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Biomedical subjects

N Lavi

Publications and source records attributed to N Lavi.

11 recordsLinked to original sources
PubMed2006

HPGe virtual point detector for radioactive disk sources.

Validity of the model of a virtual point detector (implying existence of a point where all interactions virtually occur) was confirmed for measurements of radioactive disk sources with HPGe detectors. The existing correlation of the count rates with the distance between the virtual plain detector and the detector face makes it possible to inter- and extrapolate calibration curves for disk radioactive sources for use at different source-detector face distances. The dependence of the distance between the virtual plane detector and the detector face on the photon energy was studied for sources of various radii.

Journal Article↗
PubMed2005

The dependence of the counting efficiency of Marinelli beakers for environmental samples on the density of the samples.

The effect of the density of the radioactive material packed in a Marinelli beaker on the counting efficiency was studied. It was found that for all densities (0.4-1.7 g/cm(3)) studied the counting efficiency (epsilon) fits the linear log-log dependence on the photon energy (E) above 200 keV, i.e. obeying the equation epsilon=alphaE(beta) (alpha, beta-parameters). It was found that for each photon energy the counting efficiency is linearly dependent on the density (rho) of the matrix. epsilon=a-brho (a, b-parameters). The parameters of the linear dependence are energy dependent (linear log-log dependence), leading to a final equation for the counting efficiency of Marinelli beaker involving both density of the matrix and the photon energy: epsilon=alpha(1) x Ebeta1 - alpha2Ebeta2rho.

Environmental Monitoring↗
PubMed2005

On the high-resolution gamma-ray spectrometric measurement of 40K in natural and synthetic materials.

Many regulatory agencies require that all building materials and industrial waste be tested for their naturally occurring radioactive material (NORM) concentrations before they can be used or thrown away. Usually the NORM concentrations of 40K, 232Th and 238U are measured by gamma-ray spectrometry using high-purity germanium or NaI(Tl) detectors. 40K is measured through its 1460.8 keV gamma line, which is mixed with 1459.2 keV line of 228Ac from the chain of 232Th. This fact ignored till now, requires a correction in the computation of 40K concentration. Although in many cases the error is <1%, there are cases where there have been higher errors. It should be emphasised that even if the correction in 40K concentration is large, the correction of the external dose index is negligible owing to the weighing factor being higher for 232Th than for 40K (by at least a factor of 10).

Gamma Rays↗
PubMed2004

Development and application of Marinelli beaker standards for monitoring radioactivity in Dairy-Products by gamma-ray spectrometry.

Marinelli (reentrant) beakers are recommended for measurement of low-activity radioactive environmental samples, in both liquid and solid phase. The preparation of Marinelli beaker standards of milk powder containing 232ThO2 at secular equilibrium with its daughter radionuclides was studied. Standards were prepared by mixing of known amounts of solid ThO2 and milk powder. The densities of the standards were 0.5-0.7 kg dm(-3). Measurements of calibrated Marinelli beaker standards with HPGe detector showed that the energy dependence of the efficiency is similar to that of a point source, i.e. an almost linear dependence of log-efficiency vs. log-energy in the 200-2000 keV range, however the parabolic correlation fits better. The validity of these standards was checked by comparison with certified standard reference material IAEA-152-Milk powder containing radiocesium and radiopotassium. The results obtained were found to be in a good agreement with the published certified data. The limit of detection for the determination of radiocesium by gamma ray spectrometry under the prevailing experimental conditions is 0.03 Bq (i.e. 0.8 pCi), for samples of dairy products having lower densities of 0.7 kg dm(-1).

Dairy Products↗
PubMed1995

Low-dose acetylsalicylic acid use and hemoglobin levels. Effects in a primary care population.

OBJECTIVE: To determine the prevalence of acetylsalicylic acid therapy and effect of the drug on hemoglobin concentration over time. DESIGN: Retrospective, observational study. SETTING: Primary care population in a university-affiliated family medicine clinic. PATIENTS: A population-based sample of 80 patients receiving low-dose ASA for secondary prevention of cardiovascular disease was studied. Of 84 patients receiving the drug after a cardiovascular problem, four were excluded: one man died of a recurrent stroke during the study; the file of a second man was unavailable; another man developed a bleeding ulcer; and one woman had been taking ASA for only 1 month when the data were collated. MAIN OUTCOME MEASURES: Demographic variables of patients taking low-dose ASA, duration of ASA use, and two successive measures of hemoglobin level. RESULTS: The frequency of ASA administration was 7.7% for men aged 60 and older and 2.9% for women. Women had no significant change in hemoglobin levels, while men had a mean loss of 0.472 g/dL (95% confidence interval, .198 to .746; P = .009). For the study population as a whole (80 patients), the average decline was 0.294 g/dL (95% confidence interval, .039 to .549; P = .029). CONCLUSIONS: Although the clinical significance of these findings is uncertain, they suggest the need for a prospective investigation of the influence of low-dose ASA on hemoglobin levels.

