Ultrasonic Characterization of Carotid Plaques and Its Clinical Implications

Abstract

In recent years, it has become apparent that the severity of an asymptomatic carotid stenosis is not sufficient to assess the risk of stroke. Although the risk of stroke increases with increasing grades of stenosis, and as a result a stenosis of ≥80% is used by many surgeons as an indication for surgery, this subgroup does not contain the majority of strokes that will subsequently occur. In addition, because the severity of stenosis cannot identify subgroups with stroke risk higher than 2.5%, a very large number of operations (approximately 90) with an asymptomatic stenosis of ≥80% would need to undergo carotid endarterectomy to prevent one stroke for 1 year of follow-up.

The aim of this chapter is to present the rationale and practical development of image analysis of ultrasonic plaque images for the identification of texture features that can be used to stratify patients according to stroke risk.

Two important advances contributed to the success of this approach. First, image analysis has enabled us to obtain reproducible measurements of gray scale from the same plaques irrespective of equipment and gain used. Second was the realization that, similar to plaque histology, not a single feature on imaging could by itself detect all the structural abnormality characteristic of potentially unstable and high-risk plaques.

The ability of a combination of texture features to identify unstable plaques and stratify patients according to stroke risk was tested in both cross-sectional studies and validated in a large prospective cohort (ACSRS study).