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Results for “Measuring algorithm”

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PubMed1999

An adaptive Bayesian pruning for neural networks in a non-stationary environment.

Pruning a neural network to a reasonable smaller size, and if possible to give a better generalization, has long been investigated. Conventionally the common technique of pruning is based on considering error sensitivity measure, and the nature of the problem being solved is usually stationary. In this article, we present an adaptive pruning algorithm for use in a nonstationary environment. The idea relies on the use of the extended Kalman filter (EKF) training method. Since EKF is a recursive Bayesian algorithm, we define a weight-importance measure in term of the sensitivity of a posteriori probability. Making use of this new measure and the adaptive nature of EKF, we devise an adaptive pruning algorithm called adaptive Bayesian pruning. Simulation results indicate that in a noisy nonstationary environment, the proposed pruning algorithm is able to remove network redundancy adaptively and yet preserve the same generalization ability.

Bayes Theorem↗

PubMed2006

Digital diagnostics: Three-dimensional modelling.

Three-dimensional imaging techniques, such as computed tomograms (CT), structured light, and stereophotogrammetry, can be used to capture three-dimensional coordinate data, but comprehensive analysis is required to transform these techniques into powerful diagnostic tools. The object of this review is to highlight analytical functionality using software developed to study three-dimensional digital imaging and communications in medicine (DICOM) based digital data for diagnosis, planning of treatment, and evaluation of craniofacial changes. My specific aim was to apply three-dimensional software routines using geometric morphometrics or conventional measurements. These routines rely on robust algorithms to construct mean objects by manipulating the three-dimensional x, y, and z coordinates of all the objects' vertices. Conventional measurements and statistical tests can then be applied to the changes in the vertices, say, before and after treatment. Using graphical and geometric morphometric techniques such as finite-element analysis and principal components analysis, clinical craniofacial modelling can be used for the localisation and quantification of soft and hard tissue changes; diagnostic modelling can be undertaken for planning of treatment, and data-driven predictive modelling can be undertaken for the planning of many procedures based on the surgeon's own experience, patients, and resources. Three-dimensional modelling of digital data may therefore have added value for clinical diagnosis, and planning and assessment of treatment, including audit.

Algorithms↗

PubMed1998

New Down syndrome screening algorithm: ultrasonographic biometry and multiple serum markers combined with maternal age.

OBJECTIVE: We compared the Down syndrome screening efficiency of a new algorithm that combines humerus length measurement and serum analytes versus that of the traditional triple-analyte serum screen. STUDY DESIGN: Humerus length measurements were obtained prospectively in 1743 midtrimester (14 to 24 weeks) singleton fetuses before genetic amniocentesis. All patients had triple-marker serum screening before amniocentesis. Data on humerus length were expressed as multiples of the median, and were normalized by log transformation. Backward multiple stepwise logistic regression analysis was performed to determine which combination of biometry and serum markers best predicted fetal Down syndrome. The screening efficiency of the traditional triple-analyte algorithm was compared with that of a new multivariate gaussian algorithm that combined biometry and serum markers. RESULTS: There were 31 (1.8%) fetuses with Down syndrome in the study population. In the regression analysis humerus length, human chorionic gonadotropin, alpha-fetoprotein, and maternal age were significant predictors of Down syndrome, but unconjugated estriol was not. The combined algorithm (humerus length, human chorionic gonadotropin, and alpha-fetoprotein and age) was superior to the traditional triple screen for Down syndrome detection. The sensitivities at fixed false-positive rates were consistently higher in the combination than in the triple-screen protocol. For example, at a 10% false-positive rate the sensitivities were 65.0% and 52.3%, respectively. Similarly, at a 15% false-positive rate the sensitivities were 73.5% and 55.0%, respectively. CONCLUSION: A new screening algorithm combining humerus length and serum analytes was superior to the traditional triple screen. Although we used a high-risk population in this study, it is expected that the observed superiority of the combination screen would persist in a population of younger women. The development of a combined biometric and serum analyte screening algorithm for estimating individual odds could represent an advance in prenatal Down syndrome screening.

