Supplementary Material for: Intra-Plaque Vessels on Contrast-Enhanced Ultrasound Sonography Predict Carotid Plaque Histology

Background and Purpose: Although the echogenicity of carotid plaques on carotid enhanced ultrasound (CEUS) was reported to correlate with the historological density of intra-plaque neovessels, it is unclear whether the intra-plaque vessel size is associated with carotid plaque vulnerability. We evaluated the relationship of size of intra-plaque vessels on CEUS with carotid plaque histology. Methods: We prospectively registered patients with carotid stenosis who were hospitalized to receive carotid endarterectomy between 2012 and 2016. CEUS was performed by ultrasound specialists using a 7-MHz linear transducer (GE LOGIQ7; GE Healthcare, Milwaukee, WN, USA). Sonazoid® was used for conducting CEUS. The sizes of microbubbles inside the plaques were scored at 0, 1, 3, and 5 min after the injection of contrast agent, and were categorized according to our defined vascular score (Vas-S; 0: the effect of contrast was not recognized; 1: the microbubbles were visible, but so blurred and vague that their shape could not be recognized; 2: dot or string-like microbubbles with movement, localized in part or the whole site of the plaque). At histological examination, we simplified the modified American Heart Association classification and defined as an atherosclerotic category (Ath-cat; 1: unruptured plaque; 2: ruptured plaque; 3: healed plaque). We then assessed the correlation of Vas-S with Ath-cat, which describes the process of rupture and restoration of carotid plaques. Results: A total of 97 patients were included in this study. A higher Ath-cat was significantly associated with higher Vas-S at any time. Spearman signed-rank test indicated that Vas-S at 1 min was most strongly correlated with Ath-cat (ρ = 0.43, p = 0.001). Receiver operating curve analysis indicated that a Vas-S of 0 at 1 min was significantly associated with an unruptured plaque (area under curve [AUC] 0.72, p = 0.006), while a Vas-S of 2 at 1 min was significantly associated with a healed plaque (AUC 0.72, p = 0.001). Conclusion: Vas-S values of 0 and 2 at 1 min indicated unruptured and healed plaques respectively. Thus, a Vas-S of 1 at 1 min is an indicator of a ruptured plaque. The intra-plaque vessel size on CEUS was significantly associated with carotid plaque histology, and may predict the process of plaque rupture and restoration.