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At least 865 records · Page 48Linked to original sources
PubMedDate not supplied

Parametric three-way receiver operating characteristic surface analysis using mathematica.

Three-way receiver operating characteristic (ROC) surface analysis involves the calculation of a volume under an ROC surface (VUS), which is a measure of discriminatory accuracy of 2 diagnostic tests for 3 diseases. Nonparametric methods for calculating VUS and its standard error have been developed. The author presents the code for roc3D, a Mathematica computer program for performing parametric ROC surface analysis. roc3D calculates VUS assuming a multinormal distribution of test results in the 3 diseased populations, provides user-specified pointwise confidence limits for VUS, and displays a 3-dimensional plot of the ROC surface. Limitations of the roc3D program are discussed.

Alcoholism↗
PubMed2004

Quantifying pulmonary perfusion in primary pulmonary hypertension using electron-beam computed tomography.

Traditionally, a gravitational distribution of pulmonary perfusion has been described in normal subjects. How this may vary in patients with primary pulmonary hypertension (PPH), which is characterised by vascular obstruction due to intimal thickening, smooth muscle cell proliferation and episodes of thrombosis in small and medium sized pulmonary arteries, is unclear. In this study the potential of electron-beam computed tomography in quantifying the distribution of pulmonary perfusion in patients with PPH was investigated. Contrast-enhanced sections were obtained during inspiration in the supine position at baseline and during administration of the vasodilator adenosine in five healthy subjects and five patients with PPH. Under each experimental condition, regions of interest were placed along the nondependent-to-dependent axis and values for relative perfusion derived. In healthy individuals, a marked nondependent-to-dependent gradient in perfusion was observed. By contrast, in PPH, perfusion values were significantly lower and were uniform across the lung section, although the administration of adenosine resulted in increased perfusion in all regions of interest. Electron-beam computed tomography provides physiological and structural information about the pulmonary circulation in subjects with pulmonary vascular disease.

Adenosine↗
PubMed2003

Simulation of drug use and urine screening patterns.

Urine drug screens are used extensively in substance-abuse treatment, especially methadone maintenance treatment programs, as well as criminal-justice and clinical research settings. While positive urinalysis generally indicates drug use, no information is provided about the context or pattern of use. A computer generated model was created to examine the influence of drug use patterns and drug screen schedules upon urine test results. The results indicate that (1) when urine testing is performed at a rate of eight times per year, the probability of testing positive in a given month is little better than 50-50 even for daily use, (2) infrequent drug use is difficult to detect regardless of drug testing frequency, and (3) the benefits of more frequent drug testing are greatest with moderate drug use. The data presented provide a guide for clinicians to match drug screen schedules to frequency or pattern of suspected drug use.

Appointments and Schedules↗
PubMed1994

[Effect of clamping tensile strength on load distribution in paired mounted spinal internal fixators].

Paired internal spinal fixation devices are not necessarily loaded symmetrically when the vertebrae are unable to support one another directly. A finite element model has been developed to predict the influence of clamping rigidity on the load distribution. If the stiffness of one clamping element is significantly reduced, the corresponding implant will bear only about 30 percent of the outer bending moment. The theoretical results were confirmed experimentally with sensor-loaded internal spinal fixation devices.

Biomechanical Phenomena↗
PubMed2002

Coronary flow quantification by Fourier velocity encoded MRI.

Recently, the feasibility of measuring coronary blood flow using fast magnetic resonance (MR) techniques was reported. Thus, MR holds potential to non-invasively assess significance of coronary stenosis. However, the accurate determination of flow and vessel area still remains challenging. High spatial and temporal resolution is required to assess reliable flow profiles within the coronary arteries. For this purpose, Fourier velocity encoding (FVE) was implemented with a small number of encoding steps. Simulations and in-vitro experiments have been performed to demonstrate the benefit of FVE for flow quantification. Further, initial volunteer measurements have shown its potential for invivo application.

Blood Flow Velocity↗
PubMed2003

Creating a portable data-collection system with Microsoft Embedded Visual Tools for the Pocket PC.

This paper describes an overview and illustrative example for creating a portable data-collection system using Microsoft Embedded Visual Tools for the Pocket PC. A description of the Visual Basic programming language is given, along with examples of computer code procedures for developing data-collection software. Program specifications, strategies for customizing the collection system, and troubleshooting tips are also provided.

Behavior Therapy↗
PubMed1994

Sequential Optimum Selection: a categorical alternative to discriminant analysis for conducting research in assessment.

Sequential Optimum Selection, SOS, a nonparametric computer-assisted alternative to discriminant analysis, was introduced and explicated. SOS is an iterative procedure that develops ongoing decision rules for discriminating among groups, successively expunging frequency distributions or classes until all cases are accounted for. In three illustrative comparisons using clinical assessment data, SOS proved competitive with discriminant analysis in terms of over-all hit rates for parsimonious extraction of meaningful variables. Further, in one demonstration using parametric data, SOS held up better on cross-validation. While discriminant analysis will, in most cases, yield better discrimination than SOS, the latter does not make parametric assumptions and should therefore be considered a viable alternative as an exploratory procedure.

Diagnosis, Computer-Assisted↗
PubMed1998

The changing face of MMPI practice.

