Characterization of coronary atherosclerotic plaque using multicontrast MRI acquired under simulated in vivo conditions

Abstract

Purpose:To compare coronary atherosclerotic plaque characterization using multicontrast MRI on: 1) freshly excised vessels under simulated in vivo conditions, and 2) preserved vessels. Materials and Methods:T1-weighted (T1W), T2-weighted (T2W), proton density-weighted (PDW), and diffusionweighted (DW) MR images were acquired on 13 freshly excised human coronary arteries from explanted hearts. Vessels were imaged in an MR-compatible tissue culture chamber using a 4.7 Tesla small-bore MR scanner. Eight vessels were then preserved in buffered formalin and rescanned following the same imaging protocol. A threedimensional spatially penalized fuzzy C-means (3D-SPFCM) technique was applied to classify different plaque constituents. The classification results from vessels under "fresh" and "preserved" conditions were compared with corresponding histological sections. Results:For most plaque constituents, the plaque characterization results show no significant difference between fresh and preserved scans, and little difference between scans and the histological reference standard. In the case of thrombus, apparent signal changes between fresh and preserved images were identified. Overall, MR scans conducted under preserved conditions provided a 1.8% to 17.5% greater signal-to-noise ratio (SNR) than those conducted in the fresh stage. Conclusion:Preservation of coronary vessels did not alter the contrast between plaque tissues on multicontrast MRI, and did not significantly change the results of plaque constituent characterization. CARDIOVASCULAR DISEASE (CVD) is a multifaceted disease that includes coronary artery disease, stroke, and congestive heart failure. It has a variety of manifestations, but the majority of CVD cases can be related to atherosclerosis. Accurate identification of "vulnerable" atherosclerotic plaques that are prone to rupture is important for the management and treatment of the clinical manifestations of atherosclerosis. The positive remodeling feature of human atherosclerotic plaques (1,2) implies that vulnerable plaques are not necessarily associated with a reduction in lumen size. Therefore, characterization and quantification of the specific constituents and morphology of the atherosclerotic plaque itself become important factors in atherosclerosis assessment. Magnetic resonance imaging (MRI) is well suited for examining plaque constituents because of its excellent soft-tissue contrast and abundant contrast mechanisms.Multicontrast MRI is a technique that combines several MR scans with different contrast mechanisms. It has the potential to identify major plaque constituents and their structures in human atherosclerotic lesions (3). Currently, most in vivo applications of multicontrast MRI focus on carotid plaque imaging (4 -6) because of the relatively large size of the vessel, minimal motion effects, and superficial location. Although several advances (7-11) have been achieved in in vivo coronary atherosclerosis imaging, technical difficulties still preclude the quantification of plaque constit...

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