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PubMed1992

EMSA: a SAAM service for the estimation of population parameters based on model fits to identically replicated experiments.

This paper presents a new technique for the aggregation of models to produce population parameter estimates based on a set of identically replicated experiments. After describing the theoretical basis for the technique we discuss tactical and strategic issues associated with its implementation in the SAAM software. Finally, we demonstrate its utility in the aggregation of models fitted to four simulated experiments.

Algorithms↗
PubMed1992

Intuitive user interfaces (IUI): a CASE starting point for design and programming.

The acceptance of a software product depends to a considerable extent on the user interface. The class of graphic-oriented user interfaces that are called Intuitive User Interfaces (IUI) is described. These interfaces allow the user to learn to operate software programs quickly. In the following the graphical layout put to use in an IUI is elaborated. All images the layout consists of are created with the aid of a paint program. Using these images, a procedure for creating, programming and linking an IUI to software applications is discussed and recommendations are made concerning software and hardware demands for easily creating IUIs. Practical experience of the authors with this procedure, mainly in the medical area, is described.

Computer Graphics↗
PubMed1992

On the assessment of bioequivalence in a two-period cross-over design.

The results obtained with Meineke and De Mey's algorithm for posterior probability distributions in the nonparametric evaluation of two-period cross-over bioequivalence studies are critically discussed. Suggestions for improvement of their program NEWPARM are given. It is shown that this program in its present form cannot handle the results from bioequivalence studies in which more than 15 subjects participated. For larger study sizes, conversion to a more powerful programming language capable of handling large three-dimensional arrays, is mandatory. An alternative algorithm, allowing large sample sizes to be analysed nonparametrically without program conversion, is offered. A general bioequivalence program written by the author, into which this alternative algorithm is implemented, has been in use by a number of pharmaceutical companies and drug regulatory agencies since February 1990; its most recent update is Version 3.7 (BIOEQV37.EXE) of October 1990.

Algorithms↗
PubMed1992

APIS: a software for model identification, simulation and dosage regimen calculations in clinical and experimental pharmacokinetics.

APIS is a software package based on mathematical modelling which provides a reliable approach in optimizing drug therapy. It was designed to assist clinicians in interpreting blood drug levels so that drug therapy may be better and more cost-effective. It is a methodological approach to describe, predict and control the kinetic behaviour of a drug. This software incorporates the principle of Bayesian procedures, i.e. one can use all available patient information (population) to determine patient-specific parameter estimates. These estimates can then be used to design an optimal and individualized drug regimen. APIS is an attractive and useful tool for clinical and experimental pharmacokinetics. APIS may be used on any IBM compatible computer using the Microsoft-Windows environment. The software is menu driven to provide a very user-friendly tool for analysing pharmacokinetic data and for designing dosage regimens.

Amikacin↗
PubMed1992

A microcomputer program for determining turnover rates during non-steady state conditions: application to monoamine turnover.

A program to calculate the turnover rate of monoaminergic neurotransmitters was written for use on microcomputers. The program is based on non-steady state models, i.e., measuring the rate of change of levels of neurotransmitters or their metabolites after pharmacological inhibition of synthetic or degradative enzymes. Methods have been developed to estimate monoamine turnover by measuring the rate of decrease of catecholamine levels after treatment with alpha-methyl-p-tyrosine (AMPT), a tyrosine hydroxylase inhibitor, or the increase in serotonin levels after pargyline, an inhibitor of monoamine oxidase. This program is suitable for examining either linear increases or exponential decreases in monoamine levels. The program has been tested in our laboratory for the determination of serotonin, dopamine or norepinephrine turnover after hormonal or pharmacological manipulations. The program is readily adaptable for calculation of the turnover rate of other biological molecules under non-steady state conditions.

Biogenic Monoamines↗
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↗
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↗
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↗
PubMed1990

Clinical evaluation of an automatic sensitivity adjustment feature in a dual chamber pacemaker.

The clinical evaluation of a new automatic sensitivity adjustment feature in the Cosmos II, Model #284-05 is described. This feature, designed to maintain a 2:1 safety margin for sensing intrinsic signals, was activated by way of special programmer software in ten patients at two centers. While the feature worked satisfactorily in some cases, it did not perform as expected, and undersensing in both chambers was observed. This may have been due to biasing the adjustment toward maximum rather than minimum electrograms. This study suggested that electrograms may vary by more than 100% which underscores the importance of this feature, and reinforces the need for continued development.

Algorithms↗
PubMed1990

Activation times for "emergency back-up" programs.

A bench study was performed on 34 different pulse generators to evaluate the time necessary to actuate an "emergency back-up" (EBU) program. Pacemakers were programmed to loss of capture before the EBU was activated. Two pauses were measured that included the total pause from captured beat to captured beat and the time from the first pacing artifact showing loss of capture to the first captured beat resulting from EBU activation. Special features for threshold testing such as temporary pacing, auto threshold, Vario, and an alternating pulse ventricular threshold test were also evaluated. Activation times of the EBU ranged from 1.8 to 11.1 seconds with total pauses of 2.7 to 13.2 seconds, respectively. There were considerable variations in EBU times even within a single manufacturers' pulse generators. The special features for threshold testing resulted in pauses measuring 0.6 to 3.0 seconds with total pauses of 1.2 to 4.0 seconds, respectively, and in all cases were faster than using the EBU. Utilization of the EBU to regain capture during threshold testing in pacemaker dependent patients may result in prolonged pauses and syncope or near syncopal episodes.

Electrocardiography↗
PubMed1991

A computer program designed for the analysis of data from rat caries studies.

The Keyes method for scoring dental caries in the rat animal model has been used as the basis for a computer-assisted scoring system on the Apple Macintosh personal computer that is described here. The program provides the ability to draw on diagrams of the rat molar dentition and to enter enamel lesion scores (L, E) and dentinal lesion scores (Ds, Dm, and Dx) for all aspects of the molars. The scores and drawings may be changed at any time. Total carious teeth and totals of L, E, Ds, Dm, and Dx are automatically calculated and presented upon user command. Error trapping for typographical errors is provided. In addition, the program provides automatic storage of the collected information, searching and sorting on any of the experimental parameters and on-disk help files that can be accessed from any place within the program. The capacity to obtain printed copy of any or all of the stored information is provided in the program. The program also enables the creation of external data files containing totals for carious teeth, in addition to L, E, Ds, Dm, and Dx totals for each animal of each group represented in the data base. These files are suitable for the transfer of data to commercially available programs for graphical and statistical analyses. The programming technique we describe could be extended to other model systems with standardized scoring for oral disease.

Animals↗