To assess the status of changing MMPI practice a questionnaire was sent by mail to 368 licensed psychologists in Kansas with a 40% response rate (N = 147). The modal respondent had 14.2 yr. of experience. Virtually all reported that they currently used the MMPI: 37.0% reported using the MMPI, 80.1% MMPI-2, and 40.4% MMPI-A. A majority (67.6%) used computerized scoring with local scoring used by three out of four respondents. Computerized administration was used by 15.9% and computerized interpretation by 43.8%. Most used both High Point Codes (91%) and Elevation (84.7%) for interpretations. Two of three respondents thought that the High Point Codes and Elevations for the MMPI and MMPI-2 are related. The results of this survey of current practice suggest that many practitioners may be making false assumptions about the nature of the MMPI-2 and MMPI-A and their relationships with the original MMPI. If the MMPI is to retain its hard-fought presence as a diagnostic, forensic, and selection tool, we must pay greater attention to these issues.

Diagnosis, Computer-Assisted↗
PubMed1987

A new hearing aid variant. Preliminary evaluation.

An attempt was made to combine the advantages of a behind-the-ear (BTE) hearing aid (trouble-free use, powerful amplification, room for high-quality components, space for large energy source, use of extra equipment), with the advantages of the in-the-ear (ITE) hearing aid (improved intelligibility, improved directional hearing, improved signal/noise ratio). A BTE hearing aid was equipped with filters and provided with an external microphone. A first experiment, carried out in an anechoic chamber on KEMAR (Knowles Electronic Manikin for Acoustical Research), showed that directional variation of the frequency response of the hearing aid microphone was better in the new hearing aid than in the original BTE. A second experiment was carried out with a group of 6 normal-hearing persons concerning the frequency characteristic of sound transmission from twelve angles in the horizontal plane without a hearing aid, with a normal BTE aid, with the 'new aid', and with an ITE aid. The new instrument gave significantly better directional hearing than the original BTE aid. A clinical study will be started to verify and extend the experimental results obtained.

Computer Simulation↗
PubMedDate not supplied

Heat loss and blood flow during hyperthermia in normal canine brain. I: Empirical study and analysis.

The effects of blood flow and thermal conduction during microwave hyperthermia were investigated in normal canine brain. Heating was accomplished with an external microstrip spiral antenna and temperature measurements were made using a multichannel fluoroptic thermometry system. In order to determine cooling rates, temperature measurements made during cooling were fitted with a model consisting of a constant value and an exponential term. Data from experiments in both perfused and non-perfused brains could be fitted with this simple model. The resulting cooling rates indicated that heat loss by conduction is comparable to that by blood flow. In another series of experiments, temperature measurements were made during several 1 min cooling intervals in which the power was shut off intermittently during a 35 min heating episode. Results were consistent with a 2-3-fold increase in blood flow rate which occurred gradually throughout the course of heating. Parameters that affect the determination of cooling rates are discussed in terms of the bioheat transfer equation. These investigations demonstrate that a simple heat sink model provides a good representation of the cooling data for the thermal distributions obtained.

Animals↗
PubMed2001

Polytomous modeling of cognitive errors in computer adaptive testing.

In the past two decades of psychometric research, an array of extended item response models has been proposed to capture the complex nature of human cognition. While the literature abounds in model fit analysis, the debate on model selection in different testing conditions continues. This study examines the problems of model selection in computer adaptive testing (CAT) of cognitive errors by comparing the relative measurement efficiency of polytomous modeling over dichotomous modeling under different scoring schemes and termination criteria. Monte Carlo simulation was adopted as the inquiry paradigm to generate 1000 subjects and 100 items in the calibration sample and 200 simulees in the CAT sample. The results suggest that polytomous CAT yields marginal gains over dichotomous CAT when termination criteria are more stringent (shorter test length or smaller standard error of ability estimate). When the conventional dichotomous scoring scheme is adopted, in which all partially correct answers are scored as incorrect, polytomous CAT cannot prevent the non-uniform gain in test information as was observed in paper-and-pencil testing.

Computer Simulation↗
PubMed2002

Elastic registration of medical images through multiquadric method.

OBJECTIVE: To improve the precision and reliability of elastic registration of the medical images and to simplify the registration process. METHODS: Previous study concerning elastic registration mostly focused on manual selection of the landmarks and then use of adequate interpolating for elastic transformation. The landmarks extraction, however, was prone to error that often showed impact on the registration results, besides the difficulty and time consumption of manual identification of the landmarks. On the basis of Multiquadric method that allowed smooth adjustment of the parameters, we utilized a semi-automatic method to extract the landmarks by combining these 2 steps, and proposed a novel registration method. RESULTS: Using this method for medical image elastic registration, rapid and accurate registration between standard and deformed images was achieved. CONCLUSION: The method proposed presently is accurate, convenient and reliable.

Automation↗
PubMed2002

Preliminary study of a new real-time ultrasound method for measuring spinal and rib rotation in preoperative patients with adolescent idiopathic scoliosis.

A portable ultrasound machine with a linear array transducer was used by one observer (ASK) to evaluate the reproducibility for each of spinal (laminal) rotation and rib rotation in 13 preoperative patients with AIS (thoracic 7, thoracolumbar 6, mean Cobb angle 50 degrees, right 9, left 4, age 15.4 years, girls 10). With the subject in a prone position and her head supported, readings of spinal (laminal) and rib rotations were made directly on the back at 18 and 12 levels respectively. The subject was repositioned after walking around the room and a second set of spinal and rib rotations obtained (repeats). Conclusious. Repositioning the patient significantly alters some single level readings of lam inal rotation and rib rotation. Although the mean average spinal rotation and rib rotation each have acceptable reproducibility, repositioning the patient significantly alters the findings. In the appraisal of surgery by ultrasound the positional change reported here for (I) single level laminal rotation and rib rotation, and (2) mean average rotation imposes caution on the interpretation of the findings. The method enables the axial spine-nh rotation differences to be evaluated which is the subject of a separate paper.

Adolescent↗