Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Accuracy”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources
PubMed2001

Accuracy evaluation of a CAS system: laboratory protocol and results with 6D localizers, and clinical experiences in otorhinolaryngology.

OBJECTIVES: The objective of the study reported in this article was to evaluate (1) localizer inaccuracies, one of the major sources of errors in Computer-Assisted Surgery (CAS) systems, and (2) the final errors obtained using surface-based registration in ear, nose, and throat (ENT) surgery. These objectives were met through (1) a technical evaluation of the accuracy and usability of several optical localizers under laboratory test conditions, and (2) a clinical measure of the global errors obtained when using a CAS system including one of the standard localizer systems (Flashpoint 5000) in Functional Endoscopic Sinus Surgery (FESS). PATIENTS AND METHODS: The technical evaluation of localizers consisted of series of geometric tests on four commercial systems. Clinical evaluation included the development of a laboratory CAS system using a markerless, skin surface registration method. This was based on a standard optical digitizing system (Flashpoint 5000), which eliminates the need for the second CT scan, which is normally performed specifically to process the position of the fiducial markers. Global accuracy was then evaluated on 20 patients by subjective and visual comparison when placing a calibrated pointer on anatomical landmarks. RESULTS: The results of the technical study indicate that the four commercial systems tested have levels of inaccuracy deemed acceptable for most CAS applications, including ENT surgery. The clinical study obtained a registration and calibration accuracy of less than 1.5 mm in 89.2% (SD = 0.20 mm) of the cases studied. Our markerless skin surface points registration method is reliable, and allows patient head movements during the procedure. The accuracy tests performed show that this type of system can be used for ENT surgery with satisfaction. CONCLUSION: CAS systems enable the surgeon to have a more thorough understanding of the complicated anatomy of paranasal sinuses, and may be especially helpful in revision surgery when normal anatomic landmarks are lacking. Further studies are necessary in FESS to improve the CAS systems that are currently available, and to determine whether these systems can minimize the overall risk of complications.

Computer Systems↗
PubMed1995

Impact of soft tissue on in vivo accuracy of bone mineral measurements in the spine, hip, and forearm: a human cadaver study.

The impact of soft tissue in vivo on accuracy of bone mineral density (BMD) measurements of the spine and hip by dual energy X-ray absorptiometry and of the forearm by single photon absorptiometry was assessed by use of 14 human cadavers. The in vivo accuracy errors (SEE%) were: forearm 3-5%, anteroposterior spine 5.3%, lateral spine 10-12%, and femoral greater trochanter, neck, total, intertrochanteric, and Ward's triangle 3%, 6.5%, 6.7%, 8%, and 11-13%, respectively. Except from the lateral spine and the greater trochanter, the slopes of the linear regressions of in vivo BMD against in vitro BMD were not significantly different from 1 (p > 0.05). The calculated random accuracy error of BMD measurements due to fat inhomogeneity was estimated to 3-4% for the anteroposterior spine and 9-14% for the lateral spine (from abdominal computed tomography in 26 healthy women). In conclusion, acceptable accuracy errors below 6-7% (of soft tissue in vivo) of BMD measurements were obtained in the anteroposterior spine, the forearm, and the neck, greater trochanter, and total proximal femur.

Absorptiometry, Photon↗
PubMed2005

In vitro validation of phase-contrast flow measurements at 3 T in comparison to 1.5 T: precision, accuracy, and signal-to-noise ratios.

