation bias phenomena.

A broad empirical literature demonstrates what has been termed a confirmation bias or positive test strategy heuristic in reasoning (Klayman & Ha, 1987), a potentially maladaptive pattern of data preferences that coexists with more normative preferences for highly diagnostic information (Skov & Sherman, 1986). A model is developed to account for these variations in test strategies, beginning with the premise that cognitive processes are adapted to reducing particularly costly errors rather than to detecting "truth" (Cosmides & Tooby, 1992). By specifying the information required to minimize various errors of primary concern, the model clarifies the adaptiveness of certain confirmatory preferences, identifies conditions under which such preferences should diminish, and outlines how error minimization goals might produce data preferences coincidentally consistent with normative prescriptions.

Attention↗

PubMed2003

An empirical exploration of data quality in DNA-based population inventories.

I present data from 21 population inventory studies - 20 of them on bears - that relied on the noninvasive collection of hair, and review the methods that were used to prevent genetic errors in these studies. These methods were designed to simultaneously minimize errors (which can bias estimates of abundance) and per-sample analysis effort (which can reduce the precision of estimates by limiting sample size). A variety of approaches were used to probe the reliability of the empirical data, producing a mean, per-study estimate of no more than one undetected error in either direction (too few or too many individuals identified in the laboratory). For the type of samples considered here (plucked hair samples), the gain or loss of individuals in the laboratory can be reduced to a level that is inconsequential relative to the more universal sources of bias and imprecision that can affect mark-recapture studies, assuming that marker systems are selected according to stated guidelines, marginal samples are excluded at an early stage, similar pairs of genotypes are scrutinized, and laboratory work is performed with skill and care.

Animals↗

PubMed2001

Patient safety in guideline-based decision support for hypertension management: ATHENA DSS.

The Institute of Medicine recently issued a landmark report on medical error.1 In the penumbra of this report, every aspect of health care is subject to new scrutiny regarding patient safety. Informatics technology can support patient safety by correcting problems inherent in older technology; however, new information technology can also contribute to new sources of error. We report here a categorization of possible errors that may arise in deploying a system designed to give guideline-based advice on prescribing drugs, an approach to anticipating these errors in an automated guideline system, and design features to minimize errors and thereby maximize patient safety. Our guideline implementation system, based on the EON architecture, provides a framework for a knowledge base that is sufficiently comprehensive to incorporate safety information, and that is easily reviewed and updated by clinician-experts.

Artificial Intelligence↗

PubMed2000

A blind review and an informed review of interval breast cancer cases in the Limburg screening programme, the Netherlands.

OBJECTIVE: To investigate the proportion of interval breast cancers that could have been detected at the previous screening examination, and to gain more insight into the characteristics of these tumours. SETTING: Breast cancer screening programme in mid- and southern Limburg, the Netherlands. METHOD: Firstly, previous screening mammograms of 92 interval cancer cases were blindly reread by the radiologists from two different units as part of their daily screening workload. Secondly, a separate informed review was conducted, in which all of the cases (except for two) were subclassified into four categories: screening error; minimal signs; radiologically occult both at previous screening and at diagnosis; or radiologically occult at previous screening. Trends in recall rates and false and true positive rates were calculated to study potential changes during and after the blind review. RESULTS: In the blind review, 15% of the interval cancers were detected in both rereadings and 21% in one rereading. In the informed review, 25% were classified as a screening error and 24% as minimal signs present; 74% of the cases classified as a screening error had been recalled at least once in the blind review. Recall rates and false positive rates in daily screening practice increased significantly during and after the study period. CONCLUSIONS: About one third of the interval cancers could have been detected in the previous screening round. In order to diminish the number of avoidable interval cancers, review and classification of interval cancers is an important tool for continuing the education of screening radiologists. Therefore, further development of review training procedures is necessary.

Aged↗

PubMed2002

Delta13C and delta18O isotopic composition of CaCO3 measured by continuous flow isotope ratio mass spectrometry: statistical evaluation and verification by application to Devils Hole core DH-11 calcite.

