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At least 145 records · Page 8Linked to original sources
PubMed1995

WENDEC: a deconvolution program for processing hormone time-series.

The estimation of the glandular secretory rate from time-series of hormone concentration in plasma can be formulated as a deconvolution problem. In particular, the paper addresses the analysis of frequently sampled data collected in order to study spontaneous pulsatile secretion. Standard deconvolution methods do not allow for the non-negativity constraint and the presence of high-frequency components in the secretory rate. In order to overcome the intrinsic ill-conditioning of the problem, the maximum entropy method is used to obtain a probabilistic representation of the prior knowledge concerning the unknown secretory signal, thus leading to a White Exponential Noise (WEN) model. The deconvolution problem is then posed within a Bayesian framework and solved by means of Maximum-A-Posteriori estimation. The program that implements the algorithm handles non-negativity constraints, provides confidence intervals, and is computationally and memory efficient.

Algorithms↗
PubMed1995

Software tools for using a personal computer as a timer device to assess human kinematic performance: a case study.

Frequently, the assessment of the physical condition of a sportsman depends on the evaluation of different tests, based on biomechanical performance. The data acquisition in these tests is usually hand made, because its automatization is difficult. But when movements are constrained by means of their specific nature, simple tools can be used to achieve that data acquisition. In this paper, a simple and inexpensive system is described to make use of the timing capabilities of a personal computer (PC) to use it as a timer, with applications in biomechanics and sport training. The data acquisition method is based on a PC that, using a specific programming dealing with event timing, gets signals through the printer port, from a receptor device that detects cuts in an infrared cell beam. Low level procedures are provided that can be used in higher level algorithmic designs, problem dependent, to build specific systems. The case of the evaluation of the Wingate Anaerobic Test is discussed.

Algorithms↗
PubMed1995

An event recorder for infant feeding research.

An Event Recorder program was developed for the HP 48 calculator to record the durational events associated with breastfeeding behavior. The Event Recorder menu structure is flexible and allows for the recording of response variables such as menstrual history and fertility symptoms. A Windows program was written in Visual C++ to give a graphical representation of the time-series data and to extract useful measures of breastfeeding activity from the raw data for each 24-h day postpartum. These time varying covariates include the mean and median bout length, median interbout interval, breastfeeding frequency and total 24-h suckling duration. The HP 48 calculator has proven to be a robust instrument for the self-recording of breastfeeding data collected as part of a prospective study on the factors that maintain postpartum amenorrhea. We have found also that the behavioral data collected are easily transferred electronically each month when our field workers make home visits.

Breast Feeding↗
PubMed1990

Testing a 3-D radiation therapy planning program.

This report describes a systematic effort to test all functions of a large 3-D radiation therapy planning program, including graphics and user interaction. Previous studies in quality assurance for radiation therapy programs do not adequately address the problem of programming errors. They compare dose estimates calculated by planning programs to actual doses measured in phantoms, so they cannot distinguish programming errors from measurement errors or physical unsoundness of the beam model. Moreover, they fail to exercise graphics and user interaction functions. This report describes a different methodology: test cases are derived from the program specification, results are calculated by an independent technique, and compared to program output. Derivation of test cases is described in detail. Effectiveness of testing is assessed by reporting the number of errors revealed by testing and comparing to the number of errors discovered during routine use in five successive program versions. The size of the test set is related to the total program size, and the effort devoted to deriving and performing tests is compared to the total program development effort. We conclude that systematic testing can reveal errors that are not found by informal testing, routine program use, or comparison with measurements. However, additional errors remain that are only discovered during use. This study suggests that a typical large planning system may include more than 100 errors when it is released for clinical use. Methods for increasing testing effectiveness are recommended.

Radiotherapy, Computer-Assisted↗
PubMed1990

Portal dose images. I: Quantitative treatment plan verification.

