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At least 397 records · Page 22Linked to original sources
PubMed2006

Hand volume estimates based on a geometric algorithm in comparison to water displacement.

Assessing changes in upper extremity limb volume during lymphedema therapy is important for determining treatment efficacy and documenting outcomes. Although arm volumes may be determined by tape measure, the suitability of circumference measurements to estimate hand volumes is questionable because of the deviation in circularity of hand shape. Our aim was to develop an alternative measurement procedure and algorithm for routine use to estimate hand volumes. A caliper was used to measure hand width and depth in 33 subjects (66 hands) and volumes (VE) were calculated using an elliptical frustum model. Using regression analysis and limits of agreement (LOA), VE was compared to volumes determined by water displacement (VW), to volumes calculated from tape-measure determined circumferences (VC), and to a trapezoidal model (VT). VW and VE (mean +/- SD) were similar (363 +/- 98 vs. 362 +/-100 ml) and highly correlated; VE = 1.01VW -3.1 ml, r=0.986, p<0.001, with LOA of +/- 33.5 ml and +/- 9.9 %. In contrast, VC (480 +/- 138 ml) and VT (432 +/- 122 ml) significantly overestimated volume (p<0.0001). These results indicate that the elliptical algorithm can be a useful alternative to water displacement when hand volumes are needed and the water displacement method is contra-indicated, impractical to implement, too time consuming or not available.

Adult↗
PubMed1999

Metrics and similarity measures for hidden Markov models.

Hidden Markov models were introduced in the beginning of the 1970's as a tool in speech recognition. During the last decade they have been found useful in addressing problems in computational biology such as characterising sequence families, gene finding, structure prediction and phylogenetic analysis. In this paper we propose several measures between hidden Markov models. We give an efficient algorithm that computes the measures for left-right models, e.g. profile hidden Markov models, and briefly discuss how to extend the algorithm to other types of models. We present an experiment using the measures to compare hidden Markov models for three classes of signal peptides.

Algorithms↗
PubMed2003

Estimation of the local statistical noise in positron emission tomography revisited: practical implementation.

The purpose of this report is to implement novel modifications to overcome the limitations of an existing algorithm for estimating the local statistical noise in a positron emission tomography (PET) image without performing repeated measures. The original algorithm is based on a modification of the filtered back-projection algorithm that allows the variance to be estimated using only a single sinogram. In addition, the effects of photon absorption, random coincidences, radioactive decay, and detector nonuniformity are taken into account. However, there are some limitations when applying this method with modern scanners. In particular, it is common practice to interleave the projections in the sinogram (to increase the sampling rate along each projection) and to perform an interpolation when actually back-projecting to reconstruct the images. Both of these procedures introduce covariance among the elements of the projections, which is cumbersome and impractical to deal with using the existing technique for creating a variance image. An alternative image reconstruction scheme that is shown to be equivalent to image reconstruction using traditional filtered back-projection greatly simplifies the estimation of the variance image. The proposed methods were tested by Monte Carlo simulations and by using repeated scans of a uniform phantom filled with F-18. Results demonstrate that the proposed methods are very rigorous and stable when compared to calculations of the local variance using either repeated measures with a large number of measurements, or region-of-interest estimates of the variance, assuming homogeneous variance structure. In addition, strategies for extending the proposed technique are discussed that would permit the estimation of the variance due to measurement error of a pixel in a brain map from both single subjects and pooled group data.

Algorithms↗
PubMed2000

Dementia diagnoses from clinical and neuropsychological data compared: the Cache County study.

OBJECTIVE: To validate a neuropsychological algorithm for dementia diagnosis. METHODS: We developed a neuropsychological algorithm in a sample of 1,023 elderly residents of Cache County, UT. We compared algorithmic and clinical dementia diagnoses both based on DSM-III-R criteria. The algorithm diagnosed dementia when there was impairment in memory and at least one other cognitive domain. We also tested a variant of the algorithm that incorporated functional measures that were based on structured informant reports. RESULTS: Of 1,023 participants, 87% could be classified by the basic algorithm, 94% when functional measures were considered. There was good concordance between basic psychometric and clinical diagnoses (79% agreement, kappa = 0.57). This improved after incorporating functional measures (90% agreement, kappa = 0.76). CONCLUSIONS: Neuropsychological algorithms may reasonably classify individuals on dementia status across a range of severity levels and ages and may provide a useful adjunct to clinical diagnoses in population studies.

