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At least 217 records · Page 12Linked to original sources

PubMed1991

An algorithm for associating the features of two images.

In this paper we describe an algorithm that operates on the distances between features in the two related images and delivers a set of correspondences between them. The algorithm maximizes the inner product of two matrices, one of which is the desired 'pairing matrix' and the other a 'proximity matrix' with elements exp (-rij2/2 sigma 2), where rij is the distance between two features, one in each image, and sigma is an adjustable scale parameter. The output of the algorithm may be compared with the movements that people perceive when viewing two images in quick succession, and it is found that an increase in sigma affects the computed correspondences in much the same way as an increase in interstimulus interval alters the perceived displacements. Provided that sigma is not too small the algorithm will recover the feature mappings that result from image translation, expansion or shear deformation--transformations of common occurrence in image sequences--even when the displacements of individual features depart slightly from the general trend.

Algorithms↗

PubMed1989

The use of adaptive algorithms for obtaining optimal electrical shimming in magnetic resonance imaging (MRI).

A method of determining the dc coil current values to electrically shim the static magnetic fields used in magnetic resonance imaging (MRI) using modified steepest descent adaptive algorithm is described. Using a 32 cm diameter by a 40 cm long water phantom as the test volume, the algorithm achieved field homogeneities of 0.2 parts per million (ppm) peak-to-peak within a 20 cm diameter spherical imaging volume, and 1.3 ppm peak-to-peak within the entire phantom. The algorithm achieved an inhomogeneity variance of 0.18 ppm2. The shim system was successfully modeled as a sum of adaptive linear combiners. The model contains 13 parameters that can be varied, 12 shim coil currents, and the receiver mixer frequency. The model was then used to predict key adaptive algorithm parameters. Experimental verification of these parameters lends support to the accuracy of the model.

Algorithms↗

PubMed1990

A comparison of the noise sensitivity of nine QRS detection algorithms.

The noise sensitivities for nine different QRS detection algorithms were measured for a normal, single-channel lead II, synthesized ECG corrupted with five different types of synthesized noise. The noise types were electromyographic interference, 60 Hz powerline interference, baseline drift due to respiration, abrupt baseline shift, and a composite noise constructed from all of the other noise types. The percentage of QRS complexes detected, the number of false positives, and the detection delay were measured. None of the algorithms were able to detect all QRS complexes without any false positives for all of the noise types at the highest noise level. Algorithms based on amplitude and slope had the highest performance for EMG-corrupted ECG. An algorithm using a digital filter had the best performance for the composite noise corrupted data.

Algorithms↗

PubMed1991

A semiclosed-loop algorithm for the control of blood glucose levels in diabetics.

In this paper, a theoretical analysis of the control of plasma glucose levels in diabetic individuals is undertaken using a simple mathematical model of the dynamics of glucose and insulin interaction in the blood system. Mathematical optimization techniques are applied to the mathematical model to derive insulin infusion programs for the control of blood levels in diabetic individuals. Based on the results of the mathematical optimization, a semiclosed-loop algorithm is proposed for continuous insulin delivery to diabetic patients. The algorithm is based on three hourly plasma glucose samples. A theoretical evaluation of the effectiveness of this algorithm shows that it is superior to two existing algorithms in controlling hyperglycemia. A glucose infusion term representing the effect of glucose intake resulting from a meal is then introduced into the model equations. Various insulin infusion programs for the control of plasma glucose levels following a meal are then assessed. The theoretical results suggest that the most effective short-term control is achieved by an insulin infusion program which incorporates an injection to coincide with the meal.

Algorithms↗

PubMed1989

Improved rate responsive algorithm in QT driven pacemakers--evaluation of initial response to exercise.

The QT pacemaker is a rate modulated pacemaker that uses the evoked QT interval as an indicator to determine its optimal pacing rate. Despite the generally favorable clinical results with this form of pacing, some flaws in the system have been reported, such as the frequently observed rather slow initial response of the pacing rate to physical exercise, and the phenomenon of oscillation of the heart rate. These problems can be attributed to the rate adaptive algorithm used in the current QT pacemaker. Recently, in a reexamination of the relationship between evoked QT interval and pacing rate, a curvilinear relationship between these parameters has been demonstrated. As a result, a new algorithm has been developed for the next generation of the QT pacemaker. Before this new algorithm was implemented in new implantable devices, it was evaluated in a multicenter clinical investigation, with emphasis on the initial response of the pacing rate to exercise. This study was carried out by means of special software in the programmer of the QT pacemaker. By employing real-time bidirectional telemetry, it was possible to submit the study population, consisting of 37 patients with implanted QT pacemakers of the current generation, to identical exercise tests. Comparing these exercise tests, it appears that a considerable gain in speed of response to exercise can be achieved by using the same sensor with a faster reacting, nonlinear rate adaptive algorithm.

