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PubMed2003

Assessment of the validity of and adherence to sexually transmitted infection algorithms at a female sex worker clinic in Abidjan, Côte d'Ivoire.

BACKGROUND: Algorithms for sexually transmitted infection (STI) case management were designed in a female sex worker (FSW) clinic in Abidjan, Côte d'Ivoire, in 1993. GOAL: The goal was to evaluate the long-term validity of the algorithms for returning clients of the clinic and to assess the adherence of the health workers to their application. STUDY DESIGN: A cross-sectional study was conducted from 1999 to 2000 among FSWs attending as returning clients. RESULTS: The prevalences of genital infections were as follows: Neisseria gonorrhoeae and/or Chlamydia trachomatis, 8.2%; Trichomonas vaginalis, 16.7%; bacterial vaginosis, 62.3%; and Candida albicans, 6.2%. The sensitivity of the algorithms was 20% and the positive predictive value was 14% for cervical infection. The proportion of cases for which all steps of the algorithm were correctly applied was 30%. CONCLUSION: Algorithms for the treatment of STIs in FSWs should be periodically reevaluated and adapted to the changing population. To maintain healthcare workers' adherence to the algorithms, supervision should be ongoing and reinforced.

Adolescent↗

PubMed2001

Validation of a new algorithm for the BPM-100 electronic oscillometric office blood pressure monitor.

BACKGROUND: To test the accuracy of a new algorithm for the BPM-100, an automated oscillometric blood pressure (BP) monitor, using stored data from an independently conducted validation trial comparing the BPM-100(Beta) with a mercury sphygmomanometer. DESIGN: Raw pulse wave and cuff pressure data were stored electronically using embedded software in the BPM-100(Beta), during the validation trial. The 391 sets of measurements were separated objectively into two subsets. A subset of 136 measurements was used to develop a new algorithm to enhance the accuracy of the device when reading higher systolic pressures. The larger subset of 255 measurements (three readings for 85 subjects) was used as test data to validate the accuracy of the new algorithm. METHODS: Differences between the new algorithm BPM-100 and the reference (mean of two observers) were determined and expressed as the mean difference +/- SD, plus the percentage of measurements within 5, 10, and 15 mmHg. RESULTS: The mean difference between the BPM-100 and reference systolic BP was -0.16 +/- 5.13 mmHg, with 73.7% < or = 5 mmHg, 94.9% < or = 10 mmHg and 98.8% < or = 15 mmHg. The mean difference between the BPM-100 and reference diastolic BP was -1.41 +/- 4.67 mmHg, with 78.4% < or = 5 mmHg, 92.5% < or = 10 mmHg, and 99.2% < or = 15 mmHg. These data improve upon that of the BPM-100(Beta) and pass the AAMI standard, and 'A' grade BHS protocol. CONCLUSION: This study illustrates a new method for developing and testing a change in an algorithm for an oscillometric BP monitor utilizing collected and stored electronic data and demonstrates that the new algorithm meets the AAMI standard and BHS protocol.

Adolescent↗

PubMed2004

Validation of a clinical algorithm to diagnose stress urinary incontinence for large studies.

PURPOSE: We assessed the accuracy with which a clinical diagnostic algorithm for stress urinary incontinence (SUI) based on symptoms and signs without including urodynamics predicted the observation of urodynamic SUI and the condition of SUI. Such an algorithm would have applicability to ensure that the majority of women entering large SUI clinical trials would have urodynamic SUI and/or the condition of SUI without performing urodynamic testing in all subjects. MATERIALS AND METHODS: A total of 1455 women with urinary incontinence at least 3 months in duration were enrolled in 3 randomized clinical trials (1 phase 2 and 2 phase 3 trials) of duloxetine vs placebo for the treatment of SUI in Europe and North America. Subjects were identified as having SUI based on a clinical algorithm that required a predominant symptom of SUI with a weekly incontinence episode frequency of 4 or greater (phase 2 study), or 7 or greater (phase 3 studies), absent predominant urge symptoms, normal diurnal and nocturnal frequency, a bladder capacity of 400 ml or greater, and a positive cough stress (sign of SUI) and stress pad test. Multichannel urodynamic studies were performed in a subset of 184 women at 23 study sites. Of these urodynamic tracings 173 (94%) were of adequate quality to make an assessment of the filling phase and assign a diagnosis of urodynamic SUI, detrusor overactivity or a normal filling phase. Two-sided 95% exact CIs for the proportions were calculated. RESULTS: The clinical algorithm had a positive predictive value of 90.2% for urodynamic SUI with or without detrusor overactivity and 76.9% for urodynamic SUI only (pure urodynamic SUI). The positive predictive value for the condition of pure SUI was 85.0%, while for the condition of SUI in pure and mixed forms the positive predictive value was 98.3%. Patient age, previous continence surgery or the severity of incontinence did not influence algorithm accuracy. CONCLUSIONS: The algorithm is suitably feasible and sufficiently predictive to be used in large clinical trials designed to evaluate conservative treatment for women with SUI. It ensures that the overwhelming majority of the study population would have urodynamic SUI and the condition of SUI.