PURPOSE: To evaluate the signal-to-noise ratio (SNR), precision, and accuracy of phase-contrast flow measurements at 3 T with the help of an in vitro model and to compare the results with data from two 1.5-T scanners. MATERIALS AND METHODS: Using an identical setup of a laminar flow model and sequence parameters, measurements were done at one 3-T and at two 1.5-T systems. Precision, accuracy, and SNR were obtained for velocity encodings ranging from 55 up to 550 cm(-1). SNRs were calculated from the magnitude as well as the flow encoded images. RESULTS: Precision and accuracy for the in vitro flow model were similarly high in all scanners with no significant difference. For velocity encodings from 55 cm(-1) up to 550 cm(-1), the SNR in magnitude as well as phase encoded images of the 3-T measurements was approximately 2.5 times higher than the SNR obtained from the two 1.5-T systems. CONCLUSION: Even without optimization for the 3-T environment, flow measurements show the same high accuracy and precision as is known from clinical 1.5-T scanners. The superior SNR at 3 T will allow further improvements in temporal and spatial resolution. This will be of interest for small-size vessels like coronary arteries or for slow diastolic flow patterns.

Blood Flow Velocity↗
PubMed2007

Diagnostic accuracy of high-resolution MRI using a microscopy coil for patients with presumed DCIS following mammography screening.

PURPOSE: To prospectively evaluate the accuracy of high-resolution (HR)-MRI as a secondary examination in women with abnormal calcifications detected on mammography. MATERIALS AND METHODS: We used a 4.7-cm microscopy coil to acquire HR-MRI signal data. We examined 52 women with breast lesions preoperatively using HR-MRI and vacuum-assisted core needle biopsy. The lesions were suspicious of malignancy, classified as category 3-5 on mammography (Breast Imaging Reporting and Data System [BI-RADS]), and without a palpable mass. All visualized suspicious lesions were correlated with histological findings. We compared the HR-MRI and pathological findings and calculated the sensitivity, specificity, and accuracy. RESULTS: We compared the breast HR-MRI results with the gold standard of pathological results for studies of malignancy (DCIS and invasive cancer), and found a sensitivity of 88.5%, specificity of 92.3%, and accuracy of 90.4%. The positive predictive value (PPV) was 92%, and the negative predictive value (NPV) was 88.9%. When breast MRI was compared with pathological results for studies that diagnosed DCIS only, the results revealed a sensitivity of 88.6%, specificity of 88.2%, accuracy of 88.5%, PPV of 93.9%, and NPV of 78.9%. CONCLUSION: HR-MRI using a microscopy coil is a useful, reliable, safe, and minimally invasive procedure that is a good choice for secondary assessment of abnormal calcification in the breast.

Adult↗
PubMed2005

Optimized sample preparation for isotopic analyses of CO2 in air: systematic study of precision and accuracy dependence on driving variables during CO2 purification process.

A systematic analysis of efficiency, reproducibility and accuracy of cryogenic purification of CO(2) from air samples for isotopic analyses is presented. The technical characteristics of the cryogenic line are given in detail. To study the cryogenic process, three different operating parameters are considered: flow rate of the gas entering the line, pressure of the gas in the line, and CO(2)-trap shape. Experimental results demonstrate that efficiency, reproducibility and accuracy strongly depend on the CO(2)trap shape. Moreover, a dependence of reproducibility and accuracy on the flow rate of the gas is found, but not on its pressure. High precision (< or =0.02 per thousand for delta(13)C and < or =0.05 per thousand for delta(18)O) and good accuracy (<0.09 per thousand for delta(13)C and <0.14 per thousand for delta(18)O) is achieved after applying the N(2)O correction.

Journal Article↗
PubMed1991

Trunk positioning accuracy in the frontal and sagittal planes.

The accuracy with which the head and spine could be positioned in the frontal and sagittal planes relative to the pelvis was measured and compared in ten healthy adult males. Subjects were tested with eyes closed, while standing with their pelvis externally restrained. The positions of markers, attached to the back of the head and over each of the T1, T6, T11, and L3 spinous processes, were measured to the nearest mm using strain-gaged flexible beam transducers. Subjects were tested for their accuracy in sensing return of the trunk to an initial neutral position under different test conditions. Results showed that positioning was 16-45% more accurate in the frontal than in the sagittal plane, although the difference did not reach statistical significance. T1 could be centered to within 7 and 10 mm in the frontal and sagittal planes, respectively. No significant differences were found between active and passive positioning accuracies. Presence of an external trunk moment did not significantly affect trunk positioning accuracy, although it systematically caused overshoot of the neutral position. Lastly, lateral trunk shifts exceeding 12 mm may be classified as abnormal in young adults.