Aged↗

PubMed1990

A new algorithm to solve endless loop tachycardia in DDD pacing: a multi-center study of 91 patients.

ELTs (endless loop tachycardias) are a common occurrence associated with DDD pacing. In order to detect and treat ELTs, an innovative automatic pacemaker algorithm was devised and evaluated. The basic principle of the algorithm rests on the relative stability of the ventriculoatrial conduction time (VACT) during ELTs. ELTs are suspected when the VACT remains stable and adheres to certain programmable limits referred to as VACT stability (16 or 31 msec); it is confirmed when the VACT remains stable after a programmable shortening of the AV delay (AVD) value, referred to as AVD shortening (47 or 63 msec). Ninety-one patients, 54 males and 37 females, were implanted with such an algorithm-specific device between January 10 and September 9, 1989. The reasons for implantation were as follows: 55 patients were implanted for AV block, 31 for sinus node dysfunction, and 2 for carotid sinus syndrome. Pacing parameters were programmed to favor ELT initiation (long AVD, short postventricular atrial refractory period [PVARP] and high atrial sensitivity) followed by basic programming of the algorithm (VACT stability set at 16 msec and AVD shortening set at 47 msec. Once this was done, a 24-hour Holter recording was obtained. Eighty-eight patients were thus analyzed, three being excluded from the final report due to the poor quality of the Holter tracings. In 43.2% of the sampling (38 patients), multiple episodes of ELT were identified, exhibiting a mean rate of 120 beats/min. In 26 of 38 cases (68.4%), the rate of ELT was found to be slower than the upper rate limit (URL).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Multiresolution, error-convergence halftone algorithm.

A new halftone algorithm is described. The algorithm is designed for implementation on a parallel architecture in order to provide fast, progressive coding of moderate-resolution images. The design is based on a multiresolution, hierarchical, pyramidal structure. At each pyramid level, the binarized image is compared with the original, gray-tone image over a successively larger window of pixels for calculation of a weighted averaged error. Within each level, selected binarized pixels are tested for possible changes in the binary assignment. The binary assignment is changed if the change results in a lower average error over the entire window. Varying the selection of test pixels can cause the same process to provide clustered-dot patterns and dithering. A comparison of performance with the best implementation of the error-propagation algorithm is presented visually. Quality is compared also in terms of isotropy of the texture and the appropriate blue-noise characteristics in areas of uniform gray tone. The benefits of this algorithm are realized with moderate-resolution display of the order of 512 dots X 512 dots. The processing can be carried out on smaller blocks since the results can be combined without any visible seams or edge effects.

Algorithms↗

PubMed2025

Algorithms to reconstruct past indels: The deletion-only parsimony problem.

Ancestral sequence reconstruction is an important task in bioinformatics, with applications ranging from protein engineering to the study of genome evolution. When sequences can only undergo substitutions, optimal reconstructions can be efficiently computed using well-known algorithms. However, accounting for indels in ancestral reconstructions is much harder. First, for biologically-relevant problem formulations, no polynomial-time exact algorithms are available. Second, multiple reconstructions are often equally parsimonious or likely, making it crucial to correctly display uncertainty in the results. Here, we consider a parsimony approach where only deletions are allowed, while addressing the aforementioned limitations. First, we describe an exact algorithm to obtain all the optimal solutions. The algorithm runs in polynomial time if only one solution is sought. Second, we show that all possible optimal reconstructions for a fixed node can be represented using a graph computable in polynomial time. While previous studies have proposed graph-based representations of ancestral reconstructions, this result is the first to offer a solid mathematical justification for this approach. Finally we provide arguments for the relevance of the deletion-only case for the general case.

Algorithms↗

PubMed1991

Clinical algorithms.

Clinical flow charts or algorithms are becoming an increasingly popular means of summarizing the management of a given clinical situation. However they vary greatly in complexity between authors, making comparisons difficult, and detracting from their overall usefulness to medical personnel. We have therefore reviewed the strengths and weaknesses of many published algorithms. As a result of both this and our own experience with clinical algorithms we have identified seven essential elements of clinical management. We believe that acceptance of these elements would improve the efficiency of clinical algorithms, both as a teaching format and as an aid to clinical management.

