80 research outputs found
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
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