Quantitative assessment of carotid plaque surface irregularities and correlation to cerebrovascular symptoms

Abstract

Background: The purpose of this study was to determine whether surface irregularities measured from ultrasound images of carotid artery plaques and quantified using a novel method, correlate with the presence of ipsilateral hemispheric cerebrovascular symptoms.

Methods: A plaque surface irregularity index (SII) was measured in 47 carotid artery plaques (32 subjects, stenosis range 10% -95%, 49% symptomatic) using ultrasound image sequences spanning several cardiac cycles. The differences in the distribution of SII in plaques with ipsilateral hemispheric symptoms versus those without symptoms and the correlation between the SII of plaques and the degrees of stenosis of the corresponding arteries were assessed. Diagnostic performance of plaque SII was evaluated on its own and in combination with the degree of stenosis.

Results: The mean SII was significantly greater for plaques with ipsilateral hemispheric symptoms (1.89 radians/mm) than for asymptomatic plaques (1.67 radians/mm, p = 0.03). There was no statistically significant association between the SII and the degree of stenosis (p = 0.30). SII predicted the presence of cerebrovascular symptoms with an accuracy of 66% (sensitivity 65%, specificity 67%) on its own and with an accuracy of 83% (sensitivity 96%, specificity 71%) in combination with the degree of stenosis.

Conclusions: Quantitative assessment of carotid plaque surface irregularities using a novel SII parameter correlates with the presence ipsilateral hemispheric cerebrovascular symptoms and may increase diagnostic performance beyond that provided by the degree of stenosis.

Figure 1

Two plaques of markedly different surface irregularity indices: (a) a symptomatic plaque with an SII of 2.25 radians/mm; and (b) an asymptomatic plaque with an SII of 1.57 radians/mm. The plaque surface is the boundary between the plaque and the arterial lumen (where the pink and green dashed lines overlap). (a) is also a plaque qualitatively classified as having an irregular surface, while (b) is a plaque qualitatively classified as having a smooth surface.

Figure 2

Full-size ultrasound images corresponding to the close-up plaque views shown in Figure 1. (top row) the symptomatic plaque, (bottom row) the asymptomatic plaque.

Figure 3

Distribution of plaque SII (left), degrees of stenosis (DOS, middle) and the product of the two (right) in the symptomatic and asymptomatic plaque groups. Degrees of stenosis are given as degree of stenosis (%)/100% (i.e. 0.5 corresponds to 50%, etc.).

Figure 4

Scatter plot of the plaque surface irregularity index versus the degree of stenosis of the corresponding artery (left) and the plaque area (right), illustrating a lack of association between these parameters.

Figure 5

Distribution of plaque SII across the plaque groups qualitatively classified as having an irregular or smooth surface.

Figure 6

Comparison between ROC curves for plaque surface irregularity index (SII), the degree of stenosis (DOS) and their product (DOS × SII).