Algorithms↗

PubMed2003

Assessing dietary and exercise stage of change to optimize weight loss interventions.

OBJECTIVE: According to the Transtheoretical Model (TM), tailoring interventions to patients' readiness to change can enhance patient progress and help patients use therapeutic resources more effectively. However, tailoring an intervention depends on accurate assessment of patients' stage of change (SOC). This study describes a multi-item algorithm of SOC (M-SOC) for weight loss-related behaviors that attempts to overcome some of the conceptual and methodological difficulties encountered in previously SOC assessments. RESEARCH METHODS: Data were collected from participants randomly assigned to the treatment arm of a clinical trial comparing a TM-based, cognitive-behavioral intervention with enhanced usual care for weight loss. RESULTS: The stair-step relationships hypothesized by the TM between assessed SOC and key behavioral measures were found for all algorithms (p < 0.05), indicating that the M-SOC algorithm performs as well as single item algorithms. However, 50% fewer patients were classified in action or maintenance for dietary fat intake and portion control (p < 0.05) by the multiple-item algorithms, providing staging more consistent with the clinical presentation of obese individuals. In addition, logistic regression analyses indicated that the single-item algorithms were not sufficient predictors of these behavioral domains. DISCUSSION: To the extent that treatment is guided by assessed SOC, there is potential for a considerable variability in interventions with different approaches to staging. For weight-loss interventions that target portion control and decreased fat intake, the multi-item SOC algorithms seem to be better guides for matching treatments to SOC.

Algorithms↗

PubMed2006

Optimization of extracranial stereotactic radiation therapy of small lung lesions using accurate dose calculation algorithms.

BACKGROUND: The aim of this study was to compare and to validate different dose calculation algorithms for the use in radiation therapy of small lung lesions and to optimize the treatment planning using accurate dose calculation algorithms. METHODS: A 9-field conformal treatment plan was generated on an inhomogeneous phantom with lung mimics and a soft tissue equivalent insert, mimicking a lung tumor. The dose distribution was calculated with the Pencil Beam and Collapsed Cone algorithms implemented in Masterplan (Nucletron) and the Monte Carlo system XVMC and validated using Gafchromic EBT films. Differences in dose distribution were evaluated. The plans were then optimized by adding segments to the outer shell of the target in order to increase the dose near the interface to the lung. RESULTS: The Pencil Beam algorithm overestimated the dose by up to 15% compared to the measurements. Collapsed Cone and Monte Carlo predicted the dose more accurately with a maximum difference of -8% and -3% respectively compared to the film. Plan optimization by adding small segments to the peripheral parts of the target, creating a 2-step fluence modulation, allowed to increase target coverage and homogeneity as compared to the uncorrected 9 field plan. CONCLUSION: The use of forward 2-step fluence modulation in radiotherapy of small lung lesions allows the improvement of tumor coverage and dose homogeneity as compared to non-modulated treatment plans and may thus help to increase the local tumor control probability. While the Collapsed Cone algorithm is closer to measurements than the Pencil Beam algorithm, both algorithms are limited at tissue/lung interfaces, leaving Monte-Carlo the most accurate algorithm for dose prediction.

Algorithms↗

PubMed2007

Multilevel quality-guided phase unwrapping algorithm for real-time three-dimensional shape reconstruction.

A multilevel quality-guided phase unwrapping algorithm for real-time 3D shape measurement is presented. The quality map is generated from the gradient of the phase map. Multilevel thresholds are used to unwrap the phase level by level. Within the data points in each level, a fast scan-line algorithm is employed. The processing time of this algorithm is approximately 18.3 ms for an image size of 640x480 pixels in an ordinary computer. We demonstrate that this algorithm can be implemented into our real-time 3D shape measurement system for real-time 3D reconstruction. Experiments show that this algorithm improves the previous scan-line phase unwrapping algorithm significantly although it reduces its processing speed slightly.

