الفهرس 
Anatomy of Coronary Arteries and Their Normal VariantsOnly 14 pages are availabe for public view
 |  | from | 100 |  |  |
| | | from | 100 | | |
Abstract
Percutaneous coronary intervention (PCI) has gained widespread acceptance as the treatment of choice for managing symptomatic coronary disease. The most important advance in the field of PCI was the introduction of coronary stent implantation in the 1990s because this lead to a reduction in both the risk of acute major complications and the incidence of restenosis, as compared with the risks after balloon angioplasty.
While its technical success rate exceeds 95%, stent restenosis remains a clinical problem. The introduction of drug eluting stents into clinical practice has dramatically reduced the occurrence of restenosis compared with the use of bare metal stents. Yet, even at this low rate, stent restenosis remains an important problem And so an efficient diagnostic tool for follow up after stent placement is needed. Coronary angiography is presently the standard procedure for assessing the vessel lumen after stent placement. However, this method may involve major complications due to its invasiveness.
Coronary In stent restenosis is associated more with bare metal stent, drug eluting stent provide less incidence restenosis, yet, the major disadvantage is slowing the rate of re –endothelium repair raising the possibility of early / late thrombus formation.
Significant ISR is Clinically defined as the presentation of recurrent angina or objective evidence of myocardial ischemia or dyspnea with exertion, whereas angiographic ISR is the presence of >50% diameter stenosis in the stented segment. Traditionally, ISR has been classified based on the length of the lesion, as focal (<10 mm) or diffuse (>10 mm). in stent intimal hyperplasia causing narrowing less than 50% is considered less significant, high grade ISR is defined as 75 % or more narrowing of coronary stent.
The main factor of ISR is neo-intimal hyperplasia, pathogenesis including many explanation, most important cause is due to endothelial injury after stenting which stimulate inflammatory response with fibrin and platelet deposition in early phase & stimulate smooth muscle aggregation and formation of extracellular matrix in late phase.
MDCT Imaging protocol include patient preparation (heart rate control) optimum contrast enhancement and post processing interpretation, although 16 MDCT has good results in assessing ISR, 64 MDCT is of choice in contribution with more spatial and temporal resolution, many limiting factors is associated in technique including blooming artefacts, partial volume average, residual cardiac motion and type, size (preferred to be 3mm or more in diameter) and strut thickness of the involved stent making the study is more feasible in only selected patients. Yet with more advanced post processing technique including convolution filters, retrospective gated ECG postprocessing, curved multi-planer reformatting and windows setting display these problems become more liable to be overcomed and making in-stent luminal visualization is more interpretable & so, Knowledge of the different types of artefacts and how they can be compensated for with dedicated post-processing and appropriate image views and window settings is a prerequisite for reliable depiction of the in-stent lumen.
The direct visualization of the in-stent lumen is the most important for assessing patency & not on distal run off attenuation measurements, because collateral vessels may be feeding vessel segment distal to the occluded stent in a retrograde direction. Non occlusive in-stent neointimal hyperplasia is characterized by the presence of a darker rim between the stent and the contrast-enhanced vessel lumen, The stent may be considered to be occluded if the lumen inside the device appears darker than the contrast-enhanced vessel lumen proximal to the stent.
Many studies after exclusion of uninterpretable stents revealed a good sensitivity (88-92 %) high specificity and with a negative predictive value of (94- 98.5% (& accuracy reaching up to of 90%, it is found that the accuracy of coronary CT angiography was better for stents with 50% or more reduction of in-stent luminal diameter. However, the accuracy of coronary CT angiography was inferior for stents with less than 50% reduction in luminal diameter, false positive results are seen in comparative to complementary invasive coronary angiography mostly due to stent diameter less than 3 mm with thick strut & multiple coronary artery calcifications.
In selected patients, Contrast-enhanced especially 64-section coronary CT angiography can be used as a promising, accurate non invasive test to evaluate stent restenosis and hence, can have substantial clinical implications for screening patients suspected of having coronary artery stent restenosis.
Despite that, with presence of non condoned percentage of false positive results & uninterpretable stents due to many factors, still the role of MDCT coronary stent angiography is of questionable role in patients with emergent typical chest pain with laboratory and ECG results indicting of possibility of infarction as a primary line of investigation. & still the invasive coronary angiography is the gold standard and first line of choice.
In future, the development of biodegradable & bioabsorbable stents may create optimal conditions like transparency for noninvasive postimplantation follow-up with multidetector CT.