Analysis of scattering lengths in Co/Cu/Co and Co/Cu/Co/Cu spin-valves using a Ru barrier

We use uncoupled Co/Cu/Co and Co/Cu/Co/Cu spin-valve structures with a Ru barrier shifted through the top Co and Cu layer, respectively, to measure the longest of the electron mean free paths in Co and Cu as originally suggested by Parkin. From semiclassical transport calculations and careful analysis of the magnetoresistance data we conclude that the exponential behavior of ¿G is uniquely related to the longest of the Co and Cu mean free paths under the condition of effective spin-dependent filtering at the interfaces or in the bulk of the Co. In this regime we have compared ¿long in Co and Cu with bulk conductivities (~¿short+¿long), yielding no strong evidence for bulk spin-dependent scattering in Co

Formation of nonmagnetic c-Fe_{1-x}Si in antiferromagnetically coupled epitaxial Fe/Si/Fe

Low-energy electron diffraction, Auger electron spectroscopy, and conversion electron Mössbauer spectroscopy have been applied to study antiferromagnetically exchange-coupled epitaxial Fe/Si/Fe(100). It is shown that a bcc-like (100) structure is maintained throughout the layers after a recrystallization of the spacer layer by Fe/Si interdiffusion. Direct experimental evidence is presented that c-Fe1-xSi (

Compositional dependence of the giant magnoresistance in FexRh1-x thin films

In this article we report on the magnetic and transport properties of FexRh1-x thin films, prepared by evaporation in high vacuum, in the composition range 0.4

Temperature dependence of the resistivity and tunneling magnetoresistance of sputtered FeHf(Si)O cermet films

We have studied the tunneling resistivity and magnetoresistance of reactive sputter deposited FeHfO and FeHfSiO thin granular films. Maximum magnetoresistance ratios at room temperature of 2% and 3.2% were observed for films with compositions of Fe47Hf10O43 and Fe40Hf6Si6O48, respectively. The magnetoresistance shows a decrease with temperature, which cannot be explained by spin-dependent tunneling only. We propose that spin-flip scattering in the amorphous FeHf(Si)O matrix causes this decrease as function of temperature. A two current model for the tunnel magnetoresistance, taking into account spin-flip scattering, is presented which can describe the observed temperature dependence of the magnetoresistance

Contrast enhancement by differently sized paramagnetic MRI contrast agents in mice with two phenotypes of atherosclerotic plaque

Interest in the use of contrast-enhanced MRI to enable in vivo specific characterization of atherosclerotic plaques is increasing. In this study the intrinsic ability of three differently sized gadolinium-based contrast agents to permeate different mouse plaque phenotypes was evaluated with MRI. A tapered cast was implanted around the right carotid artery of apoE-/- mice to induce two different plaque phenotypes: a thin cap fibroatheroma (TCFA) and a non-TCFA lesion. Both plaques were allowed to develop over 6 and 9 weeks, leading to an intermediate and advanced lesion, respectively. Signal enhancement in the carotid artery wall, following intravenous injection of Gd-HP-DO3A as well as paramagnetic micelles and liposomes was evaluated. In vivo T1-weighted MRI plaque enhancement characteristics were complemented by fluorescence microscopy and correlated to lesion phenotype. The two smallest contrast agents, i.e. Gd-HP-DO3A and micelles, were found to enhance contrast in T1-weighted MR images of all investigated plaque phenotypes. Maximum contrast enhancement ranged between 53 and 70% at 6¿min after injection of Gd-HP-DO3A with highest enhancement and longest retention in the non-TCFA lesion. Twenty-four hours after injection of micelles maximum contrast enhancement ranged between 24 and 35% in all plaque phenotypes. Administration of the larger liposomes did not cause significant contrast enhancement in the atherosclerotic plaques. Confocal fluorescence microscopy confirmed the MRI-based differences in plaque permeation between micelles and liposomes. Plaque permeation of contrast agents was strongly dependent on size. Our results implicate that, when equipped with targeting ligands, liposomes are most suitable for the imaging of plaque-associated endothelial markers due to low background enhancement, whereas micelles, which accumulate extravascularly on a long timescale, are suited for imaging of less abundant markers inside plaques. Low molecular weight compounds may be employed for target-specific imaging of highly abundant extravascular plaque-associated target

Deep tissue injury : how deep is our understanding?

No abstract

Visualizing the 3D collagen structure of human atherosclerotic plaques using Diffusion Tensor Imaging

Introduction Ischemic strokes and heart attacks are mainly caused by rupture of the fibrous cap of an atherosclerotic plaque. Reliable prediction of the fibrous cap rupture is, therefore, crucial to prevent these potentially lethal cardiovascular events. Since cap rupture occurs when the stresses in the cap exceed the strength of the cap, biomechanical modeling may help to improve cap rupture prediction. Biomechanical models depend strongly on the material parameters used as input. Previous studies focused on the anisotropic mechanical behaviour of atherosclerotic plaques and produced stiffness values for the collagen fibers in plaques [1]. However, for a more complete characterization knowledge of the global 3D collagen architecture in atherosclerotic plaques is required. Therefore, for the first time diffusion tensor imaging (DTI) was used to investigate the 3D collagen structure of human atherosclerotic plaques. Methods Until now five human carotid atherosclerotic plaques were obtained from endarterectomy patients and embedded in 4 % type VII agarose. The samples were placed in a 9.4 T horizontal-bore MRI scanner to conduct DTI. DTI enabled the tracking of the fiber directions and visualisation of the collagen fibers [2]. Results The consistent results of five different plaques suggest that collagen fibers are deposited in a new layer in a different direction during the development of atherosclerosis (see figure for one representative result). Two distinct layers of collagen fibers were found; an outer layer, where the collagen is aligned in the circumferential direction (14.5°±28.0°), similar to healthy arteries [2], and an inner layer where the collagen follows a longitudinal direction (77.4°±22.4°). Conclusions DTI allowed the visualization of the global 3D collagen architecture of atherosclerotic plaques. The inner collagen layer showed a surprising result and implies a change of strain distribution in the artery during the later stage of atherosclerosis, possibly due to the thickening and stiffening of the diseased intimal tissue. These data, combined with collagen stiffness data found in previous studies [1], will be used as input for biomechanical models including the anisotropic mechanical behaviour of plaque tissue. Models using general over-simplified assumptions like isotropic behaviour can be replaced by models including the anisotopic behavior and thereby improve the stress analysis of plaques. Improved models might help in the diagnosis and treatment of plaque rupture preventing heart attacks and ischemic strokes. References [1] Chai C-K, Akyildiz AC, Speelman L, Gijsen FJH, Oomens CWJ, Sambeek MRHM, van der Lugt A, Baaijens FTP, Anisotropic mechanical behaviour of carotid atherosclerotic plaques at large strain, The 8th international symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, 2013. [2] Ghazanfari S, Driessen-Mol A, Strijkers GJ, Kanters FMW, Baaijens FPT, Bouten CVC, A comparative analysis of the collagen architecture in the carotid artery: Second harmonic generation versus diffusion tensor imaging, Biochemical and Biophysical Research Communications, 426(1): 54-58, 2012