 Coronary Computed Tomography Angiogram CCTA is a non-invasive imaging modality that has high sensitivity and negative predictive value for the detection of coronary artery disease CAD. The main limitations of CCTA are its poor specificity and positive predictive value, as well as its inherent lack of physiologically relevant data on hemodynamic significance of coronary stenosis, a data that is provided either by non-invasive stress tests such as myocardial perfusion imaging MPI or invasively by measurement of the Fractional Flow Reserve FFR. Recent advances in computational fluid dynamic techniques applied to standard CCTA are now emerging as powerful tools for virtual measurement of FFR from CCTA imaging CT-FFR. These techniques correlate well with invasively measured FFR 1-4. The primary purpose of this study is to evaluate the incremental benefit CT-FFR as compared to CCTA in triaging chest pain patients in ED settings who are found to have obstructive CAD upon CCTA generally 30 and 90 stenosis. Invasive FFR and short term clinical outcomes 90 days will be correlated with each diagnostic modality in order to evaluate positive and negative predictive value of each when used incrementally with CCTA. 