الفهرس 
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Abstract
CHD is the leading cause of mortality world wide, is responsible for one out of every five deaths (Asakura et al., 1990) Treatment of cardiovascular risk factors has resulted in a 50 percent decrease in deaths from CHD over the past 30 years (Ford et al., 2007).The CCTA allows non invasive assessment of luminal stenosis as well as plaque morphology (Hamon et al., 2007; Motoyama et al., 2007; Kashiwagi et al., 2009). Several reports have confirmed CTA’s diagnostic accuracy for identifying significantly obstructive disease, and the severity of such stenosis was also predictive of major adverse cardiac events (Hulten et al., 2011; Shmilovich et al., 2011; Hadamitzky et al., 2013). The opportunity for more efficient use of CTA in the management of patients with chest pain may arise from the ability of CTA to accurately assess plaque characteristics, such as positive remodeling, spotty calcium, low HU attenuation, and napkin-ring sign (Hoffmann et al., 2006; Motoyama et al., 2007; Pundziute et al., 2008; Kashiwagi et al., 2009; Kitagawa et al., 2009; Gauss et al., 2011; Obaid et al., 2013). The recent CAD-RADS guidelines of the Society of Cardiovascular CT (SCCT) support the reporting of the presence of these HRP features (Cury et al., 2016) as These image findings reflect the characteristics of TCFA which possess abundant necrotic core (Virmani et al., 2002). In our study, We conducted a prospective observational single-center study including fifty three patients who underwent CCTA due to chest pain and suspected CAD to compare the performance of different pre-test cardiac risk score models which included; DFM, DCS, and CAD Consortium 1&2 scores and the ability of different scores to predict obstructive CAD, and HRP characteristics as assessed by CCTA. All patients were subjected to full clinical history, 12 –lead ECG, laboratory investigations include lipogram to detect dyslipidemia and kidney function test before performing CCTA. DF, DCS and CAD consortium 1&2 risk scores were calculated for every patient and patients were classified into low, intermediate and high risk according to these scores. We found that Consortium CAD-1 and consortium CAD-2 scores had significant difference than other risk scores across all CCTA findings including low attenuation plaque, spotty calcification, positive remodeling and NRS which are associated with significant stenosis, so it’s the best score for prediction of CAD and detection of HRP While DCS was better for prediction of low attenuation plaque, spotty calcification, remodeling and significant stenosis and DF was considered for prediction of low attenuation plaque only and overestimate the prediction of CAD. Conclusion: from our study we concluded that Consortium CAD-1 and consortium CAD-2 scores had significant difference than other risk scores across all CCTA findings including low attenuation plaque, spotty calcification, positive remodeling and NRS which are associated with significant stenosis, so it’s the best score for prediction of CAD and detection of HRP.While DCS was better for prediction of low attenuation plaque, spotty calcification, remodeling and significant stenosis and DF was considered for prediction of low attenuation plaque only and overestimate the prediction of CAD Also the presence of HRP criteria was associated with significant stenosis. Finally CCTA had been established as a reliable noninvasive imaging modality for the evaluation of CAD and detection of HRP in patients presented with chest pain with normal or non-conclusive ECG changes with normal cardiac enzymes assay. The greatest limitation of our study is the small sample size of patients. Logistic issues were related to such small sample size. Follow up information was not available. Following patients up for clinical endpoints would have had important clinical implications. However, with such small sample size clinical endpoints would have been scarce and inconclusive.
• The study is a single center study that included patients admitted in a limited period. Quantitative plaque assessment was not feasible. Although it is time-consuming, and not widely used in clinical practice, yet it would have added important clinical information.
Data for individual coronary artery segments were not available for this study.