Duplex ultrasound assessment of carotid arterial atherosclerotic disease : investigation of direct stenosis measurement methods and image analysis for vulnerable plaque identification

Abstract

Purpose: Ultrasound assessment of carotid disease is currently based on stenosis haemodynamic effects. The accuracy of direct stenosis measurement remains unclear, while research on atherosclerosis suggests identification of other plaque characteristics beyond size. The aim of the study is to investigate whether direct stenosis measurement and plaque ultrasound image analysis could potentially be used for more accurate diagnostic investigation. Method and material: Eighty-seven patients with cardiovascular disease had a carotid duplex ultrasound scan and velocity and B-mode measurements data were recorded for direct diameter measurement evaluation. Forty patients were scanned for quantitative plaque analysis and association of several parameters with symptoms was investigated. Results: For the degree of stenosis, ECST method indicated greater agreement among direct measurement methods with velocity criteria, however in cases of mild stenosis difference was reported. ECST method measurements showed considerably better agreement with MRA stenosis calculations compared with other methods. Intima-media grey scale level was associated with plaque echogenicity but the correlation was not significant, however there was an association with blood cholesterol levels. Percentages of plaque area with grey scale value less than 35 and 40 showed good accuracy in identifying symptomatic patients. As far as fibrous cap is concerned, a thickness less than 300 μm was well correlated with symptomatic disease, however no association was noted for its echogenicity. Conclusion: ECST direct stenosis measurement method could potentially be used for better stenosis classification in cases with inconclusive haemodynamic estimations. Quantitative plaque analysis, such as fibrous cap thickness measurement and grey level analysis, shows promising results in association with symptomatic disease and particular plaque characteristics.