Adult↗

PubMed2006

A practical application of practice-based learning: development of an algorithm for empiric antibiotic coverage in ventilator-associated pneumonia.

BACKGROUND: Development of practice-based learning (PBL) is one of the core competencies required for resident education by the Accreditation Council for Graduate Medical Education, and specialty organizations including the American College of Surgeons have formed task forces to understand and disseminate information on this important concept. However, translating this concept into daily practice may be difficult. Our goal was to describe the successful application of PBL to patient care improvement with development of an algorithm for the empiric therapy of ventilator-associated pneumonia (VAP). METHODS: The algorithm development occurred in two phases. In phase 1, the microbiology and timing of VAP as diagnosed by bronchoalveolar lavage was reviewed over a 2-year period to allow for recognition of patterns of infection. In phase 2, based on these data, an algorithm for empiric antibiotic coverage that would ensure that the large majority of patients with VAP received adequate initial empiric therapy was developed and put into practice. The period of algorithm use was then examined to determine rate of adequate coverage and outcome. RESULTS: : In Phase 1, from January 1, 2000 to December 31 2001, 110 patients were diagnosed with VAP. Analysis of microbiology revealed a sharp increase in the recovery of nosocomial pathogens on postinjury day 7 (19% < day 7 versus 47% > or = day 7, p = 0.003). Adequate initial antibiotic coverage was seen in 74%. In Phase 2, an algorithm employing ampicillin- sulbactam for coverage of community- acquired pathogens before day 7 and cefipime for nosocomial coverage > or =day 7 was then employed from January 1, 2002 to December 31, 2003. Evaluation of 186 VAP cases during this interval revealed a similar distribution of nosocomial cases (13% < day 7 versus 64% > or = day 7, p < 0.0001). Empiric antibiotic therapy was adequate in 82% of cases or =day 7: overall accuracy improved to 83% (p = 0.05). Mortality from phase 1 to phase 2 trended toward a decrease (21% versus 13%, p = 0.1). CONCLUSIONS: Application of the concept of PBL allowed for identification of local patterns of infection and development of an institution specific treatment algorithm that resulted in >80% adequate initial empiric coverage for VAP with a trend toward decreased mortality. PBL allows for alteration in practice based on local patterns and outcomes and has the potential to improve patient care.

Algorithms↗

PubMed2000

Evaluation of an algorithm for treatment of status epilepticus in adult patients undergoing video/EEG monitoring.

Convulsive or generalized tonic clonic status epilepticus (SE) is a neurological emergency that can lead to transient or permanent brain damage or even death. An algorithm was designed to aid nursing and medical staff members in decision making about the type of SE and pharmacological intervention needed to stop prolonged or repetitive seizures. Fifteen registered nurses at a northern New England medical center's epilepsy unit participated in educational sessions on classification of seizures and status epilepticus prior to use of the algorithm. A pretest-posttest design with an investigator-developed tool was used to measure SE knowledge before and after educational intervention. There was a significant improvement in scores on the posttest of the classification of status epilepticus (Z = -2.93, p = .003). Twenty-nine medical records of patients who had experienced SE between February 1992 and December 1997 were reviewed. Nineteen patients experienced SE before the algorithm was implemented, and 10 patients experienced SE after the algorithm was implemented. A total of 16 patients experienced generalized convulsive SE with 12 episodes occurring before and 4 episodes after algorithm implementation. The mean time taken to stop the episode of SE after pharmacologic treatment began was compared in both groups using a t-test. The mean difference between the groups was 235 minutes (t = 2.57, p = .026). The findings of this project demonstrate that combining a treatment algorithm with education of staff members on its use has benefits in the practice setting of an inpatient comprehensive epilepsy program. Episodes of SE are more accurately classified and successful treatment of the episodes occurs earlier.

