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PubMed2003

The role of information technology in reducing medical errors.

This Article summarizes the discussion at a breakout session held at the American Health Lawyers Association's (Health Lawyers') 2003 Public Interest Colloquium,' Minimizing Medical Errors: Legal Issues in the Debate on Improving Patient Safety, held February 28-March 1, 2003, in Washington, DC. The authors developed a series of core questions identifying relevant legal and policy issues relating to the use of information technology in reducing medical errors, and facilitated the breakout discussion.

Humans↗

PubMed1993

Learning procedure in a neural control model for the urinary bladder.

A continuous neural network coupled to a dynamical model of the urinary bladder is defined. The neural network is trained to control the bladder model to track a prescribed volume fluctuation, by adjusting weights and time constants. The gradients of the error in the output neurons of the neural network are unknown. Therefore, the learning procedure discussed here minimizes the error functional without using gradient descent.

Animals↗

PubMed1990

Urinary zinc excretion in a patient with burns: a caveat when using bladder catheters in urine zinc studies.

The results of a longitudinal study on plasma and urine zinc concentrations in a patient with 68 per cent burns are described. Special attention was paid to possible zinc contamination due to the use of bladder catheters for urine sampling. The course of the plasma and urine zinc concentrations during the first 50 days in hospital was comparable to those reported in the literature. It was shown that surgery was associated with a pronounced rise in urine zinc level, while catheter replacement caused no significant increase in urinary zinc content in this particular patient. However, measurements of zinc content of and zinc release from three types of bladder catheters showed that the two types of latex-based catheters contained about 0.25 per cent zinc, versus 0.01 per cent in the siliconelastomer equivalent. During an 8 h perfusion latex catheters released about 1.2 mumols zinc (2.5 mumols/l). Possible errors in urine zinc determinations due to zinc contamination from catheters are calculated. Recommendations are made for minimizing these errors.

Adult↗

PubMed2005

Triphasic MRI of pelvic organ descent: sources of measurement error.

PURPOSE: To identify sources of error when measuring pelvic organ displacement during straining using triphasic dynamic magnetic resonance imaging (MRI). MATERIALS AND METHODS: Ten healthy nulliparous woman underwent triphasic dynamic 1.5 T pelvic MRI twice with 1 week between studies. The bladder was filled with 200 ml of a saline solution, the vagina and rectum were opacified with ultrasound gel. T2 weighted images in the sagittal plane were analysed twice by each of the two observers in a blinded fashion. Horizontal and vertical displacement of the bladder neck, bladder base, introitus vaginae, posterior fornix, cul-de sac, pouch of Douglas, anterior rectal wall, anorectal junction and change of the vaginal axis were measured eight times in each volunteer (two images, each read twice by two observers). Variance components were calculated for subject, observer, week, interactions of these three factors, and pure error. An overall standard error of measurement was calculated for a single observation by one observer on a film from one woman at one visit. RESULTS: For the majority of anatomical reference points, the range of displacements measured was wide and the overall measurement error was large. Intra-observer error and week-to-week variation within a subject were important sources of measurement error. CONCLUSION: Important sources of measurement error when using triphasic dynamic MRI to measure pelvic organ displacement during straining were identified. Recommendations to minimize those errors are made.

Adolescent↗

PubMed2005

Comparative analyses of linac and Gamma Knife radiosurgery for trigeminal neuralgia treatments.

