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Results for “Error minimization”

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At least 127 records · Page 7Linked to original sources

PubMed1998

Comparison of the E test with broth microdilution for antifungal susceptibility testing of yeasts.

The susceptibilities of 26 recent invasive clinical isolates to amphotericin B (AMP), 5-flucytosine (5FC), fluconazole (FLU) and itraconazole (ITR) were determined by a broth microdilution modification of the NCCLS M27P method and also by E test. Using breakpoint criteria each result was classified as either sensitive (S), intermediate (I) or resistant (R). Taking the optical density (OD)80 as the standard, the results were further classified into major (M) or minor (m) errors. E test: AMP = 0M 0m, 5FC = 0M 5m, FLU = 1M 12m, ITR = 1M 5m errors. Minimal inhibitory concentrations (MIC): AMP = 0M 2m, 5FC = 0M 0m, FLU = 3M 4m, ITR = 1M 7m errors. The E test was quick and relatively simple to perform. Results using the E test compared favourably with those of the OD80 and it should be suitable for the routine susceptibility testing of yeasts to antifungal agents.

Amphotericin B↗

PubMed1993

Analysis of systematic and random error in MR volumetric flow measurements.

The spatial aspects of error in 2D MR cine phase-velocity mapping are considered in order to define acquisition strategies which will minimize error in measuring volumetric flow. Error was separated into two categories: systematic and random. Potential sources of systematic error examined were intravoxel phase dispersion (IVPD), partial volume effects, misalignment of flow axis and flow-encoding gradients, and improper choice of vessel voxels for flux calculations. Random error was addressed using analysis of propagation of variance. Analytical expressions for sources of error were derived; and computer models were used to test the analytical models. Flow phantom studies examining error in MR volumetric flow measurements were performed and compared with error predicted by the analytical models. Expected error in several clinical situations of interest was then derived to find appropriate acquisition strategies. Spatial resolution, signal to noise ratio, velocity sensitivity and the ratio of the modulus of moving isochromats to that of static isochromats were found to be the most important parameters in controlling error and were found to cause competing effects with respect to systematic and random error.

Artifacts↗

PubMed2005

Parallel magnetic resonance imaging with adaptive radius in k-space (PARS): constrained image reconstruction using k-space locality in radiofrequency coil encoded data.

A parallel image reconstruction algorithm is presented that exploits the k-space locality in radiofrequency (RF) coil encoded data. In RF coil encoding, information relevant to reconstructing an omitted datum rapidly diminishes as a function of k-space separation between the omitted datum and the acquired signal data. The proposed method, parallel magnetic resonance imaging with adaptive radius in k-space (PARS), harnesses this physical property of RF coil encoding via a sliding-kernel approach. Unlike generalized parallel imaging approaches that might typically involve inverting a prohibitively large matrix for arbitrary sampling trajectories, the PARS sliding-kernel approach creates manageable and distributable independent matrices to be inverted, achieving both computational efficiency and numerical stability. An empirical method designed to measure total error power is described, and the total error power of PARS reconstructions is studied over a range of k-space radii and accelerations, revealing "minimal-error" conditions at comparatively modest k-space radii. PARS reconstructions of undersampled in vivo Cartesian and non-Cartesian data sets are shown and are compared selectively with traditional SENSE reconstructions. Various characteristics of the PARS k-space locality constraint (such as the tradeoff between signal-to-noise ratio and artifact power and the relationship with iterative parallel conjugate gradient approaches or nonparallel gridding approaches) are discussed.

Algorithms↗

PubMed1988

Errors between sites in restriction site mapping.

Restriction site mapping programs construct maps by generating permutations of fragments and checking for consistency. Unfortunately many consistent maps often are obtained within the experimental error bounds, even though there is only one actual map. A particularly efficient algorithm is presented that aims to minimize error bounds between restriction sites. The method is generalized for linear and circular maps. The time complexity is derived and execution times are given for multiple enzymes and a range of error bounds.

Algorithms↗

PubMed1991

DNA measurement errors with a scanning microdensitometer in cytologic and histologic samples of breast cancers.