Journal Article↗

PubMed2006

Neighborhood-pixels algorithm combined with Sono-CT in the diagnosis of cirrhosis: an experimental study.

The goal was to investigate the role of neighborhood-pixels algorithm (NPA) in analyzing the echogram of experimental cirrhosis and the value of high frequency real-time compound imaging (Sono-CT) in improving texture analysis. A cirrhosis model was established by subcutaneously injecting CCl(4) in 80 rats. The total group of rats were divided into a control group and four treatment groups (treated for 6, 8, 10 and 12, weeks respectively). The texture of hepatic-echograms was analyzed using a "neighborhood-pixels" algorithm. Images were obtained under conventional imaging mode and Sono-CT, respectively. The second texture parameter (FP(2)) was estimated and compared in different groups and under different modes. FP(2) increased gradually with the time of treatment and group differences were significant (p < 0.01). In these groups, FP(2) was higher under Sono-CT than under conventional condition (p < 0.01) and group differences in FP(2) under both conditions were significant (p < 0.01). Thus, FP(2) measured by neighborhood-pixels algorithm can reflect the dynamic change of the texture of echogram of cirrhosis in rats and Sono-CT can improve texture analysis by neighborhood-pixels algorithm, thus facilitating the early diagnosis of cirrhosis.

Algorithms↗

PubMed2004

Automated analysis of the auditory brainstem response using derivative estimation wavelets.

In this paper, we describe an algorithm that automatically detects and labels peaks I-VII of the normal, suprathreshold auditory brainstem response (ABR). The algorithm proceeds in three stages, with the option of a fourth: (1) all candidate peaks and troughs in the ABR waveform are identified using zero crossings of the first derivative, (2) peaks I-VII are identified from these candidate peaks based on their latency and morphology, (3) if required, peaks II and IV are identified as points of inflection using zero crossings of the second derivative and (4) interpeak troughs are identified before peak latencies and amplitudes are measured. The performance of the algorithm was estimated on a set of 240 normal ABR waveforms recorded using a stimulus intensity of 90 dBnHL. When compared to an expert audiologist, the algorithm correctly identified the major ABR peaks (I, III and V) in 96-98% of the waveforms and the minor ABR peaks (II, IV, VI and VII) in 45-83% of waveforms. Whilst peak II was correctly identified in only 83% and peak IV in 77% of waveforms, it was shown that 5% of the peak II identifications and 31% of the peak IV identifications came as a direct result of allowing these peaks to be found as points of inflection.

Adolescent↗

PubMed1995

[Assessment of right ventricular function by magnetic resonance imaging of old myocardial infarction].

The usefulness of magnetic resonance imaging (MRI) for estimating right ventricular function and the influence of left ventricular dysfunction on the performance of the right ventricle were assessed in 43 patients with chronic myocardial infarction (MI) and 14 control subjects (N) using electrocardiography-gated MRI and cardiac catheterization. Patients with MI were divided into three groups according to the location of the coronary lesions; 22 patients with left coronary artery lesion (LCA group), 13 with right coronary artery lesion (RCA group), and 8 with both left and right coronary artery lesions (L+R group). The right ventricular end-diastolic volume (RVEDV) and right ventricular ejection fraction (RVEF) were measured by Simpson's rule algorithm on transverse images of the right ventricle obtained at the end-systolic and end-diastolic phases. In 34 of the 43 patients, the same parameters of right ventricular function were calculated by the thermodilution method using a Swan-Ganz catheter with rapid response thermistor. Left ventricular ejection fraction (LVEF) and end-diastolic volume were determined from left ventriculography. The intraobserver reproducibility (11 cases, r = 0.97) and interobserver reproducibility (11 cases, r = 0.92) of RVEF measured by MRI were excellent. The RVEF and RVEDV determined from MRI were significantly correlated with those from the thermodilution method (RVEF: r = 0.56, RVEDV: r = 0.52). There was no difference in right ventricular end-diastolic volume index in any patient group. The RVEF was decreased in the L+R (41.0 +/- 4.5%, p < 0.01) and RCA (45.9 +/- 6.6%) groups, but there was no difference between the LCA (50.6 +/- 6.6%) and N (48.9 +/- 4.3%) groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1998

Comparative investigations of algorithms for the detection of breaths in newborns with disturbed respiratory signals.

