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Biomedical subjects

S J Starr

Publications and source records attributed to S J Starr.

17 recordsLinked to original sources
PubMed1999

Comparisons of a proposed five-seed assay method with the single-seed and batch assay methods for I-125 seeds in ultrasound-guided prostate implants.

A simple five-seed assay method was proposed and investigated. A commercial well ion chamber system with an NIST-traceable single-seed calibration constant was used for the single-seed assays. A batch seed holder was used for batch assays. For the five-seed assays, a second single-seed holder was modified such that all five seeds were loaded in a central region of the well ion chamber. Compared with the same seed in the standard single-seed holder, the relative chamber responses for the five seed positions were 0.993, 0.993, 1.000, 1.001, and 0.977, respectively, indicating little or no position-dependent chamber response and no self-attenuation among seeds. Subsequent comparison of assays with the single-seed and five-seed methods indicated only 0.4% difference in charge collection. The five-seed calibration constant was therefore taken to be the same as the single-seed calibration constant. The reproducibility of the five-seed assay method was found to be better than 0.8%. When a dummy seed replaced an active seed, a nearly 20% reduction in charge was found, indicating that the proposed five-seed assay method can detect a dead seed. Clinical comparison of all three assay methods showed that they produced qualitatively the same assay results when the batch assay method was performed with extra care. Compared with the single-seed assay method, the five-seed method is equally simple, rigid, and reproducible, but it demands much less assay time. Compared with the batch assay method, the five-seed method is much more reproducible and reliable because of its rigid assay geometry; it only demands a moderate amount of assay time and can detect dead seeds. The American Association of Physicists in Medicine Task Group 40 (AAPM TG40) states that, for brachytherapy, ideally every (i.e., 100%) loose seed should be calibrated. For procedures involving large number of loose seeds, it then recommends that 10% of seeds be calibrated. The proposed five-seed assay is very simple to implement. It will facilitate the compliance of the "10%" recommendation from the AAPM TG40; it will make the "ideally 100%" statement from AAPM TG40 a more realistic and practical QA procedure in seed assaying.

Brachytherapy↗
PubMed1985

Relating posture to discomfort in VDT use.

To identify sources of discomfort in video display terminal (VDT) work stations, the working postures of 100 telephone operators who used VDTs to retrieve directory listings were photographed. Attempts to correlate postural angles and distances derived from the photographs with subjective judgments of physical discomfort reported on a questionnaire were unsuccessful. Possible explanations for the failure of the postural parameters to predict discomfort are discussed, and the absence of other postural data that may be appropriately applied to the specification of VDT work stations is noted. It is concluded that recommendations for VDT work stations that are phrased in terms of static angles and distances are currently unsubstantiated and, thus, are not yet ready to be codified as formal standards.

Adult↗
PubMed1984

Properties of electroretinographic intensity-response functions in retinitis pigmentosa.

Dark-adapted electroretinogram (ERG) b-wave amplitudes and implicit times were recorded as a function of stimulus luminance for 15 retinitis pigmentosa (RP) patients and 15 normal subjects. B-wave amplitude as a function of log stimulus luminance was fit by non-linear regression with the Naka-Rushton equation, which has 3 independent parameters: The maximum response (Rmax), slope (n) and half-saturation constant (K). B-wave implicit-time as a function of log stimulus luminance was fit by linear regression. Compared to normal, the RP Rmax values were markedly reduced, suggesting response compression; the RP K values were elevated by an average of 0.76 log unit, suggesting relatively small losses in retinal sensitivity. There was no correspondence between Rmax and visual field area for the RP patients (coefficient of correlation = -0.02). All but 2 of the 15 RP patients had normal or shallower-than-normal implicit-time intensity-response functions, indicating that over most of the dynamic range of the ERG, the implicit-times were either normal or faster-than-normal. These results are discussed in terms of possible RP disease mechanisms.

Adolescent↗
PubMed1983

A study of video display terminal workers.

Workers who operate video display terminals (VDTs) are sometimes reported to experience high levels of physical and psychological distress. In an effort to investigate these reports, a study was conducted that compared the responses of 145 Directory Assistance operators who used VDTs to retrieve listings with 105 controls who referred to printed paper directories. The comparison was made on the basis of a single questionnaire that was administered to both groups. The questionnaire asked about the experience of 15 physical discomforts of the sort that are sometimes attributed to work with VDTs. There was only one statistically significant difference in the incidence of complaint: VDT operators were more likely to complain of neck discomfort. On the whole, VDT operators expressed greater satisfaction with their jobs than did operators who used paper records. VDTs may pose special problems, particularly if they are selected or installed without adequate regard for the physical limitations of workers who must use them. Several of these problems are discussed.

