Recent studies have demonstrated that atherosclerotic plaque surface morphology in the carotid arterial system represents an independent risk factor for embolus formation and subsequent cerebrovascular occlusive events. The primary aim of the current retrospective study is to enhance the clinical utility of this key finding by developing and evaluating objective, quantitative methods for characterizing plaque surface irregularity from Gadolinium-enhanced magnetic resonance angiography (MRA) studies. Nine metrics were analyzed for correlation with percent stenosis in 78 arteries from 43 patients with carotid artery disease. Most of the metrics comprised measurements obtained from a surface model of the stenotic lesion derived from the MRA via the Marching Cubes algorithm with application of the Isosurface Deformable Model. Percent stenosis was determined through real-time volume rendering of 3D MIP MRA studies in Vitrea2. Six of the analyzed metrics revealed significant correlation to percent stenosis (p<0.01). Reproducibility of all metrics was evaluated in a set of 14 randomly selected arteries from 13 patients by way of a single-trial, two-observer analysis. Six of the nine metrics demonstrated significant inter-observer reproducibility by way of single-factor ANOVA analysis (p<0.02). Collectively, the findings reported herein demonstrate an objective and reliable method for quantifying carotid plaque surface irregularity from standard MRA techniques with possible future clinical application in refining risk of ischemic cerebrovascular events and associated need for prophylactic intervention.
Bond inspection is one of the most critical NDE tasks addressing the aging aircraft problem. This paper is aimed at reviewing and furthering the use of ultrasonic guided waves for the inspection of bonded components, particularly lap joints between thin plates such as those found in aircraft skins. The transfer matrix theory of wave propagation in multilayered components is used to predict the sensitivity of the wave dispersion behavior to the bond state. The experimental study includes the use of non- contact air-coupled transducers to excite and detect guided waves in a pitch-catch arrangement. It is shown that by monitoring the ultrasound amplitude leaking through the bondline it is possible to detect disbonds as well as low- strength bonds. A photoelastic study confirms this result. It is reaffirmed that those modes with predominant shear- type deformations at the bondline are the most sensitive to the bond state.
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