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ABSTRACT: Hemodynamics factors and biomechanical forces play key roles in atherogenesis, plaque development and final rupture. In this paper, we investigated the flow field and stress field for different degrees of stenoses under physiological conditions. Disease is modelled as axisymmetric cosine shape stenoses with varying diameter reductions of 30%, 50% and 70%, respectively. A simulation model which incorporates fluid-structure interaction, a turbulence model and realistic boundary conditions has been developed. The results show that wall motion is constrained at the throat by 60% for the 30% stenosis and 85% for the 50% stenosis; while for the 70% stenosis, wall motion at the throat is negligible through the whole cycle. Peak velocity at the throat varies from 1.47 m/s in the 30% stenosis to 3.2m/s in the 70% stenosis against a value of 0.78 m/s in healthy arteries. Peak wall shear stress values greater than 100 Pa were found for > or =50% stenoses, which in vivo could lead to endothelial stripping. Maximum circumferential stress was found at the shoulders of plaques. The results from this investigation suggest that severe stenoses inhibit wall motion, resulting in higher blood velocities and higher peak wall shear stress, and localization of hoop stress. These factors may contribute to further development and rupture of plaques.
Journal of Biomechanics 01/2007; 40(16):3715-24. · 2.43 Impact Factor
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ABSTRACT: A method for segmentation of arteries in ultrasound B-mode images using a modified balloon model is presented. The external force which pulls the contour to the arterial boundary is the combination of the gradient and the second order derivative of the image. For 3D segmentation the contour of the first slice is found, and this is used as the initial position for the next slice. As the initial position of the contour may be outside the artery, the pressure term is decided by comparing the feature of texture inside and outside of the contour, allowing the contour to expand or shrink. The model has been tested on 55 images from carotid arteries. The 'gold standard' boundary drawn by a radiologist and the segmented boundary showed an average difference of 0.40±0.30mm. 3D data was obtained using an anatomically correct carotid bifurcation flow phantom and gridded ready for CFD.
Biomedical Imaging: Nano to Macro, 2004. IEEE International Symposium on; 05/2004
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ABSTRACT: The effect of fiber loss, amplification, and sliding-frequency filters on the evolution of optical pulses in nonlinear optical fibers is considered, this evolution being governed by a perturbed nonlinear Schrödinger (NLS) equation. Approximate ordinary differential equations (ODE's) governing the pulse evolution are obtained using conservation and moment equations for the perturbed NLS equation together with a trial function incorporating a solitonlike pulse with independently varying amplitude and width. In addition, the trial function incorporates the interaction between the pulse and the dispersive radiation shed as the pulse evolves. This interaction must be included in order to obtain approximate ODE's whose solutions are in good agreement with full numerical solutions of the governing perturbed NLS equation. The solutions of the approximate ODE's are compared with full numerical solutions of the perturbed NLS equation and very good agreement is found.
Physical Review E 06/2001; 63(5 Pt 2):056604. · 2.26 Impact Factor
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