3.1 Strain Discontinuities in Carotid Atherosclerotic Plaques - A Novel Marker for Plaque Vulnerability?

Abstract

Objective

Rupture of atherosclerotic plaques is ultimately a biomechanical event. We aim to develop and validate a novel method using ultrasound radiofrequency (RF) measurements to determine intraplaque inhomogeneities in the strain distribution with a high axial resolution which may identify rupture-prone plaques.

Methods

Ultrasound examinations were performed on CCAs and ICAs of 17 patients with recent stroke/TIA and 5 asymptomatic patients (39 CCAs and ICAs). Strain distribution was computed from RF data with a depth resolution <0.5 mm. In the plaque-free CCA, radial wall strain was compared with distension for validation. Two observers analyzed the data. In the ICAs, strain inhomogeneities in the plaque were studied.

Results

Within the CCA wall, the strain (observer 1: −7.4 ± 2.7%, observer 2: −6.4 ± 2.6%) had good intra-subject precision (1.6%), accuracy (correlation with relative distension, observer 1: r = 0.69; p < 0.0001, observer 2: r = 0.68; p < 0.0001) and intra-observer variability (ICC of 0.681). In the ICA, strain inhomogeneities demarcated in 58% of cases the plaque-adventitia boundary. The percentage of ICAs with >1 strain inhomogeneities was increasing with the degree of stenosis (p = 0.03, 95%-CI). Strain inhomogeneities were more frequent in ICAs at the symptomatic side of stroke/TIA (odd’s-ratio = 4.7; p = 0.07). Strain in the deviating strain regions was higher at the symptomatic compared to the asymptomatic side (p = 0.02). Conclusion: The proposed method to assess local radial strain distribution proved to be accurate and precise. In ICA, areas with high strain inhomogeneities were more frequent in symptomatic plaques vs asymptomatic plaques. These strain inhomogeneities could be a promising novel marker for plaque vulnerability.

Crude B-mode (echo, left panels) and corresponding strain distribution in the ICA (right panels); blood flow direction is from right to left Note that in some cases the strain distribution is rather homogeneous (A), whereas in other cases a more heterogeneous distribution of strain is observed (B-D). Narrow but elongated regions with highly deviating strain (indicated by the white arrows) are often found near the boundary between the plaque and the supporting adventitia layer (B and D ) and can appear either as diastolic-to-syslolic wall compression (B) or as wall tension (C and D).