The influence of various DNA measurement errors using a commercially available scanning microdensitometer was evaluated on Feulgen-stained cytologic and histologic samples prepared from paraffin blocks containing invasive ductal breast cancers. The overall average total measurement error was 5.5% for the cytologic specimens and 10.9% for the 4 micron histologic sections. Components of the error included microscopic adjustment variation and focussing errors (3.5% and 1.1%, respectively, for both cytologic and histologic samples) and background intensity estimation errors (3.0% for the cytologic samples and 10.0% for the histologic samples). Measurements of the integrated optical density had a minimal error of 0.5% and an average error of 1.0%. Limitations due to the histologic architecture and/or heterogeneous cell population gave rise to large differences in the selection of nuclei when differently sized scanning masks were used. To improve the reproducibility, masks used should be based on the individual cell size, and background intensity values should be carefully estimated in the vicinity of the selected cells. Overall, the cytologic tumor samples were preferable to the histologic samples for static DNA measurements. It was easier to select cells suitable for measurement in the cytologic samples, and the cytologic measurements were less time consuming and produced a smaller measurement error.

Breast Neoplasms↗

PubMed1984

Detection of heterozygous carriers for phenylketonuria by a L-[2H5]phenylalanine stable isotope loading test.

Oral loading with 25 mg/kg of pentadeuterated L-phenylalanine has been used for the discrimination between normozygous subjects and carriers for phenylketonuria. The test provides five types of data derived from plasma Phe and Tyr concentrations on which the discrimination can be based: fasting phenylalanine/tyrosine ratios, total Phe levels, total Phe/total Tyr ratios, absolute L-[2H5]phenylalanine plasma levels, and L-[2H5]Phe/L-[2H4]Tyr ratios. Absolute L-[2H4]Tyr and total L-Tyr concentrations provide the poorest discrimination with statistical classification errors around 30%. The corresponding classification error of fasting Phe/fasting Tyr ratios was circa 13%, and both labelled Phe/labelled Tyr and total Phe/total Tyr concentration ratios gave minimal errors below 2%.

Deuterium↗

PubMed2004

Urinary excretion: does it accurately reflect relative differences in bioavailability/systemic exposure when renal clearance is nonlinear?

PURPOSE: The purpose of this study was to assess the influence of nonlinear renal clearance on the ability of urinary excretion data to accurately determine relative differences in systemic exposure and bioavailability. METHODS: Serum concentration and urinary excretion-time profiles were simulated assuming an open one-compartmental model with first-order absorption, linear nonrenal clearance, and either linear or nonlinear renal clearance (saturable secretion). Renal clearance comprised 5% or 95% of total clearance. Doses were varied over a 100-fold range (10-fold decrease/increase from the reference dose). Relative systemic exposures were based on the ratios of AUC and C(max) and the corresponding ratios of cumulative amount excreted in urine (A(e)) and the maximum urinary excretion rate. Relative bioavailability was based on the ratios of A(e) and the test to reference dose (D(ratio)). RESULTS: When renal clearance was linear and urinary excretion data were used to assess relative systemic exposure and relative bioavailability, no significant errors in accuracy were observed. However, when renal clearance was nonlinear, errors in the accuracy of estimation of relative bioavailability (Clr =5% only) and relative systemic exposure ranged from -53% to +125%; minimal error in accuracy existed in the estimation of relative bioavailability when Clr = 95% (-3% to +6%). CONCLUSIONS: Prior to the use of urinary excretion data to assess relative systemic exposure or bioavailability, the relationship between serum concentration and renal clearance should be established.

Algorithms↗

PubMedDate not supplied

Pneumonectomy in the mouse: technique and perioperative management.

Thoracic surgery in mice is challenging due to difficult intubation and ventilation, lack of intravenous access, and the risk of hemorrhage. We developed a rapid and safe technique for murine unilateral pneumonectomy in order to study compensatory lung growth. Under general anesthesia, 81 mice were intubated with an angiocatheter using a 2.7-mm, 0-degree endoscope. A left thoracotomy was performed. The lung was gently extracted from the thoracic cavity, ligated at the hilum, and resected. Postoperatively, warming lights and subcutaneous saline injections were used to ensure minimal morbidity. The survival rate for the scope-assisted intubation and pneumonectomy was 88%. Perioperative mortality was due to technical error. Minimal long-term morbidity was appreciated. This general operative technique and perioperative management may be applied to all types of murine thoracic procedures used for surgical research.

Animals↗

PubMed1998

Reversible inactivation of monkey superior colliculus. II. Maps of saccadic deficits.

