Abstract
We hypothesize that high-resolution magnetic resonance imaging (MRI) in vivo can accurately quantify carotid plaque volume and differentiate carotid plaque elements that are related to ischemic events. A randomized, placebo-controlled pilot study in patients with clinically stable carotid atherosclerosis (n = 60) is currently underway using quantitative micro-MRI techniques to determine the effect of aggressive low-density lipoprotein (LDL) lowering (simvastatin 80 mg), moderate LDL lowering (simvastatin 10 mg), and LDL lowering with high-density lipoprotein elevation (simvastatin 20 mg and Niaspan [extended-release niacin; Kos Pharmaceuticals, Inc., Miami, FL] 2,000 mg) on MRI plaque characteristics over 12 months. MRI (1.5 T) consisted of 3D time-of-flight magnetic resonance angiography of the carotid bifurcation, axial T1-weighted spin echo, axial proton density fast spin echo (FSE), and axial T2-weighted FSE at the level of the bifurcation (approximately ± 1.6 cm). Total plaque volume was estimated from computer-assisted measurement of plaque cross-sectional area plaque area × slice thickness × number of slices (typically 2.0 mm × 16 slices). The intraclass correlation coefficient for plaque volume from repeat baseline scans (n = 8) was 0.95 using fat-suppressed proton density FSE images. In these patients, plaque volume was estimated at 1.34 ± 0.38 cm3 (mean ± SD). Plaque calcification, fibrous tissue content, lipid content, and hemorrhage are currently being estimated using the multiparametric imaging data. The effect of treatment on MRI indices will be correlated with changes in lipoproteins, serum inflammatory markers and urinary isoprostanes, indices of oxidant stress in vivo. Noninvasive micro-MRI techniques applied to carotid atherosclerosis in humans in vivo offers the potential to assess the longitudinal effect of therapies on quantitative indices of plaque morphology.
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