• Non-invasive vascular elastography (NIVE) provides additional information in vascular ultrasound • Ultrasound NIVE is feasible in patients with significant carotid stenosis • Ultrasound NIVE detects a lipid core with high sensitivity and moderate specificity • Studies on plaque progression with NIVE are required to identify vulnerable plaques.

No abstract

Non-invasive vascular ultrasound elastography (NIVE) was recently introduced to characterize mechanical properties of carotid arteries for stroke prevention. Using the Lagrangian speckle model estimator (LSME), the four components of the 2D deformation matrix (delta), which are the axial strain (delta(yy)) and shear (delta(yx)) and the lateral strain (delta(xx)) and shear (delta(xy)), can be computed. This paper overviews four different implementations of the LSME and addresses their reliability. These implementations include two unconstrained (L&M and L&M+) and one constrained (ITER(c)) iterative algorithms, and one optical flow-based (OF-based) algorithm. The theoretical frameworks were supported by biomechanical simulations of a pathology-free vessel wall and by one single layer vessel-mimicking phantom study. Regarding simulations, the four LSME implementations provided similar biases on axial motion parameters, except the L&M that outperformed other methods with a minimum strain bias of -3%. LSME axial motion estimates showed good consistence with theory, namely the OF-based algorithm that in a specific instance estimated delta(yy) with no relative error on the standard deviation. With regards to lateral motion parameters, ITER(c) exhibited a minimum strain bias of -8.5% when ultrasound beam and motion mostly run parallel, whereas L&M performs strain and shear estimates with less than 23% bias independently of orientations. The in vitro vessel phantom data showed LSME delta(yy) and delta(yx) maps that were qualitatively equivalent to theory, and noisy delta(xx) and delta(xy) elastograms. In summary, the authors propose to promote the OF-based LSME as an optimal choice for further applications of NIVE, because of its reliability to compute both axial strain and shear motion parameters and because it outperformed the other implementations by a factor of 30 or more in terms of processing time.

Angle-dependence may be an important factor to consider in avoiding potentially distort clinical diagnoses. Results, reported in this article, suggest that the LSME-based compensative model might be considered as a very interesting and promising clinical tool for NIVE applications.

Carotid plaque rupture leading to stroke involves alteration of arterial wall mechanical properties. This paper addresses reproducibility and potential clinical impact of non-invasive vascular elastography. Fifteen symptomatic and 15 asymptomatic patients with greater than 50% stenoses of their internal carotids, and 15 control subjects were scanned independently by two radiologists. Radio-frequency cine-loops were acquired on left and right common and proximal internal carotids. For control subjects, homogeneous strains with successive compression and dilatation of the vascular wall from systole to diastole and few shear patterns were observed. The axial strain did not differ between recording sites, sides and radiologists (ANOVA, p > 0.19). For patients, heterogeneous axial strain patterns with both compression and dilatation of tissues within plaques were noted along with shear concentrations at interfaces of tissue structures. Despite similar blood pressures, larger mean instantaneous axial strains were measured in symptomatic (1.5 ± 0.6%) versus asymptomatic (1.2 ± 0.5%) patients in systole for common carotids (t-test, p < 0.02). To conclude, reproducible results were obtained for control subjects and in patients, larger axial strains in common carotids may be associated with plaque rupture. This new imaging method may become a unique approach to characterize vulnerable plaques for stroke prevention.