Computers↗
PubMed1980

Vector magnitude operation in color vision models: derivation from signal detection theory.

Using the theory of signal detection, we have derived an expression for the detectability of a visual stimulus in terms of the general zone theory of color and brightness vision. This derived relationship elicidates the theoretical foundation of the Guth vector model for color vision by showing that the nonlinear vector magnitude operation used by Guth may arise from the observer decision-making process. Testable predictions of stimulus detectability are generated by the derived expression.

Color Perception↗
PubMed1979

Bilateral symmetry of vision disorders in typical retinitis pigmentosa.

Bilateral symmetry of disorders of vision is examined in 60 typical patients with retinitis pigmentosa. We observed a very high degree of interocular congruence in the patterns of both kinetic visual field defects and threshold profiles and in abnormalities of foveal colour discrimination and visual acuity. Abnormalities of foveal colour vision are highly correlated with the extent of visual field loss.

Adolescent↗
PubMed1978

Visual function in acute posterior multifocal placoid pigment epitheliopathy.

We examined a 19-year-old woman with acute posterior multifocal placoid pigment epitheliopathy one week after she noted blurring of central vision. Her corrected visual acuity was R.E.: 6/7.5 (20/25), and L.E.: 6/12 (20/40). The visual fields showed 10-degree pericentral scotomas. A color vision defect and an abnormal Stiles-Crawford effect were present. Dark adaptation showed a delayed time course, with normal final thresholds. The electro-oculogram was subnormal, suggesting widespread abnormality of the retinal pigment epithelium. Active lesions resolved within three weeks, but fluorescein angiography showed characteristic widespread residual changes. Within three weeks, she had normal visual acuity and a normal electro-oculogram. Other tests of visual function showed recovery with a slower time course. By one year, the visual fields, color matching, Stiles-Crawford effect, and dark adaptation were almost normal. Analysis of the color-matching data and Stiles-Crawford effect indicated that the abnormalities of macular function were caused by an underlying lesion of the pigment epithelium and photoreceptors. This caused a physical distortion of the photoreceptor layer and metabolic disfunction of the photoreceptors.

Adult↗
PubMed1978

A comparison of optimum detector spatial resolution in nuclear imaging based on statistical theory and on observer performance.

An expression for the expected image of a spherical tumour in a uniform background was derived in terms of background thickness and concentration of radioactivity, the tumour size, depth and uptake ratio, the gamma-ray energy and the detector response function. Three models of human observer performance for tumour detection were developed from different signal-to-noise ratio measures based on the statistical theory of detection. The optimum detector spatial resolution predicted by each model was then compared to that obtained from an observer performance study in which the subjects viewed computer-simulated scintigrams. The predictions from two of these models seem to be consistent with the results of the observer performance study. Model II involves a comparison of the counts integrated over the tumour region with the counts integrated over a background region of the same area. Model III compares the count density estimates of signal-plus-background and background obtained from application of non-uniform weighting functions to the image data.

Gamma Rays↗
PubMed1976

Observer performance in detecting multiple radiographic signals. Prediction and analysis using a generalized ROC approach.

The theories of decision processes and signal detection provide a framework for evaluation of observer performance. Some radiological procedures involve a search for multiple similar lesions, e.g., plain radiographic examinations for gallstones or pneumoconiosis. Presuming knowledge of the conventional ROC curve for detection of a single radiographic signal, a model is presented which is used to predict observer performance in an experiment requiring detection of more than one such signal. An experiment tests the validity of this model for detecting radiographically the presence of zero, one, or two low-contrast, 2-mm diameter, Lucite beads. Results confirm the validity of the model and suggest that observer performance in relatively complex detection tasks can be predicted from simpler experiments.

Decision Making↗
PubMed1975

Visual detection and localization of radiographic images.

In conventional receiver-operating-characteristic (ROC) curve analysis of visual detection performance, the observer is credited with a true-positive response if a visual signal is present somewhere in a radiograph called "positive" by the observer; however, the measured true-positive rate can be different for a given false-positive rate if the observer is required to identify the correct location of the visual signal in order to receive credit for a true-positive response. The authors describe and have confirmed experimentally a model which can be used to predict observer performance in an experiment requiring both detection and localization on the basis of the conventional ROC curve determined in a detection experiment. Implications for the use of signal detection theory in the assessment of radiographic image quality are discussed.

Humans↗