Multidector CT Imaging of Coronary Artery Stents: Is This Method Ready for Use?

Coronary artery stenting has become the most important nonsurgical treatment for coronary artery disease. However, in-stent restenosis occurs at a relatively high rate and this problem has led to the routine use of invasive angiography for assessing stent patency. Although coronary angiography is the clinical gold standard and it is a very effective diagnostic tool for detecting such in-stent restenosis, it’s clearly an invasive procedure with its associated morbidity and mortality risks. Therefore, a noninvasive technique for detecting in-stent restenosis would be of great interest and use for following up patients after coronary angioplasty. Multidetector-row CT (MDCT) is being increasingly used for noninvasive coronary artery imaging as it has high diagnostic accuracy for detecting coronary artery stenosis in native, non-stented, coronary arteries. However, the application of MDCT to stent imaging is somewhat difficult. It is generally accepted that visualizing the in-stent lumen with using 4-slice MDCT is impossible because of the modality’s low temporal and spatial resolution. There is increased visualization of the stent lumen on 16-slice MDCT, and so in-stent restenosis can be detected in assessable stents. Yet for stents with small diameters (<3 mm) and/or thicker struts, visualization of instent stenosis remains a problem. The recently introduced 64-slice CT offers more improved spatial and temporal resolution than does 16-slice CT and this results in superior visualization of the stent lumen and in-stent restenosis. However, although 64-slice MDCT allows for improved stent visualization, a relevant part (up to 47%) of the stent lumen is still not assessable. There are many factors that interfere with the assessment of the real stent lumen even on 64-slice CT. The metal of the stents can cause blooming artifacts that prevent the accurate interpretation of a lumen’s patency. The blooming effect is caused by a combination of partial volume averaging and beam hardening, and this results in higher CT attenuation values in the stent lumen and this enlarges the apparent size of the stent struts, thus leading to a pseudo-narrowing of the lumen. Regarding the type of stent, the gold or gold-coated stents along with the stents made of tantalum, cause the most severe artifacts, while the stainless steel and cobalt stents can be more accurately visualized. Cardiac motion, poor contrast filling, the oblique course of the coronary vessels and calcification may also decrease the ability to assess a stent’s lumen. To improve a stent’s visualization, numerous methods have been attempted such as dedicated post-processing or the use of dual-source CT. However, because of its presently limited sensitivity and high radiation exposure, MDCT should not be used as the first-line test to screen for in-stent restenosis in asymptomatic patients. Given its high specificity and negative predictive value, MDCT might be valuable for confirming stent occlusion in symptomatic patients. Such stent evaluation should focus on the proximal coronary artery segments and on those stents with a diameter greater than 3 mm. (Korean Circ J 2007;37:521-529)