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PubMed1991

A computational model of approximate Bayesian inference for associating clinical algorithms with decision analyses.

The lack of rationale or explanation is a major deficiency of clinical algorithms. To address this issue, the authors present a computational model for associating decision analyses with clinical algorithms. Automata theory is used to model categorical reasoning with approximate Bayesian inference based on probability intervals. This approximation reduces the number of computations to linear-order instead of the exponential-order combinations of clinical findings in exact Bayes. The linkage of decision analyses and clinical algorithms by means of this model exploits a new concept of "regular" clinical algorithms and their equivalency in theory and provides valuable perspectives in practice for developers of clinical algorithms.

Algorithms↗

PubMed1990

[A comparison of two algorithms for determining renal whole body clearance following simultaneous acquisition with a partially shielded whole-body counter and a gamma camera].

The influence of instrumentation, algorithm, and the time of blood sampling on whole-body renal clearance as defined by effective renal plasma flow (ERPF) was investigated. The study involved simultaneous sampling with a partially shielded whole-body counter (WBC) and a gamma camera to assess ERPF. The results obtained using two different analysis algorithms for each modality are compared. Although ERPF as determined by the Oberhausen technique was significantly higher than that obtained using an algorithm developed by the authors, for each algorithm there was no significant difference between the WBC and gamma camera-derived values within the range of 100 to 800 ml/min. Furthermore, positioning of the ROI was not critical for gamma camera-derived ERPF (SD less than 1% for multiple crescentic ROIs and approximately 4% for multiple rectangular ROIs). However, the time of blood sampling did appear more important since the average ERPF derived from the 10- and 20-min samples compared with that from the 15- and 25-min samples differed significantly for both analysis algorithms. The methodology which we have validated provides a more precise tool for further investigations of the influence of medication, posture, and exercise stress on renal function.

Algorithms↗

PubMed1988

Performance of two new algorithms for estimating within- and between-method carryover evaluated statistically.

Accurate and precise algorithms for estimating within-method carryover, based on the minimization of a unique "carryover sum of squares," and between-method carryover, based on a weighted Deming regression of first sample recovery vs carryover-corrected "true" recovery, are described and compared with traditional methods by use of a Monte Carlo study. In addition, I have studied the experimental parameters that influence the accuracy and precision of carryover estimation. The new algorithm for estimating within-method carryover is unbiased under most conditions, whereas the traditional algorithm is biased low under most conditions. The new algorithm is also more precise, owing to more-efficient utilization of information contained in an analytical run performed for carryover estimation. Between-method carryover in a random-access analyzer is estimated quantitatively by the second proposed algorithm and is found to be readily and precisely determinable. Use of these methods in combination to evaluate analytical interaction should allow the prediction of carryover error under most current analytical situations.

Algorithms↗

PubMed1986

Pitfalls in the use of clinical algorithms.

The algorithm is a very useful tool in medical practice. Like any other tool, it has advantages and disadvantages. The wise physician avoids a modality until he has learned how to use it. The same should be true of algorithms. Obtain some computer primers that explain the writing of algorithms. Experiment with algorithms of your own creation. When you reach the level where you can easily write your own algorithms, you are ready to use those written by others, making any modifications necessary to suit your own philosophy and experience.

Algorithms↗

PubMed1986

An algorithm for comparing two-dimensional electrophoretic gels, with particular reference to the study of mutation.

An algorithm dedicated to the detection of presumed mutational events involving the polypeptides displayed with two-dimensional polyacrylamide gel electrophoresis has been described. Because of the large number of gels necessary in most studies of mutation, the algorithm has been designed to minimize operator intervention in its execution. The basic principle involves a comparison of the graph structures of the gels of a father, mother, and one or more children, searching for protein spots in the child not found in either parent. These so-called "orphan" spots are considered a probable manifestation of mutation only after other possible causes of such an isolated event have been excluded as rigorously as possible. At present, the analysis of gels prepared from a platelet or erythrocyte lysate yields about 2% "false-positive" findings, i.e., results in the incorrect designation of a unique spot in a child. These errors can be disposed of by technician intervention. In an experiment designed to simulate the occurrence of mutational events, the algorithm operated with 70% accuracy. Most of the "errors" ("false negatives") occurred when the position of the simulated mutant polypeptide coincided in whole or part with that of a preexisting polypeptide, resulting in a class of mutation not detectable by the eye either. With correction for this fact, the accuracy was 84%. Possible improvements in the algorithm which would substantially increase accuracy have been discussed at some length, as have some ideas as to how to manage the large body of data resulting from the operation of the algorithm. A murine experiment designed to validate the approach has been outlined.

