Background: The results of studies of advanced lesions of atherosclerosis suggest that the thickness of the fibrous cap that overlies the necrotic core distinguishes the stable lesion from one that is at high risk for rupture and thromboembolic events. We have developed a high-resolution MRI technique that can identify the fine structure of the lesion, including the fibrous cap, in vivo. The aim of the present study was to determine the agreement between in vivo MRI and lesion architecture as seen on histology and gross tissue examination to identify fibrous cap thickness and rupture.
Methods and results: Twenty-two subjects who were scheduled for carotid endarterectomy underwent MRI with a 3-dimensional multiple overlapping thin slab angiography protocol. The appearance of the fibrous cap was categorized as (1) an intact, thick, (2) an intact, thin, or (3) a ruptured fibrous cap on MRI, gross, and histological sections. Thirty-six sites were available for comparison between MRI and histology. There was a high level of agreement between MRI and histological findings: 89% agreement, kappa (95% CI)=0.83 (0.67 to 1. 0), weighted kappa=0.87. Spearman's correlation coefficient was 0.88 (significant to the 0.01 level).
Conclusions: These findings indicate that high-resolution MRI with a 3-dimensional multiple overlapping thin slab angiography protocol is capable of distinguishing intact, thick fibrous caps from intact thin and disrupted caps in atherosclerotic human carotid arteries in vivo. This noninvasive technique has the potential to permit studies that examine the relationship between fibrous cap changes and clinical outcome and to permit trials that evaluate therapy intended to "stabilize" the fibrous cap.