Evaluation of Symptomatic Carotid Plaques by Tissue Characterization Using Integrated Backscatter Ultrasound and Magnetic Resonance Imaging

Background: Unstable carotid plaques that consist of large lipid pool and intraplaque hemorrhage are more likely to cause cerebral infarction. We previously developed an integrated backscatter (IBS) ultrasound color-coded mapping method to evaluate the tissue characteristics of plaques. The purpose of this study was to determine whether 3-dimensional IBS color-coded mapping and signal intensity ratio (SIR) from magnetic resonance imaging (MRI) could distinguish the early symptomatic plaques from late symptomatic plaques. Methods: We performed quantitative tissue characterization of carotid plaques measuring IBS values and the SIR from T-1-weighted MRI images in 95 carotid plaques (>50% stenosis) in 95 patients (45 symptomatic, 50 asymptomatic). Results: The percent unstable component volume (UCV) that consisted of lipid pool and intraplaque hemorrhage and the SIR of symptomatic carotid plaques were higher than those of asymptomatic plaques (57.8 +/- 25.1 vs. 46.8 +/- 25.1%, p = 0.036; 1.31 +/- 0.25 vs. 1.21 +/- 0.26, p = 0.047). In patients that were imaged within 3 days of symptom onset, the %UCV and SIR were significantly higher than the values in patients that were imaged 30-180 days after symptom onset (73.1 +/- 18.4 vs. 38.7 +/- 18.4%, p < 0.001; 1.38 +/- 0.22 vs. 1.22 +/- 0.26, p = 0.031). From the analysis of receiver operating characteristic curves, a %UCV of 50% (measured by IBS) and an SIR of 1.25 (measured by MRI) were the most optimal cutoff values for identifying early symptomatic plaques. Conclusions: Noninvasive quantitative tissue characterization of atherosclerotic lesions in carotid arteries using IBS ultrasound and MRI is useful to distinguish early symptomatic plaques from late symptomatic plaques. Copyright (C) 2011 S. Karger AG, Basel