Acoustic inhomogeneity of carotid arterial plaques determined by GHz frequency range acoustic microscopy.

Characterization of the structure and composition of carotid arterial plaques is important to predict the risk of embolic and thrombotic events. In clinical echography, echolucent lesions seem to be more associated with stroke than echogenic lesions, and a low grey-scale median is associated with a fivefold increase in the incidence of silent infarcts. In the present study, five fixed human carotid atherosclerotic lesions were observed by GHz-range scanning acoustic microscopy (SAM). The atherosclerotic lesions were characterized by either thickened fibrosis with dense collagen fibers or lipid accumulation with sparse collagen network by optical microscopy. SAM revealed that the fibrosis was classified into type I and III collagen by attenuation of ultrasound (US) and that the sound field of lipid accumulation lesions became inhomogeneous. The results would provide the scientific basis for the images of vulnerable plaques being produced in diagnostic US.