HYPOTHESIS: Atherosclerotic stenosis and plaque characteristics can be more accurately assessed by the combination of routine 2D ultrasound, contrast enhanced ultrasound (CEUS), and 3-dimensional (3D) ultrasound. TCDM, CEUS and 3D visualization of the carotid plaque improve the differentiation of stroke etiology and quantification of plaque vulnerability, and aid the prediction of future risk for cerebrovascular events in the individual patient.