Adolescent↗
PubMed1996

Improving MR quantification of regional blood volume with intravascular T1 contrast agents: accuracy, precision, and water exchange.

The goal of this work was to develop a comprehensive understanding of the relationship between vascular proton exchange rates and the accuracy and precision of tissue blood volume estimates using intravascular T1 contrast agents. Using computer simulations, the effects of vascular proton exchange and experimental pulse sequence parameters on measurement accuracy were quantified. T1 and signal measurements made in a rat model implanted with R3230 mammary adenocarcinoma tumors demonstrated that the theoretical findings are biologically relevant; data demonstrated that over-simplified exchange models may result in measures of tumor, muscle, and liver blood volume fractions that depend on experimental parameters such as the vascular contrast concentration. As a solution to the measurement of blood volume in tissues with exchange that is unknown, methods that minimize exchange rate dependence were examined. Simulations that estimated both the accuracy and precision of such methods indicated that both the inversion recovery and the transverse-spoiled gradient echo methods using a "no-exchange" model provide the best trade-off between accuracy and precision.

Adenocarcinoma↗
PubMed1992

Divergent productive thinking factors and accuracy of nursing diagnoses.

Theories of diagnosis in nursing (Carnevali, 1983; Gordon, 1982) and a model of intelligence (Guilford, 1979) were integrated to provide a theoretical basis for this study. In contrast to previous studies, accuracy of nursing diagnoses was measured as a continuous variable. It was hypothesized that three factors of divergent productive thinking, fluency, flexibility, and elaboration, would correlate positively with accuracy of nursing diagnoses. The sample consisted of 86 female nurses, graduates of generic baccalaureate programs with 1 to 5 years experience, who met the criterion of knowledge. Three written case studies (CS1, CS2, CS3) served as the criterion for accuracy. With CS1, none of the hypotheses were supported. With CS2, the three hypotheses were supported (p less than .05) and 10% of the variance was explained by one factor, fluency (p less than .01). With CS3, elaboration and accuracy were correlated (p less than .05). The findings provide beginning support for inclusion of exercises for divergent thinking in nursing education and practice.

Adult↗
PubMed2001

Accuracy of prediction of walking for young stroke patients by use of the FIM.

BACKGROUND AND PURPOSE: Clinical prediction of walking outcome after a stroke is essential for effective discharge planning. However, its accuracy has hardly been explored. This study took place in a regional unit admitting patients with complex neurological disabilities for specialist inpatient rehabilitation. The aim was to compare predicted outcome (goal score) with achieved outcome (discharge score) on the seven-point locomotion subscale of the Functional Independence Measure (FIM), to evaluate its precision and identify factors influencing accuracy. METHOD: Admission, goal and discharge scores were analysed retrospectively for 141 subjects (90 M; 51 F) admitted consecutively to the Unit with median age 54 years (range 15-68 years) with median length of stay 13.6 weeks (range 3-35 weeks). RESULTS: Ninety subjects (64%) gained from two to six points; 50 subjects (35%) gained one point or showed no change. One patient deteriorated by two points. Excluding patients admitted with the highest score (FIM level 7), the overall level of agreement between predicted and discharge scores was moderate (weighted kappa 0.47). Prediction was accurate to +/- 1 point in 113 subjects (80%). Overprediction by > or = 2 points occurred in 16 subjects (11%) and underprediction by > or = 2 points in 12 subjects (9%). Analysis of the most-disabled cohort, admitted with FIM levels 1 or 2 scores, revealed a higher sensitivity for predicting 'independence' (FIM levels 5-7) (78%) than 'dependence' (FIM levels 1-4) (65%). Accuracy was not affected by age, gender or side of stroke. Inaccurate predictions were associated with lower admission FIM level scores (p = -0.26; p = 0.002) and a greater length of stay (p = 0.36; p < 0.001). Subjects with quadriplegia were more likely to have inaccurate outcome predictions made than those with hemiplegia (p = 0.025) and those with neglect were more likely to have inaccurate outcome predictions made than those without neglect (p = 0.017). CONCLUSION: Further investigation into clinical prediction and the variables which confound accuracy is needed for effective planning.