Aged↗
PubMed2004

An algorithm to predict implantable cardioverter-defibrillator lead failure.

OBJECTIVES: The goal of this analysis was to test an algorithm that identifies implantable cardioverter-defibrillator (ICD) lead problems before clinical failure and/or inappropriate therapy. BACKGROUND: The ICD lead failures typically present as inappropriate shock therapy. Identifying lead failures before their clinical presentation may prevent patient discomfort, improve device longevity, and avoid device-induced proarrhythmia. METHODS: We tested an algorithm that uses two measures of oversensing and one measure of abnormal impedance to detect a lead failure. The oversensing measures consisted of a counter for RR intervals <140 ms and nonsustained ventricular tachycardia episodes with mean RR interval <200 ms. The impedance measure tracked lead impedances every day and each week. Abnormal impedance was defined as a decrease in impedances or an outlier value compared with baseline. Lead failures were identified when both oversensing measures were met or abnormal impedance and one oversensing measure occurred. The stored data from 696 patients with an ICD were analyzed to determine the sensitivity and specificity of the algorithm to detect lead failures. RESULTS: Twenty-nine patients demonstrated clinical lead failures with an average of 6 +/- 9 inappropriate shocks per patient. The two oversensing measures used in the algorithm predicted 72% (21 of 29) of the lead failures. Fulfilling at least two of the three impedance and oversensing measures, the sensitivity of our algorithm was 83% (24 of 29) with a 100% (667 of 667) specificity. CONCLUSION: Oversensing combined with abnormal impedance trends may be used to identify ICD lead failures with high sensitivity and very high specificity.

Algorithms↗
PubMed2002

Infrequent confirmation of visual field progression.

OBJECTIVE: To evaluate the effects of the repeatability criteria on the detection of change in visual fields by six progression algorithms used in standard automated perimetry. DESIGN: Retrospective, observational case series PARTICIPANTS: Fifty-one glaucoma patients, each with multiple visual fields performed between May 1990 and December 1998, were included. METHODS: Each patient's set of visual fields were analyzed using the glaucoma change probability, the Early Manifest Glaucoma Trial (EMGT) algorithm, a modified glaucoma change probability score, a modified EMGT score, the Advanced Glaucoma Intervention Study algorithm, and the Collaborative Initial Glaucoma Treatment Study algorithm. MAIN OUTCOME MEASURES: The effects of repeatability on the detection of field change, the level of agreement among algorithms, as well as the number of eyes identified as changed with each algorithm, were assessed. RESULTS: Mean follow-up was 34 months (range, 12-87 months). The average percentage of eyes with change based on three consecutive follow-up fields was 8.2% (4.0%-12.5%). However, of those showing change on the initial follow-up, this change from baseline was observed in subsequent examinations on average in 23% (18%-33%), depending on the algorithm. When change was based on just one field, four of the six algorithms noted a significantly greater number of eyes with change. The algorithms, however, did not differ significantly when confirmation of field change required two versus three consecutive follow-up visual fields. CONCLUSIONS: Although current algorithms may help identify change, there are inconsistencies among them. We found that requiring repeatable change from baseline significantly reduces the number of changed eyes identified with each subsequent follow-up field. Identification and confirmation of change in visual fields plays an important role in helping to identify true glaucoma progression; however, the specific methods to do so have yet to be determined.

Adult↗
PubMed2006

Predicting gene functions from text using a cross-species approach.

We propose a cross-species approach for assigning Gene Ontology terms to LocusLink genes based on evidence extracted from biomedical journal articles. We make use of information from orthologous genes to derive and merge two sets of GO codes for a given target gene. For the first set, we restrict GO code assignments to be selected from only those codes which have already been assigned to the target gene's ortholog. Since this approach results in high precision but low recall, for the second set, we allow any GO code to be a candidate, but then eliminate those codes which are illogical to pair with a GO code that is known to be associated with the orthologous gene. Experimental results on three datasets show that the F-measure obtained with this algorithm is consistently higher than the F-measure of other current solutions.

Algorithms↗
PubMed2004

A novel algorithm for the reduction of undersampling artefacts in magnetic resonance images.