Adult↗
PubMed1991

Metabolism of 25-OH-vitamin D3 by peritoneal macrophages from CAPD patients.

The active metabolite of vitamin D, 1,25-dihydroxycholecalciferol (1,25(OH)2D3), is produced mainly by the kidney, but there is evidence for extrarenal production in certain circumstances. We studied whether peritoneal macrophages (PM) from CAPD patients were capable of metabolizing 25-OH-D3 to 1,25(OH)2D3. We found that PM were able to metabolize 25-OH-D3 in vitro; the main product following 16 hours of incubation was 19-nor, 10-oxo, 25-OH-D3 with smaller amounts of 1,25(OH)2D3. However, after shorter incubations of three and five hours a larger portion of 1,25(OH)2D3 was produced. The metabolism of 25-OH-D3 was greatly enhanced in PM harvested during episodes of peritonitis. This property was specific for PM of CAPD patients, and was not found in PM from normal subjects. However, incubation of control PM with peritoneal effluent from CAPD patients resulted in induction of the ability of these cells to metabolize 25-OH-D3. This induction was enhanced by preincubation with peritoneal effluent from CAPD patients suffering from peritonitis. Prostaglandin E2 was found to be involved in this synthesis: addition of PGE2 to normal PM induced metabolism of 25-OH-D3, and incubation of PM from CAPD patients with indomethacin decreased the metabolism of 25-OH-D3. The vitamin D metabolites produced by PM from CAPD patients could have a role in immunological resistance to peritoneal infections.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1990

Determination of trace amounts of cadmium, cobalt, chromium, iron, molybdenum, nickel, selenium, titanium, vanadium and zinc in blood and milk by neutron activation analysis.

The concentrations of Cd, Co, Cr, Fe, Mo, Ni, Se, Ti, V and Zn in biological fluids, human blood serum and market milk were determined by neutron activation analysis, with enrichment by coprecipitation. The pre-concentration of these trace elements was accomplished by converting the dissolved trace metal ions into their pyrrolidinedithiocarbamate (1-pyrrolidinecarbodithioate) chelates, followed by coprecipitation with a metal carrier such as Ni, Pb or Bi. The coprecipitation was carried out prior to irradiation for the short-lived nuclides (V, Ti and Se) and after irradiation for the other elements. The validity of the method was checked using certified biological reference materials; the concentrations of trace elements found by the proposed method agreed well with the published certified data. The limits of detection for Cd, Co, Cr, Fe, Mo, Ni, Se (obtained through the long-lived isotope 75Se) and Zn under the present experimental conditions were found to be 5, 5, 10, 520, 5, 70, 10 and 150 ng, respectively, for 5 ml of biological liquor. The limits of detection for Ti and V obtained (through their short-lived radionuclides 51Ti and 52V, respectively) were found to be 180 and 1.4 ng, respectively, for 50 ml of market milk, or 70 and 0.7 ng for 1 ml of blood serum.

Animals↗
PubMed1982

Development of a reliable Hg-195m--Au-195m generator for the production of Au-195m, a short-lived nuclide for vascular imaging.

A new mercury-195m (T1/2: 41 hr) leads to gold-195m (T1/2: 30.6 sec) generator suitable for first-pass as well as steady-state radionuclide angiography studies has been developed. The distribution coefficients, Kd, for mercury (Hg-195m) and gold (Au-196), experimentally evaluated on chelating resin Chelex 100, showed this resin to be suitable as the column packing. Mercury-195m in a Trisma buffer solution at pH 7.40 was loaded on a chelating resin Chelex 100 column, together with gold carrier. Au-195m was eluted with an aqueous solution of 5% glucose in a 0.01M Trisma buffer at pH 7.70 (25 degrees C). Chemical assessment of the eluate has ensured that the eluted carrier-free gold is by no means colloidal: 80% is found in an ionic form, 20% as an uncharged species. Safe clinical use for routine diagnosis in humans is possible.

Gold Radioisotopes↗