In vivo observation of blood echogenicity variation during a cardiac cycle on human carotid arteries

A cyclic variation of blood echogenicity from human iliac arteries in vivo was first observed using an intravascular 30 MHz ultrasound imaging device. Several studies have confirmed the temporal variation of the backscattered power during a flow cycle but they were all from in vitro experiments. In this paper, cyclic variation of echogenicity in vivo on human carotid arteries (7 males and 3 females) was observed from harmonic images of a GE LOGIQ 700 expert system with an M12L probe. Blood echogenicity increased at early systole, reaching a maximum at peak systole, and then decreased to be weak during diastole. Echogenicity during systole was about 40 to 60 % higher than that during diastole for all radial positions. The ratio of the maximum echogenicity during systole to the mean echogenicity during diastole was small at the center and near the vessel wall, and became large between them. The cyclic variation of blood echogenicity is thought to be due to erythrocyte aggregation enhancement by the combined effects of flow acceleration and shear rate during systole.