An innovative algorithm is presented which is effective in reducing the truncation artefacts occurring in magnetic resonance images due to missing k-space samples. The algorithm works first by filling the incomplete matrix of coefficients with zeroes and then adjusting, by an iterative process, the missing coefficients by performing a reduction of the undersampling artefacts. Then, this set of coefficients is used as a basis for a superresolution algorithm that estimates the missing coefficients by modeling the data as a linear combination of increasing and decreasing exponential functions using Prony's method. In fact, the Prony's method consists of the interpolation of a given data set with a sum of exponential functions: the MRI signals can be well represented as a sum of exponential functions and the missing data can be extrapolated by this representation. The algorithm has been proven to perform better than either a simple algorithm, which detects and then reduces the undersampling artefacts, or an algorithm that models the measured data with approximation functions. The presented algorithm is quite simple and is applicable both to missing rows (phase-frequency acquisitions) and to radial-missing angle (acquisition from projections) undersampling. Experimental results are reported; comparisons, made between the results obtained using the presented algorithm and the alternative methods described above, clearly demonstrate the superiority of the algorithm.

Algorithms↗
PubMed2002

Verification of the accuracy of a photon dose-calculation algorithm.

An extensive set of measured data was developed for the purpose of verifying the accuracy of a photon dose-calculation algorithm. Dose distributions from a linear accelerator were measured using an ion chamber in a water phantom and thermoluminescent dosimeters in a heterogeneous anthropomorphic phantom. Test cases included square fields, rectangular fields, fields having different source-to-surface distances, wedged fields, irregular fields, obliquely incident fields, asymmetrically collimated fields with wedges, multileaf collimator-shaped fields, and two heterogeneous density cases. The data set was used to validate the photon dose-calculation algorithm in a commercial radiation treatment planning system. The treatment planning system calculated photon doses to within the American Association of Physicists in Medicine (AAPM) Task Group 53 (TG-53) criteria for 99% of points in the buildup region, 90% of points in the inner region, 88% of points in the outer region, and 93% of points in the penumbra. For the heterogeneous phantoms, calculations agreed with actual measurements to within +/-3%. The monitor unit tests revealed that the 18-MV open square fields, oblique incidence, oblique incidence with wedge, and mantle field test cases did not meet the TG-53 criteria but were within +/-2.5% of measurements. It was concluded that (i) the photon dose calculation algorithm used by the treatment planning system did not meet the TG-53 criteria 100% of the time; (ii) some of the TG-53 criteria may need to be modified, and (iii) the generally stated goal of accuracy in dose delivery of within 5% cannot be met in all situations using this beam model in the treatment planning system.

Algorithms↗
PubMed2004

Effects of electric stimulation on C and A delta fiber-mediated thermal perception thresholds.

OBJECTIVE: To determine if interferential current (IFC) or transcutaneous electric nerve stimulation (TENS) alters C and A delta fiber-mediated thermal perception thresholds. DESIGN: Single-blind, randomized controlled trial. SETTING: Laboratory. PARTICIPANTS: One hundred forty healthy women volunteers (mean age +/- standard deviation, 20.6+/-2.7 y). INTERVENTIONS: Subjects were randomly and exclusively assigned to 1 of 7 groups (n=20 in each): 0, 5, and 100 Hz of IFC; 5 and 100 Hz of TENS; placebo and control stimulation. Stimulation was applied through 2 electrodes placed over the median nerve. Warm sensation, cold sensation, hot pain, and cold pain perception thresholds were measured from the thenar eminence by using a quantitative sensory testing device and a method of limits algorithm. MAIN OUTCOME MEASURES: Warm sensation, cold sensation, hot pain, and cold pain thresholds (degrees C) before, during, and after stimulation. RESULTS: There was a statistically significant effect of time for all 4 thermal perception thresholds (separate 2-way analyses of variance with repeated measures, all P<.001). There were no statistically significant differences between experimental groups, nor any interaction effects (all P>.05). CONCLUSIONS: Neither IFC nor TENS altered C and A delta fiber-mediated thermal perception thresholds. The results suggest that any analgesic mechanisms with these modalities are likely to be complex.

Adolescent↗
PubMed2003

Development of memory structures for homographs using pathfinder network representations.

Some studies with children have shown that there is no semantic priming at short stimulus onset asynchrony (SOA) in lexical decision and naming tasks for homographs. The predictions of spreading activation theories might explain this missing effect. There may be differences in children's and adults' memory structures. We have explored this hypothesis. The development of memory structure representations for homographs was measured by a Pathfinder algorithm. In Experiment 1, the three dependent variables were: the number of links in the network, closeness measures (C), and distances between nodes. Results revealed developmental differences in network structure representations in adults and children. In Experiment 2, results revealed that these differences were not due to the cohort effect. In Experiment 3, the relationship between associative strength, as measured by associative norms, and distances, as measured by Pathfinder algorithm, was explored. The results of these three experiments and empirical research from semantic priming experiments show that these differences in memory structure representations could be one of the sources of the missing semantic priming effect in children.