Algorithms↗

PubMed1992

An algorithm for a selective use of throat swabs in the diagnosis of group A streptococcal pharyngo-tonsillitis in general practice.

A prospective evaluation was made of an algorithm for a selective use of throat swabs in patients with sore throat in general practice. The algorithm states that a throat swab should be obtained (a) in all children younger than 15 years; (b) in patients aged 15 years or more who have pain on swallowing and at least three of four signs (enlarged or hyperaemic tonsils; exudate; enlarged or tender angular lymph nodes; and a temperature > or = 38 degrees C); and (c) in adults aged 15-44 years with pain on swallowing and one or two of the four signs, but not both cough and coryza. Group A streptococci were found by laboratory culture in 30% of throat swabs from 1783 patients. Using these results as the reference, the algorithm was 95% sensitive and 26% specific, and assigned 80% of the patients to be swabbed. Its positive and negative predictive values in this setting were 36% and 92%, respectively. It is concluded that this algorithm may be useful in general practice.

Acute Disease↗

PubMed1992

An algorithm for the clinical differentiation of malaria and typhoid: a preliminary communication.

The objective of this study was to determine which clinical features of typhoid and malaria are most helpful in distinguishing the two diseases among Papua New Guinean highlanders. In a study of 35 patients with culture-positive typhoid and 49 with blood-slide-positive malaria (Group 1), the odds of typhoid were increased most in patients with altered bowel habit, an illness of more than 2 week's duration, tremor or the presence of typhoid facies. The odds of typhoid were lowest in patients with pallor or jaundice. These findings were used to derive a clinical diagnostic algorithm, which was then evaluated in a further group of 34 typhoid patients and 41 malaria patients (Group 2). The sensitivity of the algorithm in diagnosing malaria was 91% in Group 1 and 71% in Group 2, with specificities of 85% and 79% respectively. For typhoid, the sensitivity of the algorithm was 85% and 79% for Groups 1 and 2, respectively, and the specificities were 91% and 71%. We conclude that the algorithm merits further evaluation in a primary health care setting and may prove useful in making an earlier diagnosis of typhoid.

Algorithms↗

PubMed1992

Determining the efficacy of edge detection algorithms.

Edge detection is an important process in the interpretation of image data. Four types of edge detection algorithms (the Local Variance, Correlation, Laplacian and Frequency Peak algorithms) are compared for their ability to discriminate the edges present in an image with precisely defined edges. The variety of techniques are discussed in terms of their sensitivity to the presence of edges and their sensitivity to the applied noise. Both computational and empirical analyses are presented, and the relative merits of each discussed in terms of signal-to-noise ratio, sensitivity and computational difficulty. It is shown that local variance edge detection is an acceptable method for edge detection which simplifies the computation needed for image convolution. The means through which to devise more sophisticated edge detection algorithms is outlined, and the use of difference images to discriminate edges in an image is discussed. The results are also discussed in terms of the implementation of edge detection algorithms as part of a computer visual system which has an architecture modeled after the mammalian visual system.

Algorithms↗

PubMed1991

[A computer algorithm for diagnostic assessment with DSM-III in the early course of schizophrenic diseases].

The purpose of the computer algorithm described here is the evaluation of diagnostic criteria according to DSM-III for schizophrenia and schizophreniform disorders. It also dates the first time point of the assessment of these diagnoses. The necessary information comes from a semistructured interview, called IRAOS (Interview for the Retrospective Assessment of the Onset of Schizophrenia). With this interview early indicators of a beginning schizophrenia can be evaluated in their chronological order and their type of course. The algorithm was first used in a sample of patients admitted for the first time with a diagnosis of either schizophrenia or paranoid psychosis. One third of these patients fulfills the DSM-III-criterion of a duration of at least six months. The other patients fulfill criterion B of a schizophreniform disorder. To strengthen the validity of a diagnosis including the criteria A up to E successively, the sample is reduced to 70%. The average time point of the first assessment of the diagnosis by the computer algorithm is about 1.5 years before the index-admission. Together with the IRAOS the computer algorithm allows an operationalized assessment of the real onset of schizophrenia.

Adult↗

PubMedDate not supplied

A new reconstruction algorithm for improvement of corneal topographical analysis.

