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Biomedical subjects

S H Levine

Publications and source records attributed to S H Levine.

13 recordsLinked to original sources
PubMed1991

Monte Carlo calculation and silicon detector measurement of the hot particle dose.

In our study, we quantitatively compared the hot particle dose calculated by our microcomputer Monte Carlo electron transport code, Eltran3, with the values calculated by the VARSKIN code. For a weightless source, the VARSKIN code overestimated the skin dose by 14% to 37% because the VARSKIN code is based on the data table for point sources in an unbounded medium. Five 60Co hot particles were measured in the current and pulse mode operations of an ion-implanted silicon detector. The measurements were converted to skin dose rates and compared by use of Eltran3 and VARSKIN calculations. Measured values of the skin dose rates for four of the five hot particles agreed well with expected values. The skin dose rate per kBq of the four hot particles ranged from 0.70 to 0.85 mGy h-1 kBq-1. One of the five hot particles showed the presence of a pure beta-emitting radionuclide, which was not detected through gamma-ray measurements.

Cobalt Radioisotopes↗
PubMed1991

Group psychotherapy for HIV-seropositive patients with major depression.

Patients were recruited from the UCLA AIDS Research Center who had previously been referred to psychiatry for participation in an open-label pilot treating patients with major depression with fluoxetine. They chose to participate in group therapy for continuing distress in coping with their HIV-seropositive status, dissolution of their support system, "accepting patienthood," and on being placed on an experimental medical protocol. The group was a closed, twenty-session, homogeneous (for patient characteristics), psychoeducational, supportive, and cognitively oriented psychotherapy group. We found this to be a successful intervention in helping patients manage HIV illness and in providing the coping skills and social support necessary to function at home, work, and in their interaction with their health care providers.

AIDS-Related Complex↗
PubMed1990

Pseudotumor cerebri associated with lithium therapy in two patients.

The authors report two cases of pseudotumor cerebri in patients taking lithium for treatment of bipolar disorder. Pseudotumor cerebri is a poorly understood syndrome characterized by chronic headaches, bilateral papilledema, and increased intracranial pressure without localized neurologic signs or symptoms, intracranial mass, or hydrocephalus. Ventriculography, computed tomography, and nuclear magnetic resonance imaging reveal normal or small ventricles. Multiple etiologies may include Vitamin A toxicity, obesity, head trauma, hypothyroidism or hyperthyroidism, prolonged steroid therapy or its withdrawal, Addison's disease, Cushing's disease, pituitary insufficiency, and lithium therapy. Patients treated with lithium whose antidiuretic hormone-cyclic adenosine monophosphate mechanism is disturbed are most likely to develop pseudotumor cerebri via disregulation of sodium balance, thyroid-stimulating hormone production, and glucose metabolism. The authors recommend careful medical monitoring to avoid iatrogenic effects of lithium, including pseudotumor cerebri.

Adult↗
PubMed1989

Pyometra involving uterus masculinus in a cat.

A neutered male cat with a history of intermittent antibiotic-responsive fever and strangury had pyometra involving uterus masculinus. The infected structure was removed, and episodes of infection and strangury ceased.

Animals↗
PubMed1989

Beta skin dose determination using TLDs, Monte-Carlo calculations, and extrapolation chamber.

The beta doses produced by 90Sr-Y and 204 Tl beta sources were determined using three methods: Monte-Carlo calculations, measurements with TLDs, and measurements with an extrapolation chamber. Excellent agreement was obtained by all three methods, except a TLD nonlinear response to beta s was observed, which gives doses approximately 20% high for the 90Sr-Y source and 5% low for the 204Tl source. Also, analyses performed with low-energy beta s using these methods can determine errors in shield thickness covering TLD elements. Direct measurement of skin dose is not possible by the TLDs because the minimum shield thickness for the elements is 13 mg cm-2. A thinner shield for the elements must be used or the data must be extrapolated. Presently, thinner shields for TLD elements are not available, and the thick shields can lead to significant errors in skin dose when exposed to low-energy beta s.

Filtration↗
PubMed1987

Diaphragmatic hernia.

This article describes the anatomy, etiology, and pathophysiology associated with congenital and traumatic diaphragmatic hernias. Suggestions on preoperative and post-operative maintenance are presented as are various techniques for surgical correction.

Animals↗
PubMed1987

Experimental and computational techniques for beta-particle dosimetry.

This paper reports the experimental and the computational techniques that were specifically developed to provide dose response data for a new method of beta dosimetry, which is reported in an accompanying article (Sh87). The specific experimental techniques consist of setting up, calibrating and obtaining backscattering and resolution corrections for a plastic-scintillator-based beta spectrometer. The computation techniques involve (1) adapting a Monte Carlo electron transport computer code to use measured beta energy distributions as input data and (2) using the code to calculate the energy deposition of these distributions of electrons in a slab of material. The energy deposition of backscattered electrons incident on the slab is also taken into account. Codes, which were developed to calculate the energy deposited by photons in LiF, are used to derive a theoretical value for the TLD response calibration factor. This factor compares well to the experimentally derived result which was obtained by exposing TLDs to a calibrated 137Cs/137mBa photon source.

Algorithms↗
PubMed1987

An optimized computational method for determining the beta dose distribution using a multiple-element thermoluminescent dosimeter system.

This paper describes an optimization method for determining the beta dose distribution in tissue, and it describes the associated testing and verification. The method uses electron transport theory and optimization techniques to analyze the responses of a three-element thermoluminescent dosimeter (TLD) system. Specifically, the method determines the effective beta energy distribution incident on the dosimeter system, and thus the system performs as a beta spectrometer. Electron transport theory provides the mathematical model for performing the optimization calculation. In this calculation, parameters are determined that produce calculated doses for each of the chip/absorber components in the three-element TLD system. The resulting optimized parameters describe an effective incident beta distribution. This method can be used to determine the beta dose specifically at 7 mg X cm-2 or at any depth of interest. The doses at 7 mg X cm-2 in tissue determined by this method are compared to those experimentally determined using an extrapolation chamber. For a great variety of pure beta sources having different incident beta energy distributions, good agreement is found. The results are also compared to those produced by a commonly used empirical algorithm. Although the optimization method produces somewhat better results, the advantage of the optimization method is that its performance is not sensitive to the specific method of calibration.

Algorithms↗
PubMed1977

Persistence and convergence of ecosystems: an analysis of some second order difference equations.

Three second order difference equation models are analyzed and numerical solutions computed. It is shown that two concepts of ecosystem stability, the local property of convergence and the global property of persistence, do not coincide, and that the exislity are obtained and shown as parameter space diagrams. Examples of solution trajectories representative of different regions of this space are computed and discussed. A wide range of oscillatory behavior, as noted in recent papers by several authors, results. In addition, the erratic nature of regions of convergence to stable solutions is discussed.

Ecology↗