Dedicated linac-based radiosurgery has been reported for trigeminal neuralgia treatments. In this study, we investigated the dose fall-off characteristics and setup error tolerance of linac-based radiosurgery as compared with standard Gamma Knife radiosurgery. In order to minimize the errors from different treatment planning calculations, consistent imaging registration, dose calculation and dose volume analysis methods were developed and implemented for both Gamma Knife and linac-based treatments. Intra-arc setup errors were incorporated into the treatment planning process of linac-based deliveries. The effects of intra-arc setup errors with increasing number of arcs were studied and benchmarked against Gamma Knife deliveries with and without plugging patterns. Our studies found equivalent dose fall-off properties between Gamma Knife and linac-based radiosurgery given a sufficient number of arcs (>7) and small intra-arc errors (<0.5 mm) were satisfied for linac-based deliveries. Increasing the number of arcs significantly decreased the variations in the dose fall-off curve at the low isodose region (e.g. from 40% to 10%) and also improved dose uniformity at the high isodose region (e.g. from 70% to 90%). As the number of arcs increased, the effects of intra-arc setup errors on the dose fall-off curves decreased. Increasing the number of arcs also reduced the integral dose to the distal normal brain tissues. In conclusion, linac-based radiosurgery produces equivalent dose fall-off characteristics to Gamma Knife radiosurgery with a high number of arcs. However, one must note the increased treatment time for a large number of arcs and isocentre accuracies.

Dose-Response Relationship, Radiation↗

PubMed1995

Registration in neurosurgery and neuroradiotherapy applications.

Because of the high level of accuracy needed in neurosurgery, many computer-assisted surgery (CAS) and augmented reality techniques have been developed in this field. A common issue with all of these techniques is registration between preoperative three-dimensional images (computed tomography and magnetic resonance imaging) and the patient in the operating room. We present, in the first part of this paper, a survey of the latest CAS technologies, using fully automatic registration without fiducial landmarks. All of the registration algorithms described are based on minimization of a cost function. We then describe our approach. Our cost function is simply the mean square error (MSE), minimized by the iterative closest point algorithm (ICP). Because the weak point of the ICP algorithm is the closest point computational cost, we precalculate it by a "closest point map," inspired from classical distance map. We finally perturb the found solution to eliminate local minima close to the global minimum. This paper summarizes the various methods presented. We study the shape of the different cost functions and show that there is no need for a complex cost function. MSE has sufficiently good convergence properties to reach a position very close to the global minimum. We also demonstrate the influence of a final perturbation of the found solution to improve registration. Finally, we test the registration on different regions of the patient's head.

Algorithms↗

PubMedDate not supplied

[Errors of impulse photometers].

Errors of pulse photometers intended for clinical biochemical studies have been analyzed. The recommendations are given how to minimize the errors and to improve metrologic parameters of pulse photometers.

Photometry↗

PubMed1983

The errors of thymidine labelling in breast cancer.

The site to site error and reproducibility of counting error have been assessed in the routine thymidine labelling of breast cancer. Despite modifications of technique designed to minimize these errors both were found to be inaccurate to within 0.5 labelling index %. Since the majority of tumours had labelling indices below 2% this measurement is not a critical determinant of tumour behaviour.

Breast Neoplasms↗

PubMed1995

Conditions for electron tomographic data acquisition.

The conventional algorithms employed in electron microscope tomography require that the series of images obtained from different orientations of the specimen each represent a parallel orthographic projection under uniform magnification. Electron microscope optics can produce distortions in images that may affect the accuracy of a tomographic reconstruction. These distortions result in images with differential rotation and magnification of regions of a thick or highly tilted specimen located at different distances with respect to the plane of focus. The distortions increase in magnitude and may significantly affect the accuracy of the tomographic data when images are acquired under current center misalignment or non-eucentric positioning of the specimen. An additional source of error can be introduced if the condenser lenses are adjusted to compensate for the intensity attenuation due to the increased beam path length as the specimen is tilted. The change in beam crossover position due to adjustment of the condensers alters the beam divergence and may introduce systematic changes in magnification over the tilt series. The process of alignment of the tilt series will propagate these errors to more central regions of the image. In most cases, with proper consideration, it is possible to minimize these errors to levels where they will have negligible effects on the resolution of the tomographic reconstruction.

Algorithms↗

PubMed2005

Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review.

