Imaging description

Evaluation of coronary stents with cardiac CT is challenging due to artifacts associated with the metal stent struts. Several artifacts adversely affect CT imaging of stents, the most important of which are blooming, partial volume averaging, and beam hardening. Both blooming and partial volume effects result in the stent struts appearing larger than reality, obscuring visualization of the lumen, and resulting in under-estimation of true lumen diameter (Figure 34.1). Beam hardening artifacts occur due to absorption of low-energy photons by the metal stent struts resulting in primarily high-energy photons passing to the detectors. The result is low- attenuation areas adjacent to stent struts that can mimic instent restenosis. Stent-related artifacts are most pronounced in smaller stents, and current recommendations suggest that imaging of coronary stents should be restricted to patients with larger stents, at least 3 mm in diameter or more. Stents of similar size from different manufacturers can also have variable artifact severity, due to differences in the type of materials used to create the stent. Widening the window width will reduce the blooming effect of stent struts and improve lumen visualization. (Figure 34.1). Visualization can also be optimized and artifacts reduced through the use of the thinnest possible slices, sharp reconstruction kernels, and iterative reconstruction techniques (Figure 34.2).

Importance

Misdiagnosis of in-stent restenosis on cardiac CT can lead to inappropriate cardiac catheterization and the risks and costs associated with the procedure.

Typical clinical scenario

In-stent restenosis, defined as > 50% luminal narrowing, is a common problem in patients with prior percutaneous coronary intervention. Neointimal hyperplasia within the stent is the primary cause of in-stent restenosis. Restenosis rates are approximately 40% with bare metal stents and are reduced to < 10% with drug-eluting stents.

Differential diagnosis

Stent-related artifacts should be distinguished from true in-stent restenosis or occlusion due to neointimal hyperplasia (Figure 34.3). For stents < 3 mm in size, this may be difficult due to limitations of current scanner technology.