The correct detection of the beginning of inspiration and expiration in the respiratory signals is an essential prerequisite for accurate lung function testing in newborns. Five algorithms for breath detection using pneumotachographically measured flow and volume signals were investigated with regard to the error rate. To compare and to evaluate the reliability of these algorithms 12 minimally and 12 severely disturbed flow and volume signals from spontaneously breathing newborns were used. With the exception of an algorithm based on Walsh-transformed signals, all algorithms work reliably (error rate <1.1%) if disturbances are minimal. In severely disturbed signals there is a great difference between the algorithms. The most robust algorithm tested (trigger of the flow signal with an additional plausibility check of the recognized breath) resulted in an error rate of <3.4%. Not all algorithms tested are suitable for real-time applications because they differ considerably in delay time for breath detection.

Algorithms↗

PubMed2005

Automatic selection of parameters for vessel/neurite segmentation algorithms.

An automated method is presented for selecting optimal parameter settings for vessel/neurite segmentation algorithms using the minimum description length principle and a recursive random search algorithm. It trades off a probabilistic measure of image-content coverage against its conciseness. It enables nonexpert users to select parameter settings objectively, without knowledge of underlying algorithms, broadening the applicability of the segmentation algorithm, and delivering higher morphometric accuracy. It enables adaptation of parameters across batches of images. It simplifies the user interface to just one optional parameter and reduces the cost of technical support. Finally, the method is modular, extensible, and amenable to parallel computation. The method is applied to 223 images of human retinas and cultured neurons, from four different sources, using a single segmentation algorithm with eight parameters. Improvements in segmentation quality compared to default settings using 1000 iterations ranged from 4.7%-21%. Paired t-tests showed that improvements are statistically significant (p < 0.0005). Most of the improvement occurred in the first 44 iterations. Improvements in description lengths and agreement with the ground truth were strongly correlated (p = 0.78).

Algorithms↗

PubMed2000

Field characterization of therapeutic ultrasound phased arrays through forward and backward planar projection

Spatial planar projection techniques propagate field measurements from a single plane in front of a transmitter to arbitrary new planes closer to or further away from the source. A linear wave vector frequency-domain projection algorithm is applied to the acoustic fields measured from several focused transducer arrays designed for ultrasound therapy. A polyvinylidene difluoride hydrophone is first scanned in a water tank over a plane using a three-dimensional positioning system to measure the complex pressure field as a function of position. The field is then projected to a series of new planes using the algorithm. Results of the projected fields are compared with direct measurements taken at corresponding distances. Excellent correlation is found between the projected and measured data. The method is shown to be accurate for use with phase-controlled field patterns, providing a rapid and accurate method for obtaining field information over a large spatial volume. This method can significantly simplify the characterization procedure required for phased-array application used for therapy. Most significantly, the wavefront propagated back to a phased array can be used to predict the field produced by different phase and amplitude settings of the array elements. A field back-projected to the source could be used as an improved source function in acoustic modeling.

Journal Article↗

PubMed2006

An effectiveness study comparing algorithm-based antihypertensive therapy with previous treatments using conventional and ambulatory blood pressure measurements.