BACKGROUND: An assessment of energy needs is a necessary component in the development and evaluation of a nutrition care plan. The metabolic rate can be measured or estimated by equations, but estimation is by far the more common method. However, predictive equations might generate errors large enough to impact outcome. Therefore, a systematic review of the literature was undertaken to document the accuracy of predictive equations preliminary to deciding on the imperative to measure metabolic rate. METHODS: As part of a larger project to determine the role of indirect calorimetry in clinical practice, an evidence team identified published articles that examined the validity of various predictive equations for resting metabolic rate (RMR) in nonobese and obese people and also in individuals of various ethnic and age groups. Articles were accepted based on defined criteria and abstracted using evidence analysis tools developed by the American Dietetic Association. Because these equations are applied by dietetics practitioners to individuals, a key inclusion criterion was research reports of individual data. The evidence was systematically evaluated, and a conclusion statement and grade were developed. RESULTS: Four prediction equations were identified as the most commonly used in clinical practice (Harris-Benedict, Mifflin-St Jeor, Owen, and World Health Organization/Food and Agriculture Organization/United Nations University [WHO/FAO/UNU]). Of these equations, the Mifflin-St Jeor equation was the most reliable, predicting RMR within 10% of measured in more nonobese and obese individuals than any other equation, and it also had the narrowest error range. No validation work concentrating on individual errors was found for the WHO/FAO/UNU equation. Older adults and US-residing ethnic minorities were underrepresented both in the development of predictive equations and in validation studies. CONCLUSIONS: The Mifflin-St Jeor equation is more likely than the other equations tested to estimate RMR to within 10% of that measured, but noteworthy errors and limitations exist when it is applied to individuals and possibly when it is generalized to certain age and ethnic groups. RMR estimation errors would be eliminated by valid measurement of RMR with indirect calorimetry, using an evidence-based protocol to minimize measurement error. The Expert Panel advises clinical judgment regarding when to accept estimated RMR using predictive equations in any given individual. Indirect calorimetry may be an important tool when, in the judgment of the clinician, the predictive methods fail an individual in a clinically relevant way. For members of groups that are greatly underrepresented by existing validation studies of predictive equations, a high level of suspicion regarding the accuracy of the equations is warranted.

Adolescent↗

PubMed1997

Iterative total least-squares image reconstruction algorithm for optical tomography by the conjugate gradient method.

We present an iterative total least-squares algorithm for computing images of the interior structure of highly scattering media by using the conjugate gradient method. For imaging the dense scattering media in optical tomography, a perturbation approach has been described previously [Y. Wang et al., Proc. SPIE 1641, 58 (1992); R. L. Barbour et al., in Medical Optical Tomography: Functional Imaging and Monitoring (Society of Photo-Optical Instrumentation Engineers, Bellingham, Wash., 1993), pp. 87-120], which solves a perturbation equation of the form W delta x = delta I. In order to solve this equation, least-squares or regularized least-squares solvers have been used in the past to determine best fits to the measurement data delta I while assuming that the operator matrix W is accurate. In practice, errors also occur in the operator matrix. Here we propose an iterative total least-squares (ITLS) method that minimizes the errors in both weights and detector readings. Theoretically, the total least-squares (TLS) solution is given by the singular vector of the matrix [W/ delta I] associated with the smallest singular value. The proposed ITLS method obtains this solution by using a conjugate gradient method that is particularly suitable for very large matrices. Simulation results have shown that the TLS method can yield a significantly more accurate result than the least-squares method.

Algorithms↗

PubMed1995

The effect of magnification on the performance of fixed prosthodontic procedures.

This study attempts to quantify the effect of magnifiers on the quality of typical procedures in fixed prosthodontics that are technique-sensitive and have significant increase in clinical success when errors are minimized. Dental students who performed fixed prosthodontic procedures while using magnifiers were found to have committed half as many errors as students who performed the same preparation without the aid of a magnifier.

Dental Equipment↗

PubMed2006

Methods to classify familial relationships in the presence of laboratory errors, without parental data.

