Stroke is commonly caused by thromboembolic events originating from ruptured carotid plaque, with rupture potential related to plaque composition. We have previously shown that soft (intraplaque hemorrhage/necrotic core) and stiff (collagen/calcium) plaque components are differentiated with high sensitivity and specificity by peak displacement (PD) in Acoustic Radiation Force Impulse (ARFI) imaging. However, PD showed low performance for distinguishing between soft and between stiff features. We hypothesize that soft and stiff feature delineation will be improved using a new ARFI outcome metric - the variance of acceleration (VoA). We test our hypothesis using histological validation.