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Background: One disadvantage of carotid artery stenting (CAS) is a high incidence of distal embolism (DE) during or after the procedure. Also, irregular plaque protrusion (PP) after stent placement has been suggested as one of the major causes of post procedural ischemic complications. The aim of this study was to evaluate the relationship between unstable plaque identified on black-blood magnetic resonance imaging (BB-MRI) and the occurrence of irregular PP after CAS using optical frequency domain imaging (OFDI).Materials and Methods: We enrolled 41 patients who underwent CAS with OFDI image acquisition. We measured signal intensity ratios (SIR) from T1 weighted images of all carotid plaques. The plaque with high SIR is considered as unstable plaque with intraplaque hemorrhage (IPH) according to previously published criteria. Cross-sectional OFDI images were evaluated at every 0.125-mm intervals within the stented segments, and assessed the relationships among the occurrence of irregular PP (I-PP), smooth PP (S-PP) or non-PP, and SIR measured by MRI.Results: PP and I-PP were detected in 34 cases (83%) and in 20 cases (49%), respectively. There were two minor strokes in the I-PP group. There was a positive correlation between PP volume and SIR (r=0.47, p<0.01). The SIR was significantly higher in the I-PP group than the S-PP or non-PP groups [I-PP vs. S-PP or non-PP: 1.67 (IQR: 1.39-1.9) vs. 1.36 (IQR: 1.25-1.62), p<0.01]. From analysis of receiver operating characteristic curves, a SIR of 1.57 on BB-MRI was the most reliable cutoff values for predicting I-PP. In multivariate logistic regression analysis, the independent predictor of I-PP was SIR (p=0.012) even after adjusted by plaque volume.Conclusions: Quantitative tissue characterization of carotid plaques using BB-MRI was useful to predict I-PP. These data suggest that identification of carotid plaque components such as IPH by BB-MRI before CAS may improve the clinical outcome of this procedure.