Small-animal MRI: signal-to-noise ratio comparison at 7 and 1.5 T with multiple-animal acquisition strategies

Objective: The purpose of this study was to compare the signal-to-noise ratio (SNR) of phantom and rat brain images performed at 1.5 T on a clinical MR system and at 7 T on a small-animal experimental system. Comparison was carried out by taking into account SNR values based on a single sample acquisition at 1.5 and 7 T as well as on simultaneous imaging of multiple samples at 1.5 T. Methods: SNR was experimentally assessed on a phantom and rat brains at 1.5 and 7 T using 25 mm surface coils and compared to theoretical SNR gain estimations. The feasibility of multiple-animal imaging, using the hardware capabilities available on the 1.5 T system, was demonstrated. Finally, rat brain images obtained on a single animal at 7 T and on multiple animals acquired simultaneously at 1.5 T were compared. Results: Experimentally determined SNR at 7 T was far below theoretical estimations. Taking into account chemical shift, susceptibility artifacts and modifications of T1 and T2 relaxation times at higher field, a 7-T system holds limited advantage over a 1.5-T system. Instead, a multiple-animal acquisition methodology was demonstrated on a clinical 1.5-T scanner. This acquisition method significantly increases imaging efficiency and competes with single animal acquisitions at higher field. Conclusion: Multiple-animal imaging using a standard clinical scanner has a great potential as a high-throughput acquisition method for small animals.     

Mass‐transfer enhancement by a reversible chemical reaction across the interface of a bubble rising under Stokes flow

Mass transfer around a bubble rising in a liquid under Stokes regime is investigated when a reversible chemical reaction, , is taken into account. Four dimensionless parameters control the interfacial transfer rate: the Péclet and Damköhler numbers, the ratio of the diffusion coefficient of both species, and the reaction equilibrium constant. The mass‐transfer equations are solved numerically with a finite element technique. A boundary layer approach is also proposed and solved with a coupled technique of finite difference and Chebyshev‐spectral method. The equilibrium constant and the ratio of diffusion coefficients have a strong influence on the coupling between the chemical reaction and mass transfer leading to an increase of the Sherwood number. The interaction between the chemical reaction and advection is clearly established by the simulations. Conditions corresponding to Péclet number larger than the Damköhler number reduces the effect of the chemical reaction. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3376–3388, 2014     

Novel Heterobimetallic Radiotheranostic: Preparation,Activity, and Biodistribution

A novel Ru^II(arene) theranostic complex is presented. It is based on a 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid macrocycle bearing a triarylphosphine and can be tracked in vivo by using the γ emission of ¹⁵³Sm atoms. Notably, the heteroditopic ligand can be selectively metalated with ruthenium at the phosphorus atom despite the presence of other functionalities that are prone to metal coordination. Subsequent labeling with radionuclides such as ¹⁵³Sm can then be performed easily. The resulting heterobimetallic complex exhibits favorable solubility and stability properties in biologically relevant media. It also shows in vitro cytotoxicity in line with that expected for this type of metallodrug, and is nontoxic to the organism as a whole. As a proof of concept, initial studies in healthy mice were performed to obtain information about the uptake, biodistribution, and excretion of the radiolabeled complex.     

MA‐NOTMP: A Triazacyclononane Trimethylphosphinate Based Bifunctional Chelator for Gallium Radiolabelling of Biomolecules

In the past few years, gallium‐68 has demonstrated significant potential as a radioisotope for positron emission tomography (PET), and the optimization of chelators for gallium coordination is a major goal in the development of radiopharmaceuticals. Methylaminotriazacyclononane trimethylphosphinate (MA‐NOTMP), a new C‐functionalized triazacyclononane derivative with phosphinate pendant arms, presents excellent coordination properties for ⁶⁸Ga (low ligand concentration, labelling at low pH even at room temperature). A “ready‐to‐be‐grafted” bifunctional chelating agent (p‐NCS‐Bz‐MA‐NOTMP) was prepared to allow ⁶⁸Ga labelling of sensitive biological vectors. Conjugation to a bombesin_(7–14) derivative was performed, and preliminary in vitro experiments demonstrated the potential of MA‐NOTMP in the development of radiopharmaceuticals. This new chelator is therefore of major interest for labelling sensitive biomolecules, and further in vivo experiments will soon be performed.     

