From the microscope to the clinic: MR assessment of atherosclerotic plaque

MRI of coronary artery atherosclerosis in rabbits: Histopathology-MRI correlation and atheroma characterization

BACKGROUND AND OBJECTIVES: We report in vivo magnetic resonance imaging (MRI) characteristics and histopathology correlation of the thrombus formation in atherosclerosis the rabbit animal model. DESIGN AND METHODS: Atherosclerosis was induced in white male rabbits with vegetable ghee followed oxidized diet. Baseline MRI of atherosclerosis-recruited rabbits was done and later animals were used for atheroma histopathology characterization. Contiguous cross-sectional T2-weighted fast spin echo MRI images were compared by coronary histopathology. In all animals, coronary aortic wall thickening and atheroma size was measured using MRI. RESULTS: MRI images and digitized histological sections confirmed intraluminal thrombus in 6 (67%) of the 9 animals. MRI data showed correlation with the histopathology for aortic wall thickness (R2 = 0.82, P < 0.0001), lumen area (R2 = 0.88, P < 0.0001) and plaque size (R2 = 0.77, P < 0.0001). Optimized TE and TR parameters and multicontrast enhancement generated better MRI visibility of vulnerable plaque components. The MRI data evaluated % stenosis, plaque burden. Frequency of plaques, plaque height in aorta and coronary artery atheroma was also assessed by histology. In vivo, MRI determined the presence and size of the thrombus in this animal model of atherosclerosis and histopathology defined the plaque disruption. CONCLUSION: The combination of in vivo MRI and comparison with histopathology images of rabbit coronary thrombus may be a research tool for understanding of the pathogenesis of acute coronary plaques.

Arterial wall MRI characteristics are associated with elevated serum markers of inflammation in humans

Inflammation contributes to atherosclerosis, but assessment in humans is largely restricted to measurement of markers in blood. We determined whether MRI properties of large arteries were associated with markers of inflammation in serum. Double inversion recovery, fast spin-echo images of the common carotid arteries and infrarenal aorta were obtained at 1.5 T both before and after gadolinium-DTPA (0.1 mmol/kg) in 52 subjects > or =40 years of age, 17 of whom had no risk factors for atherosclerosis and thus served as controls. Twenty-two study participants had increases in wall thickness (14), T2-weighted signal intensity (11), and/or contrast enhancement values (7) that were >2 standard deviations (SDs) from control group mean values. Ten subjects in this group had evidence of focal plaques in the carotids (5) and/or aorta (6). Compared with the remaining 30 subjects, these 22 had significantly higher levels of interleukin-6 (3.53 +/- 2.46 vs. 1.97 +/- 1.37 pg/mL, P = 0.004), C-reactive protein (0.56 +/- 0.98 vs. 0.30 +/- 0.52 mg/dL, P = 0.019), vascular cell adhesion molecule-1 (572 +/- 153 vs. 471 +/- 130 ng/mL, P = 0.012), and intercellular adhesion molecule-1 (244 +/- 80 vs. 202 +/- 45 ng/mL, P = 0.015), and nonsignificant differences in levels of E-selectin (46.1 +/- 18.9 vs. 42.3 +/- 11.3 ng/mL, P = 0.369). Thus, MRI characteristics of the aorta and carotid arteries were associated with elevated serum markers of inflammation, frequently in the absence of definite atheroma. MRI of large arteries may provide a new approach to investigate the contribution of inflammation to atherogenesis.

In vivo magnetic resonance imaging of experimental thrombosis in a rabbit model

The process of atherosclerotic plaque disruption has been difficult to monitor because of the lack of an animal model and the limited ability to directly visualize the plaque and overlying thrombus in vivo. Our aim was to validate in vivo magnetic resonance imaging (MRI) of the thrombus formation after pharmacological triggering of plaque disruption in the modified Constantinides animal model of plaque disruption. Atherosclerosis was induced in 9 New Zealand White male rabbits (3 kg) with aortic balloon endothelial injury followed by a high cholesterol (1%) diet for 8 weeks. After baseline (pretrigger) MRI, the rabbits underwent pharmacological triggering with Russell's viper venom and histamine, followed by another MRI 48 hours later. Contiguous cross-sectional T2-weighted fast spin echo images of the abdominal aorta were compared by histopathology. In all animals, aortic wall thickening was present on the pretrigger MRI. On MRIs performed 48 hours after triggering, a histologically confirmed intraluminal thrombus was visualized in 6 (67%) of the 9 animals. MRI data correlated with the histopathology regarding aortic wall thickness (R=0.77, P<0.0005), thrombus size (R=0.82, P<0.0001), thrombus length (R=0.86, P<0.005), and anatomic location (R=0.98, P<0.0001). In vivo, MRI reliably determines the presence, location, and size of the thrombus in this animal model of atherosclerosis and plaque disruption. The combination of in vivo MRI and the modified Constantinides animal model could be an important research tool for our understanding of the pathogenesis of acute coronary syndromes.