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81.
Zaid Q. Ababneh Helene Beloeil Charles B. Berde Anas M. Ababneh Stephan E. Maier Robert V. Mulkern 《Magnetic resonance imaging》2009
The diffusion coefficient of lipids, Dl, within bone marrow, fat deposits and metabolically active intracellular lipids in vivo will depend on several factors including the precise chemical composition of the lipid distribution (chain lengths, degree of unsaturation, etc.) as well as the temperature. As such, Dl may ultimately prove of value in assessing abnormal fatty acid distributions linked to diseases such as cystic fibrosis, diabetes and coronary heart disease. A sensitive temperature dependence of Dl may also prove of value for MR-guided thermal therapies for bone tumors or disease within other fatty tissues like the breast. Measuring diffusion coefficients of high molecular weight lipids in vivo is, however, technically difficult for a number of reasons. For instance, due to the much lower diffusion coefficients compared to water, much higher b factors than those used for central nervous system applications are needed. In addition, the pulse sequence design must incorporate, as much as possible, immunity to motion, susceptibility and chemical shift effects present whenever body imaging is performed. In this work, high b-factor line scan diffusion imaging sequences were designed, implemented and tested for Dl measurement using a 4.7-T horizontal bore animal scanner. The gradient set available allowed for b factors as high as 0.03 μs/nm2 (30,000 s/mm2) at echo times as short as 42 ms. The methods were used to measure lipid diffusion coefficients within the marrow of rat paws in vivo, yielding lipid diffusion coefficients approximately two orders of magnitude smaller than typical tissue water diffusion coefficients. Phantom experiments that demonstrate the sensitivity of lipid diffusion coefficients to chain length and temperature were also performed. 相似文献
82.
Two new approaches, Magnetic Drug Targeting (MDT) and Magnetic Hyperthermia, are being investigated in order to reduce side effects generated by common ways of cancer treatment. MDT and MHT are based on the use of magnetic nanoparticles: for MDT the nanoparticles are used as drug carriers and for MHT the nanoparticles are used to induce local heat transfer within the tumour. The success of these therapeutic approaches depends among other things on the correct distribution of the magnetic nanoparticles within the tumour tissue. Computed tomography analysis has been performed on tumour tissue after MDT in order to examine this distribution. The measurements have been performed in two different laboratories, one based on a synchrotron radiation, and another one on a cone X–ray source. First results show that the drug carriers are contained in the vessel system of the tumour as well as concentrated in the surrounding area of the veins. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
83.
David H. Frakes Kerem Pekkan Lakshmi P. Dasi Hiroumi D. Kitajima Diane de Zelicourt Hwa Liang Leo Josie Carberry Kartik Sundareswaran Helene Simon Ajit P. Yoganathan 《Experiments in fluids》2008,45(6):987-997
Complex applications in fluid dynamics research often require more highly resolved velocity data than direct measurements
or simulations provide. The advent of stereo PIV and PCMR techniques has advanced the state-of-the-art in flow velocity measurement,
but 3D spatial resolution remains limited. Here a new technique is proposed for velocity data interpolation to address this
problem. The new method performs with higher quality than competing solutions from the literature in terms of accurately interpolating
velocities, maintaining fluid structure and domain boundaries, and preserving coherent structures. 相似文献
84.
Summary. By coupling two arbitrary riemannian connections Γ and Γ˜ on a riemannian manifold M, we perform the stochastic calculus of ɛ-variation on the path space P(M) of the manifold M. The method uses direct calculations on Ito’s stochastic differential equations. In this context, we obtain intertwinning
formulas with the Ito map for first order operators on the path space P(M) of M. By a judicious choice of the second connection Γ˜ in terms of the connection Γ, we can prolongate the intertwinning formulas to second order differential operators. Thus, we obtain expressions of heat
operators on the path space P(M) of a riemannian manifold M endowed with an arbitrary connection. The integration by parts of the laplacians on P(M) leads us to the notion of dilatation vector field on the path space.
Received: 18 April 1995 / In revised form: 18 March 1996 相似文献
85.
86.
