Reducing Radioisotope Dose: the Half-Dose CZT Study

Inclusion Criteria: * ≥ 18 years of age and referred for a clinically-indicated stress SPECT MPI study * suspected or known coronary artery disease * written informed consent Exclusion Criteria: * Evidence of a normal baseline scan after at least 50% of the protocol acquired baseline scans have been interpreted as being normal * Participation in another investigational study within the preceding month * Pregnant and/or breast-feeding female * ECG evidence of left bundle branch block or paced rhythm * Evidence of non-ischemic cardiomyopathy * Presence of hypertrophic cardiomyopathy and/or severe valvular heart disease * Severe claustrophobia or inability to lie flat for 20 minutes (the anticipated amount of time to complete the procedure) * Known allergy to technetium-99m * Potential contraindications to regadenoson use, due to severe lung disease; severe bradycardia (heart rate \< 40 beats/min); second- or third degree atrioventricular heart block; sick sinus syndrome; long QT syndrome; severe hypotension; or decompensated heart failure.