Atherosclerotic aortic component quantification by noninvasive magnetic resonance imaging: An in vivo study in rabbits

OBJECTIVES We sought to demonstrate the ability that noninvasive in vivo ma gnetic resonance imaging (MRI) has to quantify the different components wit hin atherosclerotic plaque. BACKGROUND Atherosclerotic plaque composition plays a critical role in both lesion stability and subsequent thrombogenicity. Noninvasive MRI is a prom ising tool for the characterization of plaque composition. METHODS Thoracic and abdominal aortic atherosclerotic lesions were induced in rabbits (n = 5). Nine months later, MRI was performed in a 1.5T system. Fast spin-echo sequences (proton density-weighted and T2-weighted [T2W] ima ges) were obtained (in-plane resolution: 350 x 350 microns, slice thickness : 3 mm). Magnetic resonance images were correlated with matched histopathol ogical sections (n = 108). RESULTS A significant correlation (p < 0.001) was observed for mean wall th ickness and vessel wall area between MRI and histopathology (r = 0.87 and r = 0.85, respectively). The correlation was also present un subanalysis of the thoracic and upper part of the abdominal aorta, susceptible to respirat ory mot-ion artifacts. There was a significant correlation for plaque compo sition (p < 0.05) between MRI and histopathology for the analysis of lipidi c (low signal on T2W, r = 0.81) and fibrous (high signal on T2W, r = 0.86) areas with Oil Red O staining. Ta-weighted images showed greater contrast t han proton density-weighted between these different components of the plaqu es as assessed by signal intensity ratio analysis with the mean difference in signal ratios of 0.47 (S.E. 0.012, adjusted for clustering of observatio ns within lesions) being significantly different from 0 (t(1) = 39.1, p = 0 .016). CONCLUSIONS In vivo noninvasive high resolution MRI accurately quantifies f ibrotic and lipidic components of atherosclerosis in this model. This may p ermit the serial analysis of therapeutic strategies on atherosclerotic plaq ue stabilization. (J Am Coll Cardiol 2001;37:1149-54) O 2001 by the America n College of Cardiology.