A Framework for Local Mechanical Characterization of Atherosclerotic Plaques: Combination of Ultrasound Displacement Imaging and Inverse Finite Element Analysis

Biomechanical models have the potential to predict plaque rupture. For reliable models, correct material properties of plaque components are a prerequisite. This study presents a new technique, where high resolution ultrasound displacement imaging and inverse finite element (FE) modeling is combined, to estimate material properties of plaque components. Iliac arteries with plaques were excised from 6 atherosclerotic pigs and subjected to an inflation test with pressures ranging from 10 to 120 mmHg. The arteries were imaged with high frequ

High shear stress relates to intraplaque haemorrhage in asymptomatic carotid plaques

Background and aims Carotid artery plaques with vulnerable plaque components are related to a higher risk of cerebrovascular accidents. It is unknown which factors drive vulnerable plaque development. Shear stress, the frictional force of blood at the vessel wall, is known to influence plaque formation. We evaluated the association between shear stress and plaque components (intraplaque haemorrhage (IPH), lipid rich necrotic core (LRNC) and/or calcifications) in relatively small carotid artery plaques in asymptomatic persons. Methods Participants (n = 74) from the population-based

How non-native English-speaking staff are evaluated in linguistically diverse organizations: A sociolinguistic perspective

The aim of this paper is to examine the effects of evaluations of non-native speaking staff?s spoken English in international business settings. We adopt a sociolinguistic perspective on power and inequalities in linguistically diverse organizations in an Anglophone environment. The interpretive qualitative study draws on 54 interviews with non-native English-speaking staff in 19 UK business schools. We analyze, along the dimensions of status, solidarity and dynamism, the ways in which non-native speakers, on the basis of their spoken English, are evaluated by themselves and by listeners. We show how such evaluations refer to issues beyond the speaker?s linguistic fluency, and have consequences for her or his actions. The study contributes to the literature on language and power in international business through offering fine-grained insights into and elucidating how the interconnected evaluative processes impact the formation and perpetuation of organizational power relations and inequalities. It also puts forward implications for managing the officially monolingual, yet linguistically diverse organizations

Biomechanical analysis for abdominal aortic aneurysm risk stratification

No abstract

Wall stress analysis of abdominal aortic aneurysms using 3D ultrasound

\u3cp\u3eWall stress analysis of abdominal aortic aneurysms is a novel tool that has proven high potential to improve risk stratification of abdominal aortic aneurysms (AAAs). Wall stress analysis is based on computed tomography (CT) and magnetic resonance imaging, however, 3D ultrasound (US) has not been used yet. In this study, the feasibility of 3D US based wall stress analysis is investigated and compared to CT. Three-dimensional US and CT data were acquired in 15 patients (diameter 35 - 90 mm). US data were segmented manually and compared to automatically acquired CT geometries by calculating the similarity index (SI) and Hausdorff distance (HD). Wall stresses were simulated at p = 140 mmHg using a non-linear material model (Raghavan & Vorp). The SI of US vs CT was 0.75 - 0.91, with a median HD of 5 - 15 mm, with the higher values found at the proximal and distal sides of the AAA. Wall stresses were in accordance with literature and a good agreement was found between US and CTbased median stresses and inter-quartile stresses. Stress values of US were typically higher, the result of geometrical irregularities, caused by the manual segmentation of the US data. In future work, an automated segmentation approach is the essential point of improvement.\u3c/p\u3

Importance of initial stress for abdominal aortic aneurysm wall motion: Dynamic MRI validated finite element analysis

Currently the transverse diameter is the primary decision criterion to assess rupture risk in patients with an abdominal aortic aneurysm (AAA). To obtain a measure for more patient-specific risk assessment, aneurysm wall stress, calculated using finite element analysis (FEA), has been evaluated in literature. In many cases, initial stress, present in the AAA wall during image acquisition, is not taken into account. In the current study the effect of initial stress incorporation (ISI) is determined by directly comparing wall displacements extracted from FEA and dynamic MRI. Ten patients with an aneurysm diameter > 5.5 cm were scanned with cardiac triggered MRI. Semi-automatic segmentation of the AAA was performed on the diastolic phase. The segmented in-slice contours were propagated through the remaining cardiac phases using an active contour model as to track wall displacements on MRI. Consequently, FEA with and without ISI (no-ISI) was performed using the diastolic geometry with simultaneously measured intra-aneurysm pressure values as boundary condition. Contours extracted from FEA were compared with MRI contours at corresponding cardiac phases by distance and relative area differences. The wall displacements from FEA with ISI show significant better correspondence with wall motion from MRI data in comparison with the no-ISI FEA (deviation in wall displacement 1.7% vs. 12.4%; p <0.001). Based on these results it can be concluded that incorporation of initial stress significantly improves wall displacement accuracy of FEA and therefore it should be incorporated in future analyses. © 2009 Elsevier Ltd. All rights reserved

Initial stress and nonlinear material behavior in patient-specific AAA wall stress analysis

An abdominal aortic aneurysm (AAA) is a local dilation in the abdominal aorta of more than 50% of the original diameter and occurs in about 1 of 20 men over 65 years of age [1]. The largest threat for an AAA is rupture. Aortic repair is considered when the risk of rupture exceeds the risk of the surgical procedure. Currently, clinicians use the maximum AAA diameter as rupture risk estimator. A higher sensitivity and specificity was reached by computing the maximum AAA wall stress with finite element analysis, thus incorporating the total AAA geometry [2]