Adolescent↗
PubMed1995

Analysis of the inherent error of the TMS-1 Topographic Modeling System in mapping a radially aspheric surface.

The potential spherical bias of the Topographic Modeling System (TMS) in measuring a radially aspheric surface was investigated. The radii of curvature of an ellipsoidal surface were measured experimentally using the TMS, and calculated using both an instantaneous radius of curvature formula and a spherically biased algorithm for comparison. Measurements were made aligned and under four conditions of misalignment. A sphere with the same radius of curvature as the apex of the ellipsoid was used to document the fundamental performance of the system. The TMS demonstrated increasing error from center to periphery in measurement of an ellipsoid with 7.5 mm apical radius of curvature and 0.5 eccentricity. Greater than 3 D of error was present at 4 mm from the apex. The misalignment error was small compared to the inherent error in the system performance. The TMS does not accurately measure the instantaneous radii of curvature of an ellipsoidal surface due to an inherent spherical bias. In addition, the spherically biased system may not detect subtle shifts in curvature in the peripheral regions, causing potentially inaccurate reconstruction of patterns of curvature.

Algorithms↗
PubMed2006

Muscle enhancement using closed-loop electrical stimulation: volitional versus induced torque.

In cases of partial deficiency of muscle activation capacity, force augmentation can be achieved by hybrid activation, i.e., by combining electrical stimulation (ES) with volitional activation. In this activation modality the shares of the volitional and induced torques within the overall hybrid torque are unknown. The purpose of this study was to suggest a computational approach to parcel out the volitional and stimulation induced components of joint torque generated during combined voluntary and electrical activation of the Tibialis Anterior muscle (TA). For this purpose, isometric contraction of the TA was studied on 5 healthy subjects, using an activation protocol involving ES alone, volitional activation alone and hybrid activation. Ankle torque and TA EMG were measured. A computational algorithm was developed to dissociate the volitional from the overall torque, based on EMG filtering and on pre-measured calibration curves of volitional torque versus EMG. The results indicated that for a certain hybrid torque there is a linear decaying relationship between the induced torque and the volitional torque shares. Moreover, based on a defined enhancement ratio, the results indicate that within the range of stimulation intensities, there exist regions of increased facilitation, in which the stimulation efficiency is higher under combined compared to isolated conditions.

Adult↗
PubMed1995

Application of polynomial regression modeling to automatic measurement of periods of EMG activity.

We have developed a new algorithm for automatic detection and measurement of on/off periods of EMG burst and examined validity and reliability of the measuring technique. Mean EMG amplitude (M) during a semi-stationary state of an EMG data array [EMG] is calculated. Because M was determined to be significantly correlated with g(T(on)) (or g(Tend)) which represent amplitude on a polynomial regression curve g(t) which best-fitted to the [EMG], the estimate ]g(T(on) (or ĝ(T(end)) is calculated by substituting M into a regressive equation f(M) which explains the association between the M and g(T(on)) (or g(T(end)). T(on) and T(end) are human-determined on/off burst times for the [EMG]. The on/off periods of the EMG burst are finally computed as roots of the g(t) when ĝ(T(on)) and ĝ(T(end)) are subtracted from the constant of the polynomial. Application of the current method to the human masticatory muscle activity during chewing revealed that the absolute differences between human- and computer-determined measurements were smaller than 10 ms, and these measurements did not differ significantly. We conclude that the proposed algorithm is useful and effective for automatic detection and measurement of on/off periods of EMG burst.

Adult↗
PubMed2005

Automatic measurement of atrial pacing thresholds in dual-chamber pacemakers: clinical experience with atrial capture management.