Accurate methods for the analysis of corneal topography are essential for the evaluation and management of corneal refractive errors. Photokeratoscopy has been used clinically to evaluate corneal shape anomalies, and methods have been developed to reconstruct the shape of the corneal surface from keratoscope photographs. However, the 2-dimensional information on the keratoscope image is insufficient for uniquely reconstructing a 3-dimensional corneal surface. Algorithms currently used make assumptions necessary for calculation, but lead to considerable error, especially at the periphery of radially aspheric corneas. This article proposes an improved algorithm that avoids some of the earlier assumptions for improved accuracy. The new algorithm was tested on both spherical and aspherical calibration surfaces. The result of this algorithm is identical to earlier methods for spherical surfaces, but the new method substantially increases accuracy in reproducing the aspherical surfaces at the cost of increased computation time.

Algorithms↗

PubMedDate not supplied

[Nozometric algorithms in stomatology].

The intensive development of medical informatics and cybernetics led to the creating of an impressive mathematical apparatus, associated with algorithmization of medical activities and processes. In that aspect, special attention is paid to the nozometric algorithms, applied in the most responsible medical field--therapeutic-diagnostic process. The existing nozometric algorithms are reviewed, with consideration given to the specificity of the stomatological diagnostics. An algorithm set has been systematized that is recommended for use in the field of stomatology.

Algorithms↗

PubMed1989

Treatment of type I decompression sickness using the U.S. Navy treatment algorithm.

The effectiveness of the U.S. Navy (USN) Diving Manual treatment algorithm in treating pain-only decompression sickness (DCS) was analyzed. Treatment logs from the Naval Diving and Salvage Training Center and the Navy Experimental Diving Unit during the decade 1976-1986 were examined. Two hundred and ninety-two cases diagnosed initially as pain-only DCS were identified. Using the treatment algorithm, 208 cases were completed on USN Treatment Table 5 (TT-5), and 84 cases completed on USN Treatment Table 6 (TT-6). Recurrence of symptoms was 4.3% after TT-5, and 3.6% following TT-6. Difference in rate of recurrence was not statistically significant between treatment tables. Overall, the success rate for following the USN treatment algorithm was 95.9%. These data support the use of the shorter TT-5 in accordance with the Navy treatment algorithm.

Algorithms↗

PubMed1989

A diagnostic algorithm for osteonecrosis of the femoral head.

For patients considered at risk for osteonecrosis (ON) of the femoral head, an algorithm for the efficient and appropriate use of diagnostic tests can be developed. Such an algorithm requires a clear idea of the evolution of the disease process and an understanding of the limitations of each of the modalities by which the disease process can be identified. The role of each of the diagnostic tests available for the diagnosis of ON and the results of prospective evaluations to assess their sensitivity, specificity, and predictive values are reviewed. No single diagnostic test is 100% accurate in the diagnosis of the disease. Thus, one must consider an algorithm that accounts for the variable nature of the disease presentation. The goal of such an algorithm is the accurate identification and staging of the disease. For disease not roentgenographically apparent, an approach using magnetic resonance imaging and bone scanning is recommended. For disease that is apparent roentgenographically, tomography is used to define the extent of the disease and the presence or absence of subchondral fracture. The accuracy of diagnosis is critical to understanding the role of the various treatment modalities prescribed for ON. For this purpose, it is necessary to reach a consensus as to what constitutes a successful outcome of treatment. Once diagnosis of the disease is accepted, clinical success of treatment outcomes should be reported in three ways: by a standard hip rating system, by ability to prevent roentgenographic deterioration, and by survival of the femoral head (the absence of further treatment intervention).(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed1989

The Computer-Assisted Postmortem Identification (CAPMI) system: sorting algorithm improvements.

Refinements to the original Computer-Assisted Postmortem Identification (CAPMI) software algorithms and general data handling were suggested as a result of observations made following the Gander plane crash of 1985. The presence of highly fragmented and scattered remains following most plane crashes suggested that changes to procedure might improve CAPMI performance for use in these types of disasters. A total of 162 ante- and postmortem dental records which had been used successfully to identify victims of the Gander disaster were coded for anonymity and used for this investigation. Changes in data construction and management were made to CAPMI, according to concepts which were thought might improve system performance, and tested. Although most tested techniques improved CAPMI performance, the data suggested that replacement of "virgin" chartings with "data unknown" results in improved performance of CAPMI largely independent of other factors. Of 162 possible record matches, the original algorithm successfully listed the true record match in the top 20 possibilities 74% of the time; the tested variations on the original algorithm yielded results across a range of 38 to 83% successes, with most techniques performing better than the original algorithm. Results of this investigation have been incorporated into improved CAPMI procedures and software.

Accidents, Aviation↗