Discrimination of components in atherosclerotic plaques from human carotid endarterectomy specimens by magnetic resonance imaging ex vivo Joel Morrisett a,b, *, Wesley Vick c , Rakesh Sharma a , Gerald Lawrie d , Michael Reardon d , Edward Ezell e , Joseph Schwartz e , Glen Hunter f , David Gorenstein e a The Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA b Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030, USA c Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA d Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA e The Sealy Center for Structural Biology and Human Biological Chemistry and Genetics, University of Texas Medical Branch-Galveston, TX 77555, USA f Department of Surgery, University of Texas Medical Branch, Galveston, TX 77555, USA Received 28 August 2002; accepted 27 October 2002 Abstract Specific MRI techniques have been used to determine the dimensional and compositional properties of atherosclerotic lesions in carotid endarterectomy tissues. A quantitative comparison of areas of specific features in typical tissue segments was performed using MR images and histologic images. The mean difference for the measurements by the two methods was 4.5% for the total vessel, 5.3% for the internal carotid artery lumen, and 5.0% for the external carotid lumen. For other less abundant components, the mean difference was 14.2%. For direct characterization, individual tissue components were isolated by microdissection and their T1 and T2 relaxation times measured. Highly calcified areas typically had rather short T1 (452-837 ms) and short T2 (10.4-18.4 ms). In contrast, regions enriched in lipid had much longer T1 (1380-1480 ms) and longer T2 (35.3-49.0 ms). Other components such as thrombus had intermediate T1 (1180 ms) and short T2 (15.4 ms). T2 parametric imaging was used as a complementary approach for segmentation and quantitation of tissue components. In fresh tissue, several different components exhibited different T2 ranges: calcified/solid lipid (13-18 ms). cellular/ECM (9-30 ms), fluid lipid (35-40 ms): fibrous (50-60 ms). These results demonstrate the utility of MRI for identifying and quantifying specific components of atherosclerotic plaque ex vivo, and suggest its value for these measurements in vivo as well. © 2003 Elsevier Inc. All rights reserved. 1. Introduction Severe stenosis of the carotid artery (70%) in patients with transient ischemic attacks (TIAs) is associated with significant risk for stroke [1]. However, many atheroscle- rotic lesions of carotid arteries with this degree of stenosis are asymptomatic, while many TIAs or strokes attributable to carotid artery disease involve lower degrees of carotid stenosis This anomaly suggests that plaque size is not al- ways the determining factor in patient symptomatology and that other plaque characteristics such as surface ulceration, subintimal hemorrhage, and composition may play a signif- icant role in plaque pathogenicity. Indeed, plaques removed from symptomatic patients contain more extractable lipid than plaques from asymptomatic patients [1]. Lipid-laden plaques with low levels of collagen are often associated with plaque ulceration, subintimal hemorrhage, and isch- emic neurologic symptoms, suggesting that plaque compo- sition may be an important factor in the pathophysiology of carotid atherosclerosis. Recent clinical and pathoanatomic observations indicate that plaque type (composition and biology) is a more significant determinant than plaque size (degree of stenosis) in the development of thrombus-medi- ated acute coronary syndromes [2]. Thus clinical risk may Abbreviations: TBS = Tris buffered saline; MRI = magnetic reso- nance imaging; CHA = calcium hydroxyapatite; OCT = imbedding me- dium for frozen tissue specimens; RC = ruptured cap; FC = fibrous cap; EM = extracellular matrix; HB = hemorrhaged blood; SS = surgical slit; LU = lumen; T1 = spin lattice relaxation time; T2 = spin-spin relaxation time * Corresponding author. Tel.: +1-713-798-4164; fax: +1-713-798-4121. E-mail address: morrriset@bcm.tmc.edu (J. Morrisett). Magnetic Resonance Imaging 21 (2003) 465– 474 0730-725X/03/$ – see front matter © 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0730-725X(02)00643-4