We consider the problem of accurate classification of family relationship in the presence of laboratory error without parental data. We first propose an adjusted version of the test statistic proposed by Ehm and Wagner based on the summation over a large number of genetics markers. We then propose use of the Bayes factor as a classification rule. We prove theoretically that the Bayes factor is the optimal classification rule in that the total classification error is minimized. We show via simulations that both the adjusted Ehm and Wagner method and Bayes factor classification rule reduce misclassification errors, and that the Bayes factor classification rule is robust against under-estimation or over-estimation of laboratory errors. For monozygotic twins versus dizygotic twins, the correct classification rate of the Bayes rule is over 99%. For full-siblings versus half-siblings, the Bayes factor classification rule generally outperforms Ehm and Wagner's method (in Am J Hum Genet 62:181-188, 1998), especially when full-sibling proportion is high.

Diagnostic Errors↗

PubMedDate not supplied

Issues in handling impression materials.

Implant restorations require extreme accuracy since the implants are rigidly fixed. Although impression materials can be highly accurate, small inaccuracies are acceptable because the periodontal ligament allows for tooth movement. This luxury is not available with implants. A problem is the rotation of direct impression copings and distortion of interabutment positions in the master cast. Wee investigated the amount of torque required to displace a coping in eight impression material groups and the positional accuracy of the materials. The initial examination of torque narrowed the acceptable materials to a medium viscosity polyether, a high viscosity addition silicone, and a medium viscosity polysulfide-condensation silicones were eliminated. The results showed that the polyether and addition silicone produced casts with minimal distortion. Finally, it always is prudent to read the manufacturer's recommendations for use of impression materials. Catalyst-to-base ratios vary, as do working and setting times, depending on exact compositions. Impression materials also have various degrees of compatibility with stone, particularly the hydrocolloids, and it is advisable to use the recommended stone. Adhesives should be applied at least 15 minutes prior to loading the impression material. If at all possible, use of a rigid tray is recommended and impressions should be poured in the dental office; this minimizes the error produced at the beginning of the fabrication process. Elimination of errors early in fabrication of a prosthesis help prevent their magnification and result in a better-fitting restoration, requiring minimal adjustment in the end.

Colloids↗

PubMed1987

Quality control in radiotherapy: the reduction of field placement errors.

A 'blind' study using treatment verification films has been performed on two series of patients to assess the accuracy of placement of complex infradiaphragmatic fields planned to include para-aortic nodes. Sequential verification films (VF) for each field on all patients studied were compared to determine variations in field position relative to the anatomy, especially lymph nodes, and the simulator plan. Nodes included in the plan but partially or completely missed by one or more treatments were identified, as were the error types involved. In series I, 21% of 157 VF showed a nodal miss, and after changes in practice designed to minimize the error types responsible for those, the figure was reduced in series II to 5.5% of 194 VF. In series II a 50% reduction in magnitude of the average systematic lateral shift and rotation of posterior fields is attributed mainly to the discontinuation of the practice of treating posterior fields through the couch. Apart from a prescribed width of less than 9 cm, three quantitative key factors were derived: greater than 6 mm lateral shift, greater than 7 mm field narrowing, 2 degree or more rotation of fields. The correction of these errors if identified on verification films, should eliminate the subsequent occurrence of node misses. The value of routine clinical treatment verification films at the start of treatment to identify and correct systematic errors is emphasized, as is the importance of precise and standardized technical practice.

Humans↗

PubMed1994

Assessment of cartilage volume in the femorotibial joint with magnetic resonance imaging and 3D computer reconstruction.

