Anionic iron oxide nanoparticles are efficiently internalized into macrophages where they concentrate within micrometric endosomes, conferring on them a high magnetic susceptibility. The uptake of anionic maghemite nanoparticles by macrophages was quantified by an electron spin resonance (ESR) experiment. MR spin-echo sequences were performed with various TEs and TRs. The contrast enhancement was compared between two types of agarose phantoms with the same equivalent ferrite concentrations but containing either dispersed isolated nanoparticles or magnetically labeled macrophages. It is shown that the intracellular confinement of maghemite nanoparticles within micrometric endosomes results in a significant decrease of the longitudinal relaxivity and a moderate decrease of the transverse relaxivity compared to the relaxivities of the dispersed isolated nanoparticles. As a consequence, the signature of endosomal magnetic labeling consists of a negative contrast on T 1 -weighted images in the whole ferrite concentration range, whereas the presence of extracellular isolated nanoparticles can result in a positive enhancement. Magn Reson Med 49:646 -654, 2003.

Magnetic resonance imaging showed that the 3D architecture of fibrous septae couldn't be modelled simply as perpendicular planes for women and tilted planes at 45 degrees for men. MR spectroscopy did not confirm the hypothesis of increased water content in the adipose tissue of women with cellulite as suggested by others, except if such water would be located in the connective septae.

MR imaging can help accurately define the location and limits of glomus tumors before excision.

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MR imaging can aid in the evaluation of recurrent glomus tumors.

The cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRo(2)) are major determinants of the contrast in functional magnetic resonance imaging and optical imaging. However, the coupling between CBF and CMRo(2) during cerebral activation remains controversial. Whereas most of the previous models tend to show a nonlinear coupling, experimental studies have led to conflicting conclusions. A physiologic model was developed of oxygen transport through the blood-brain barrier (BBB) for dynamic and stationary states. Common model simplifications are proposed and their implications for the CBF/CMRo(2) relation are studied. The tissue oxygen pool, the BBB permeability, and the hemoglobin dissociation curve are physiologic parameters directly involved in the CBF/CMRo(2) relation. We have been shown that the hypothesis of a negligible tissue oxygen pool, which was admitted by most of the previous models, implies a tight coupling between CBF and CMRo(2). By relaxing this hypothesis, a real uncoupling was allowed that gives a more coherent view of the CBF/CMRo(2) relation, in better agreement with the hypercapnia data and with the variability reported in experimental works for the relative changes of those two variables. This also allows a temporal mismatch between CBF and CMRo(2), which influences the temporal shape of oxygenation at the capillary end.

Computational fluid dynamics (CFD) and magnetic resonance (MR) gas velocimetry were concurrently performed to study airflow in the same model of human proximal airways. Realistic in vivo-based human airway geometry was segmented from thoracic computed tomography. The three-dimensional numerical description of the airways was used for both generation of a physical airway model using rapid prototyping and mesh generation for CFD simulations. Steady laminar inspiratory experiments (Reynolds number Re = 770) were performed and velocity maps down to the fourth airway generation were extracted from a new velocity mapping technique based on MR velocimetry using hyperpolarized (3)He gas. Full two-dimensional maps of the velocity vector were measured within a few seconds. Numerical simulations were carried out with the experimental flow conditions, and the two sets of data were compared between the two modalities. Flow distributions agreed within 3%. Main and secondary flow velocity intensities were similar, as were velocity convective patterns. This work demonstrates that experimental and numerical gas velocity data can be obtained and compared in the same complex airway geometry. Experiments validated the simulation platform that integrates patient-specific airway reconstruction process from in vivo thoracic scans and velocity field calculation with CFD, hence allowing the results of this numerical tool to be used with confidence in potential clinical applications for lung characterization. Finally, this combined numerical and experimental approach of flow assessment in realistic in vivo-based human airway geometries confirmed the strong dependence of airway flow patterns on local and global geometrical factors, which could contribute to gas mixing.