High‐resolution, multicontrast three‐dimensional‐MRI characterizes atherosclerotic plaque composition in ApoE–/– mice ex vivo

Abstract

Purpose To systematically investigate intrinsic MR contrast mechanisms that would facilitate plaque characterization and quantification in the aortic root and brachiocephalic artery of ApoE^–/– mice ex vivo. Materials and Methods To establish unambiguous MR parameters for routinely analyzing atherosclerotic plaque ex vivo at 11.7 T, relaxation times of plaque components were quantitatively assessed. Magnetization transfer and lipid‐proton three‐dimensional MR imaging was investigated for visualization of collagen‐ and lipid‐rich plaque regions, respectively. A three‐dimensional multiecho sequence with a spatial resolution of 47 × 47 × 63 μm was implemented providing a variable degree of T₂‐weighting. Results Relaxation time measurements showed clear tissue heterogeneity between atherosclerotic plaque components in the T₂‐values, but similar T₁‐values at 11.7 T (T₁/T₂ mean ± SD; cellular plaque component: 1.2 ± 0.3 seconds/26.3 ± 0.4 msec; fibrofatty plaque component: 1.1 ± 0.2 seconds/13.7 ± 2.0 msec). The three‐dimensional multiecho sequence allowed the calculation of the intrinsic proton density and T₂‐maps. The sum of the multiecho data provided strong T₂‐weighting that facilitated quantification of various components of atherosclerotic plaque in the mouse aortic root and correlated well with histology (P < 0.0001). Conclusion High‐resolution MRI allows for accurate classification and quantification of atherosclerotic plaque components in the aortic root of mice. J. Magn. Reson. Imaging 2004;20:981–989.