The comparison of a predicted portal dose image, calculated during treatment planning, with the measured image obtained during treatment is proposed as an approach to verify the correct implementation of a patient treatment plan. The comparison inherently verifies both the geometric alignment and the dose delivered. Feasibility studies were conducted with 60Co irradiation of a modular plastic phantom, an anthropomorphic phantom and a patient with lung cancer. Calculations were made with the 3-dimensional scatter ray-trace Delta Volume method. Calculated distributions and/or selected points of transmitted dose correction factors were compared with measurements made with TLD, scanning ionization chamber and film. For the two phantom studies, excellent agreement, usually to within 3%, was achieved when positioning of the phantoms were accurate. The patient study showed that selected point comparisons were inadequate in identifying the cause of errors when disagreement occurred. Simple subtraction of the calculated and measured images showed a 4 mm translational misalignment. The results are encouraging and demonstrate that portal dose images can be used to detect large geometric and dosimetric discrepancies between treatment plan calculations and measurements. The results also show that perfect verification is virtually impossible in the clinical situation. More work is required to use the verification information for improving the estimation of dose to the patient.

Cobalt Radioisotopes↗
PubMed1990

Portal dose images. II: Patient dose estimation.

Due to the many sources of uncertainties in radiotherapy, conventional treatment planning can only provide a nominal presentation of the dose delivered to the patient. Provided that large setup errors can be detected and corrected, we propose that measured and calculated portal dose images can be used to improve estimation of patient dose. The iterative approach described in this paper requires an accurate method of dose calculations, 3-dimensional CT data that closely represents the patient and the measured portal dose image. From the CT data, a portal dose image is calculated for comparison with the measured one. The differences are then used to modify the original CT data so that a new image can be calculated. The process is repeated until the calculated and measured images agree to satisfaction. At that point, the internal dose is calculated using the modified CT data. If the method is successful, daily portal dose images could be used to cumulatively estimate patient dose throughout the course of treatment. This manuscript describes 60Co simulation results to demonstrate the feasibility of the approach.

Cobalt Radioisotopes↗
PubMed1990

On-line radiotherapy imaging with an array of fiber-optic image reducers.

In the optical approach for on-line radiotherapy imaging, a large metal sheet-fluorescent screen combination is used to convert the radiation intensity distribution into a visible light image. Data are then captured via a mirror with a camera located out of the beam. Although usable portal images can be acquired, presence of the large mirror renders the system impractical in many treatment geometries. We have overcome this limitation by replacing the mirror with an array of 16 by 16 bundles of plastic fiber-optic image reducers. Each bundle, in turn, is made up of 16 by 16 individual optical fibers. The total of 256 by 256 fibers spans an input area of 40 cm by 40 cm with each individual fiber viewing an area of 1.6 mm by 1.6 mm. Within a height of 12 cm, each fiber is reduced to an area of 0.1 mm by 0.1 mm. The reduced portal image is then turned and "piped" to a final 3.0 cm by 3.0 cm output area. For data acquisition and digitization, the fiber output is directly coupled to the sensor of a TV camera interfaced to a small computer via a 512 by 512 frame grabber. In this initial evaluation, the imaging system has been characterized in terms of its line spread function, noise and resistance to radiation damage. Adequate phantom and patient images are presented.

Fiber Optic Technology↗
PubMed1990

Full integration of the beam's eye view concept into computerized treatment planning.

A complete set of beam's eye view (BEV) and beam portal design features have been integrated into a computerized 3-dimensional radiotherapy treatment planning system. Among the features implemented is the ability to mix BEV graphics with gray-scale images such as simulator and verification radiographs, and digital reconstructed radiographs. Image processing techniques have been developed to both enhance verification images and to detect radiation field boundaries. These portal simulation and presentation techniques are being used clinically to design and verify radiation fields with manual or automatically-designed field shaping blocks. The ability to perform computer dose calculations for planes which are parallel or perpendicular to a specified beam's central axis is available and this feature has also proven useful for treatment plan evaluation and optimization. Finally, direct comparison of computer-generated portal images with actual simulation and verification radiographs is also possible. These techniques allow the direct integration of "CT-directed treatment planning" with block design, simulator films and port films, and other Beam's Eye View-type displays.

Computer Simulation↗
PubMedDate not supplied

3D base: a geometrical data base system for the analysis and visualisation of 3D-shapes obtained from parallel serial sections including three different geometrical representations.

In this paper we discuss a geometrical data base that includes three different geometrical representations of one and the same reconstructed 3D shape: the contour-pile, the voxel enumeration, and the triangulation of a surface. The data base is tailored for 3D shapes obtained from plan-parallel serial sections. It is explained how this geometrical data base is useful with the different processing approaches of a 3D shape, such as analysis and visualisation. Methods of conversion between the geometrical representations are discussed. Examples of the operation of the data base as it is embedded in a data base management system are given by illustrations of retrieval of geometrical information.