The structure of 1-chloro-1-silabicyclo(2.2.2)octane as determined by gas-phase electron diffraction
Helene Schei Quang Shen Robert F. Cunico Richard L. Hilderbrandt 《Journal of Molecular Structure》1980,63(1):59-71
The structure of 1 -chloro-1 -si labicyclo( 2.2.2 )octane is determined by gas-phase electron diffraction. The molecule is found to have a large amplitude twisting motion with a double minimum quartic potential function of the form V(φ) = Vo[1 + (φ/φo)4 - 2(φ/φo)2]. Least-squares analysis of the experimental data gives values of 1.4(0.8) kcal mole? for Vo and 17.5(2.5)° for φo. Other structural parameters for the “quasi-C3v” cage-like molecule include: rg(Si-Cl) = 2.061(3) Å, rg(Si-C) = 1.863(3) Å, rg(C-Cav) = 1.559(2) Å, and rg(C-Hav) = 1.098(7) Å. Several valence angles exhibit large deviations from tetrahedral values, e.g. ∠Cl-Si-C2 = 114.6(0.2)°, ∠Si-C2-C3 = 105.8(0.4)°, ∠C2-C3-C4 = 114.2(1.2)°, ∠C-3-C4-C5 = 111.4(0.8)° and ∠C2-Si-C6= 103.9(0.2)°. Many of the structural features in this strained polycyclic compound. Including the nature of the quartic potential function, can be rationalized in terms of a simple molecular mechanics model. A new method for the calculation of an analytical Jacobian of the intensity function with respect to parameters of the potential function is also discussed. 相似文献
87.
88.
Russom A Haasl S Ohlander A Mayr T Brookes AJ Andersson H Stemme G 《Electrophoresis》2004,25(21-22):3712-3719
A miniaturized bead-based dynamic allele-specific hybridization (DASH) approach for single-nucleotide polymorphism analysis is presented. Chips with integrated heater and temperature sensors for open-surface DNA analysis were microfabricated. Microcontact printing using a poly(dimethylsiloxane) (PDMS) stamp was employed to create monolayers of immobilized beads on the surface of the chip. This chip allows fast, well-controllable temperature ramping. The temperature distribution was homogeneous over the entire heater area. All three possible variants of an SNP site of a synthesized oligonucleotide were accurately scored using the bead-based DASH approach. Our assay has a nonoptimized temperature ramping rate of 4 degrees C-6 degrees C/min compared to earlier reported values of 2 degrees C-3 degrees C/min, thereby reducing the total analysis time by a factor of 2. Reliable DASH measurement data from areas as small as 12 x 13 microm was achieved. Our bead-based DASH approach has enabled a dramatic volume reduction and is a step towards developing a cost-effective high-throughput DASH method on arrays of single beads. 相似文献
89.
This paper presents a novel method to embed, anchor, and cultivate cells in a controlled 3-D flow-through microenvironment. This is realized using an etched silicon pillar flow chamber filled with extracellular matrix (ECM) gel mixed with cells. At 4 degrees C, while in liquid form, ECM gel is mixed with cells and injected into the chamber. Raising the temperature to 37 degrees C results in a gel, with cells embedded. The silicon pillars both stabilize and increase the surface to volume ratio of the gel. During polymerization the gel shrinks, thus creating channels, which enables perfusion through the chip. The pillars increase the mechanical stability of the gel permitting high surface flow rates without surface modifications. Within the structure cells were still viable and proliferating after 6 days of cultivation. Our method thus makes it possible to perform medium- to long-term cultivation of cells in a controlled 3-D environment. This concept opens possibilities to perform studies of cells in a more physiological environment compared to traditional 2-D cultures on flat substrates. 相似文献
90.
Emmelkamp J Wolbers F Andersson H Dacosta RS Wilson BC Vermes I van den Berg A 《Electrophoresis》2004,25(21-22):3740-3745
A novel method for studying unlabeled living mammalian cells based on their autofluorescence (AF) signal in a prototype microfluidic device is presented. When combined, cellular AF detection and microfluidic devices have the potential to facilitate high-throughput analysis of different cell populations. To demonstrate this, unlabeled cultured cells in microfluidic devices were excited with a 488 nm excitation light and the AF emission (> 505 nm) was detected using a confocal fluorescence microscope (CFM). For example, a simple microfluidic three-port glass microstructure was used together with conventional electroosmotic flow (EOF) to switch the direction of the fluid flow. As a means to test the potential of AF-based cell sorting in this microfluidic device, granulocytes were successfully differentiated from human red blood cells (RBCs) based on differences in AF. This study demonstrated the use of a simple microfabricated device to perform high-throughput live cell detection and differentiation without the need for cell-specific fluorescent labeling dyes and thereby reducing the sample preparation time. Hence, the combined use of microfluidic devices and cell AF may have many applications in single-cell analysis. 相似文献