الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
Multislice CT is a recent development in the spiral CT. The MSCT scanners are equipped with multiple and thinner detector rows and have faster tube rotation speed creating two major advantages; high spatial resolution and short acquisition time that enable high-quality examinations. By this increase in the data acquisition volume per unit time, CT assessment of the coronary arteries has become possible.
Challenges in evaluating the coronary arteries at CT are the small size and tortuous courses of the vessels and their continuous movements being intimately related to the cardiac chambers. Controlled heart rate and good breath-holding help to reduce cardiac and respiratory motion artifacts respectively. Retrospective ECG gating and proper choice of the reconstruction window would significantly improve the examination quality.
To date, the main indications for CT angiography are:
-The noninvasive detection and grading of coronary artery stenosis.
-Follow up after coronary bypass surgery.
-Detection of coronary stent patency.
-Detection of suspected coronary anomalies.
Contraindications to CTCA include irregular heart beats (arrhythmias), contra-indications to iodinated contrast material including allergy and renal insufficiency and contra-indications to radiation exposure e.g., pregnancy.
In this study, 45 patients scheduled for elective conventional coronary angiography for known or suspected CAD were enrolled for MSCT angiography. Findings of CT angiography were compared to those of conventional angiograms. Evaluation was performed on a per segment basis, considering the results of the selective coronary angiography as the gold standard.
Our study revealed an overall sensitivity of 99%, specificity of 94.5%, PPV of 83.5%, NPV of 97.5 % and accuracy of 95.5%. Results of this study matches with the results of those studies published at 2005-2010 that were performed on a comparable MSCT scanners (64-channel systems). In view of the high NPV, it seems probable that patients without significant coronary artery disease would be selected accurately at CT, and hence, avoiding the unnecessary invasive coronary angiography.
Regarding the patients with previous CABG surgery, in our study; all the origins and bodies of the grafts were identified correctly by CT. However, CT angiographic results regarding evaluation of the anastomotic sites are still lower than those of conventional angiography.
As regard the assessment of coronary stents, CT correctly detected the stent patency however the degree of in-stent restenosis was not adequately assessed mainly due to the beam hardening artifact by the metallic stent.
The current results revealed that the MSCT angiography is a good non-invasive coronary imaging modality that is able to delineate the coronary anatomy and early detect and grade coronary lesions competing with other noninvasive examinations used to detect CAD, such as exercise stress testing. Because of its high negative predictive value, CT angiography might be employed to exclude significant CAD and thus avoid unnecessary coronary angiograms in certain groups of patients.
Various artifacts associated with data creation and reformation, post-processing methods, and image interpretation can impair accurate diagnosis. These artifacts can be related to cardiac or respiratory motions, partial volume averaging, and high-attenuation entities (e.g. dense coronary calcifications, stents and surgical clips). Some of these artifacts have already been resolved with technical advances, whereas others represent partially inherent limitations for coronary CT angiography.
Problems and limitations remain, as always, and will trigger scientific and technical efforts. Accepted strategies to improve scanner performance include evaluation of the electron beam CT (EBCT) detectors to allow simultaneous acquisition of multiple sections and trial of the dual-source computed tomography (DSCT) equipped with two X-ray tubes and two corresponding groups of detectors mounted on the rotating gantry aiming at improvement of the temporal resolution.
Conclusion
Non-invasive CT angiography of the coronary arteries is a challenging and rapidly advancing technique. MDCT provides very high spatial resolution and allows for excellent visualization of the coronary arteries. Hemodynamically significant stenoses can be detected and excluded with high accuracy. Current limitations of CT angiography include gantry rotation speed, arrhythmias and the presence of severe coronary calcifications. Continued technical progress is expected to overcome most of these limitations.