Algorithms↗
PubMedDate not supplied

A gray-level thinning method for delineation and representation of arteries.

The quantification of three dimensional (3D) properties of coronary arteries is of significant importance. The performance of the 3D analysis is critically based on low-level representation of the arterial tree for different projections. A skeletal representation of arteries can provide appropriate data structure for registration of multiple angiographic projections and it can be further utilized for 3D reconstruction of the arterial tree. This paper presents an automated method for extracting the skeletal points of an arterial tree directly from the gray-level information without determining the edges a priori. It offers the advantage of improved reliability compared to methods based on detecting dual edges of the arteries. Novel application of filtering techniques provide accurate estimates of the statistics of the background. A recursive search scheme is used to aggregate the skeletal representation at multiple resolutions. Results on a set of Digitally Subtracted Angiograms (DSA) have been presented.

Algorithms↗
PubMed1994

[Continuous administration of drugs by infusion pumps. Presentation of an infusion rate mathematical computing software].

Intensive therapy includes continuous delivery of drugs with infusion pump. This article describes an infusion rate computing programme using a Macintosh micro-computer and the HyperCard 2 software. The latter permits the classification of data onto cards collected in stacks. The card that is displayed when the programme is launched shows fifteen buttons assigned to various drugs. Click upon a button opens the corresponding card which displays the presentation of the drug and suggests a dilution. The next step associates input of patient's weight into the appropriate field and a click on the main button. A display then indicates for various standard dosages, the corresponding rate of infusion in mL.h-1 and the daily consumption of the drug. In order to avoid casual or voluntary changes of the setting, soft securities have been inserted in the programme.

Humans↗
PubMed1993

An adaptive, object oriented strategy for base calling in DNA sequence analysis.

An algorithm has been developed for the determination of nucleotide sequence from data produced in fluorescence-based automated DNA sequencing instruments employing the four-color strategy. This algorithm takes advantage of object oriented programming techniques for modularity and extensibility. The algorithm is adaptive in that data sets from a wide variety of instruments and sequencing conditions can be used with good results. Confidence values are provided on the base calls as an estimate of accuracy. The algorithm iteratively employs confidence determinations from several different modules, each of which examines a different feature of the data for accurate peak identification. Modules within this system can be added or removed for increased performance or for application to a different task. In comparisons with commercial software, the algorithm performed well.

Algorithms↗
PubMed1992

Reproducibility and accuracy of angle measurements obtained under static conditions with the Motion Analysis video system.

The development of computerized and semi-automated motion analysis systems has made the study of human motion more widely available in research and clinical settings. Although many of these systems are currently used by physical therapists, the accuracy and reproducibility of some of these systems in estimating joint angles have not been reported. In this study, the accuracy and reproducibility of angle measurements obtained by use of the Motion Analysis video system were evaluated under static conditions using a standard goniometer. Reflective markers placed on a goniometer were recorded by two video cameras at 17 angles, from 20 to 180 degrees, in 10-degree increments. Recordings of the goniometer were made at three locations within the field of view of the cameras. The intraclass correlation coefficient for each location tested was .99. Average within-trial variability was less than 0.4 degree at all locations. A linear regression of the system-calculated angles and reference angles for all locations had slopes near unity (ie, 1) and intercepts that were not statistically different from zero. A preliminary evaluation of the system under dynamic conditions revealed that distances were slightly underestimated, regardless of where the movement occurred within the calibration cube.

Algorithms↗
PubMed1992

Influence of a computer database and problem exercises on students' knowledge of bacteriology.

This study compared the performances of students at the University of North Carolina at Chapel Hill School of Medicine who had access to sets of problem exercises and a computer database to support their learning of bacteriology with the performances of students at the University of Iowa College of Medicine who did not have such access. The study also examined the extent of a student's database use as a predictor of posttest performance. The students studied were randomly selected groups of 32-44 first-year students per year at each school; the study was conducted in three academic years (1988-1990) with some modifications in the intervention as the host environment evolved. The criterion measure was a posttest created from the same pool of problems used to generate the problem sets. The students at the intervention school scored significantly higher on the posttest in two of the three years, and overall. Also in two of the three years and overall, there was a significant relationship between the extent of a student's database use and his or her posttest score. Although the observed effects may have been due to other factors in this quasi-experimental design, the authors conclude that the use of problem sets and a computer database had a positive influence on the students' learning.

