Contrast-enhanced ultrasound imaging detects intraplaque neovascularization in an experimental model of atherosclerosis

Objectives The aims of this study were to investigate the feasibility of contrast-enhanced ultrasound (CEU) imaging for in vivo visualization of intraplaque neovascularization and to correlate the in vivo observations with histological assessment of neovessel density and plaque composition in an experimental animal model of advanced atherosclerosis. Background Recent evidence has linked plaque angiogenesis with enhanced atherosclerotic plaque progression and vulnerability. Increased neovascularization has been detected in ruptured human lesions and is associated with clinical manifestations of plaque rupture. Methods Advanced aortic atherosclerosis was induced in New Zealand white rabbits (n = 21; high cholesterolrich diet/double-balloon aortic denudation). Animals underwent standard and CEU imaging at the end of the atherosclerosis induction period. Six age-matched animals served as control subjects. Within 24 h, animals were euthanized and aortas processed for histopathological evaluation of plaque composition and neovascularization. Imaged plaques were classified as contrast enhanced (CE) positive or CE negative, according to their contrast enhancement on CEU imaging. The lesions were also classified as class III (predominantly echogenic) or class II (predominantly echolucent), according to their echogenicity on non-CEU images. Results No contrast enhancement was observed in control animals. In atherosclerotic animals, class III lesions showed an increased contrast enhancement compared with class II lesions and CE-positive lesions showed greater neovascularization than CE-negative plaques. Macrophage density, but not smooth muscle cell density, was significantly higher in CE-positive than CE-negative lesions. As expected, class III lesions showed increased macrophage density compared with class II plaques. Intraplaque neovessel density at histology was significantly higher in CE-positive than in CE-negative lesions. Class III plaques showed a significantly higher neovessel density compared with class II lesions. A strong correlation between intraplaque neovessels and contrast enhancement was found. Conclusions CEU imaging is a feasible noninvasive imaging modality to evaluate intraplaque neovascularization. A noninvasive imaging modality to assess lesion neovascularization could be of great importance to identify vascularized, "high-risk" lesions before rupture.