294 Assessment of the Diagnostic Utility of Non-Invasive Cardiac Imaging Modalities in Accurately Excluding Obstructive Coronary Artery Disease in Low to Intermediate Risk Patients. A Calcium Score of Zero is Predictive of a Negative Myocardial Perfusion Study and Thus can be Utilized in the Absence of an MPS for Exclusion of Obstructive Coronary Artery Disease