Effectiveness trials in hypertension enable the efficacy and safety of new drugs to be compared with previous therapy. Since these open-label trials could inadvertently be influenced by observer bias, this study has used ambulatory blood pressure monitoring (ABPM) to provide a rigorous blinded end point to validate the study conclusions. The study was performed in 675 patients with stage 1 or 2 hypertension despite receiving single-agent or fixed-dose combination therapy. After baseline ABPM, the previous treatment was replaced by telmisartan 40 mg daily; if control (office blood pressure <140/90 mm Hg) was not achieved in 2 weeks, the dose was increased to 80 mg, and if necessary, a fixed combination with hydrochlorothiazide 12.5 mg was used after a further 4 weeks. ABPM was repeated after 4 weeks on final therapy. Overall, 50% of patients finished on monotherapy and 50% on combination therapy. By office measurements, there was a decrease (mean +/- SEM) of 16.8+/-0.5/10.3+/-0.3 mm Hg (p<0.001) when telmisartan-based treatment replaced previous treatment; by ABPM, the decrease was 8.2+/-0.4/5.0+/-0.2 mm Hg (p<0.001). The decreases were significant for comparisons with each of the prior drug classes. A treatment algorithm based on the angiotensin receptor blocker, telmisartan, was confirmed by the blinded end point of ABPM as an efficacious alternative to other antihypertensive regimens in clinical practice.

Aged↗

PubMed1993

Intensive conventional insulin therapy for type II diabetes. Metabolic effects during a 6-mo outpatient trial.

OBJECTIVE: To determine whether tight glycemic control can be obtained using intensive conventional split-dose insulin therapy in the outpatient management of type II diabetes without development of unacceptable side effects. RESEARCH DESIGN AND METHODS: Fourteen type II diabetic subjects were treated with an intensive program of conventional insulin (subcutaneous NPH and regular insulin before breakfast and supper) for 6 mo. Insulin dose adjustments were based on an algorithm built on frequent CPG measurements (4-6 times/day). Patients were monitored biweekly as outpatients and admitted 1 day/mo for metabolic evaluation. RESULTS: Glycemic control was achieved by 1 mo (mean plasma glucose fell from 17.5 +/- 0.9 to 7.7 +/- 0.7 mM, P < 0.001) and remained in this range thereafter. Hypoglycemic events at 1 mo were infrequent (mean +/- SE events per patient per month: 4.1 +/- 0.3) and mild in nature, and progressively decreased to 1.3 +/- 0.5 events/mo by 6 mo. After treatment, basal HGO fell 44% from 628 +/- 44 to 350 +/- 17 mumol.m-2.min-1 (P < 0.001), and maximal rates of glucose disposal measured by hyperinsulinemic euglycemic clamp (1800 pmol.m-2.min-1) improved from 1418 +2- 156 to 1657 +/- 128 mumol.m-2.min-1 (P < 0.05). The total dose of exogenous insulin required was 86 +/- 13 U at 1 mo and 100 +/- 24 U at 6 mo. During treatment, mean serum insulin levels increased from 308 +/- 80 to 510 +/- 102 pM (P < 0.05), while body weight increased from 93.5 +/- 5.8 to 102.2 +/- 6.8 kg (P < 0.001). Both pre- and posttreatment glucose disposal rates correlated with the total exogenous insulin dose required to achieve glycemic control (r = -0.75 and -0.78, both P < 0.005). Weight gain was inversely related to the pretreatment glucose disposal rate (r = -0.53, P < 0.05) and directly correlated with both mean day-long serum insulin level (r = 0.67, P < 0.01) and total exogenous insulin dose (r = 0.62, P < 0.02). CONCLUSIONS: Intensive CIT, when combined with CBG measurements, can be used to rapidly improve glycemic control in type II diabetes without development of unacceptable hypoglycemia. This degree of metabolic improvement, however, requires large doses of exogenous insulin to overcome peripheral insulin resistance and results in greater hyperinsulinemia with progressive weight gain.

Algorithms↗

PubMed1989

Correcting for the thermodynamic characteristics of a body plethysmograph.

