Quantification of plaque neovascularization using contrast ultrasound: a histologic validation

Abstract

The density of vasa vasorum within atherosclerotic plaque correlates with histologic features of plaque vulnerability in post-mortem studies. Imaging methods to non-invasively detect vasa vasorum are limited. We hypothesized that contrast ultrasound (CUS) can quantify vasa vasorum during atherosclerosis progression. New Zealand white rabbits received a high-fat diet for 3 weeks, and bilateral femoral artery stenosis was induced by balloon injury. Contrast ultrasound femoral imaging was performed at baseline and 2, 4, and 6 weeks post injury to quantify adventitial videointensity. At each imaging time point 10 vessels were sectioned and stained with haematoxylin and eosin and von-Willebrand factor. Adventitial vasa vasorum density was quantified by counting the number of stained microvessels and their total cross-sectional area. Plaque size (per cent lumen area) progressed over time (P < 0.001), as did adventitial vasa vasorum density (P < 0.001). Plateau peak videointensity also progressed, demonstrating a strong linear correlation with histologic vasa vasorum density (P < 0.001). Receiver operating characteristic analysis indicated that a three-fold increase in median adventitial videointensity had a sensitivity of 100% and specificity of 88% for predicting abnormal neovascularization. We have histologically validated that CUS quantifies the development of adventitial vasa vasorum associated with atherosclerosis progression. This imaging technique has the potential for characterizing prognostically significant plaque features.