الفهرس 
Review of LiteratureOnly 14 pages are availabe for public view
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Abstract
Cardiovascular diseases are the number one cause of death globally. The number of people who die from cardiovascular diseases, mainly from coronary heart disease and stroke, will increase to reach 23.3 million by 2030 from an estimated 17.3 million deaths in 2008. Cardiovascular diseases are projected to remain the single leading cause of death by 2030 globally.
Acute myocardial infarction and sudden cardiac death remain the first manifestations of coronary atherosclerosis in the majority of the population (50% of men and 64% of women), which accounts for these unfavourable statistics. Most individuals do not, therefore, experience any symptoms or warning signs before the coronary event occurs. Prevention of acute coronary events seems to be the only effective strategy to reduce the burden of cardiovascular disease and improve mortality and morbidity rates. Considerable efforts are ongoing to predict where acute coronary events will happen on an individual plaque level. The identification of patients at high risk of developing acute coronary events remains a major challenge in cardiovascular imaging.
MDCT is a great noninvasive option for characterization of coronary atheromatous plaque it can quantify; and, to a certain extent, characterize coronary atherosclerotic plaque. It can predict and so prevent ACS. Imaging findings associated with vulnerable plaque include spotty calcification, presence of napkin ring sign low mean Hounsfield units heterogenous attenuation soft tissue plaque composition as well as positive remodelling. All these factors had a lot of contribution in predicting plaque vulnerability thus facilitating a more rapid medical action.
However, CT characterization of coronary atherosclerotic plaque remains challenging and requires optimization of image quality. Imaging barriers for correct analysis of plaque components with CT include limited contrast and spatial resolutions, motion artifacts, heterogeneous plaque composition, and a lack of standardization regarding the assessment of coronary lesions. However, it can be expected that further technical improvements regarding data acquisition and reconstruction as well as an increasing number of prognostic and outcome studies will help to establish CT as a tool for early identification of patients at increased risk for coronary events. The specific patient groups that benefit from such forms of testing remain to be clearly defined.
The study showed that Napkin ring sign and plaque attenuation pattern both had the largest AUC followed by plaque-type and finally spotty calcifications. However, Napkin ring sign and plaque attenuation pattern were better than spotty calcifications in the differentiation of unstable and stable plaques. No significant difference was seen between the AUCs of plaque-type and spotty calcifications.
The composition of atherosclerotic plaques in the coronary arteries displays substantial variability and is associated with the likelihood for rupture and downstream ischemic events. Accurate identification and quantification of coronary plaque components on CT is challenging because of the limited temporal, spatial, and contrast resolutions of current scanners.
There were several limitations in this study that should be avoided in further studies. These include in the first place the inclusion criteria which should have included an IVUS scan and not only clinical symptoms but unfortunately, the IVUS was not available. Also, the spatial resolution of current CT scanners is under the threshold needed for identifying microcalcification. Another problem faced was the presence of spotty calcification within the outer hyperdense rim of NRS so its prevalence may be overestimated.
The use of IVUS would be highly recommended for the inclusion/exclusion criteria as well as increasing the sample size. Also, increasing the measured factors to include the grade of microcalcification this can be done by the aid of 18F-sodium fluoride PET which is a promising new technique to visualize microcalcifications.
16 of Unstable patients showed mixed plaques and 10 were soft and only 4 patients showed calcified plaques while in stable patients most of the plaques were calcified only 2 patient showed soft plaques and 4 patient s showed mixed plaques
As for the attenuation pattern 18/46 of the plaque with heterogeneous attenuation on follow up was seen in the unstable clinical group.
28/46 of the plaques showed homogenous attenuation 16 of the cases were stable suggesting that heterogeneous plaques were always seen in unstable cases
Regarding the Napkin ring sign it was positive in 18/46 of the plaques and the 18 patients on follow up were found to be unstable,
As for spotty calcification, it was found in 8 plaques only and all patients proved to be unstable clinically. Spotty calcification was not present in stable cases and was present in 22 plaques that were unstable indicating that once positive spotty calcification is present it indicates means instability
In comparing results obtained radiologically with clinical follow-up Remodeling index was higher in the unstable group with a median of 1.4. As well as the plaque burden which was also higher in the unstable group. Plaques in the unstable clinical group also showed low hounse field units while the stable group showed a lot higher hounse field units. There was not any association between neither Stability nor the degree of stenosis.
Results from preliminary radiological classification regarding plaque instability factors Composition, Plaqueburden, Remodelling index, Attenuation pattern, Spotty calcification, Napkin-ring sign, Mean hounse field units proved to link significantly to the clinical classification where patients with unstable radiological findings proved on clinical follow up to show an unstable clinical picture. Therefore CT is a good modality in detecting and differentiating between stable and unstable plaques and hence it could be used for risk stratification to save lives.