Structure of plaque at carotid bifurcation - High-resolution MRI with histological correlation

Background and Purpose-The composition of carotid atherosclerosis was visua lized by using 3D MRI at high resolution with 200-mum(3) voxels. Magnetic r esonance signal characteristics were correlated with plaque components, inc luding collagenous cap, necrotic core, and calcification, to define resolut ion and other requirements for future clinical carotid MRI. Methods-Twenty-one en bloc carotid endarterectomy specimens were imaged ex vivo by 3D gradient-echo MRI by using a 1.5-T clinical scanner with repetit ion time, echo time, and flip angle of 40 ms. 18 ms, and 20 degrees, respec tively. Plaques were placed in Gd-saline and imaged in a solenoid radiofreq uency coil. For quantitative tissue-specific signal analysis, techniques we re developed to match tissue sections analyzed by MRI and histology. Results-Three-dimensional imaging resolved complex morphological features n ot visualized by density- or T-2-weighted 2D spin-echo imaging. The collage nous cap, necrotic core, and areas of focal calcification showed differing signal characteristics: mean contrast-to- noise ratio for cap versus underl ying core was 20. The signal distributions for media and necrotic core over lapped but were resolvable in most specimens. The signal from thrombus was variable. Conclusions-En bloc specimens provide a useful model for studying plaque MR I. By use of isotropic submillimeter resolution, the collagenous cap and un derlying necrotic core typically can be distinguished, and calcification ca n be identified. Thrombus displays a wide variation in signal intensity. Th e techniques presented could facilitate future clinicohistological correlat ion studies for atherosclerotic plaque MRI.