However, in some patients, multidetector CT angiography may be appropriate and safer than routine invasive angiography for this purpose. Indications and contraindications to CT angiography, including subsets of patients for whom it can be considered, are discussed in the 2010 expert consensus document on CT angiography18 and the 2010 appropriate use criteria for cardiac CT.19 Although coronary angiography is considered the gold standard for the diagnosis of CAD, it has inherent limitations and shortcomings. Angiographic assessment of stenosis sever- ity relies on comparison to an adjacent, nondiseased reference segment. In diffusely diseased coronary arteries, lack of a normal reference segment may lead to underestimation of lesion severity by angiography. Multiple studies have documented significant interobserver variability in the grading of coronary artery steno- with disease severity overestimated by visual assessment when coronary stenosis is 50%.21,22 Although quantitative coro- nary angiography provides a more accurate assessment of lesion severity than does visual assessment, it is rarely used in clinical practice because it does not accurately assess the physiological significance of lesions.23 Many stenoses considered to be severe by visual assessment of coronary angiograms (ie, 70% luminal narrowing) do not restrict coronary blood flow at rest or with maximal dilatation, whereas others considered to be insignifi- cant (ie, <70% luminal narrowing) are hemodynamically sig- Coronary angiography also cannot assess whether an atherosclerotic plaque is stable or vulnerable (ie, likely to rup- ture and cause an acute coronary syndrome). 