Percentage White: A New Feature for Ultrasound Classification of Plaque Echogenicity in Carotid Artery Atherosclerosis

Abstract 

Atherosclerotic stenotic and nonstenotic plaques of the carotid artery with low echogenicity have been shown to be associated with cardiovascular disease. The aim was to develop a new method for semiautomated ultrasound image analysis to classify nonstenotic carotid plaques, evaluate cases with multiple plaques and examine the association between a new image analysis feature of echogenicity and predictors of cardiovascular disease. The new image analysis feature, percentage white (PW), represents the fraction of bright structures inside a plaque and is integrated in an objective semiautomated method to evaluate echogenicity (SAMEE) in carotid plaques. PW was constructed to take into account overall echogenicity of the image as well as noise surrounding the plaque. Consecutive ultrasound examinations of carotid plaques from a population-based screening of 64-year-old women with varying risk for cardiovascular disease were selected for the present project; 92 far-wall and 47 near-wall plaques were used as a training dataset to develop the SAMEE algorithm with visual classification according to Gray-Weale as reference; 273 plaques were used to validate the method. All plaques were included in an analysis relating predictors of cardiovascular to average PW in all plaques, PW in the biggest plaque and to the plaque with lowest PW in each subject, respectively. In the training dataset the intermethodological variability between SAMEE and visual classification showed a κ of 0.78 and a sensitivity and specificity of 96% and 81%, respectively. In the validation set, SAMEE and visual classification showed a κ of 0.77, a sensitivity of 96% and a specificity of 80%. The reproducibility of PW was high, evidenced by r = 0.96 and CV = 9.85% at repeated examinations. Average PW values were associated with several predictors of cardiovascular risk: lipoprotein (a), HbA1c, blood glucose, apolipoproteinB/apolipoproteinA-I; and associated negatively with the levels of adiponectin and apolipoprotein A-I. In conclusion, PW integrated within a SAMEE is a new feature for assessment of echogenicity in carotid plaques and shows excellent reproducibility and agreement with visual assessment. (E-mail: ulrica.prahl@wlab.gu.se).

Key Words: Ultrasound, Atherosclerosis, Carotid artery, Plaque, Image interpretation, Computer-assisted, Classification