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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2007;27:1440.)
© 2007 American Heart Association, Inc.

Atherosclerosis and Lipoproteins

Identification of Atherosclerotic Lipid Deposits by Diffusion-Weighted Imaging

Ye Qiao; Itamar Ronen; Jason Viereck; Frederick L. Ruberg; James A. Hamilton

From Department of Physiology and Biophysics (Y.Q., J.V., J.A.H.), Department of Anatomy and Neurobiology (I.R.), Department of Neurology (J.V.), Departments of Medicine and Radiology (F.L.R.), Boston University School of Medicine, Boston, Mass; Department of Biomedical Engineering (J.A.H.), Boston University, Boston, Mass.

Correspondence to James A. Hamilton, Boston University School of Medicine, 715 Albany Street (W302), Boston, MA 02118. E-mail jhamilt{at}bu.edu

Objectives— The content and distribution of lipids is an important aspect of plaque vulnerability, but lipids are present within a heterogeneous environment, impeding detection by magnetic resonance imaging. Our goal was to achieve accurate detection of mobile lipids by a single magnetic resonance imaging sequence.

Methods and Results— Carotid endarectomy specimens (n=23) were imaged ex vivo at a high magnetic field (11.7 T) within 24 hours after surgery. Three contrast-weighted (T1W, T2W, and diffusion-weighted imaging [DWI]) image sequences were acquired and then coregistered with histological preparations for lipids (Oil red O and polarized light microscopy) and fibrous tissue (trichrome). Contrast-to-noise ratios were measured and compared for the 3 contrast weightings. Contrast-to-noise ratio measurement in regions identified as lipid versus fibrous tissue showed greater differences by DWI (4.5±0.63 versus 0.64±0.08; P<0.05) as compared with T2W (2.83±0.36 versus 1.36±0.37; P<0.05). We validated the presence and distribution of lipids (mainly cholesteryl esters) by both histology and image-guide spectroscopy. The basis for distinguishing mobile lipid and water inside the plaque was illustrated by diffusion-weighted spectroscopy.

Conclusions— Biophysical properties of plaque lipids can confer selective identification by DWI, as opposed to standard T1W and T2W imaging sequences. Successful translation of DWI in vivo could identify of features of vulnerable plaque.

Compared with detection of triglyceride in fat depots, MRI of mobile atherosclerotic plaque lipids (mainly CE) is difficult because CE is relatively dilute and present in a heterogeneous environment. DWI is superior to commonly used imaging protocols because it confers very high contrast of the fluid lipid.

Key Words: atherosclerosis • carotid arteries • diffusion-weighted image • lipids • MRI

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