A constant volume body plethysmograph is used to measure changes in total body volume by relating pressure changes measured inside a closed chamber to changes in its volume. The relationship between pressure and volume, however, is complicated by the fact that rapid changes in pressure are accompanied by changes in the temperature of the gas in the plethysmograph. The rate at which the temperature of the gas subsequently approaches that of the environment affects the frequency response of the plethysmograph as a volume measuring instrument. In this paper it is shown that the transient response in plethysmograph pressure to a step change in volume must be a multi-component function, due to the gas near the walls of the plethysmograph approaching thermal equilibrium with the environment at a faster rate than gas near the center. The step response of a 200 L plethysmograph was determined experimentally and found to be well described empirically by a sum of two decaying exponential functions of time. The fitted exponentials were used to construct an algorithm for digitally correcting a measured pressure signal for the effects of the plethysmograph response. When applied to a hypothetical volume waveform over a single breath, an almost perfect correction was obtained.

Animals↗

PubMed2002

High-precision shape measurement by white-light interferometry with real-time scanner error correction.

White-light interferometric techniques allow high-precision shape measurement of objects with discontinuous structures by detecting the peak of the coherence envelope. These techniques assume a specific change in the optical path difference (OPD) between the interfering beams; however, the scanning device effecting that change often introduces OPD errors that are carried over to the measurements. We present a technique for measuring OPD changes from the collected interference fringes during each measurement. Information about the scan is directly fed into the algorithm, which compensates for the errors, resulting in improved measurement accuracy. The method corrects not only the scanner errors but also slowly varying vibrations. In addition, this technique can be easily adapted to any existing low-coherence interferometer because no large data storage or postprocessing is required.

Journal Article↗

PubMedDate not supplied

Creating an online dictionary of abbreviations from MEDLINE.

OBJECTIVE: The growth of the biomedical literature presents special challenges for both human readers and automatic algorithms. One such challenge derives from the common and uncontrolled use of abbreviations in the literature. Each additional abbreviation increases the effective size of the vocabulary for a field. Therefore, to create an automatically generated and maintained lexicon of abbreviations, we have developed an algorithm to match abbreviations in text with their expansions. DESIGN: Our method uses a statistical learning algorithm, logistic regression, to score abbreviation expansions based on their resemblance to a training set of human-annotated abbreviations. We applied it to Medstract, a corpus of MEDLINE abstracts in which abbreviations and their expansions have been manually annotated. We then ran the algorithm on all abstracts in MEDLINE, creating a dictionary of biomedical abbreviations. To test the coverage of the database, we used an independently created list of abbreviations from the China Medical Tribune. MEASUREMENTS: We measured the recall and precision of the algorithm in identifying abbreviations from the Medstract corpus. We also measured the recall when searching for abbreviations from the China Medical Tribune against the database. RESULTS: On the Medstract corpus, our algorithm achieves up to 83% recall at 80% precision. Applying the algorithm to all of MEDLINE yielded a database of 781,632 high-scoring abbreviations. Of all the abbreviations in the list from the China Medical Tribune, 88% were in the database. CONCLUSION: We have developed an algorithm to identify abbreviations from text. We are making this available as a public abbreviation server at \url[http://abbreviation.stanford.edu/].

Abbreviations as Topic↗

PubMedDate not supplied

DISSIM: a program for the analysis of chemical diversity.

As interest in database searching and compound selection has grown, there has been a concomitant growth in interest in the quantification of chemical similarity. Described here is a computer program called DISSIM, which addresses the problem of selecting diverse subsets from larger collections of chemical compounds. It is a pragmatic solution combining a maximum dissimilarity search algorithm and a general multidimensional measure of chemical similarity based on the combination of different molecular descriptors. The problem of correlation between descriptors is addressed and appropriate schemes for weighting and normalisation are described. The specific application of these techniques to the comparative analysis of topological indices and their use in the area of chemical diversity analysis and compound selection are also described.

Algorithms↗