Adolescent↗
PubMed1996

Topology prediction for helical transmembrane proteins at 86% accuracy.

Previously, we introduced a neural network system predicting locations of transmembrane helices (HTMs) based on evolutionary profiles (PHDhtm, Rost B, Casadio R, Fariselli P, Sander C, 1995, Protein Sci 4:521-533). Here, we describe an improvement and an extension of that system. The improvement is achieved by a dynamic programming-like algorithm that optimizes helices compatible with the neural network output. The extension is the prediction of topology (orientation of first loop region with respect to membrane) by applying to the refined prediction the observation that positively charged residues are more abundant in extra-cytoplasmic regions. Furthermore, we introduce a method to reduce the number of false positives, i.e., proteins falsely predicted with membrane helices. The evaluation of prediction accuracy is based on a cross-validation and a double-blind test set (in total 131 proteins). The final method appears to be more accurate than other methods published: (1) For almost 89% (+/-3%) of the test proteins, all HTMs are predicted correctly. (2) For more than 86% (+/-3%) of the proteins, topology is predicted correctly. (3) We define reliability indices that correlate with prediction accuracy: for one half of the proteins, segment accuracy raises to 98%; and for two-thirds, accuracy of topology prediction is 95%. (4) The rate of proteins for which HTMs are predicted falsely is below 2% (+/-1%). Finally, the method is applied to 1,616 sequences of Haemophilus influenzae. We predict 19% of the genome sequences to contain one or more HTMs. This appears to be lower than what we predicted previously for the yeast VIII chromosome (about 25%).

Algorithms↗
PubMed2003

Predictive accuracy and explained variation.

Measures of the predictive accuracy of regression models quantify the extent to which covariates determine an individual outcome. Explained variation measures the relative gains in predictive accuracy when prediction based on covariates replaces unconditional prediction. A unified concept of predictive accuracy and explained variation based on the absolute prediction error is presented for models with continuous, binary, polytomous and survival outcomes. The measures are given both in a model-based formulation and in a formulation directly contrasting observed and expected outcomes. Various aspects of application are demonstrated by examples from three forms of regression models. It is emphasized that the likely degree of absolute or relative predictive accuracy often is low even if there are highly significant and relatively strong covariates.

Austria↗
PubMed2006

Measuring and estimating diagnostic accuracy when there are three ordinal diagnostic groups.

This article studies the problem of measuring and estimating the diagnostic accuracy when there are three ordinal diagnostic groups. We use a receiver operating characteristic (ROC) surface to describe the probabilities of correct classifications into three diagnostic groups based on various sets of diagnostic thresholds of a test and propose to use the entire and the partial volume under the surface to measure the diagnostic accuracy. Mathematical properties and probabilistic interpretations of the proposed measure of diagnostic accuracy are discussed. Under the assumption of normal distributions of the diagnostic test from three diagnostic groups, we present the maximum likelihood estimate to the volume under the ROC surface and give the asymptotic variance to the estimate. We further propose several asymptotic confidence interval estimates to the volume under the ROC surface. The performance of these confidence interval estimates is evaluated in terms of attaining the nominal coverage probability based on a simulation study. In addition, we develop a method of sample size determination to achieve an adequate accuracy of the confidence interval estimate. Finally, we demonstrate the proposed methodology by applying it to the clinical diagnosis of early stage Alzheimer's disease based on the neuropsychological database of the Washington University Alzheimer's Disease Research Center.

Alzheimer Disease↗
PubMed2007

Statistical methods for determining the accuracy of quantitative polymerase chain reaction-based tests.

