Variation of longitudinal strain along the arterial wall adjacent to the asymptomatic carotid plaque

The motion, and resulting strain, of the arterial wall nearby an atheromatous plaque is believed to be affected by the plaque and therefore may carry important information about disease status. Strain of the arterial wall in the longitudinal direction, i.e. along its length, has recently gained attention as determinant of cardiovascular risk. In this work, longitudinal strain (LS) was estimated along the wall proximal to asymptomatic carotid plaque, in an attempt to highlight the significance of arterial wall kinematics in atherosclerotic subjects without cerebrovascular events. Twenty five atheromatous carotid arteries of elderly male adults (59-81 y.o., 50-100% stenosis) were imaged in longitudinal sections, and videos of B-mode images were analysed using a previously developed method based on optical flow. The analysis consisted in the estimation of the longitudinal positions of three regions of interest (ROIs) on the posterior wall. LS was subsequently defined as the normalised difference of the longitudinal positions between two ROIs, and was assessed at two locations along the wall. A longitudinal strain index (LSI) was then calculated as the average of the amplitudes of the LS curves over 2-3 cardiac cycles. LSIs at location 1 (closer to the plaque) were significantly higher than at location 2 (4.74 +/- 1.66 vs. 2.54 +/- 1.08, p-value= 1.25E-06). This indicates that the wall closer to the plaque undergoes higher strain than the wall farther from it, which may be due to the effect of the presence and motion of the nearby lesion; an effect, which seems to be extended to the area around it. These findings show promise toward better understanding the complex mechanical phenomena taking place not only within the plaque but also in the neighbouring tissues

Ultrasound-image-based texture variability along the carotid artery wall in asymptomatic subjects with low and high stenosis degrees: unveiling morphological phenomena of the vulnerable tissue

Valid identification of the vulnerable asymptomatic carotid atherosclerosis remains a crucial clinical issue. In this study, texture differences were estimated along the atherosclerotic arterial wall, namely at the plaque, the wall adjacent to it and the plaque shoulder, i.e. the boundary between wall and plaque, in an attempt to reveal morphological phenomena, representative of the high stenosis (considered vulnerable) cases. A total of 25 arteries were interrogated, 11 with low (50-69%) and 14 with high (70-100%) degrees of stenosis. The two groups had similar ages. Texture features were estimated from B-mode ultrasound images, and included four second-order statistical parameters (contrast, correlation, energy and homogeneity), each calculated at four different image directions (0 degrees, 45 degrees, 90 degrees, 135 degrees), yielding a total of 16 features. Texture differences between (a) wall and plaque and (b) wall and plaque shoulder were quantified as the differences in texture feature values for each tissue area normalised by the texture feature value of the wall, which was considered as reference, as illustrated in the following equation: dTF(i) = (TFi,W - TFi,P/S)/TFi,W, where dTF(i) the estimated texture difference, TFi,W the texture of the wall, and TFi,P/S the texture of the plaque (P) or the shoulder (S). Significant differences in texture variability of wall vs. shoulder were observed between high and low stenosis cases for 3 features at diastole and 7 features at systole. No differences were observed for wall vs plaque, although wall texture was significantly different than plaque texture, in absolute values. These findings suggest that texture variability along the atherosclerotic wall, which is indicative of tissue discontinuities, and proneness to rupture, can be quantitatively described with texture indices and reveal valuable morphological phenomena of the vulnerable tissue. (C) 2015 The Authors. Published by Elsevier B.V