Dual-frequency intravascular ultrasound imaging of microbubble contrast agents: Ex vivo and in vivo demonstration

Development of atherosclerotic plaques and related cardiac events are correlated with increased development of vasa vasorum, however, no currently-available diagnostic imaging method has been demonstrated effective at identifying vulnerable plaques. We present a new intravascular ultrasound (IVUS) imaging method using a dual-frequency transducer to visualize contrast flow in microvessels with high specificity. This method uses a specialized transducer capable of exciting contrast agents at a low frequency (5.5 MHz) and receiving superharmonic echoes at a much higher frequency (37 MHz). This dual-frequency transducer was used to image a cellulose micro-tube external to an ex vivo porcine artery and also using the chorioallantoic membrane of a developing chicken embryo. Using dual-frequency contrast-specific imaging, we were able to resolve vessels of a similar size to those found in vulnerable atherosclerotic plaques with clinically-relevant attenuation. The results of this study suggest contrast-specific intravascular ultrasound imaging for the detection of vulnerable plaques in atherosclerosis may provide additional diagnostic information.