Adolescent↗

PubMed2001

Algorithms for deriving crystallographic space-group information. II. Treatment of special positions.

Algorithms for the treatment of special positions in three-dimensional crystallographic space groups are presented. These include an algorithm for the determination of the site-symmetry group given the coordinates of a point, an algorithm for the determination of the exact location of the nearest special position, an algorithm for the assignment of a Wyckoff letter given the site-symmetry group, and an alternative algorithm for the assignment of a Wyckoff letter given the coordinates of a point directly. All algorithms are implemented in ISO C++ and are integrated into the Computational Crystallography Toolbox. The source code is freely available.

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PubMed2003

Numerically stable algorithms for the computation of reduced unit cells.

The computation of reduced unit cells is an important building block for a number of crystallographic applications, but unfortunately it is very easy to demonstrate that the conventional implementation of cell reduction algorithms is not numerically stable. A numerically stable implementation of the Niggli-reduction algorithm of Krivý & Gruber [Acta Cryst. (1976), A32, 297-298] is presented. The stability is achieved by consistently using a tolerance in all floating-point comparisons. The tolerance must be greater than the accumulated rounding errors. A second stable algorithm is also presented, the minimum reduction, that does not require using a tolerance. It produces a cell with minimum lengths and all angles acute or obtuse. The algorithm is a simplified and modified version of the Buerger-reduction algorithm of Gruber [Acta Cryst. (1973), A29, 433-440]. Both algorithms have been enhanced to generate a change-of-basis matrix along with the parameters of the reduced cell.

Algorithms↗

PubMed1995

Two new algorithms for tracking arterial parameters in nonstationary noise conditions.

Two new algorithms with reduced sensitivity to the changing environment are applied to tracking arterial circulation parameters. They are variants of the Least-Squares (LS) algorithm with Variable Forgetting factor (LSVF), and of the Constant Forgetting factor-Covariance Modification (CFCM) LS algorithm, devised to overcome their main practical deficiencies related to noise level sensitivity and the high number of design variables, respectively. To this end, adaptive mechanisms are incorporated to estimate observation noise variance in LSVF and the rate of change for the different parameters in CFCM. Specific computer simulation experiments are presented to compare their effectiveness with the original counterparts and to provide guidelines for their optimal tuning at different noise levels. Moreover, algorithm performance degradation, consequent on changes in the noise level compared to that assumed during the tuning phase, is analyzed. In particular, it is shown that, when the noise level changes with respect to the tuning value, the new LSVF algorithm is much more robust than the original one, whose performance degrades rapidly. The new CFCM algorithm is characterized by a reduced number of design variables with respect to its original counterpart. Nevertheless, it can be preferred only when low noise signals are used for estimation.

Algorithms↗

PubMed1996

A novel family of compression algorithms for ECG and other semiperiodical, one-dimensional, biomedical signals.

In this paper, a novel family of compression algorithms is presented, which is designed to exploit the redundancy of one-dimensional (1-D) semiperiodical biomedical signals resulting from the cyclic nature of the underlying physical process. The basic idea is that a pool of past-seen cycles is maintained and cycles to be encoded can be stored as transformed versions of those residing in the pool. Conceptually, this approach is an extension of dictionary-based coding schemes used for text compression to signal patterns residing in an n-dimensional space. A cycle transformation method is introduced in order to render the pattern matching process practical and to enable cycle substitution. Based on the principles of the algorithmic family and this transformation method, an electrocardiogram (ECG)-oriented algorithm is implemented and thoroughly tested. The performance of this implementation is examined theoretically and deductions about the optimal algorithm settings are made. The ECG compression algorithm is superior to the average beat subtraction algorithm as proposed by Hamilton and Tompkins in cases where high compression ratios are required.

Algorithms↗

PubMed1999

Monotonic algorithms for transmission tomography.

We present a framework for designing fast and monotonic algorithms for transmission tomography penalized-likelihood image reconstruction. The new algorithms are based on paraboloidal surrogate functions for the log likelihood. Due to the form of the log-likelihood function it is possible to find low curvature surrogate functions that guarantee monotonicity. Unlike previous methods, the proposed surrogate functions lead to monotonic algorithms even for the nonconvex log likelihood that arises due to background events, such as scatter and random coincidences. The gradient and the curvature of the likelihood terms are evaluated only once per iteration. Since the problem is simplified at each iteration, the CPU time is less than that of current algorithms which directly minimize the objective, yet the convergence rate is comparable. The simplicity, monotonicity, and speed of the new algorithms are quite attractive. The convergence rates of the algorithms are demonstrated using real and simulated PET transmission scans.

