In order to support animal experiments of chronic radionuclides intake with realistic dosimetry, voxel-based three-dimensional computer models of mice and rats of both sexes and three ages were built from magnetic resonance imaging. Radiation transport of mono-energetic photons of 11 energies and electrons of 7 energies was simulated with MCNPX 2.6c to assess specific absorbed fractions (SAFs) of energy emitted from 13 source regions and absorbed in 28 target regions. RODES software was developed to combine SAF with radiation emission spectra and user-supplied biokinetic data to calculate organ absorbed doses per nuclear transformation of radionuclides in source regions (S-factors) and for specific animal experiments with radionuclides. This article presents the design of RODES software including the simulation of the particles in the created rodent voxel phantoms. SAF and S-factor values were compared favourably with published results from similar studies. The results are discussed for rodents of different ages and sexes.

The knowledge of the absorbed radiation dose is essential in order to

H Miloudi, M Locatelli, G Autret, D Balvay, A Desbrée, E Blanchardon, J M Bertho: application of RODES software to experimental biokinetic data for dose assessment in mice and rats. In support of experimental studies of chronic, long-term contamination in rodents, voxel-based computer models were built representing adult mice and juvenile, adult and elderly rats of both sexes. RODES software was created to calculate absorbed radiation doses to organs with these specific anatomical models. Absorbed doses were then calculated starting from previously published biokinetic data. Whole body doses showed less than 5% differences between calculation with RODES and calculation with the ICRP Publication 108 model for long term exposure to Sr of mice. Similar results were obtained for long term exposure toCs. Dose distribution for Sr internal contamination also showed that the dose to the skeleton is six fold more as compared to the whole body dose while radiation dose to other organs is less than the mean whole body dose. These results underline the importance of using specific anatomical models according to the age and the sex of experimental animals.

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Reçu le 18 avril 2017 / Accepté le 12 décembre 2017Résumé -Cette étude vise à optimiser le protocole des rochers d'un scanner Siemens Somatom Sensation 40. Ainsi, plusieurs acquisitions du fantôme Catphan 600 sont réalisées pour évaluer quantitativement la qualité d'image. Pour cela, l'écart type du nombre CT et la fonction de transfert de modulation (FTM) sont mesurés à partir des images acquises. La qualité d'image est également évaluée visuellement par le radiologue, à partir d'images issues de patients. Trois critères sont considérés : la visualisation du tympan, la visualisation des osselets et la texture du bruit. L'utilisation de la table plutôt que de la têtière comme support conduit à une augmentation moyenne du bruit de 10 %. L'évaluation qualitative des images issues de patients a permis quant à elle de réduire les mAs effectifs de 28 % et donc l'IDSV de 150,8 mGy à 109,1 mGy. De plus, l'utilisation d'un filtre plus dur a conduit à une amélioration de la visualisation des plus petites structures de l'oreille interne. Ainsi, cette étude a permis d'assurer une qualité d'image satisfaisante pour le diagnostic tout en réduisant la dose délivrée au patient de 28 %.Abstract -Optimization of a computed tomography (CT) scan protocol of the temporal bone. This study aims to optimize the CT scan protocol for temporal bone for a Somatom Sensation 40CT scanner by SIEMENS. Several acquisitions of Catphan 600 phantom are realized in order to quantitatively assess the image quality. The standard deviation of the CT Hounsfield Unit and the Modulation Transfer Function (MTF) are measured from the images acquired. The image quality is visually evaluated by the radiologist thanks to the patient images considering three criteria: visualization of the eardrum, visualization of the ossicles and noise texture. Using the cradle as the main support, in place of the headrest, a noise increment of around 10% was observed. Qualitative assessments of the patient images allowed a reduction of the effective mAs of 28% and therefore the volumetric computed tomography dose index (CTDIvol) from 150.8 mGy to 109.1 mGy. In addition, the use of a harder filter led to improved visualization of the smallest structures of the inner ear. The study results allowed to find the best compromise between the highest image quality required to realize a confident diagnostic and a considerable reduction of the dose delivered to the patient (of 28%).