Technology – Intravascular Ultrasound

Intravascular Ultrasound

Sunny Kasoji

Cardiovascular disease is the leading cause of death in the world, causing more deaths that both stroke and cancer. Atherosclerosis is the build-up of fatty deposits within the lumen of arteries and is responsible for the majority of cardiovascular related deaths. Identifying and assessing plaques that are vulnerable to rupture is critical for mitigating cardiovascular events such as embolisms, stroke, or myocardial infarctions. One of the causes of plaque vulnerability is the invasion of vasa vasorum. Vasa vasorum are tiny capillaries that feed larger arteries and in a diseased state, can invade regions of plaque build-up, reducing the structural integrity of the plaque. Intravascular ultrasound (IVUS) is used for guiding certain interventional procedures or for imaging; however it is challenging to visualize vasa vasorum flow without a contrast agent. Conventional contrast enhanced IVUS has been tried however it lacks the resolution and sensitivity for detecting vasa vasorum. Recently, Acoustic Angiography, a dual-frequency contrast enhanced ultrasound imaging modality has demonstrated the ability to imaging microvasculature with remarkable resolutions.

In collaboration with Xiaoning Jiang’s Lab at NCSU, we are developing a single element dual-frequency transducer for IVUS imaging. Due to the small form factor required for IVUS, there are inherent technical challenges in adapting acoustic angiography using small scale transducers. To date we have demonstrated the ability to detect micro-scale vessels through an ex-vivo porcine artery. Our next goal is to perform in-vivo large animal imaging as a proof-of-concept for clinical translation.

Figure 1. Example in-vivo images. Photograph taken of the chorioallantoic membrane at 14 days showing microvasculature. The IVUS transducer was positioned relative to the vessels of interest (arrows) where a 4 mm pullback was performed.

Cardiovascular disease is the leading cause of death worldwide, surpassing both stroke and cancer related mortality with 17.5 million deaths in 2014 alone. Atherosclerosis is the build-up of fatty deposits within arteries and is responsible for the majority of cardiovascular related deaths. Over the past decade, research in atherosclerosis has identified that a key limitation in the appropriate management of the disease is detecting and identifying dangerous fatty plaque build-ups before they dislodge and cause major cardiovascular events, such as embolisms, stroke, or myocardial infarctions. It has been noted that plaques vulnerable to rupture have several key features that may be used to distinguish them from asymptomatic plaques. One key identifier of a dangerous plaque is the presence of blood flow within the plaque itself since this is an indicator of growth and instability of the plaque. Recently, a superharmonic imaging method known as “acoustic angiography” has been shown to resolve microvasculature with unprecedented quality and could be a possible method of detecting blood vessel infiltration within these plaques.