Blood Proteins↗

PubMed1984

A synaptic modification algorithm in consideration of the generation of rhythmic oscillation in a ring neural network.

In consideration of the generation of bursts of nerve impulses (that is, rhythmic oscillation in impulse density) in the ring neural network, a synaptic modification algorithm is newly proposed. Rhythmic oscillation generally occurs in the regular ring network with feedback inhibition and in fact such signals can be observed in the real nervous system. Since, however, various additional connections can cause a disturbance which easily extinguishes the rhythmic oscillation in the network, some function for maintaining the rhythmic oscillation is to be expected to exist in the synapses if such signals play an important part in the nervous system. Our preliminary investigation into the rhythmic oscillation in the regular ring network has led to the selection of the parameters, that is, the average membrane potential (AMP) and the average impulse density (AID) in the synaptic modification algorithm, where the decrease of synaptic strength is supposed to be essential. This synaptic modification algorithm using AMP and AID enables both the rhythmic oscillation and the nonoscillatory state to be dealt with in the algorithm without distinction. Simulation demonstrates cases in which the algorithm catches and holds the rhythmic oscillation in the disturbed ring network where the rhythmic oscillation was previously extinguished.

Animals↗

PubMed1984

An automated algorithm for radionuclide angiocardiographic quantitation of circulatory shunting.

Circulatory shunting may be quantitated by analysis of time-activity curves obtained from radionuclide angiocardiography. A new automated algorithm for performing this analysis is proposed. The algorithm uses mathematical deconvolution techniques to increase the temporal separation of the components of this curve and thereby improves the accuracy of the analysis. The stability of the algorithm to random data errors was assessed by experiments on simulated time-activity curves degraded with pseudorandom noise. Excellent performance was obtained on a set of test problems previously used in the literature. The algorithm was used to quantitate left-to-right shunting in patients undergoing radionuclide angiocardiography during cardiac catheterization. A strong correlation (r = 0.96) was found between pulmonary to systemic flow ratios (Qp:Qs) obtained using the algorithm on radionuclide angiocardiographic data and Qp:Qs values obtained by oximetry at cardiac catheterization.

Adolescent↗

PubMed1983

Algorithms for processing spatial information.

Pairs of stimuli taken from a psychometric measure of spatial aptitude were shown to 9-year-olds, 13-year-olds, and adults. The stimuli in pairs were (a) either identical or mirror images, and (b) presented in orientations that differed by 0-150 degrees. Individuals judged, as rapidly as possible, if the stimuli in a pair would be identical or mirror images if presented at the same orientation. In Experiment 1, in which the stimuli were letter-like characters, at all ages most persons solved the problems using an algorithm in which an individual encodes the stimuli in working memory, mentally rotates one stimulus to the orientation of the other, compares them to determine if they are identical, and responds. In Experiment 2, the stimuli were multielement flags; here, the modal algorithm for both 9- and 13-year-olds differed from the previously described algorithm in that if the comparison process revealed that the stimuli were dissimilar, individuals did not respond immediately, but continued processing until a self-imposed deadline was reached. Among adults, the modal algorithm was the same one used in Experiment 1. Results are discussed in terms of the roles of encoding in contributing to the use of a particular algorithm.

Adolescent↗

PubMed1986

Fluid resuscitation of hypotensive emergency patients with and without an algorithm.

