Evaluation with optimal coherence tomography for vulnerable plaque detected by black-blood MRI for carotid artery stenting

Purpose: Optimal coherence tomography (OCT) is an intravascular imaging modality to assess plaque characteristics. The aim of this study is to evaluate surface and inside of vulnerable plaques in carotid stenotic lesions which are detected as high-intensity area in T1-weighted-image by MRI (Black blood method), using OCT compared with VH-IVUS before carotid artery stenting (CAS). Methods: We performed CAS in consecutive 15 patients (mean age of 76±5 years) with carotid artery stenotic lesions in which MRI (T1-weighted image by Black blood method) detected the plaque as high intensity area. It has been reported that plaques which is detected as high-intensity area in T1-weighted image of black blood-MRI are considered most vulnerable plaques. Vulnerable plaque detected by MRI were evaluated by OCT and VH-IVUS before performing CAS. Before stenting, we assessed plaque at the stenotic lesions by frequency-domain OCT (Ilumien OCT imaging system) and by VH-IVUS (Eagle Eye) which classified plaque into four color components: fibrous, fibro-fatty, calcium and necrotic core. During OCT-image acquisition carotid blood flow was replaced by dextran or contrast medium injection from the guiding catheter at 5-6 mL/sec with an injector pump. In analyzing OCT images, lipid rich plaque was defined as signal intensity-poor lesion covered by signal-rich bands that correspond to fibrous cap. Thin-cap fibroatheroma (TCFA) was defined as <65μm of cap thickness. Results: In all cases, OCT and VH-IVUS image acquisition was successfully obtained. In VH-IVUS images, vulnerable plaque included 53.0±5.2% fibrous plaque, 35.6±11.3% fibrofatty plaque, 2.4±1.8% calcium and 9.0±7.8% necrotic core. In OCT images, lipid rich plaques are detected in all patients, but deep inside of the plaque was not observed because OCT has a penetration depth of only 2-3mm. Fibrous caps which covered the vulnerable plaque were detected by OCT in all cases, whereas TCFA were detected in 8 cases (53%) and ruptured fibrous cap were detected in 8 cases (53%). Conclusions: Approximately half area of the vulnerable plaques detected by black blood-MRI consists of fibrofatty tissue and necrotic core in VH-IVUS images. Even in carotid artery, OCT is effective in evaluating superficial lipid-rich plaques and fibrous caps, especially TCFA as well as in coronary artery. OCT is a useful modality to evaluate characteristics of surface and inside of vulnerable plaques of carotid artery detected as high-intensity area in T1-weighted-image by Black-blood MRI.