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PET is the favored nuclear imaging technique because of the high sensitivity and resolution it provides, as well as the possibility for quantification of accumulated radioactivity. 44 Sc ( T 1/2 =3.97 h, Eβ + =632 keV) was recently proposed as a potentially interesting radionuclide for PET. The aim of this study was to investigate the image quality, which can be obtained with 44 Sc, and compare it with five other, frequently employed PET nuclides using Derenzo phantoms and a small-animal PET scanner. The radionuclides were produced at the medical cyclotron at CRS, ETH Zurich ( 11 C, 18 F), at the Injector II research cyclotron at CRS, PSI ( 64 Cu, 89 Zr, 44 Sc), as well as via a generator system ( 68 Ga). Derenzo phantoms, containing solutions of each of these radionuclides, were scanned using a GE Healthcare eXplore VISTA small-animal PET scanner. The image resolution was determined for each nuclide by analysis of the intensity signal using the reconstructed PET data of a hole diameter of 1.3 mm. The image quality of 44 Sc was compared to five frequently-used PET radionuclides. In agreement with the positron range, an increasing relative resolution was determined in the sequence of 68 Ga< 44 Sc< 89 Zr< 11 C< 64 Cu< 18 F. The performance of 44 Sc was in agreement with the theoretical expectations based on the energy of the emitted positrons. [ABSTRACT FROM AUTHOR]

161Tb, which emits low-energy β−- and γ-particles in addition to conversion and Auger electrons, has aroused increased interest for medical imaging and therapy. To support the use of this radionuclide, a161Tb solution was standardised using the β-γ coincidence technique, as well as the TDCR method. The solution had 4.5·10−3% of 160Tb impurities. Primary coincidence measurements, with plastic or liquid scintillators for beta detection, were carried out using both analogue and digital electronics. TDCR measurements using defocusing, grey filtering and quenching for varying the efficiency were also made. Monte Carlo calculations were used to compute the detection efficiency. The coincidence measurements with analogue electronics and the TDCR show a good consistency, and are compatible with the digital coincidence results within uncertainties. An ampoule of this solution was submitted to the BIPM as a contribution to the international reference system. • 161Tb has aroused increased interest recently for medical imaging and therapy. • 161Tb was standardised using the β(PS,LS)-γ(CeBr 3) coincidence techniques. • 161Tb was also standardised with the TDCR method using MC electron spectra. • Coincidence results are consistent with TDCR measurements. • An ampoule of the solution was submitted to the International Reference System. [ABSTRACT FROM AUTHOR]

The radiolanthanide 161Tb is being studied as an alternative to 177Lu for targeted radionuclide tumor therapy. Both β--particle emitters show similar chemical behavior and decay characteristics, but 161Tb delivers additional conversion and Auger electron emissions that may enhance the therapeutic efficacy. In this study, the half-life of 161Tb was determined by a combination of three independent measurement systems: reference ionization chamber (CIR, chambre d'ionization de référence), portable ionization chamber (TCIR) and a CeBr 3 γ-emission detector with digital electronics. The half-life determined for 161Tb is 6.953(2) days, showing a significant improvement in the uncertainty, which is one order of magnitude lower, with a deviation of 0.91% from the last nuclear data reference value. The previous large uncertainty of the half-life had a direct impact on activity measurements. Now it is no more an obstacle to a primary standardization. • The half-life obtained for 161-Tb is 6.953(2) days. • A deviation of 0.91% from the last nuclear data reference value is found. • The uncertainty is reduced by is one order of magnitude from reference value. • Stability, statistical robustness and uncertainty budget lead to an improved result. [ABSTRACT FROM AUTHOR]