Echogenicity of B-mode sonographic images of the carotid artery - Work in progress

Objective. The echogenicity of the carotid atheromatous plaque estimated from B-mode sonographic images may be related to plaque content and has been analyzed with a number of techniques. The purpose of this study was to compare plaque with surrounding muscle tissue echogenicity and to validate the use of first-order mathematical descriptors as determinants of tissue echogenicity. Methods. We estimated echogenicity descriptors for regions in the following 3 distinct areas of a typical B-mode sonographic image of a diseased carotid artery: plaque, blood, and sternocleidomastoid muscle. Two-dimensional B-mode sonographic images from 19 symptomatic and asymptomatic plaques (17 subjects) were interrogated, in which the following estimators were calculated: minimal, maximal, mean, and median gray levels, SD of gray levels, coefficient of variation, and gray level skewness, kurtosis, entropy, and energy. Plaque echogenicity was estimated at systole and diastole for studying the effect of the phase of the cardiac cycle. To assess the effect of different fascial tissue-muscle fiber composition on the first-order mathematical descriptors, we estimated echogenicity at 3 different sites within the muscle tissue. Results. Compared with the echogenicity of surrounding muscle tissue, plaque echogenicity was characterized by (1) significantly lower (Student t test, P < .05) gray level mean, median, SD, and entropy; (2) significantly higher (Student t test, P < .05) coefficient of variation, gray level skewness, and kurtosis; and (3) similar minimal and maximal gray levels and gray level energy. The phase of the cardiac cycle, systole or diastole, did not affect the estimation of plaque echogenicity. Echogenicity was found to vary within the muscle tissue. The coefficient of variation was significantly higher in the asymptomatic plaques in the small group that was investigated. Conclusions. First-order statistical descriptors may be used to characterize atheromatous plaques and the surrounding muscle tissue.