OBJECTIVE: Our goal was the development of an accurate and objective technique to depict and quantitate articular cartilage using magnetic resonance imaging (MRI) and 3D data processing. METHODS: A method of 3D image analysis has been developed that provides a noninvasive technique of measuring cartilage volume from standard diagnostic MR images. RESULTS: Using a computer workstation, cartilage from Fast Field Echo (FFE) MR images was reconstructed into 3 dimensions (3D). The accuracy and reproducibility of both thickness and volume measurements obtained from the existing computer software was tested using calibration test objects. We describe the sources of error we encountered when attempting to quantitate cartilage using the existing computer software, the methods developed to reduce these errors, and a preliminary cartilage volume study using healthy human volunteers. CONCLUSION: We have identified errors involved in attempting cartilage volume estimations using the existing 3D computer software and have developed a data processing technique that minimizes these errors. With these objective data processing techniques we have improved the reproducibility of the technique to +/- 10-15% error. This modified technique provides a promising new method for viewing and quantifying cartilage volume from standard diagnostic MR images.

Animals↗

PubMed2000

Unbiased and efficient estimation of left ventricular volumes by three-dimensional echocardiography with coaxial sections. Validation with magnetic resonance imaging.

The objective of this study was to investigate the degree of bias with coaxial three-dimensional echocardiography in an experimental animal setup and to establish the minimum number of sections needed for estimation of left ventricular (LV) volume. Epicardial coaxial echocardiography and magnetic resonance imaging (MRI) was used to measure LV volume in 14 pigs, with chronic remodeled left ventricles induced by repeated intracoronary microembolizations. In addition, six animals underwent serial MRI at baseline, immediately after intracoronary microembolization, and after 119-165 days (mean 129 days). Coaxial echocardiography was performed by rotational acquisition of long-axis sections starting from an arbitrary angle. Planimetered MRI contours of LV endocardial borders were analyzed to investigate the relationship between the number of coaxial sections, and the precision of volume estimates. The mean +/- 2SD of the differences between coaxial epicardial echocardiography with six sections and MRI were -2.5 +/- 16.4 ml, 0.8 +/- 13.1 ml, and 2% +/- 14% for end-diastolic volume (EDV), end-systolic volume (ESV), and ejection fraction (EF), respectively. Numerical analysis conducted on MRI contours of LV endocardial borders showed that with six coaxial sections the average coefficient of error was < 1% for the EDV and ESV. Three-dimensional echocardiography with six coaxial sections provides unbiased LV volume estimation with minimal geometric error.

Algorithms↗

PubMed1986

Applications of new saturation transfer electron paramagnetic resonance methodology to the rotational dynamics of the Ca-ATPase in sarcoplasmic reticulum membranes.

The presence of small amounts of weakly immobilized probes can result in large systematic errors in the measurement of correlation times (tau r) from saturation transfer EPR spectra. However, we have recently developed experimental methodology to minimize these errors (Squier and Thomas, Biophys. J., 49:921-935). In the present study we have applied this methodology to the measurement of the rotational motion of the Ca-ATPase in sarcoplasmic reticulum. This analysis involves the estimate of tau r from line-shape parameters (spectral line-height ratios) and intensity parameters (spectral integral), coupled with digital subtractions to remove spectral components corresponding to weakly immobilized probes. We have analyzed the ST-EPR spectra of the Ca-ATPase over a range of temperatures and find that, unlike line-shape parameters, intensity parameters are little affected by the subtraction of the weakly immobilized spectral component (W). Thus, tau r values from intensity parameters are a more reliable measurement of rotational motion. As reported previously, an analysis with line-shape parameters yields a nonlinear Arrhenius plot of protein mobility. However, the plot is linear when intensity parameters or corrected spectra are used, consistent with the theory for the hydrodynamic properties of a membrane protein of unchanging size and shape in a fluid bilayer. An analysis with line-shape parameters yields different effective tau r values in different spectral regions, and these tau r values are temperature-dependent. However, correction of spectra for W yields temperature-independent tau r ratios, indicating that the motional anisotropy is temperature-independent. Obtaining a good match for the weakly immobilized spectral component remains a major difficulty in the quantitative analysis of ST-EPR spectra using line-shape parameters. This study shows that intensity parameters can be used to avoid this problem, making the ST-EPR technique applicable in cases that were previously resistant to analysis.

Animals↗