Quantitative polymerase chain reaction (PCR)-based tests are used in several different scientific fields to determine levels of a target DNA sequence of interest (the target molecule). The accuracy of quantitative PCR-based tests can be assessed by using the assay to determine the number of copies of the target molecule in a sample with a known concentration of the target molecule. For example, a sample with a known concentration of a target DNA sequence is serially diluted into replicate aliquots and these are tested to determine if the observed quantity of the target is close to the expected quantity (given the concentration in the original sample and the dilution). Statistical methods that are conventionally used to assess the accuracy of these assays do not take into account the variability in the number of target molecules in each aliquot from the original sample. We develop methods that take into account this extra variation and which determine the accuracy of quantitative PCR-based tests in estimating the number of target molecules based on a set of assays of serial dilutions from an original sample with a known concentration of target molecules. These methods are applied to data from an experiment to test the accuracy of a real-time PCR assay at low HIV-1 DNA copy levels.

DNA, Viral↗
PubMed2005

Accuracy of magnetic resonance imaging for measuring fetal sheep lungs and other organs.

OBJECTIVE: Lung volume measurement by fetal magnetic resonance imaging (fetMRI) has been used to predict survival of fetuses with isolated congenital diaphragmatic hernia (CDH). So far, the accuracy and precision of fetMRI for volumetry of either the normal or hypoplastic developing lung has not been formally studied. METHODS: A total of nine sheep carrying 14 fetuses underwent fetMRI under general anesthesia at a mean of 118 days' gestational age (term = 145 days). A total of 61 organs were measured in nine normal fetal sheep and five that underwent surgical creation of diaphragmatic hernia (DH), so as to induce pulmonary hypoplasia. Lungs were measured on T2-WI (weighted images) in three different planes, while liver and kidneys were measured in the axial (T1-WI) and sagittal (T2-WI) planes, respectively. Necropsy was done within 24 h after fetMRI to determine the volume postmortem by the water displacement method. Values were linearly correlated and a Bland and Altman analysis was done for volume measurement comparison, calculating means +/- SD, bias (mean of the difference of volume measurements), precision (SD of the difference) and absolute and proportionate limits of agreement for both methods. The accuracy of fetMRI volume measurement was determined for different organ groups by calculating the median relative error and precision index, both being measures of error in proportion to the magnitude of the volume measured, as a clinically relevant proxy of potential errors. RESULTS: The fetMRI volume measurements were on average larger than postmortem volumes, except for the kidneys. Kidney volume determination had a relative error of 29%, while measurements of larger organs had larger relative errors (42% for liver). Normal lungs were less accurately measured in the coronal or sagittal than in the axial plane (relative error 53%, 73% and 38%, respectively; P < 0.05 for sagittal vs. axial). Axially-measured lung volumes were more accurate for lungs of normal sheep compared to DH lungs (relative error 38% vs. 73%, respectively; P < 0.05). CONCLUSION: FetMRI measured systematically higher volumes for organs such as fetal liver or lung. This may be related to fluid loss or lack of perfusion at the time of necropsy. Measurement of lung volume by fetMRI was most accurate in the axial plane. Measurements of lung and liver volumes by fetMRI in normal sheep were both in agreement with volumes measured at necropsy. Loss of accuracy for DH-lungs in comparison with the accuracy when measuring other similarly small organs, such as kidneys, suggests that fetMRI measurements can be less accurate for hypoplastic lungs related to CDH. With improving hardware, it might become easier to render the fetal lung and determine its volume reliably.

Algorithms↗
PubMed2001

Confidence and accuracy of near-threshold discrimination responses.

