EFFECT OF IMAGE NORMALIZATION ON CAROTID PLAQUE CLASSIFICATION AND THE RISK OF IPSILATERAL HEMISFERIC ISCHEMIC EVENTS. RESULTS FROM THE ASYMPTOMATIC CAROTID STENOSIS AND RISK OF STROKE STUDY

The aim of this study was to determine the effect of image normalization on plaque classification andthe risk of ipsilateral ischemic neurologic events in patients with asymptomatic carotid stenosis.The first 1,115 patients recruited to the Asymptomatic Carotid Stenosis and Risk of Stroke (ACSRS)study with a follow-up of 6 to 84 months (mean 37.1 months) were included in this study. Duplexultrasonography was used for grading the degree of internal carotid artery stenosis and for plaquecharacterization (types 1-5), which was performed before and after image normalization.One hundred sixteen ipsilateral ischemic hemispheric events occurred. Image normalization resultedin 60% of plaques being reclassified. Before image normalization, a high event rate was associated withall types of plaque. After image normalization, 109 (94%) of the events occurred in patients with plaquetypes 1 to 3. For patients with European Carotid Stenosis Trial (ECST) 70 to 99% diameter stenosis(equivalent to North American Symptomatic Carotid Endarterectomy Trial [NASCET] 50-99%) withplaque types 1 to 3, the cumulative stroke rate was 14% at 7 years (2% per year), and for patientswith plaque types 4 and 5, the cumulative stroke rate was 0.9% at 7 years (0.14% per year).The results suggest that asymptomatic patients with plaque types 4 and 5 classified as such afterimage normalization are at low risk irrespective of the degree of stenosis.