Evaluation of neovessels in atherosclerotic plaques of rabbits using an albumin-binding intravascular contrast agent and MRI

Purpose: To test whether B-22956/1, a novel intravascular contrast agent with a high affinity to serum albumin (Bracco, Imaging SpA.), allowed quantifying neovessel and macrophage density in atherosclerotic plaques of rabbits using MRI. Materials and Methods: A T1-weighted MRI of the aorta was acquired in 10 rabbits (7 atherosclerotic and 3 control rabbits) before and up to 2 h after intravenous injection of 100 mu mol/kg of Gd-DTPA or 75 mu mol/kg of B-22956/1. Plaque enhancement was measured at different time points. Immunohistochemistry was performed using anti-CD 31 antibodies and anti-RAM 11 antibodies to correlate to neovessel and macrophage density, respectively. Results: MRI showed a significant plaque enhancement 2 h after B-22956/1 versus Gd-DTPA in the atherosclerotic group (39.75% versus 9.5%; P < 0.0001. Early atherosclerotic plaques (n = 146) enhancement positively correlates with neovessel density on corresponding histological sections (r = 0.42; P < 0.01). Enhancement of atherosclerotic plaques 2 h after injection of B-22956/1 correlated with macrophage density (r = 0.71; P < 0.01). Conclusion: Enhancement of atherosclerotic plaques with MRI correlated with neovessel density at early time points after the injection of B-22956/1 and with macrophage density, at later time points. Hence, B-22956/1-enhanced MRI represents a promising imaging technique for the identification of "high-risk" plaques.