Carotid plaque and its effect on ultrasound carotid distension measurements

Abstract

Ultrasound is, at present, still the gold standard technique to assess atherosclerosis in superficial arteries such as the carotid artery (CA). However, vascular ultrasound applications are still 2D, while the CA has a 3D anatomy and atherosclerosis may further complicate the deformation of the artery. We studied the impact of the presence of a plaque on 2D ultrasonic measurements of vascular wall deformation. Three silicon rubber CA models were created from MRI-scans, one control and two models with a stiff (plexi glass) and soft (fat) plaque near the bifurcation. At four locations, ultrasound images were obtained with a noninvasive echotracking system (Vivid 7, GE Vingmed) while the model was subjected to pulsatile loading conditions. Relative distension was derived as ΔD/D = (Ds-Dd)/D d with D diameter, and "s" and "d" referring to systole and diastole. Three finite element models (Abaqus v6.7, Simulia) were constructed based on these geometries. A linear increase in pressure was imposed, and ΔD/D was calculated in a 2D cut-through plane at the same locations as in the experimental setup (?ultrasound measurement) to assess which aspects of carotid deformation are properly accounted for with ultrasound. Both numerical and experimental data show a decrease in relative distension with diameter. However, the experimental data did not capture all deformation effects of a plaque as proposed by the numerical data. Out-of-plane deformation (obtained from numerical data) was markedly different in the presence of a plaque. Moreover, distension measurements are very sensitive to the precise axial measuring position, especially close to the carotid bifurcation (with or without a plaque). Numerical data show a definite effect of a plaque on carotid wall deformation whereas experimental data measured with ultrasound not always do. This finding might have implications for current clinical vascular research. © 2009 Springer Berlin Heidelberg.