What are the CT and MRI imaging features of coronary arterial stents and bypass grafts?
Coronary arterial stents can be easily visualized on CT images as high-attenuation metallic mesh foci with the presence of stent struts. Different reconstruction algorithms (e.g., sharp kernels) can be used to improve the visualization of coronary stents. In the future, with improvements in spatial resolution and image noise reduction, the evaluation of in-stent restenosis will be more feasible. A sensitivity of 85% to 95% and specificity of 86% to 95% are achievable for detection of in-stent stenosis by CT compared to catheter angiography by using a sharper reconstruction kernel. The factors that affect the visualization of in-stent restenosis include motion artifacts, blooming artifacts, stent diameter, stent composition (less dense metals such as stainless steel provide better images than stents with denser metals such as tantalum), and the presence of coronary calcifications.
CT has been utilized to evaluate the patency of bypass grafts since the development of electron beam computed tomography (EBCT) in the 1980s. However, with the development of multidetector computed tomography (MDCT), coronary CTA can be utilized to evaluate the patency of bypass grafts more efficiently due to its superior spatial resolution. Specifically, anastomotic patency can now be better assessed compared to EBCT given better image quality and improved visualization software with curved planar reformats and 3D reconstructions.
Saphenous venous grafts can be effectively evaluated by CT, including jump grafts that have a side-to-side anastomosis (i.e., a diagonal branch) first and then continue to an anastomosis with a second vessel more distally (i.e., an obtuse marginal branch). Evaluation of arterial bypass grafts such as internal mammary graft and radial artery graft may be limited by the presence of multiple surgical clips associated with these grafts, which may produce extensive artifacts. However, the overall patency can usually be adequately assessed. Bypass graft stenosis, occlusion, and aneurysm formation can be identified by CTA.
Coronary MRA has been studied to evaluate the patency of coronary bypass grafts and may be an alternative modality for assessing bypass graft patency when coronary CTA is contraindicated. The evaluation of coronary artery stent patency by MRA is not yet clinically feasible given artifacts caused by the metal in stents.