Using ChromaFlo intra-vascular ultrasound (IVUS) to analyze adventitial vasa vasorum distribution: Considerations and recommendations

The adventitia and outer media of large blood vessels are supplied with nutrients by microscopic blood vessels called vasa vasorum. While vasa vasorum have been implicated in a number of diseases including atherosclerosis, understanding their functional anatomy and specific role in these diseases has been limited by the small size of the vasa vasorum and difficulty in imaging them. Micro-CT and histological methods have been used in ex-vivo animal studies of the vasa vasorum, but these techniques do not extend well to in-vivo investigation. There is very little in-vivo human data available. Intra-vascular ultrasound can acquire high-resolution anatomic images of coronary vessels. ChromaFlo IVUS has been used to identify blood flow in vessel lumens and has exciting prospect for in-vivo studies of vasa vasorum functional anatomy. In this study, ChromaFlo IVUS images of the human mid-left anterior descending coronary artery (LAD) were segmented to analyze the distribution of adventitial vasa vasorum proximal to intimal plaque. Previous studies in animals suggest that formation of intimal plaque is accompanied by increased density of adventitial vasa vasorum. The data collected with ChromaFlo ultrasound is inconsistent with the current literature. While IVUS has the fidelity to acquire high-resolution US images of the coronary arteries, ChromaFlo lacks the necessary resolving power to differentiate the vasa vasorum. Further study of IVUS and other imaging methods on a larger cohort may provide the basis for future in-vivo analysis of coronary disease.