Seventy-seven consecutive hypotensive (mean arterial pressure (MAP) less than 80 mmHg) surgical emergency patients were resuscitated according to either physicians' individual orders (38 patients) or an algorithm (39 patients). The shock was mainly caused by accidental injuries or acute gastrointestinal bleeding. The patients of the algorithm group were given more plasma expanders than the patients of the control group, while the total amount of fluids administered was similar in both groups. The primary goal of the resuscitation (MAP greater than 80 mmHg) was reached within 30 min in three cases in the control group and in seven cases in the algorithm group. The treatment times at the emergency department and the intensive care unit were similar for the groups. The number of severe and moderate pulmonary disturbances was the same, but mild disturbances were significantly more common in the control group. Renal failure was somewhat more common in the control group and the renal function disturbances were significantly more severe among the control patients. The results suggest that the physicians in some extent altered their practices in fluid resuscitation when the algorithm was put to use, and that this change, perhaps, produced the somewhat better outcome of the patients. The authors recommend the algorithm to be used as a basis of shock treatment and particularly in those emergency departments where the resuscitation of hypotensive patients is performed by junior or inexperienced physicians.

Adolescent↗

PubMed1986

An efficient string matching algorithm with k differences for nucleotide and amino acid sequences.

There are a few algorithms designed to solve the problem of the optimal alignment of one sequence, the pattern, of length m, with another, longer sequence the text, of length n. These algorithms allow mismatches, deletions and insertions. Algorithms to date run in O(mn) time. Let us define an integer, k, which is the maximal number of differences allowed. We present a simple algorithm showing that sequences can be optimally aligned in O(k2n) time. For long sequences the gain factor over the currently used algorithms is very large.

Amino Acid Sequence↗

PubMed1986

A microcomputer algorithm for solving compartmental models involving radionuclide transformations.

An algorithm for solving first-order non-recycling compartment models is described. Given the initial amounts of a radioactive material in each compartment and the fundamental transfer rate constants between each compartment, the algorithm gives both the amount of material remaining at any time t and the integrated number of transformations that would occur up to time t. The method is analytical, and consequently, is ideally suited for implementation on a microcomputer. For a typical microcomputer with 64 kilobytes of random access memory, a model containing up to 100 compartments, with any number of interconnecting translocation routes, can be solved in a few seconds; providing that no recycling occurs. An example computer program, written in 30 lines of Microsoft BASIC, is included in an appendix to demonstrate the use of the algorithm. A detailed description is included to show how the algorithm is modified to satisfy the requirements commonly encountered in compartment modelling, for example, continuous intake, partitioning of activity, and transformations from radioactive progeny. Although the algorithm does not solve models involving recycling, it is often possible to represent such cases by a non-recycling model which is mathematically equivalent.

Computers↗

PubMed1985

A new scan conversion algorithm for ultrasound compound scanning.

An improved scan conversion algorithm for ultrasound compound scanning is proposed. In this algorithm, the input data in the spatial domain is sampled by the concentric square raster sampling (CSRS) method, and the display pixel data are filled by one-dimensional linear interpolation. The reconstruction error of the proposed algorithm is much smaller than that of other algorithms, because only one-dimensional, rather than two-dimensional, interpolation is involved. This algorithm greatly simplifies implementation of a real-time digital scan converter (DSC) for spatial compounding of ultrasound images.

Mathematics↗

PubMed1985

Image reconstruction from coded data: I. Reconstruction algorithms and experimental results.

Two algorithms have been developed for reconstructing objects from their coded images and a priori knowledge of the object class. Reconstructions from both algorithms are presented, but the results appear to be largely independent of the algorithm used. One of the algorithms, a Monte Carlo approach, is used to investigate the quality of the reconstruction of two- and three-dimensional objects from simulated coded-image data with respect to viewing geometry and multiplexing (mixing) of the data. The cases examined include reconstructions from data with and without signal-dependent photon noise. It is found that reconstructing from multiplexed data is not so serious a problem as reconstructing from data obtained with a limited viewing angle. Also, when photon noise is included in the data, reconstructions obtained from multiplexed data are better than those obtained from unmultiplexed data because of the higher photon count made available by multiplexing. It appears that the fidelity of a reconstruction depends much more strongly on the design of the data-taking system (the coded apertures) than on the reconstruction algorithm.

Models, Structural↗

PubMed1982

Phased trial of a proven algorithm at a new primary care clinic.