MIL-53 and its Isoreticular Analogues: a Review of the Chemistry and Structure of a Prototypical Flexible Metal-Organic Framework

We present a review of the structural chemistry of metal-organic framework materials with the MIL-53 type structure. This family of materials is well-known for its structural flexibility, and also the wide variety of metal cations and functional ligands that can be included. This gives rise to a set of multivariate materials and isoreticular analogues, to which isoreticular functionalisation can also be applied. Starting from the parent structure, containing infinite chains of octahedral trivalent metal cations cross-linked by benzene-1,4-dicarboxylate, we illustrate the compositional variety possible: this includes materials that contain tetravalent and divalent cations, mixtures of metal cations, functionalised ligands, expanded structures from extended linkers and inclusion of pendant ligands. We emphasise the crystal chemistry of this group of materials, but will give some examples of properties, particularly those associated with the structural breathing effect of relevance to molecular sieving, and also discuss emerging practical applications.     

Study of the R-(Zr,W)-(O,N) (R = Y, Nd, Sm, Gd, Yb) oxynitride system

The replacement of tantalum by the couple Zr/W within the RTa-O-N systems (R = Y, Nd, Sm, Gd, Yb), enables the preparation of novel oxide and oxynitride phases in the R-Zr-W-O-N system. R₂Zr_2−xW_xO_7+x oxides exhibit the fluorite-type (x < 0.9) and scheelite (x ∼ 1) structures. Corresponding oxynitride compositions are of the fluorite-type and show different colors, for example in the case of ytterbium: pale yellow (x = 0.2 or 0.25), green (x = 0.5-0.8) and brown for the tungsten-rich samples (x = 0.9, 1). Photocatalytic activity measurements have been performed to investigate the overall water splitting behavior of these colored phases.     

Defect analysis and excitons diffusion in undoped homoepitaxial diamond films after polishing and oxygen plasma etching

Several 65 μm thick epitaxial diamond films prepared on (100) Ib substrates by high power pulsed microwave plasma assisted chemical vapour deposition (HP-MPCVD) are studied as a function of surface treatments by cathodoluminescence (CL) and photoluminescence (PL) spectroscopies. They are either asgrown, or polished, or etched by a microwave oxygen plasma, or after applying subsequently the two last processes. In CL spectra, bands due to defects occur at 2.3 eV, 3.07 eV, 3.7 eV and 4.7 eV, the last one being specific of polished surfaces, with nearly no contrast in the luminescence image. A fundamental result consists in demonstrating that the defects induced by polishing can be removed by oxygen plasma etching. Additionally, in order to assess how luminescence spectra originate from a peculiar depth or not, a bevelled sample is studied. PL spectra are acquired on the sample side while CL spectra are measured at several points on the bevel top side till to the Ib substrate. Comparison of the two sets of result show that the H3 signal originates from the Ib substrate even if it is present in the CL spectra of the film. An analysis of the change in the intensity of the TO free exciton line, defect bands and H3 signal, along decreasing photon energies, as a function of the thickness of the remaining HP-PMPCVD film, is performed with the help of a model taking the diffusion of the unrecombined excitonic pairs and the re-excited photoluminescence into account. CL images recorded at specific wavelengths, which do not show inverted contrast, are also assessed. From these data, the exciton diffusion length is evaluated to 11 μm in the major part of the epitaxial layer except for the first 20 μm close to the Ib substrate where it decreases down to 2 μm. This study sheds light on the interpretation of luminescence spectra excited by an electron beam in undoped diamond layers. Defects bands due to damages induced by polishing and etching processes are also documented.     

具有国际化魅力的法国美食

去年十二月份,厨师Franck Page先生加入北京佛雄食品店时正值北方大雪纷飞的日子.但按照Franck家乡的习俗,遇见()雪天意味着好兆头.在黎巴嫩著名的五星级饭店Vendome Intercontinental积累了丰富经验之后.Franck决定对自己的职业生涯做一次转折,于是他加入了享誉全球的著名法国集团佛雄,该集团刚刚在北京开办了第一家分部.Franck就这样来到了北京佛雄食品店.