This article reports four subliminal perception experiments using the relationship between confidence and accuracy to assess awareness. Subjects discriminated among stimuli and indicated their confidence in each discrimination response. Subjects were classified as being aware of the stimuli if their confidence judgments predicted accuracy and as being unaware if they did not. In the first experiment, confidence predicted accuracy even at stimulus durations so brief that subjects claimed to be performing at chance. This finding indicates that subjects's claims that they are "just guessing" should not be accepted as sufficient evidence that they are completely unaware of the stimuli. Experiments 2-4 tested directly for subliminal perception by comparing the minimum exposure duration needed for better than chance discrimination performance against the minimum needed for confidence to predict accuracy. The latter durations were slightly but significantly longer, suggesting that under certain circumstances people can make perceptual discriminations even though the information that was used to make those discriminations is not consciously available.

Attitude↗
PubMed1994

Time-accuracy functions for determining process and person differences: an application to cognitive aging.

A paradigm for the determination of time-accuracy functions (TAFs) for individual participants is introduced for two pairs of tasks differing in cognitive complexity, that is, word scanning vs cued recognition and figural scanning vs figural reasoning. TAFs can be used to test dissociations of cognitive processes beyond scale-related ambiguities of ordinal interactions. The approach is applied to examine the cognitive-aging hypothesis that a single slowing factor can account for interactions between adult age and cognitive task complexity. Twenty young and 20 old adults participated in 17 sessions. Presentation times required for 75, 87.5, and 100% accuracies were determined for each task with a variant of the psychophysical method of limits. Accuracy was fit by negatively accelerated functions of presentation time. State-trace analyses showed that different slowing factors are required for high- and low-complexity tasks. Relations to speed-accuracy and performance-resource functions are discussed.

Adult↗
PubMed2000

Structure-based evaluation of sequence comparison and fold recognition alignment accuracy.

The biological role, biochemical function, and structure of uncharacterized protein sequences is often inferred from their similarity to known proteins. A constant goal is to increase the reliability, sensitivity, and accuracy of alignment techniques to enable the detection of increasingly distant relationships. Development, tuning, and testing of these methods benefit from appropriate benchmarks for the assessment of alignment accuracy.Here, we describe a benchmark protocol to estimate sequence-to-sequence and sequence-to-structure alignment accuracy. The protocol consists of structurally related pairs of proteins and procedures to evaluate alignment accuracy over the whole set. The set of protein pairs covers all the currently known fold types. The benchmark is challenging in the sense that it consists of proteins lacking clear sequence similarity. Correct target alignments are derived from the three-dimensional structures of these pairs by rigid body superposition. An evaluation engine computes the accuracy of alignments obtained from a particular algorithm in terms of alignment shifts with respect to the structure derived alignments. Using this benchmark we estimate that the best results can be obtained from a combination of amino acid residue substitution matrices and knowledge-based potentials.

Algorithms↗
PubMed2000

Cortical activity related to accuracy of letter recognition.

Previous imaging and neurophysiological studies have suggested that the posterior inferior temporal region participates in tasks requiring the recognition of objects, including faces, words, and letters; however, the relationship between accuracy of recognition and activity in that region has not been systematically investigated. In this study, positron emission tomography was used to estimate glucose metabolism in 60 normal adults performing a computer-generated letter-recognition task. Both a region of interest and a voxel-based method of analysis, with subject state and trait variables statistically controlled, found task accuracy to be: (1) negatively related to metabolism in the left ventrolateral inferior temporal occipital cortex (Brodmann's area 37, or ventrolateral BA 37) and (2) positively related to metabolism in a region of the right ventrolateral frontal cortex (Brodmann's areas 47 and 11, or right BA 47/11). Left ventrolateral BA 37 was significantly related both to hits and to false alarms, whereas the right BA 47/11 finding was related only to false alarms. The results were taken as supporting an automaticity mechanism for left ventrolateral BA 37, whereby task accuracy was associated with automatic letter recognition and in turn to reduced metabolism in this extrastriate area. The right BA 47/11 finding was interpreted as reflecting a separate component of task accuracy, associated with selectivity of attention broadly and with inhibition of erroneous responding in particular. The findings are interpreted as supporting the need for control of variance due to subject and task variables, not only in correlational but also in subtraction designs.

Adult↗