The potential role of IDEAL MRI for identification of lipids and hemorrhage in carotid artery plaques

Abstract

Hemorrhage and lipid deposits contribute to instability in atherosclerotic plaques. Unstable carotid artery plaques can lead to cerebral ischemic events. While MRI studies have shown the ability to identify plaque components, the identification of hemorrhage and lipids has proven to be problematic. The purpose of this study was to quantitatively evaluate the potential of the MRI fat/water separation method known as iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL) to complement and improve existing methods for the identification of hemorrhage and lipids in carotid artery plaques. Fifteen asymptomatic subjects with 50-79% stenosis of at least one carotid artery were enrolled. Hemorrhage and lipid components within carotid plaques were identified using previously published criteria based on the multiple contrast-weighted (MCW) method (3D Time-of-Flight (3D-TOF), T1-Weighted (T1W) and T2-Weighted (T2W)). The hemorrhage:muscle, lipid:muscle and intra-plaque lipid:hemorrhage signal intensity ratios (SIR) and contrast to noise ratios (CNR) were measured on MCW and compared to IDEAL black-blood images. No differences were found between any of the MCW methods for any of the SIRs measured. The IDEAL Fat images had higher lipid:muscle and lipid/hemorrhage SIRs (p<0.001) compared to IDEAL Water and all MCW image sequence types. The mean values of IDEAL Fat hemorrhage:muscle SIR and CNR were nearly unity (1.1±0.6) and nearly zero (0.1±1.1), respectively. The IDEAL Water imaging was not significantly different than any of the MCW methods for any of the SIRs or for the hemorrhage:muscle CNR of 3D-TOF, while its CNRs were significantly higher than IDEAL Fat lipid:muscle (p<0.05) and lipid:hemorrhage (p<0.001) and all MCW methods (p<0.001). The addition of IDEAL Water and Fat imaging to the MCW method shows potential to improve the identification of hemorrhage and lipid structures in carotid artery plaques.

Keywords: MR angiography (MRA); Spectroscopic imaging; Spectroscopic quantitation; Vessel wall imaging; Water fat imaging.