Neurons in the superior colliculus (SC) are organized as maps of visual and motor space. The companion paper showed that muscimol injections into intermediate layers of the SC alter the trajectory of the movement and confirmed previously reported effects on latency, amplitude, and speed of saccades. In this paper we analyze the pattern of these deficits across the visual field by systematically comparing the magnitude of each deficit throughout a grid of targets covering a large fraction of the visual field. We also translate these deficits onto the SC map of the visual/movement fields to obtain a qualitative estimate of the extent of the deficit in the SC. We found a consistent pattern of substantially increased saccadic latency to targets in the contralateral visual hemifield, accompanied by slight and inconsistent increases and decreases for saccades to the ipsilateral hemifield. The initial and peak speed of saccades was reduced after the injection. The postinjection amplitude of the saccades were either hypometric or normometric, but rarely hypermetric. Although errors in the initial direction of the postinjection saccades were small, they consistently formed a simple pattern: an initial direction with minimal errors (a null direction) separating regions with clockwise and counterclockwise rotations of the initial direction. However, the null direction did not go through the center of the inactivated zone, as would be expected if the SC alone were determining saccade direction, e.g., with a population code. One hypothesis that can explain the misalignment of the null direction with the lesion site is that another system, acting in parallel with the SC, contributes to the determination of saccadic trajectory.

Animals↗

PubMed2006

An adaptive system identification model of the biomechanical response of the human trunk during sudden loading.

Sudden loading injuries to the low back are a concern. Current models are limited in their ability to quantify the time-varying nature of the sudden loading event. The method of approach used six males who were subjected to sudden loads. Response data (EMG and kinematics) were input into a system identification model to yield time-varying torso stiffness estimates. The results show estimates of system stiffness in good agreement with values in the literature. The average root mean square error of the model's predictions of sagittal motion was equal to 0.1 deg. In conclusion, system identification can be implemented with minimal error and used to gain more insight into the time-dependent trunk response to sudden loads.

Abdomen↗

PubMed2005

Epilepsy--success in clinical practice: translating trials to practice.

Success in clinical practice results from the combination of a clinician's experience, an understanding of patient preferences and factors that influence patient perceptions, and careful interpretation of data from clinical trials. However, successful clinical trials fulfil rigid methodological requirements in order to provide a basis from which to evaluate the place of a drug within a therapeutic strategy. Their translation into practice is therefore complicated by an intrinsic tension between the requirements for scientific methods that minimize error, and the need for clinically relevant data. In practice, the clinician has the flexibility to individualize epilepsy management to maximize benefits and minimize adverse effects of antiepileptic drug (AED) therapy. AED adverse effects and psychiatric comorbidity, in particular depression, have a profound impact on subjective health status; systematic screening for these confounding variables can guide clinical management and optimize quality of life. In addition, patient preferences can be acknowledged in any management plan. To achieve success in clinical practice, we need to remember that the information gleaned from clinical trials provides only part of the picture and needs to be augmented by our clinical experience, patient assessment (including routine screening for adverse effects and depression) and patient preference.

Anticonvulsants↗

PubMedDate not supplied

Regions of interest tracking in temporal scans based on statistical analysis of gray scale and edge properties and registration of images.

Precise measurement of T1 is needed for its use in temperature monitoring in vivo. Movement of tissue relative to fixed regions of interest can result in large variations in apparent T1, with consequent substantial errors in the measured temperature. This paper evaluates methods of tracking regions of interest as tissue moves during a study in an effort to minimize errors from this cause. Tracking techniques evaluated are based on maintaining constant gray scale levels, locating nearby edges and maintaining position relative to them, and global image registration.

Algorithms↗

PubMedDate not supplied

Using medical knowledge to reduce data errors.

Knowledge about the subject of a data base application can be used to reduce errors or data omissions. This article describes a data base system for a gynecologic oncology registry that uses rules incorporating knowledge about gynecologic oncology to minimize errors when a multiple-choice format is used for data entry.

Artificial Intelligence↗

PubMedDate not supplied

Partial hepatectomy in the mouse: technique and perioperative management.

Hepatic surgery in mice is challenging because of the delicate nature of the liver, lack of intravenous access, and risk of hemorrhage. In order to study the ability of the liver to regenerate after surgical resection, we developed a novel, rapid, and safe technique for partial hepatectomy in mice. We determined the relative contributions of the seven lobes of the mouse liver and resected the three most anterior lobes for a 68% hepatectomy. We used general anesthesia, a small upper midline incision, silk suture to tie off the lobes to be resected, warming pads and lights, as well as subcutaneous saline injection to ensure minimal morbidity. We have performed a safe two-thirds hepatic resection in 288 of 300 C57BL6 mice (96%). Perioperative mortality was due to technical error. Minimal long-term morbidity was appreciated. This technique may be applied to any type of hepatic resection in mice. In addition, the general operative technique and perioperative management of these mice may be applied to all types of murine intra-abdominal procedures used for surgical research.

