Geometric depolarization in patterns formed by backscattered light

We formulate a framework for the depolarization of linearly polarized backscattered light based on the concept of geometric phase, {\it i.e} Berry's phase. The predictions of this theory are applied to the patterns formed by backscattered light between crossed or parallel polarizers. This theory should be particularly adapted to the situation in which polarized light is scattered many times but predominantly in the forward direction. We apply these ideas to the patterns which we obtained experimentally with backscattered polarized light from a colloidal suspension.Comment: 3 pages and 3 figure

Tissue oxygenation mapping by combined chemical shift and T1 magnetic resonance imaging

Purpose: To propose a method for determining tissue oxygenation via the measurement of fat T1. The method is based on a 2D fat/water chemical shift-encoded and T1-weighted acquisition. Theory and Methods: A 2D data set was acquired with a fast spin echo sequence with several echo asymmetries and repetition times, wherein one dimension is related to the fat/water phase modulation and the other to the T1 saturation recovery. A joint magnitude-based process of phase modulation and T1 evolution allowed for the collection of the fat fraction and T1 maps with resolved fat or water  dominance ambiguity while avoiding the phased error problem. Results: In vitro imaging allowed for the attribution of fat content for different water/oil emulsions that demonstrated longitudinal relaxation rate (R1) sensitivity to the oxygenated emulsion environment. The fat R1 values were subsequently compared to reference values, which were measured using low receiver bandwidth acquisition to enhance water and fat signal separations. In vivo feasibility of tissue oxygenation assessment was demonstrated by investigating interscapular brown adipose tissue modifications during an air/carbogen challenge in rats. Conclusion: The proposed method offers a precise and robust estimate of tissue oxygenation illustrated by the method’s ability to detect-brown adipose tissue oxygenation modifications

Topography and instability of monolayers near domain boundaries

We theoretically study the topography of a biphasic surfactant monolayer in the vicinity of domain boundaries. The differing elastic properties of the two phases generally lead to a nonflat topography of ``mesas'', where domains of one phase are elevated with respect to the other phase. The mesas are steep but low, having heights of up to 10 nm. As the monolayer is laterally compressed, the mesas develop overhangs and eventually become unstable at a surface tension of about K(dc)^2 (dc being the difference in spontaneous curvature and K a bending modulus). In addition, the boundary is found to undergo a topography-induced rippling instability upon compression, if its line tension is smaller than about K(dc). The effect of diffuse boundaries on these features and the topographic behavior near a critical point are also examined. We discuss the relevance of our findings to several experimental observations related to surfactant monolayers: (i) small topographic features recently found near domain boundaries; (ii) folding behavior observed in mixed phospholipid monolayers and model lung surfactants; (iii) roughening of domain boundaries seen under lateral compression; (iv) the absence of biphasic structures in tensionless surfactant films.Comment: 17 pages, 9 figures, using RevTeX and epsf, submitted to Phys Rev

La plate-forme PRISM : focus sur les applications précliniques

National audienceLa présentation avait pour objectif de présenter l'activité de la PF PRISM avec un focus sur les activités de recherche, les activités de prestation et de formation dans le domaine de l'imagerie appliquée à la santé et à la nutrition

MR-liver fat volume fraction quantification using a magnitude-based technique with independent fat and water T2* estimations, T1-related bias correction and accounting for fat multiple resonances

International audienc

MR-liver fat volume fraction quantification using a magnitude-based technique with independent fat and water T2* estimations, T1-related bias correction and accounting for fat multiple resonances

International audienc

Designing an Efficient Resistive Magnet for Magnetic Resonance Imaging

We present an alternative procedure to design a 0.1 T resistive magnet for magnetic resonance imaging. The procedure considers the conductor to be uniformly located over the cylindrical surface and treats it as coil elements. It applies the linear programming method with upper and lower bounds to constrain the current density to a fixed value in order to produce a desired magnetic field over a region of interest. The approach minimizes the power and preserves the predefined homogeneity, resulting in spatial clusters that define the coil's magnet. We demonstrate the method in a practical design situation