New techniques for detecting emboli (harmful blood clots/air bubbles in arteries) have played a major role in dramatically reducing stroke rates after carotid endarterectomy. This is an operation designed to remove narrowings in the main arteries supplying the brain before they can cause a stroke. Before per-operative embolus monitoring was introduced in 1992, the intra-operative stroke rate during carotid artery procedures was 4%. Today it is 0.2%. Before post-operative monitoring was introduced in 1995, the post-operative stroke rate was 2.7%. Today it is extremely rare.