BACKGROUND: The Medtronic EnPulse pacemaker incorporates the new atrial capture management (ACM) algorithm to automatically measure atrial capture thresholds and subsequently manage atrial pacing outputs. OBJECTIVES: The purpose of this study was to evaluate the clinical performance of ACM. METHODS: Two hundred patients with an indication for a dual-chamber pacemaker underwent implantation. ACM thresholds and manually measured atrial pacing thresholds were assessed at follow-up visits. Clinical equivalence was defined as the ACM-measured threshold being within -0.25 V to +0.5 V of the manually measured threshold. The clinician analyzed all ACM measurements performed in-office for evidence of proarrhythmia. RESULTS: All 200 implanted patients had a 1-month visit, and validated manual and in-office ACM threshold data were available for 123 patients. The ACM threshold was 0.595 +/- 0.252 V, and the manual threshold was 0.584 +/- 0.233 V. The mean difference was 0.010 V with a 95% confidence interval of (-0.001, 0.021). The mean difference over all visits was 0.011 V. For all patients, the individual threshold differences were within the range of clinical equivalence at all visits. No atrial arrhythmias were observed during 892 ACM tests in 193 patients. CONCLUSION: This study demonstrated that the ACM algorithm is safe, accurate, and reliable over time. ACM was demonstrated to be clinically equivalent to the manual atrial threshold test in all patients at 1 month and over the entire follow-up period of up to 6 months. ACM ensures atrial capture, may save time during follow-up, and can be used to manage atrial pacing outputs.

Aged↗
PubMed1998

Performance assessment of standard algorithms for dynamic R-T interval measurement: comparison between R-Tapex and R-T(end) approach.

Three automatic approaches to ventricular repolarisation duration measurement (R-Tapex, R-T(end threshold) and R-T(end fitting) methods) are compared on computer-generated and real ECG signals, in relation to their reliability in the presence of the most common electrocardiographic artefacts (i.e. additive broadband noise and additive and multiplicative periodical disturbances). Simulations permit the evaluation of the amount of R-T beat-to-beat variability induced by the artefacts. The R-T(end threshold) method performs better than the R-T(end fitting) one, and, hence, the latter should be used with caution when R-T(end) variability is addressed. Whereas the R-Tapex method is more robust with regard to broadband noise than the R-T(end threshold) one, the reverse situation is observed in the presence of periodical amplitude modulations. A high level of broadband noise dose not prevent the detection of the central frequency of underlying R-T periodical changes. Comparison between the power spectra of the beat-to-beat R-T variability series obtained from three orthogonal ECG leads (X,Y,Z) is used to assess the amount of real and artefactual variability in 13 normal subjects at rest. The R-Tapex series displays rhythms at high frequency (HF) with a percentage power on the Z lead (57.1 +/- 4.9) greater than that on the X and Y leads (41.9 +/- 4.6 and 46.1 +/- 4.9, respectively), probably because of respiratory-related artefacts affecting the Z lead more remarkably. More uniform HF power distributions over X,Y,Z leads are observed in the R-T(end threshold) series (31.8 +/- 3.8, 39.2 +/- 4.1 and 35.1 +/- 4.2, respectively), thus suggesting minor sensitivity of the R-T(end threshold) measure to respiratory-related artefacts.

Algorithms↗
PubMed1992

Clinical measurement of renal clearance.

The importance of renal clearance in uronephrology has motivated the continuous reassessment of well-established methods and the relentless search for better techniques. Concerning radionuclide methods, data in the current literature confirm the validity of the simplified one-compartment model or the empirical single-sample method for renal clearance measurement, and new algorithms have been described to broaden the application of the techniques to the pediatric population. Based on the same principles, accurate measurement of renal clearance can also be obtained using contrast agents. Using the technique for determination of the glomerular filtration rate during radiographic contrast examination is recommendable. However, potential adverse effects of the contrast substances should be compared with those of other methods before using this technique for measuring renal clearance without scheduled contrast roentgenographic examination. Controversy remains concerning the validity of predicting glomerular filtration rate from plasma creatinine. Although the predicted clearance is correlated with reference clearance, analysis of individual results reveals that important differences of up to 50 mL/min frequently occur.

Algorithms↗
PubMed1991

A predictive and feedback control algorithm maintains a constant glucose concentration in fed-batch fermentations.

A combined predictive and feedback control algorithm based on measurements of the concentration of glucose on-line has been developed to control fed-batch fermentations of Escherichia coli. The predictive control algorithm was based on the on-line calculation of glucose demand by the culture and plotting a linear regression to the next datum point to obtain a predicted glucose demand. This provided a predictive "coarse" control for the glucose-based nutrient feed. A direct feedback control using a proportional controller, based on glucose measurements every 2 min, fine-tuned the feed rate. These combined control schemes were used to maintain glucose concentrations in fed-batch fermentations as tight as 0.49 +/- 0.04 g/liter during growth of E. coli to high cell densities.

Acetates↗