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Role of Magnetic Resonance and Intravascular Magnetic Resonance in the Detection of Vulnerable Plaques

Robert L. Wilensky, MD^_*,a,_*, Hee Kwon Song, PhD and Victor A. Ferrari, MD^_*,,b

^_* Cardiovascular Division, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania
Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania

View larger version (138K): [in a new window]   Figure 1 (A) A small eccentric plaque within the carotid thought to be composed of fibrous tissue (FT) (dark in time of flight [TOF], moderate/high in both T1- and proton density (PD)-weighted images) indicates a type III plaque. (B) A carotid plaque consisting of both lipid and fibrous tissue, with a region of calcium deposits (Ca) indicative of a type IV to V plaque. (C) A carotid lesion with recent intraplaque hemorrhage (arrows) demonstrating high signal intensity on all sequences, and no evidence of plaque rupture with a thick fibrous cap surrounding the lumen (arrowhead). Figure 1C reproduced, with permission, from Kampschulte et al. (12).

View larger version (71K): [in a new window]   Figure 2 Double-inversion fast spin echo black-blood images of the right coronary artery (arrow) in a normal subject. (A) Without fat suppression; (B) with fat saturation applied (inset: magnified). The vessel wall is more clearly visible in the fat-saturated images. Each image was acquired during a single 20-s breath-hold scan using a single 3-inch surface receiver coil.

View larger version (102K): [in a new window]   Figure 3 Magnetic resonance images of a diseased rabbit abdominal aorta in the sagittal (A) and transverse (B) planes and corresponding histopathology. Panel A demonstrates diffuse and heterogeneous aortic plaque enhancement longitudinally from the renal artery to the distal segment 24 h after gadofluorine injection. Three slice locations (1, 2, 3) were used for transverse magnetic resonance images (B) and H&E staining (C). (B) Differences in signal intensity vary with slice location, and reflect differing plaque composition, with greater enhancement in sections with larger lipid content. (D) Corresponding histopathological sections, and plaque composition. In slice 2, a large lipid core corresponds to greatest plaque enhancement. Plaque at level 3 has a large lipid content with corresponding well with the greatest plaque enhancement. Ad = adventitia; F = loose fibrous tissue; FC = fibrous cap; L = lumen; LC = lipid core; M = macrophages. Reproduced, with permission, from Sirol et al. (30).

View larger version (49K): [in a new window]   Figure 4 (Top) A set of in vivo spin echo images was reformatted to display a long-axis view of a diseased aorta from a hypercholesterolemic rabbit model. Orientation is from renal artery level (left) to diaphragm (right) and at single transverse slices (bottom) before (pre) and 120 min after (post) infusion of vß3-integrin targeted gadolinium-carrying perfluorocarbon nanoparticles. Semiautomated segmentation (segmented, grayish ring, panel 3) and color-coded signal enhancement (enhancement) above baseline (in percent) are shown. Reprinted, with permission, from Winter et al. (37).

View larger version (67K): [in a new window]   Figure 5 Apparent diffusion constants obtained by magnetic resonance from human aortic samples containing normal fibrous tissue, fatty streaks, and complex lipid-laden lesions are seen in photomicrographs. The apparent diffusion constant shows clear difference between the fibrous and lipid-rich tissue, with overlap noted between lipid-rich and fatty streak tissue (studies performed in collaboration with Dr. Renu Virmani).

View larger version (98K): [in a new window]   Figure 6 Intravascular magnetic resonance imaging (IVMRI) results in ex vivo human coronary arteries. Intermediate lesions on coronary angiography underwent interrogation with the IVMRI probe. Top row shows the lesions on postmortem angiography. The arrows point (left to right) to lesions in the intermediate, right coronary, and left anterior descending arteries. The middle row shows the histology of these lesions, indicating a stable plaque on the left, a stable plaque with a deep necrotic core (+) in the middle, and a thin fibrous-cap atheroma (TFCA) on the right (necrotic core, *). The bottom row is the corresponding IVMRI results, indicating (left to right) no substantial lipid deposition, lipid deposit/necrotic core deep within the arterial cross-section, and a TFCA with increased lipid deposition noted in three of four deep bands (yellow) and two of four superficial bands. Adapted from Schneiderman et al. (45).

View larger version (50K): [in a new window]   Figure 7 Left anterior descending artery angiogram (A) and intravascular magnetic resonance imaging (IVMRI) (B) of a 77-year old man with unstable angina pectoris. Arrow shows location of the IVMRI interrogation. The IVMRI cross-sectional view demonstrates increased lipid content (yellow) in all three quadrants and both bands (0 to 100 µm and 100 to 250 µm).