Bacteriology↗
PubMed1995

A reexamination of the NRMP matching algorithm. National Resident Matching Program.

Most graduating medical students in the United States find their first professional appointments through the National Resident Matching Program (NRMP). This service receives rank-order lists of preferences from students and from hospitals, and then generates final assignments of students to hospitals through the use of a specific computerized matching algorithm. The author uses recent findings from the mathematics and economics literatures to demonstrate three difficulties with the NRMP's matching algorithm and the official descriptions thereof. First, the algorithm favors hospitals over students, a feature known to the NRMP since at least 1976, but, in the author's opinion, not made clear in NRMP literature for students. Second, the author argues that the NRMP's justification that its algorithm mimics orderly, noncentralized admission processes is not correct. Institutions operating under non-centralized procedures must typically make more initial offers than there are positions, in the realization that some fraction of their offers will be declined. This arrangement enlarges the choices available to many applicants, and thereby benefits them, whereas the NRMP's algorithm unrealistically assumes that no institution would ever send out any extra offers. Third, the NRMP's algorithm contains incentives for students to misrepresent their true preferences when constructing their rank-order lists. This feature is a substantial disadvantage of the current algorithm and is incorrectly described in literature distributed to students and in published articles from the NRMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1995

The NRMP matching algorithm revisited: theory versus practice. National Resident Matching Program.

The authors examine the algorithm used by the National Resident Matching Program (NRMP) in its centralized matching of applicants to U.S. residency programs ("the Match"). Their goal is to evaluate the current NRMP matching algorithm to determine whether it still fulfills its intended purpose adequately and whether changes could be made that would improve the Match. They describe the basic NRMP algorithm and many of the variations of the matching process ("match variations") incorporated over the last 20 years to meet participants' requirements. An overview of the current state of the theory of preference matching is presented, including descriptions of the characteristics of stable matches in general, program-optimal and applicant-optimal matchings, and strategies for formulating preference lists. The characteristics of the current NRMP algorithm are then compared with the theoretical findings. Research conducted long after the original NRMP algorithm was devised has shown that an algorithm that produces stable matches is the best approach for matching applicants to positions. In the absence of requirements to satisfy match variations, the NRMP's deferred-acceptance algorithm produces a program-optimal stable match. When match variations, such as those handled by the NRMP, must be introduced, it is possible that no stable matching exists, and the resulting matching produced by the NRMP algorithm may not be program-optimal. The question of program-optimal versus applicant-optimal matchings is discussed. Theoretical and empirical evidence currently available suggest that differences between these two kinds of matchings are likely to be small. However, further tests and research are needed to assess the real differences in the results produced by different stable matching algorithms that produce program-optimal or applicant-optimal stable matches.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMedDate not supplied

Evaluating the appropriateness of a nurse expert system's patient assessment.

The Urological Nursing Information System (UNIS) is an expert-system prototype designed to help nurses perform patient assessments on elderly nursing home residents known to be incontinent of urine. A study was conducted to evaluate the appropriateness of the patient-assessment parameters stored in the knowledge base of UNIS. These parameters were stored as objects--a kind of template for holding related clusters of data, facts, rules, hypotheses, or any knowledge in a single conceptual unit. Each object was rated for its appropriateness by 14 nurse experts. Resulting scores ranged from +14 to -14. The effect of the nurse experts' educational backgrounds and work settings on their ratings were also analyzed. The results indicated that 95.6% of the objects received favorable ratings from the nurse experts. Educational background was not a significant factor chi 2 = 5.2, but work settings did have a significant affect chi 2 = 21.07, p = 0.01.

Aged↗
PubMed1992

An optimal controller for an electric ventricular-assist device: theory, implementation, and testing.

This paper addresses the development and testing of an optimal position feedback controller for the Penn State electric ventricular-assist device (EVAD). The control law is designed to minimize the expected value of the EVAD's power consumption for a targeted patient population. The closed-loop control law is implemented on an Intel 8096 microprocessor and in vitro test runs show that this controller improves the EVAD's efficiency by 15-21%, when compared with the performance of the currently used feedforward control scheme.

Computers↗