Position-sensitive detector systems, initially developed for the detection of X-rays, have been adapted for their use in electron emission channeling experiments. Each detection system consists of a 30.8×30.8 mm 2 22×22-pad Si detector, either of 0.3 mm, 0.5 mm or 1 mm thickness, four 128-channel preamplifier chips, a backplane trigger circuit, a sampling analog to digital converter, a digital signal processor, and a personal computer for data display and storage. The operational principle of these detection systems is described, and characteristic features such as energy and position resolution and maximum count rate, which have been determined from tests with conversion electrons and β − particles in the energy range 40-600 keV, are presented.

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Subitted to Nuclear Medicine and Biology 1996 OCR Output (IS 330 and IS 331) therapy using EDTMP as ligands close control of ligand concentration will be necessary.for 100 pl injected volume for the animal model used in this experiment. In radionuclide concentrations, giving highest tumor to liver ratios of enrichment, were between 1 and 10 mM reaching values close to 10 for Tm, 3 for Sm and 1 for Ac. The optimal EDTMP in tumor to that concentrated in liver are strongly influenced by the EDTMP concentration, radio-lanthanides was confirmed for all tracers used. The ratios of radioactivity concentrated methylenephosphonic acid). The strong dependence of liver uptake on the ionic radius of the solutions containing different concentrations of EDTMP (EDTMP = ethylenediaminetetra 7Tm) and 225Ac in tumor bearing nude mice. Mixtures of the radio-tracers were injected in 16 biodisuibution of carrier-free radionuclides of several lanthanides ( 141Ce, 145Sm, 149Gd, High resolution gamma spectroscopy was applied to measure simultaneously the studies. In addition to the rare earth elements 225Ac was taken into the experimental series because of its rare earth element to the next without having to change the chelator, a great advantage for optimization properties from one element to the next. In contrast to most radioisotope work, one can move from one Rare earth elements are most suitable for such studies since they show a fine graduation of chemical radio-lanthanides, and could help to design more efficient radiopharmaceuticals for diagnosis and therapy. contribute to our currently incomplete understanding on mechanisms for the tumor accumulation of the radionuclide, complex formation stability) and bio-distribution. Such information is required to to evaluate relationships between physico-chemical parameters of the injected compound (ionic radius of of our study is, rather than further collection of data on radio-tracer accumulation expressed in %/g tissue, demonstrated that EDTMP reduces significantly the liver uptake of radiolanthanides ( 5, 12, 16 ). The aim containing ligand EDTMP would favour bone uptake of Sm ( 12 ). On the other hand it has been clearly In the present study we have chosen EDTMP as the ligand. It is assumed that, as a phosphonic acid hypertonic concentrations not applicable in practice (4 ). significant influence as well. In the case of citrate we could see such an concentration effect only at for the biological behavior the overall concentration of the low molecular weight chelators must have a ligands and consequently the stability constants of the complexed ions formed play a such important role the rare earth elements are rapidly excreted via the kidney and are consequently lost. Since the chelating ( 18, 19 ). However, when injected in combination with chelating ligands forming very stable complexes ligands like or-HIB (ot-hydroxyisobutyric acid) or NTA (nitrilitriacetic acid) showed promising results species in the liver and consequently help to improve the tumor to liver ratios, and indeed...

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