Primary Outcome Measures:
Angiographically obtained fractional flow reserve (FFR) is a useful physiologic test for assessment of lesion-specific ischemia, and a valuable adjunct to anatomic assessment of coronary artery disease (CAD) as determined by invasive coronary angiography. However, the invasiveness and measuring difficulty of FFR make it unfamiliar to perform. Coronary computed tomographic angiography (CCTA) has emerged as a non-invasive test, accurately evaluate anatomic coronary artery stenosis. Although CCTA evaluation of CAD has been validated against invasive coronary angiography and intravascular ultrasound, anatomically-obstructive coronary stenosis by CCTA demonstrates an unreliable relationship to lesion-specific ischemia. Recently, with the advance of imaging reconstruction and analysis technique, several novel parameters computed from CCTA were suggested to have added value in determining the ischemia-causing coronary stenosis. In this study, diagnostic performance of transluminal attenuation gradient (TAG) and fractional flow reserve computed form CCTA (FFR-CCTA) for the presence of hemodynamically-significant coronary stenosis, as determined by FFR, will be compared to suggest best functional parameter noninvasively computed form CCTA.