A new method was developed to analyze the stable carbon and oxygen isotope ratios of small samples (400 +/- 20 micro g) of calcium carbonate. This new method streamlines the classical phosphoric acid/calcium carbonate (H(3)PO(4)/CaCO(3)) reaction method by making use of a recently available Thermoquest-Finnigan GasBench II preparation device and a Delta Plus XL continuous flow isotope ratio mass spectrometer. Conditions for which the H(3)PO(4)/CaCO(3) reaction produced reproducible and accurate results with minimal error had to be determined. When the acid/carbonate reaction temperature was kept at 26 degrees C and the reaction time was between 24 and 54 h, the precision of the carbon and oxygen isotope ratios for pooled samples from three reference standard materials was </=0.1 and </=0.2 per mill or per thousand, respectively, although later analysis showed that materials from one specific standard required reaction time between 34 and 54 h for delta(18)O to achieve this level of precision. Aliquot screening methods were shown to further minimize the total error. The accuracy and precision of the new method were analyzed and confirmed by statistical analysis. The utility of the method was verified by analyzing calcite from Devils Hole, Nevada, for which isotope-ratio values had previously been obtained by the classical method. Devils Hole core DH-11 recently had been re-cut and re-sampled, and isotope-ratio values were obtained using the new method. The results were comparable with those obtained by the classical method with correlation = +0.96 for both isotope ratios. The consistency of the isotopic results is such that an alignment offset could be identified in the re-sampled core material, and two cutting errors that occurred during re-sampling then were confirmed independently. This result indicates that the new method is a viable alternative to the classical reaction method. In particular, the new method requires less sample material permitting finer resolution and allows automation of some processes resulting in considerable time savings.

Journal Article↗

PubMed1995

Immunologic differentiation of absolute lymphocyte count with an integrated flow cytometric system: a new concept for absolute T cell subset determinations.

We describe a method to obtain results for immune status monitoring that uses a three-test panel, comprised of isotype control and 2 specific Mab tests (CD4/CD8/CD3 and CD16/CD19/CD3), in conjunction with a flow cytometer that directly measures absolute counts. Automated software is used for lineage-specific gating of three-color immunofluorescence to determine lymphocyte and lymphocyte subset counts. The autogating function of this software is shown to yield equivalent results to manual analysis by an expert user, and to be effective when as few as 25 target cells are present. The software is also shown to perform automatic quality control checks of the sample preparation, reagent, and automated analysis. We demonstrate that the sum of T (CD3+), B (CD19+), and natural killer (NK, CD16 + CD3-) cells, as a determination of all lymphocytes, correlates well with lymphocytes measured using a light scatter differential. Moreover, T + B + NK lymphocyte count is shown to be less error-prone than lymphocyte count from light scatter differential, and to minimize errors that arise from between-technician variation in sample preparation. Our data suggest that the new approach that we describe could offer an alternative to the traditional two-stage methods for measuring absolute counts of lymphocyte subsets for immune status monitoring. As such this method could reduce, through objective automated analysis, testing cost and complexity, without sacrificing the quality of results.

Algorithms↗

PubMed1999

MR phase-contrast flow measurement with limited spatial resolution in small vessels: value of model-based image analysis.

Magnetic resonance phase-contrast volume flow rate (VFR) measurement with limited resolution in small vessels is subject to two major sources of error: a) partial volume artifacts, causing systematic overestimation of the VFR, and b) errors related to the selection of vessel pixels [region of interest (ROI)], causing large inter-observer and intra-observer variability. Additionally, limited resolution results in Gibbs-ringing around vessels, which adversely affects VFR determination. In this paper, a semi-automatic model-based method is presented that effectively eliminates errors due to both partial volume effect and Gibbs-ringing and also minimizes errors from variability in the ROI selection. The model assumes a parabolic flow profile and cylindrical vessel geometry, incorporates inflow effects, and takes into account the point-spread function of the acquisition. The method automatically estimates maximum velocity, vessel radius, and VFR. The method is validated in phantoms under various conditions and evaluated in vivo. For small vessels with moderately pulsatile flow, it is demonstrated that accurate VFRs and diameter estimates are obtained, virtually independent of the ROI selection, even in vessels covered by just a few pixels. Compared with conventional VFR analysis, both accuracy and reproducibility improve significantly.

Basilar Artery↗

PubMed1988

Solution structure of apamin determined by nuclear magnetic resonance and distance geometry.

The solution structure of the bee venom neurotoxin apamin has been determined with a distance geometry program using distance constraints derived from NMR. Twenty embedded structures were generated and refined by using the program DSPACE. After error minimization using both conjugate gradient and dynamics algorithms, six structures had very low residual error. Comparisons of these show that the backbone of the peptide is quite well-defined with the largest rms difference between backbone atoms in these structures of 1.34 A. The side chains have far fewer constraints and show greater variability in their positions. The structure derived here is generally consistent with the qualitative model previously described, with most differences occurring in the loop between the beta-turn (residues 2-5) and the C-terminal alpha-helix (residues 9-17). Comparisons are made with previously derived models from NMR data and other methods.

Algorithms↗