Functional Assessment of Coronary Artery Disease by CTA Flow Encoding

Inclusion Criteria: * Inclusion Criteria A. Male or female patients, age 40 years and older. Women of child bearing potential must demonstrate a negative pregnancy test within 24 hours of the study CT. B. Referral for invasive coronary angiography for a suspicion of coronary artery disease with possible percutaneous intervention planned. C. Able to understand and willing to sign the Informed Consent Form. Exclusion Criteria: A. Patients with a known history of coronary artery bypass surgery. B. Current or previous ST elevation myocardial infarction (MI), prior MI (confirmed by persistent pathologic Q waves on ECG, clinical reports of CPK-MB or Troponin \> three times the upper limit of normal or a fixed perfusion defect on nuclear imaging) C. Current evidence of acute myocardial ischemia, unstable angina, or cardiovascular instability including troponin \> than the limit of detection (≥0.06 ng/ml), new ST depression \> 1 mm, hypotension with a systolic pressure \<90 mm Hg. D. Known allergy to iodinated contrast media E. Known or suspected intolerance or contraindication to beta-blockers including: 1. Known allergy to beta-blockers 2. History of moderate to severe bronchospastic lung disease (including moderate to severe asthma) F. Known allergy to regadenoson or aminophylline. G. Any patient not deemed medically stable by a physician. F. Known or suspected severe symptomatic aortic stenosis. G. Severe hypertrophic obstructive cardiomyopathy. H. Evidence of severe symptomatic heart failure (NYHA Class III or IV) at the time of the scan. I. Inability to lie flat. J. Atrial fibrillation or uncontrolled tachyarrhythmia, or advanced atrioventricular block (second or third degree heart block) K. Elevated serum creatinine (\> 1.5mg/dl) OR calculated creatinine clearance of \< 60 ml/min (using the Cockcroft-Gault formula) L. History of contrast-induced nephropathy M. Severe pulmonary disease or other disorder that does not allow patient to hold breath for 10 seconds or more. N. History of organ transplantation O. Acute myocarditis or pericarditis. P. Recent history of illicit drug use (past 3 months) Q. Recent use of dipyridamole containing medications. R. Current pregnancy.