Animals↗

PubMed2003

Stay safe. Medical mistakes make headlines.

Medical mistakes in ambulatory settings are not isolated events, and most errors are avoidable. Your patients can be safer--and your practice can stay off the evening news--if you implement systems and processes that will minimize errors.

Ambulatory Care Information Systems↗

PubMed1998

Stability after inferior or anterior maxillary repositioning by Le Fort I osteotomy: a biplanar stereocephalometric study.

A biplanar cephalometric stereoradiographic system was used to measure maxillary positional changes during and after Le Fort I procedures for inferior or anterior repositioning of the maxilla. Of the 29 patients studied, 25 had undergone surgical maxillary advancement, and 15 had undergone inferior repositioning. These cases were divided into subgroups based on fixation technique, presence or absence of bone grafts, age, and surgeon. The postsurgical follow-up period was at least 11 months for each patient. The landmarks used to measure maxillary positional changes consisted of skeletal features and points on wire or rigid fixation devices. Mean magnitudes of postsurgical maxillary landmark displacement were insignificant for all subgroups examined except the advancement group with wire fixation. Individual patients exhibiting the greatest postsurgical displacements tended to have had large surgical advancements and received wire fixation. Magnitudes of surgical and postsurgical change did not seem correlated on the whole, except in the maxillary advancement cases in which bone grafts had not been used. Error analysis results suggest that digitizing consistency was acceptable for maxillary landmarks; however, methodologic improvements with regard to provision of cranial reference landmarks may further minimize errors in future studies.

Adolescent↗

PubMed1997

Adaptive Finite-Element Solution of the Nonlinear Poisson-Boltzmann Equation: A Charged Spherical Particle at Various Distances from a Charged Cylindrical Pore in a Charged Planar Surface

A Galerkin finite-element approach combined with an error estimator and automatic mesh refinement has been used to provide a flexible numerical solution of the Poisson-Boltzmann equation. A Newton sequence technique was used to solve the nonlinear equations arising from the finite-element discretization procedure. Errors arising from the finite-element solution due to mesh refinement were calculated using the Zienkiewicz-Zhu error estimator, and an automatic remeshing strategy was adopted to achieve a solution satisfying a preset quality. Examples of the performance of the error estimator in adaptive mesh refinement are presented. The adaptive finite-element scheme presented in this study has proved to be an effective technique in minimizing errors in finite-element solutions for a given problem, in particular those of complex geometries. As an example, numerical solutions are presented for the case of a charged spherical particle at various distances from a charged cylindrical pore in a charged planar surface. Such a scheme provides a quantification of the significance of electrostatic interactions for an important industrial technology-membrane separation processes.

Journal Article↗

PubMed1998

A search for the optimal stimulus.

How do stimulus size and item number relate to the magnitude and direction of error on center estimation and line cancellation tests? How might this relationship inform theories concerning spatial neglect? These questions were addressed by testing twenty patients with right hemisphere lesions, eleven with left hemisphere lesions and eleven normal control subjects on multiple versions of center estimation and line cancellation tests. Patients who made large errors on these tests also demonstrated an optimal or pivotal stimulus value, i.e., a particular size center estimation test or number of lines on cancellation that either minimized error magnitude relative to other size stimuli (optimal) or marked the boundary between normal and abnormal performance (pivotal). Patients with right hemisphere lesions made increasingly greater errors on the center estimation test as stimuli were both larger and smaller than the optimal value, whereas those with left hemisphere lesions made greater errors as stimuli were smaller than a pivotal value. In normal subjects, the direction of errors on center estimation stimuli shifted from the right of true center to the left as stimuli decreased in size (i.e., the crossover effect). Right hemisphere lesions exaggerated this effect, whereas left hemisphere lesions diminished and possibly reversed the direction of crossover. Error direction did not change as a function of stimulus value on cancellation tests. The demonstration of optimal and pivotal stimulus values indicates that performances on center estimation and cancellation tests in neglect are only relative to the stimuli used. In light of other studies, our findings indicate that patients with spatial neglect grossly overestimate the size of small stimuli and underestimate the size of large stimuli, that crossover represents an "apparent" shift in error direction that actually results from normally occurring errors in size perception, and that the left hemisphere is specialized for one aspect of size estimation, whereas the right performs dual roles.

Aged↗