A previous study showed that a clinical algorithm for respiratory illnesses, consisting of a checklist, a set of instructions (logic), and computer audit/feedback, could reduce costs significantly while maintaining a high quality of care. The results of this study show that the algorithm system, developed and validated at one primary care clinic, can be successfully imported to another primary care clinic. In the present study, the algorithm system significantly improved the completeness of the medical records, reduced the use of medical tests by 20 per cent-75 per cent, and reduced non-provider costs by 36 per cent per patient visit. This study also shows that all three components of the algorithm system appear to be necessary to achieve these improvements and maintain a high quality of medical care. These results suggest that a wider use of the algorithm system for minor acute medical problems is both feasible and useful in providing high-quality cost-effective care that is auditable.

Adult↗

PubMed1983

Accuracy of deconvolution algorithms assessed by simulation studies: concise communication.

Deconvolution has been used to correct first-pass radionuclide angiocardiography for the time course of the delivery of radiopharmaceutical into the cardiopulmonary system. The extreme sensitivity of deconvolution to random errors in the data may account for some of the problems encountered in practice. We implemented several deconvolution algorithms that were suitable for use with the unimodal and multimodal superior vena caval and pulmonary curves found in left-to-right shunt quantification. The sensitivity of the algorithms to random errors was assessed using mathematical test problems degraded with pseudorandom noise. An algorithm that constrained the deconvolved pulmonary curve to be expressable as the non-negative sum of a set of lagged normal curves was found to have the smallest maximum error on the curves tested. Comparison with results from a previously published test problem indicated an error reduction of greater than 50% over previously used algorithms. Use of this algorithm may permit more accurate deconvolution of pulmonary time-activity curves and thereby improve shunt quantification.

Heart↗

PubMed1980

[Differential diagnosis of endometrial diseases by scrapings based on setting up an algorithm of the histological study].

In order to facilitate the diagnostic analysis of histologic changes in biopsies of endometrial diseases, it is suggested that the use should be made of the first order algorithm developed on the basis of the experience gained so far. This algorithm excludes the oversight of visible changes and predetermines the subsequent activities of an assistant. During differential diagnosis of endometrial diseases the staged synthesis is effected by making up the second order algorithm from the first order algorithmic elements. The suggested diagnostic procedure developed on the basis of algorithmization and probable concepts is time-saving and creats conditions for more successful verification of the pathological process.

Biopsy↗

PubMed1991

Comparison of analytic algorithms for detecting glaucomatous visual field loss.

The sensitivity and specificity of alternate analytic strategies for recognizing glaucomatous visual field loss from automated threshold perimetry (C-30-2 test of the Humphrey Field Analyzer) were compared among one eye each of 106 patients with glaucoma and 249 normal subjects. Algorithms included commercially available global indexes and cross-meridional differences (Statpac 1 and Statpac 2), as well as cross-meridional and cluster analyses that were developed independently for natural history studies and clinical trials. The sensitivity of most algorithms was high, except for those that used only diffuse loss as an indicator of abnormality. Specificity was acceptably high for all algorithms. Subjects who failed to meet the manufacturer's standard for reliability had much reduced specificity, but sensitivity was also affected. Algorithms that were based on any of the alternate definitions of localized reduction in retinal sensitivity performed equally well, which suggests that any of these approaches is useful in searching for glaucomatous visual loss as typified by this database. Availability, familiarity, and convenience may govern the selection of any one analytic approach for use in a particular setting.

Algorithms↗

PubMed1987

A comparative study of attenuation correction algorithms in single photon emission computed tomography (SPECT).

A computer based simulation method was developed to assess the relative effectiveness and availability of various attenuation compensation algorithms in single photon emission computed tomography (SPECT). The effect of the nonuniformity of attenuation coefficient distribution in the body, the errors in determining a body contour and the statistical noise on reconstruction accuracy and the computation time in using the algorithms were studied. The algorithms were classified into three groups: precorrection, post correction and iterative correction methods. Furthermore, a hybrid method was devised by combining several methods. This study will be useful for understanding the characteristics, limitations and strengths of the algorithms and searching for a practical correction method for photon attenuation in SPECT.

Algorithms↗