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- Author or Editor: A. Giussani x
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Abstract
The biokinetics of radioactive substances can be studied using stable tracers. For the highly radiotoxic actinides, for which no stable isotopes are available as tracers, the use of stable isotopes of lanthanides as chemically related surrogates has been suggested. In this work, the possibility of using activation analysis with protons, photons, or thermal neutrons for the determination of single stable isotopes of gadolinium in biological samples has been tested. All the techniques show very good linearity response, and may be considered as complementary. Whereas activation analysis with protons is recommendable for the simultaneous determination of two different isotopes, neutron and photon (gamma) activation analysis should be chosen whenever a better sensitivity or simplicity of the analysis is required.
Abstract
Information on the biokinetics of cerium can be obtained directly from humans by using stable isotopes as tracers. Neutron, photon and proton activation analysis have all been tested as analytical techniques able to quantify different isotopes of the same element in biological fluids. The experimental conditions were optimized for Ce analysis in blood plasma samples. The performances of the different techniques have been explored. The simultaneous determination of two Ce isotopes with the required sensitivity in the order of few ppb is difficult to obtain using a single technique, and, therefore, a combination of techniques can be envisaged.
Abstract
In order to estimate gut absorption by determining tracer concentration in plasma, a technique based on the administration of two stable isotopes of the same element was combined with proton activation analysis. The optimization for the determination of Zr isotopes in biological samples is presented together with the results of a preliminary study on Zr biokinetics in animals. (p,n) reactions on90Zr and96Zr resulted the most convenient. The obtained minimum detectable quantities are 3 and 2 ng/ml plasma, respectively, for90Zr and96Zr. Zr plasma clearance and Zr response to a simple oral test were studied separately in different subjects by using the natural Zr solution. The data analysis was performed measuring the concentration of90Zr to obtain indication on the time behavior and fractional level of Zr appearance in plasma depending on the administration routes. Two rabbits were intravenously injected 50 
g90Zr and a third rabbit was orally given 2.5 mg of90Zr. Concentration in plasma samples of intravenously and orally given Zr isotopes are reported, as a function of time after administration. The injected tracer concentration relative to the first two rabbits were fitted simultaneously to obtain clearance parameters. Zr intestinal absorption is evaluated to be less than 0.2%. The work confirms that proton activation is a powerful tool for biokinetic studies with stable isotopes.
Abstract
An apparatus for cyclic charged particle activation was designed, built and connected to the 7 MV Van de Graaff CN accelerator of the Laboratori Nazionali dell'Istituto Nazionale di Fisica Nucleare di Legnaro (Italy). It mainly consists of a two-sample transverse moving system controlled by a Cycle Control Module (CCM). This module is based on a Programmable Logic Device (PLD) for the definition of the requested flow-maps and functions. The CCM operates the cc motor for sample movements by means of a power width modulation technique. It also controls the beam switch and the setting mode of the acquisition system which is connected to two HPGe detectors. As a feasibility test, the best experimental conditions for aluminium determination in complex. Al-doped biological samples were found to be an irradiation time of 3.5 minutes and a measuring time of 6 minutes. The signal to background ratio is reported as a function of the number of cycles.
Abstract
Proton activation analysis has been recently applied for the determination of stable isotopes of trace metals in blood plasma samples taken from volunteers during tracer kinetic studies. The very low values of intestinal uptake for some elements, like ruthenium, make the kinetics of the excretion crucial for interpreting the bioassay data. Therefore, a procedure has been developed to process urine samples in order to have proper targets for the activation with protons. Preliminary tests with Ru-doped samples, conducted using the MC-40 Cyclotron at JRC Ispra, has confirmed the feasibility of the method. The minimum detectable concentrations, in the current operating conditions, are 16 ng 99Ru·ml−1 and 0.5 ng 101Ru·ml−1.
Summary
The nuclear properties of 186gRe make it a useful agent for radionuclide therapy and imaging. The coordination compound [186gRe]Re-HEDP has proved to be a successful bone seeking agent for palliation of metastatic bone pain. Chemical, radiochemical and radionuclidic purity of commercial radiopharmaceutical [186gRe]Re-HEDP have been checked by means by γ- and β-spectrometries, INAA and paper radio-chromatography. The results indicate a good radionuclidic purity, with levels of contamination from the short-lived 188Re well below the required specifications. After injection of the radiopharmaceutical, the radiochemical measurements conducted in vivo, on biological matrices, blood, plasma and urine, have shown that, entering the systemic circulation, 186gRe dissociates from the bis-phosphonate complex as hydrosoluble [186gRe]ReO4-, and the two chemical species follow different biokinetics.
Abstract
The feasibility of ruthenium metabolism studies by stable tracer administration, with a methodology based on proton nuclear activation, is presented. In order to test that the amount of stable tracer administered does not perturb significantly the mechanism investigated, a series of comparative experiments with administration of both radioactive and stable tracers has been performed on animals. As the most critical pathway seems to be the intravenous injection, four male rabbits were given an intravenous injection of radioactive106Ru. Successively, the rabbits were given either a further injection of radioactive106Ru or injection of different quantities of natural Ru. The activity of106Ru and the concentration of natural Ru were measured in plasma samples withdrawn at different time intervals from the injections and the results were compared. Some biokinetic parameters and tissue distribution of Ru in rabbits were determined.
Abstract
An investigation on tellurium metabolism by administration of stable tellurium isotopes124Te and126Te has been performed. Fractional intestinal absorption was determined in rabbits by the double tracer technique. The investigated subjects were given an enriched solution of one tellurium isotope orally and a few minutes later an enriched solution of the other isotope intravenously. The124Te and126Te contents in plasma samples were determined by proton nuclear activation. The methodology described offers a means to study tellurium metabolism in humans without radiation risk.
