[en] Full text of publication follows. In preclinical micro-PET imaging small rodents often have to undergo longitudinal studies involving multiple scans combined with micro-CT imaging to gather anatomical information. The radiation exposure of the animals needs to be addressed since the impact of the radiation might compromise the validity of the results. The aim of the study was to use experimentally obtained kinetic data of three [¹⁸F]-tracers and S-values derived by Monte Carlo simulations to calculate absorbed doses in mice and estimate radiation exposure in longitudinal studies. The bio-distribution of 6-[¹⁸F]fluoro-L-DOPA, 2-[¹⁸F]fluoro-L-Tyrosine and a [¹⁸F] compound under development ([¹⁸F]X) was obtained using organ harvesting (OH) at multiple time points, dynamic micro-PET imaging (DI) and hybrid method (HM), where organs are harvested post scan to improve quantification of the micro-PET. Monte-Carlo simulations were carried out using GATE v6.1 and the MOBY phantom to determine S-values of multiple source and target organs. Time activity curves were derived from experimental data and residence times for multiple source organs were calculated and used for absorbed dose calculations. The total body absorbed dose for all three [¹⁸F]-tracers and all methods were almost identical with 14.19 ± 0.11 mGy/MBq. The critical organ for 6-[¹⁸F]fluoro-L-DOPA were the kidneys with 23.61 ± 6.34 mGy/MBq for OH and the bladder wall for DI and HM with 552.44 ± 316.55 mGy/MBq and 569.73 ± 326.48 mGy/MBq, respectively. The high derived bladder wall absorbed dose is similar to values provided in literature for bladder wall from [¹⁸F]FDG in mice. For 2-[¹⁸F]fluoro-L-Tyrosine the highest dose was absorbed by the liver for all 3 methods with 48.23 ± 8.32 mGy/MBq derived by OH (DI: 41.57 ± 7.69 mGy/MBq; HM: 54.75 ± 11.03 mGy/MBq). For [¹⁸F]X the critical organ was the liver for OH with 65.14 ± 8.47 mGy/MBq and the bladder wall for DI with 57.63 ± 28.36 mGy/MBq. The calculated absorbed doses derived from the 3 experimental methods showed good agreement. When assuming multiple injected activities of 10 MBq plus additional radiation from micro-CT (multiple scan average absorbed dose of approx. 80 mGy for full body soft tissue scan, GE eXplore 120 micro-CT) an accumulated total body absorbed dose of more than 1 Gy and much higher absorbed doses for single organs can be reached possibly introducing stochastic effects. The lethal absorbed dose for a mouse is considered 6 Gy, however, studies have shown that far lower absorbed doses can alter the physiology and compromise results. (authors)

[en] This work investigates the electrochemical behavior of Pu(IV) and Pu(VI) complexes in n-tributylphosphate (TBP) as an entry to the electrochemical characterization of these complexes in organic extractants related to nuclear fuel reprocessing. Glassy carbon electrodes were used to show that Pu(IV) and Pu(VI) complexes display a reversible electrochemical reduction wave in TBP previously equilibrated with aqueous nitric acid solution. We investigated the reduction of Pu(IV) and Pu(VI) nitrato complexes extracted into TBP, with the aim to get thermodynamic (formal potential) and kinetic (diffusion coefficient) information about Pu(IV)/Pu(III) and Pu(VI)/Pu(V) redox couples in the TBP medium. The formal potentials of the two redox couples were respectively 0.510 ± 0.005 and 0.478 ± 0.005 V per SCE in TBP equilibrated with 3 mol L^-1 nitric acid at room temperature. The diffusion coefficient values of Pu(IV) and Pu(VI) species were estimated to be 0.72 * 10^-6 and 0.77 * 10^-6 cm² s^-1 respectively. Also, the Pu(IV) reduction showed a Nernstian dependence on the logarithm of nitric acid concentration in the organic phase, featuring the exchange of nitrates upon reduction of Pu(IV). (authors)

[en] In the present work, the effect of Randomly-methylated-β-cyclodextrin (Rameb) on the microviscosity of dimyristoyl-L-α phosphatidylcholine (DMPC) bilayer was investigated using the electron spin resonance (ESR) technique. The ability of Rameb to extract membrane cholesterol was demonstrated. For the first time, the percentage of cholesterol extracted by Rameb from cholesterol doped DMPC bilayer was monitored and quantified throughout a wide Rameb concentration range. The effect of cholesterol on the inner part of the membrane was also investigated using 16-doxyl stearic acid spin label (16-DSA). 16-DSA seems to explore two different membrane domains and report their respective microviscosities. ESR experiments also establish that the presence of 30% of cholesterol in DMPC liposomes suppresses the jump in membrane fluidity at lipids phase-transition temperature (23.9 ^oC).

[en] The eXplore CT 120 is the latest generation micro-CT from General Electric. It is equipped with a high-power tube and a flat-panel detector. It allows high resolution and high contrast fast CT scanning of small animals. The aim of this study was to compare the performance of the eXplore CT 120 with that of the eXplore Ultra, its predecessor for which the methodology using the vmCT phantom has already been described . The phantom was imaged using typical a rat (fast scan or F) or mouse (in vivo bone scan or H) scanning protocols. With the slanted edge method, a 10% modulation transfer function (MTF) was observed at 4.4 (F) and 3.9-4.4 (H) mm^-1 corresponding to 114 μm resolution. A fairly larger MTF was obtained by the coil method with the MTF for the thinnest coil (3.3 mm^-1) equal to 0.32 (F) and 0.34 (H). The geometric accuracy was better than 0.3%. There was a highly linear (R²>0.999) relationship between measured and expected CT numbers for both the CT number accuracy and linearity sections of the phantom. A cupping effect was clearly seen on the uniform slices and the uniformity-to-noise ratio ranged from 0.52 (F) to 0.89 (H). The air CT number depended on the amount of polycarbonate surrounding the area where it was measured; a difference as high as approximately 200 HU was observed. This hindered the calibration of this scanner in HU. This is likely due to the absence of corrections for beam hardening and scatter in the reconstruction software. However in view of the high linearity of the system, the implementation of these corrections would allow a good quality calibration of the scanner in HU. In conclusion, the eXplore CT 120 achieved a better spatial resolution than the eXplore Ultra (based on previously reported specifications) and future software developments will include beam hardening and scatter corrections that will make the new generation CT scanner even more promising.