This is an open-label, non-randomized study conducted at Thomas Jefferson University comparing pressure-gradient estimates (obtained between a carotid plaque and the carotid artery) to imaging and histology markers of plaque vulnerability. There is an inverse relationship between the subharmonic signal magnitude from contrast-enhanced ultrasound microbubbles and ambient pressure. This pressure estimation technique (referred as SHAPE) will be used to estimate the pressure gradient across the carotid plaque cap noninvasively in vivo.

Inclusion Criteria:

• Patients >18 years old and willing and able to participate. Patients with atherosclerosis scheduled for carotid endarterectomy

Exclusion Criteria:

• • Pregnancy or breast-feeding at the time of the scan

  • Patients with known hypersensitivity or allergy to any component (including perflutren) of Definity (Lantheus Medical Imaging, Billerica, MA).

  • Patients who are medically unstable, patients who are seriously or terminally ill, and patients whose clinical course is unpredictable. For example:

    • Patients on life support or in a critical care unit.
    • Patients with unstable occlusive disease (e.g., crescendo angina).
    • Patients with clinically unstable cardiac arrhythmias, such as recurrent ventricular tachycardia.
    • Patients with uncontrolled congestive heart failure (NYHA Class IV).
    • Patients with recent cerebral hemorrhage.
    • Patients who have undergone surgery within 24 hours prior to the study sonographic examination.

  • Patients with unstable cardiopulmonary conditions (acute myocardial infarction, acute coronary artery syndromes, worsening or unstable congestive heart failure, or serious ventricular arrhythmias) or respiratory distress syndrome.

  • Patients with uncontrollable emphysema, pulmonary vasculitis, pulmonary hypertension or a history of pulmonary emboli.

  • Patients who have received any contrast medium (X-ray, MRI, CT or ultrasound) in the 24 hours prior to the research ultrasound exam