Algorithms↗

PubMed2000

Reconstruction algorithm for polychromatic CT imaging: application to beam hardening correction.

This paper presents a new reconstruction algorithm for both single- and dual-energy computed tomography (CT) imaging. By incorporating the polychromatic characteristics of the X-ray beam into the reconstruction process, the algorithm is capable of eliminating beam hardening artifacts. The single energy version of the algorithm assumes that each voxel in the scan field can be expressed as a mixture of two known substances, for example, a mixture of trabecular bone and marrow, or a mixture of fat and flesh. These assumptions are easily satisfied in a quantitative computed tomography (QCT) setting. We have compared our algorithm to three commonly used single-energy correction techniques. Experimental results show that our algorithm is much more robust and accurate. We have also shown that QCT measurements obtained using our algorithm are five times more accurate than that from current QCT systems (using calibration). The dual-energy mode does not require any prior knowledge of the object in the scan field, and can be used to estimate the attenuation coefficient function of unknown materials. We have tested the dual-energy setup to obtain an accurate estimate for the attenuation coefficient function of K2 HPO4 solution.

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PubMed1997

Segmentation algorithms for detecting microcalcifications in mammograms.

The presence of microcalcification clusters in mammograms contributes evidence for the diagnosis of early stages of breast cancer. In many cases, microcalcifications are subtle and their detection can benefit from an automated system serving as a diagnostic aid. The potential contribution of such a system may become more significant as the number of mammograms screened increases to levels that challenge the capacity of radiology clinics. Many techniques for detecting microcalcifications start with a segmentation algorithm that indicates all candidate structures for the subsequent phases. Most algorithms used to segment microcalcifications have aspects that might raise operational difficulties, such as thresholds or windows that must be selected, or parametric models of the data. We present a new segmentation algorithm and compare it to two other algorithms: the multi-tolerance region growing algorithm that operates without the aspects mentioned above, and the active contour model that has not been applied previously to segment microcalcifications. The new algorithm operates without threshold or window selection, or parametric data models, and it is more than an order of magnitude faster than the other two.

Algorithms↗

PubMed1997

Dynamic image data compression in spatial and temporal domains: theory and algorithm.

Advanced medical imaging requires storage of large quantities of digitized clinical data. These data must be stored in such a way that their retrieval does not impair the clinician's ability to make a diagnosis. In this paper, we propose the theory and algorithm for near (or diagnostically) lossless dynamic image data compression. Taking advantage of domain-specific knowledge related to medical imaging, the medical practice and the dynamic imaging modality, a compression ratio greater than 80:1 is achieved. The high compression ratios are achieved by the proposed compression algorithm through three stages: 1) addressing temporal redundancies in the data through application of image optimal sampling, 2) addressing spatial redundancies in the data through cluster analysis, and 3) efficient coding of image data using standard still-image compression techniques. To illustrate the practicality of the proposed compression algorithm, a simulated positron emission tomography (PET) study using the fluoro-deoxy-glucose (FDG) tracer is presented. Realistic dynamic image data are generated by "virtual scanning" of a simulated brain phantom as a real PET scanner. These data are processed using the conventional [8] and proposed algorithms as well as the techniques for storage and analysis. The resulting parametric images obtained from the conventional and proposed approaches are subsequently compared to evaluate the proposed compression algorithm. As a result of this study, storage space for dynamic image data is able to be reduced by more than 95%, without loss in diagnostic quality. Therefore, the proposed theory and algorithm are expected to be very useful in medical image database management and telecommunication.

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PubMed2004

Analysis of a systematic search-based algorithm for determining protein backbone structure from a minimum number of residual dipolar couplings.

