الفهرس 
ANATOMYOnly 14 pages are availabe for public view
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Abstract
CT imaging has high spatial resolution, and high contrast between the blood pool and other tissues can be achieved after injection of contrast agent.MDCT imaging therefore has the ability to provide high-resolution morphological imaging of the heart. However, clinically CT imaging does not play a routine role in evaluating general cardiac morphology, because echocardiography or magnetic resonance imaging (MRI) can provide all relevant information in most clinical situations, without the need for contrast injection or exposure to radiation. However, cardiac CT imaging can be clinically helpful in a variety of selected situations, including the need for cross-sectional imaging after echocardiography in patients with pacemakers or other devices that preclude MRI. Also, CT techniques have an extremely high accuracy for the depiction of calcified structures. Clinically, the main focus of cardiac CT imaging is its use for visualization of the coronary arteries.
A recent consensus paper on appropriateness criteria for cardiac imaging by CT and MR lists the use of coronary CT angiography (CTA) as appropriate in patients with chest pain who have abnormal findings in exercise testing as well as in symptomatic patients who have an intermediate likelihood of coronary artery disease but who cannot exercise or who have an uninterpretable ECG.
Also angiography with 64-slice multi-detector CT scanner may provide reliable non-invasive imaging to exclude significant coronary artery stenoses prior to valve surgery. The negative predictive value of a normal CT scan is around 97%, thus providing a good alternative to conventional angiography in lower atherosclerotic risk patients.
Owing to its unsurpassed spatial resolution, conventional catheter angiography is widely accepted as the gold standard for the detection of CAD. However, catheter-based angiography displays only the vessel lumen and the degree of luminal narrowing in a cast-like manner. It fails to visualize the coronary artery wall. On the other hand, contrast-enhanced CT delineates calcified and non-calcified non-stenotic lesions within the coronary artery wall itself. The ability of contrast-enhanced CT to non invasively assess atherosclerotic processes within the vessel wall has sparked considerable scientific interest and may provide more valuable insight in the intricate pathogenesis of coronary atherosclerosis .As while MRI generally offers more comprehensive means for non-invasive tissue characterization compared with CT and has been shown to be capable of imaging vessel wall structures for differentiating various stages of atherosclerosis. But in vivo MRI of the coronary artery wall however is challenging due to a combination of cardiac and respiratory motion artifacts and the tortuous course, small size and location of the vessels. Development of more robust and reliable MR technology will be needed before in vivo plaque assessment in human coronary arteries becomes a viable routine clinical reality. Also another diagnostic modality characterization of coronary artery wall lesions is intravascular ultrasound. However, due to the invasive and expensive nature of this test it has not found more widespread use.
MDCT has other roles in coronary artery disease including:
Coronary CT angiography (CTA) is a reliable tool to investigate patients with known or suspected congenital coronary artery anomalies. As MDCT can classify both the origin and course of anomalous coronary vessels.
Coronary CTA has also a significant role in follow up after interventions or surgery. That the evaluation of multidetector CT for graft patency is improved over single slice CT as multidetector CT scanners combine high spatial resolution with the ability to demonstrate anatomy through volume-rendered images, also the addition of electro-cardiographic gating minimizes cardiac and coronary graft motion further improving the sensitivity and specificity of multidetector CT evaluation for graft patency. These advances have also increased the ability to estimate the extent of intraluminal graft occlusion with noninvasive imaging techniques . In addition, there are several recent reports on the merits of volume –rendered multidetector CT images in preoperative planning for repeat CABG surgery.
Also multidetector CT especially with the new scanner generations can assess coronary stents, that recent experience with the current generation of 64-section scanners suggests improved assessability of the in-stent lumen with the capability to appreciate more subtle degrees of in-stent neointimal hyperplasia.However knowledge of the different types of artifacts and how they can be compensated by the dedicated postprocessing and appropriate image views and window settings is required for reliable depiction of the in-stent lumen and leads to a more robust application of CT findings in the clinical context.
New application of MDCT is myocardial perfusion. It has been shown to demonstrate perfusion defects in arterial phase CT that correlate with myocardial infarct. It may even be possible to differentiate acute versus chronic infarct. Similar to MRI, Delayed hyperenhancement of infarcted myocardium can be imaged by MDCT, though with limitations of more radiation exposure and more contrast administration.
MDCT has rapidly emerged to become an important diagnostic tool, but its full potential in cardiovascular medicine is just beginning to be realized.