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Positron emitting radionuclides are used to label different compounds, allowing the study of the major biological systems using PET (positron emission tomography) imaging. Although there are several radionuclides suited for PET imaging, routine clinical applications are still based on a restrict group constituted by 18 F, 11 C, and, more recently, 68 Ga. However, with the enlarged availability of low-energy cyclotrons and technical improvements in radionuclide production, the use of unconventional radionuclides is progressively more common. Several examples of unconventional radionuclides for PET imaging are being suggested, and 45 Ti could be suggested as a model, due to its interesting properties such as its abundant positron emission (85%), reduced positron energy (β + endpoint energy = 1040 keV), physical half-life of 3.09 h, and interesting chemical properties. This review aims to introduce the role of cyclotrons in the production of unconventional radionuclides for PET imaging while using 45 Ti as an example to explore the potential biomedical applications of those radionuclides in PET imaging.

Titanium aluminides are a valuable alternative to superalloys in applications where the ratio resistance/density is important. Since the ordinary production routes lead to high final costs, an alternative might be the use of traditional casting techniques by induction melting of the alloy in a ceramic crucible and pouring into ceramic moulds, made by the investment casting process. However, due to the high reactivity of Ti alloys, the use of traditional ceramic materials cannot be used, as they lead to oxide formation and oxygen pick up from both the crucible and the moulding materials.In this work, the effect of low level contamination was studied by SIMS. Special attention was given to the oxygen concentration for samples obtained with different mould materials. The comparison of SIMS in-depth profiles with hardness profiles, gives insight concerning the significance of the oxygen concentration in the properties of the alloy and regarding the choice of the most suitable materials for TiAl production. #

The first pulsed microbeam for positrons in the keV energy range is described. The principle of operation and the construction details are given. The performance achieved is: 20 μm (FWHM) spot diameter; 350 ps (FWHM) time resolution; 5000 e+ /(s mCi) at 5 keV final energy.

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Rcprintn available dirstly lrom lhc publisher Pholoeopying permitted by lianw only Q 1998 OPA (Overwar Publishers Asraiation) N.V. Published by lien% under the Gordon and Breach Sc~sncc Publirhrrr imprint. P""ld in India.A theoretical study of the transient sphere motion (under the influence of gravity) through an incompressible Newtonian fluid subject to an Oseen-type drag relationship has been carried out. Exact closed form expressions for the instantaneous position, velocity and acceleration of the sphere are presented. An analytical expression developed herein also enables the delineation of the "best" sphere-fluid combination for the experimental observations of transient effects and these provide useful guidelines for designing laboratory experiments. However, this study is restricted to dense spheres falling in light liquids when the additional effects arising from the added mass and the Basset forces are negligible. Also, the boundary eKects are altogether neglected.

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