We have developed an ab initio algorithm for determining a protein backbone structure using global orientational restraints on internuclear vectors derived from residual dipolar couplings (RDCs) measured in one or two different aligning media by solution nuclear magnetic resonance (NMR) spectroscopy [14, 15]. Specifically, the conformation and global orientations of individual secondary structure elements are computed, independently, by an exact solution, systematic search-based minimization algorithm using only 2 RDCs per residue. The systematic search is built upon a quartic equation for computing, exactly and in constant time, the directions of an internuclear vector from RDCs, and linear or quadratic equations for computing the sines and cosines of backbone dihedral (phi, psi) angles from two vectors in consecutive peptide planes. In contrast to heuristic search such as simulated annealing (SA) or Monte-Carlo (MC) used by other NMR structure determination algorithms, our minimization algorithm can be analyzed rigorously in terms of expected algorithmic complexity and the coordinate precision of the protein structure as a function of error in the input data. The algorithm has been successfully applied to compute the backbone structures of three proteins using real NMR data.

Algorithms↗

PubMed2004

Dynamic algorithm for inferring qualitative models of gene regulatory networks.

It is still an open problem to identify functional relations with o(N . n(k)) time for any domain[2], where N is the number of learning instances, n is the number of genes (or variables) in the Gene Regulatory Network (GRN) models and k is the indegree of the genes. To solve the problem, we introduce a novel algorithm, DFL (Discrete Function Learning), for reconstructing qualitative models of GRNs from gene expression data in this paper. We analyze its complexity of O(k . N . n(2)) on the average and its data requirements. We also perform experiments on both synthetic and Cho et al. [7] yeast cell cycle gene expression data to validate the efficiency and prediction performance of the DFL algorithm. The experiments of synthetic Boolean networks show that the DFL algorithm is more efficient than current algorithms without loss of prediction performances. The results of yeast cell cycle gene expression data show that the DFL algorithm can identify biologically significant models with reasonable accuracy, sensitivity and high precision with respect to the literature evidences. We further introduce a method called epsilon function to deal with noises in data sets. The experimental results show that the epsilon function method is a good supplement to the DFL algorithm.

Algorithms↗

PubMed2004

The efficient algorithms for achieving Euclidean distance transformation.

Euclidean distance transformation (EDT) is used to convert a digital binary image consisting of object (foreground) and nonobject (background) pixels into another image where each pixel has a value of the minimum Euclidean distance from nonobject pixels. In this paper, the improved iterative erosion algorithm is proposed to avoid the redundant calculations in the iterative erosion algorithm. Furthermore, to avoid the iterative operations, the two-scan-based algorithm by a deriving approach is developed for achieving EDT correctly and efficiently in a constant time. Besides, we discover when obstacles appear in the image, many algorithms cannot achieve the correct EDT except our two-scan-based algorithm. Moreover, the two-scan-based algorithm does not require the additional cost of preprocessing or relative-coordinates recording.

Algorithms↗

PubMed2004

A downstream algorithm based on extended gradient vector flow field for object segmentation.

For object segmentation, traditional snake algorithms often require human interaction; region growing methods are considerably dependent on the selected homogeneity criterion and initial seeds; watershed algorithms, however, have the drawback of over segmentation. A new downstream algorithm based on a proposed extended gradient vector flow (E-GVF) field model is presented in this paper for multiobject segmentation. The proposed flow field, on one hand, diffuses and propagates gradients near object boundaries to provide an effective guiding force and, on the other hand, presents a higher resolution of direction than traditional GVF field. The downstream process starts with a set of seeds scored and selected by considering local gradient direction information around each pixel. This step is automatic and requires no human interaction, making our algorithm more suitable for practical applications. Experiments show that our algorithm is noise resistant and has the advantage of segmenting objects that are separated from the background, while ignoring the internal structures of them. We have tested the proposed algorithm with several realistic images (e.g., medical and complex background images) and gained good results.

Algorithms↗

PubMed2005

Bayesian algorithms for simultaneous structure from motion estimation of multiple independently moving objects.

In this paper, the problem of simultaneous structure from motion estimation for multiple independently moving objects from a monocular image sequence is addressed. Two Bayesian algorithms are presented for solving this problem using the sequential importance sampling (SIS) technique. The empirical posterior distribution of object motion and feature separation parameters is approximated by weighted samples. The first algorithm addresses the problem when only two moving objects are present. A singular value decomposition (SVD)-based sample clustering algorithm is shown to be capable of separating samples related to different objects. A pair of SIS procedures is used to track the posterior distribution of the motion parameters. In the second algorithm, a balancing step is added into the SIS procedure to preserve samples of low weights so that all objects have enough samples to propagate empirical motion distributions. By using the proposed algorithms, the relative motions of all the moving objects with respect to the camera can be simultaneously estimated. Both algorithms have been tested on synthetic and real-image sequences. Improved results have been achieved.

Algorithms↗