1. An ultrasonic diagnostic imaging system for the evaluation of plaque by contrast enhanced ultrasound, the system comprising: an ultrasound imaging probe having an array transducer configured to acquire a sequence of ultrasound images of a plaque region in a carotid artery during contrast agent delivery; a time intensity curve calculator configured to form a time intensity curve for each pixel in the plaque region in the ultrasound images of the sequence where contrast is present; a comparator configure to identify pixels in the plaque region where perfusion is present based on the time intensity curves for the pixels in the plaque region; and a display configured to display the degree of perfusion in the plaque region.