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

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Abstract
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 μmol/kg of Gd‐DTPA or 75 μmol/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. J. Magn. Reson. Imaging 2008;27:1406–1411.