Modeling microwave electromagnetic field absorption in muscle tissues

Absorption of electromagnetic energy in human tissues is an important issue with respect to the safety of low-level exposure. Simulation is a way to a better understanding of electromagnetic dosimetry. This letter presents a comparison between results obtained from a numerical simulation and experimental data of absorbed energy by a muscle. Simulation was done using a bidimensional double-scale homogenization scheme leading to the effective permittivity tensor. Experimental measurements were performed at 10 GHz on bovine muscle, 30 hours after slaughter, thanks to the open-ended rectangular waveguide method. Results show a good agreement between measurements and simulated data

Multi échelles, multi contrastes, l’Imagerie par Résonance Magnétique pour l’agronomie, l’agro-alimentaire et la nutrition

National audienceLa résonance magnétique nucléaire (RMN) se distingue par sa versatilité puisqu'elle offre un éventail très large de méthodes analytiques capables, pour les plus remarquables, d'identifier la structure chimique de divers composés, de quantifier la dynamique de petites molécules ou de caractériser l'agencement des constituant de la matière à différentes échelles. Sous la forme de spectres ou d'images, la RMN fournit des informations précieuses sur la composition et la structure des tissus ou matériaux, ainsi que sur le fonctionnement du vivant. Plus précisément, l’IRM (pour Imagerie par Résonance Magnétique) présente l’avantage d’être multi échelles et multi contrastes. En effet, suivant les équipements, la taille et la nature de l’échantillon, et le temps dont on dispose, il est possible d’atteindre des résolutions spatiales de quelques dizaines de micromètres à quelques millimètres. On parle également d’échelle cellulaire en IRM car les informations récoltées localement sur la mobilité des protons informent indirectement sur l’état et la nature des structures à cette échelle-là. Enfin, l’IRM est multi contrastes puisqu’elle permet de cartographier sélectivement plusieurs noyaux (1H, 23Na, 31P, 13C, 19F …) mais également d’être sélective, pour un noyau donné, d’un type de tissu particulier. La plateforme AgroResonance est une infrastructure du centre INRA Auvergne-Rhône-Alpes au service de la communauté scientifique et industrielle. Elle est située sur le site de Theix. Elle réunit des compétences et un parc technologique de haut niveau pour proposer analyses et développements afin de répondre par la RMN et l'IRM à des questions variées dans les domaines de l'agro-alimentaire, du végétal, de la nutrition et de la santé

Diffusion MRI in muscles at high b-values: towards a quantification of microscopic organelles

National audienc

Study of an optimal configuration of an X-Band ferrofluid insulator

Results of investigation concerning a new application of ferrofluids (magnetic fluids) in the doMayn of non-reciprocal X-band devices are shown. Values of ferrofluid slab position x0, biasing field and ferrofluid saturation magnetization are determined for the optimum performance of an insulator. The advantages of using ferrofluids in non-reciprocal devices are also highlighted

Moisture and temperature dependence of the dielectric properties of pharmaceutical powders

The dielectric properties of pharmaceutical powder–(paracetamol, aspirin, lactose, maize starch, adipic acid) solvent (water) mixtures were measured at 2,450 MHz at a range of moisture contents (0–1.0 kg kg−1, dry basis) and temperatures (20–70 °C). The dielectric constant (ε′), loss factor (ε″) and penetration depth (d p) were found to be dependent on frequency, moisture content, temperature and powder type. For powder–water mixtures, a linear increase in the dielectric properties with moisture content was observed, whilst the temperature dependence was of quadratic form. The penetration depth was also significantly affected by temperature and moisture content. Although, ε″ also increased with increasing temperature, variation with moisture content was temperature dependent. This information on dielectric properties is essential for mathematical description of the pharmaceutical product temperature history during microwave heating and for the design of microwave drying equipment.Scopu

NMR imaging of air spaces and metabolites in fruit and vegetables

This chapter deals with the principles and the applications of magnetic resonance imaging (MRI) for assessment of the distribution and of the amount of intercellular gas-filled spaces and major metabolites in fruit and vegetable tissues. Combining this information with measurements of water characteristics could enable the use of MRI in an integrative approach to plant characterization. In MRI, the presence of gas-filled intercellular spaces in plant tissues impacts the NMR relaxation behavior of water molecules because gas and water have different magnetic susceptibilities. This phenomenon can be exploited for the noninvasive detection of certain physiological disorders in fruit and vegetable tissues or for quantification of the spatial distribution of apparent microporosity. On the other hand, the amount and the distribution of major metabolites (sugars, starch, lipids, etc.) can be accessed by MRI using approaches based on differences in relaxation times or on chemical shift between water and metabolites protons. Here we provide an overview of the theoretical aspects of MRI methods and a description of different approaches. The imaging protocols for specific applications for both air space and metabolite imaging are discussed with respect to their application to fruits and vegetables.</p