Introduction
In this prospective study, we tried to test the feasibility of contrast-enhanced ultrasonography (CEUS) for characterizing carotid plaque.

Methods
Patients were selected when presence of carotid plaque was confirmed in carotid Duplex sonographic examination and classified into symptomatic carotid stenosis (SCS) and asymptomatic carotid stenosis (aSCS). SCS was defined as carotid stenosis with focal neurological signs or amaurosis fugax in ipsilateral side within six months. For all subjects, standardized CEUS were performed for carotid plaque and contrast enhancement was evaluated quantitatively using time-intensity curve. Parameters included in analysis were time-to-arrival, time-to-peak, enhanced-intensity in plaque (difference from baseline-intensity to peak-intensity), and the ratio of enhanced intensity in the plaque to that in the carotid artery lumen.

Results
A total of 13 patients (15 carotid arteries, male 11, age 71.87 ± 8.64) with carotid plaque were included in this study. Grade of stenosis was higher in SCS (66.52 ± 5.44) than that of aSCS (55.07 ± 14.89) without statistical significance. Enhancement of plaque was observed in 11 arteries (73.3%) and all the arteries without enhancement were included in aSCS. In terms of time-to-arrival, time-to-peak, and enhanced-intensity in plaque, there was no significant difference between SCS and aSCS except a trend of delayed time-to-arrival in SCS (aSCS 9.22 ± 4.02 and SCS, 12.99 ± 2.02; Mann-Whitney test, p = 0.052). However, there was significant difference in the ratio of enhanced intensity in the plaque to that in the carotid artery lumen (aSCS 0.108 ± 0.13, SCS 0.32 ± 0.16; Mann-Whitney test, p = 0.020).

Conclusion
CEUS is feasible and valid in characterizing carotid plaque. Further studies are requested for standardization.