The investigators plan to evaluate the correlation between carotid plaque enhancement on Contrast-enhanced ultrasound (CEUS), significant coronary artery disease (CAD), and cardiovascular (CV) outcomes in a systematic manner. The investigators hypothesize that increased levels of CEUS-detected vulnerable carotid plaque will be predictive of CV risk determined by angiography and future cardiovascular events.

Study Design: The investigators will conduct a prospective, single-center, observational study at the Cardiovascular Imaging Network at Queen's (CINQ, www.CINQLab.com). This facility allows a CEUS protocol to be conducted on the same day as the angiogram. It is anticipated that 100 participants can be recruited per month with a total target enrolment of up to 1000 participants.

Objectives

1. To determine the test characteristics (sensitivity, specificity, negative/positive predictive values) of carotid plaque by CEUS (Definity(R)) for predicting significant CAD (≥50% stenosis) in participants referred for angiography
2. To determine the test characteristics (sensitivity, specificity, predictive values) of carotid plaque by CEUS for predicting future CV events, such as death, stroke, myocardial infarction, and cardiovascular interventions.

Inclusion criteria:

1. >18 years of age
2. Outpatients referred for clinically indicated angiography for assessment of CAD
3. Low - Intermediate Framingham risk (<20%)
4. Absence of clinical contraindication to angiography
5. Able and willing to give informed consent

Exclusion criteria:

1. Patients presenting with acute coronary syndrome
2. Patients with previously known significant CAD (any lesion >50%) or percutaneous coronary intervention or coronary artery bypass surgery
3. Previous carotid surgery or angioplasty
4. Documented allergy to echo contrast

Subjects referred for outpatient coronary angiography will be screened for inclusion.