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most clinical presentations of the disease are as a result of a critical narrowing of arterial lumen or a sudden thrombotic occlusion caused by the rupture of atherosclerotic plaque .
unfortunately prediction of such clinically adverse events is difficult by clinical judgement or symptoms alone.1)2)3 ) comprehensive approach of coronary atherosclerotic plaque including qualitative and quantitative analysis is necessary for the accurate lesion assessment and treatment planning as well as for the prediction of future outcome ( fig .
1).4)5 ) conventional invasive coronary angiography ( cag ) has been regarded as the gold standard for coronary artery disease but has limitation for assessing the extent of mild to moderate coronary atherosclerosis.6 ) intravascular ultrasound ( ivus ) or optical coherence tomography ( oct ) are needed to quantitate the burden of atherosclerosis .
coronary computed tomography angiography ( ccta ) can be considered as a non - invasive method that may substitute cag and ivus.7)8 ) ccta is still limited by spatial and temporal resolution but enables non - invasive patient - friendly assessment of the extent of coronary atherosclerosis.9 ) therefore it is expected that ccta will be useful in overcoming limitations of the current diagnosis and treatment of coronary heart disease as shown below .
ccta has emerged as a new noninvasive tool for screening of coronary artery disease in place of conventional stress imag - ing or electrocardiography.10)11 ) therapeutic strategy of coronary artery disease depends on the extent and severity of coronary artery disease .
ccta can visualize the extent of severity of coronary artery disease with good sensitivity and excellent specificity.12)13 ) the performance of ccta for plaque detection has been validated by ivus and oct.7)14 ) unlike stress imaging or invasive cag , ccta can detect a wide range of coronary artery disease from mild to severe disease.15)16 )
it is difficult to predict future cardiac events through symptoms or clinical risk factors.17)18 ) clinical studies have shown that one - third of acute myocardial infarctions are asymptomatic prior to the event.19)20)21 ) most chronic total occlusions have infarct scar which is evidence of prior myocardial infarction but only half of them had a history of angina symptoms.22)23 ) a ccta is suitable to identify anatomical coronary stenosis , including calcified and non - calcified plaques , measure the atherosclerotic plaque burden and its response to treatment , and differentiate stable plaques from those that tend to rupture.24 ) positive remodeling , low density ( < 30 hounsfield units ) plaque , napkin - ring sign and spotty or micro - calcification detected by ccta has been shown to have vulnerable plaque characteristics ( fig .
2).24)25)26)27 ) these non - invasive findings have been validated by invasive ivus and oct studies.1)26)27 ) moreover , non - contrast coronary calcium ct scan is also useful to evaluate the risk of coronary artery disease using a coronary calcium score and it is well demonstrated to be related to long - term prognosis.28 ) accordingly , ccta can detect the presence of a coronary atherosclerosis most accurately and is one of the best non - invasive imaging modality to predict the clinical outcome of coronary artery disease as well.29 )
the treatment goal of coronary artery disease is the improvement of survival as well as relief of symptom .
revascularization by percutaneous coronary intervention or bypass surgery has relieved symptom but has been questioned for improved long - term outcome.30)31 ) refinement of the need of revascularization strategy would be required to achieve improved clinical outcome after revascularization procedure including percutaneous coronary intervention or bypass surgery .
the followings are proposed treatment strategy of coronary artery disease based on the ccta . first is to detect coronary atherosclerosis using ccta .
ccta has the highest diagnostic power to find coronary atherosclerosis among non - invasive imaging modalities and hence very high negative predictive value.1)16 ) second is to assess myocardial ischemia non - invasively with ccta .
the presence of myocardial ischemia is the most important factor for making a prognosis and for the decision to perform a revascularization.31 ) however less than half of coronary arteries with a diameter stenosis  50% cause myocardial ischemia in most clinical studies.31)32)33 ) it would be greatly preferable to find the functional significance of a stenosis as well as the presence of a stenosis by single ccta test .
myocardial computed tomography perfusion imaging could be utilized in clinical practice.34)35)36 ) computational fractional flow reserve based on computed fluid dynamics analysis37)38 ) and contrast gradient analysis39)40 ) are being investigated.41)42)43 ) third , it would be important to evaluate the amount of ischemic myocardial mass .
several studies have investigated the relationship between the angiographic severity of stenosis and the amount of perfused myocardial tissue .
duke jeopardy score,44)45 ) myocardial jeopardy index,46 ) and alberta provincial project for outcome assessment in coronary heart disease ( approach ) lesion score44)47 ) have been used to evaluate the burden of myocardium - at - risk based on angiographic extent of stenosis . however these scoring systems are limited by semi - quantitative grading of the severity of coronary artery disease and myocardium - at - risk .
detailed anatomical variations of individual vessels , myocardial mass , and location of stenosis is not taken account in these semi - quantitative scores .
nuclear perfusion studies have shown that the clinical benefit of revascularization became evident when the ischemic burden exceeds 12% to 15% of total myocardial mass.48)49)50 ) ccta enables exact quantitative assessment of the burden of myocardium - at - risk and the extent of coronary artery disease ( fig .
ccta can find coronary artery disease , determine the significance of coronary artery disease , and guide treatment strategy including revascularization .
now it is time to validate and investigate the role of ccta in clinical practice and the impact of ccta on the clinical outcome .
coronary computed tomography angiography ( ccta ) has high negative predictive power for detecting coronary artery disease . 
 however ccta is limited by moderate positive predictive power in the detection of myocardial ischemia . 
 this is not unexpected because the diameter of a stenosis is a poor indicator of myocardial ischemia and discrepancy between the severity of stenosis and noninvasive tests is not uncommon . 
 the value of stenosis for predicting future development of acute coronary syndrome represented by plaque rupture has been questioned . 
 ccta identifies the characteristics of high - risk plaque including positive remodeling , low density plaque and spotty or micro - calcification . 
 also , additional evaluation of myocardial ischemia using computational flow dynamics , and luminal attenuation gradient are expected to increase both diagnostic performance for hemodynamically significant stenosis and the predictive power for future cardiovascular risk . 
 technical advances in ccta would enable evaluation of both coronary artery stenosis and myocardial ischemia simultaneously with high predictive performance , and would improve vastly the clinical value of ccta .