Clinical Impact of Cardiac Photon-Counting Detector CT

Inclusion Criteria: * Patients referred for coronary artery cardiac CT imaging or nuclear medicine or MRI cardiac perfusion within the Department of Radiology or Cardiology. * Patients who are able and willing to sign the informed consent will be enrolled * Negative pregnancy test if subject is of child-bearing age (females of child-bearing potential will be screened for pregnancy using a urine pregnancy test, which will be administered by the unit study coordinator at no cost to the patient). Exclusion Criteria: * Patients unable to provide written informed consent * Pregnancy * eGFR ≤ 30 * History of prior moderate or severe contrast reaction includes: unresponsiveness, severe respiratory distress, convulsions, arrhythmia, cardiopulmonary distress, progressive angioedema, laryngeal edema, dyspnea, bronchospasm, symptomatic tachycardia, symptomatic bradycardia, hypotension, hypertensive crisis. * Any history of required premedication prior to iodinated contrast administration. * Patients that consent to participation but do not undergo their clinically-indicated, contrast-enhanced CT, or nuclear medicine or MR perfusion scanning for any reason (e.g., bad IV, infiltration, reaction, change in indication). * Patients experiencing atrial fibrillation, premature ventricular contractions or other heart rhythm abnormalities * Hospitalized patients or patients under care in the Emergency Department Specific exclusion criteria only for participation in the cardiac stress test arm of this study (requiring administration of Regadenoson): * Anything by mouth within three hours of the examination * Known hypersensitivity to Regadenoson, Adenosine, or Dipyridamole. * Active ongoing wheezing or poorly controlled asthma or COPD (hospitalized within last month or receiving treatment for flair within last month). * Second (type I or II) or third degree atrioventricular (AV) block or sinus node dysfunction unless patient has functioning artificial pacemaker. * Ingested greater than 4 oz. of caffeine within the last 12 hours. * Currently experiencing unstable coronary syndrome. * Uncontrollable seizures within the last 3 months