Pathology and postmortem studies have reported that the most important mechanism of acute coronary syndrome (ACS) is the rupture of a vulnerable plaque and subsequent thrombus formation. Such events commonly arise from the non-flow limiting atherosclerotic lesions which are prone to rupture. Thin-cap fibroatheromas (TCFA) are the most common type of vulnerable plaque. As the widely used technique for the detection of coronary arterial diseases, coronary angiography has intrinsic limitations since it only portrays the contrast agent-filled contour of the lumen and provides little information on the vessel wall and even less the characteristics of the plaques.