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CTA Assessment of Coronary Artery Stents


CCT Imaging of Coronary Stents

The accurate assessment of coronary stents remains a major challenge for cardiac CT (CCT), and although the stent itself is readily imaged, the lumen within it is not, because the stent material confers “blooming” artifact. Stents with a denser “weave” are harder to image. A stent deployed within a stent for restenosis leaves little chance of accurately depicting the lumen. Small amounts of motion during acquisition disperse the partial volume averaging effect over more voxels, increasing the depiction of the stent and further reducing the luminal depiction. Thicker struts confer greater artifact. As would be expected, the patency of large vessels or stents is easier to assess, as the blooming artifact is less likely to obscure the whole lumen. False positives occur in 5% to 10% of cases, reducing the positive predictive value. Bifurcation lesions are difficult to assess. Although CCT and intravascular ultrasound (IVUS) data generally correlate, CCT tends to overestimate stent diameter. Only studies that are either small, single-center, or select have been presented thus far, and almost always of stents of 2.5 mm or larger, which remains the lower limit of reasonable size to assess by CCT. Few series have been published with 64-CCT systems. The generally pessimistic data that were obtained in studies of older systems, such as those using 16-CCT, still are considered the norm, so that it is still thought that, in most cases, the presence or absence or extent of in-stent restenosis cannot be determined ( Tables 7-1 through 7-3 ).

TABLE 7-1
CCT for the Evaluation of Coronary Artery Stents
AUTHOR JOURNAL YEAR CT NO. PATIENTS/ STENTS NONASSESS. (%) Lesion Sensitivity (%) Specificity For ISR (%) PPV (%) NPV (%)
Schuijf et al. Am J Cardiol 2004 16 22 1 78 100 — —
Van Mieghem et al. Circ 2007 — — — 70 LMCA only 100 91 67 100
Cademartiri et al. JACC 2007 64 182 7% 192 stents all ≥2.5 mm 95 93 63 99
Gaspar et al. JACC 2005 40 65 — 72 93 65 95
Oncel et al. Radiol 2007 — 30/39 0 89 95 94 90
Oncel et al. Am J Radiol 2008 Dual source 30/39 — Stenosis and occlusion 100 94 89 100
Pugliese et al. Heart 2008 — 100/178 5 94 92 77 98
Ehara et al. JACC 2007 — 81/125 12 91 93 77 98
Rixe et al. Eur Heart J 2006 64 64/102 42% 86 98 86 98
Rist et al. Acad Radiol 2006 64 75 8% 75 92 67 94
Abdelkarim et al. JCCT 2010 64 55/122 4% 91 95 96 91
ISR, in-stent restenosis; LMCA, left main coronary artery; nonassess, nonassessable; NPV, negative predictive value; PPV, positive predictive value.

TABLE 7-2
CCT for the Evaluation of Left Mainstem Coronary Artery Stenting
AUTHOR JOURNAL YEAR CT NO. PATIENTS/ STENTS SENSITIVITY (%) SPECIFICITY (%) PPV (%) NPV (%)
Van Mieghem et al. Circ 2007 16/64 74 100 91 67 10
NPV, negative predictive value; PPV, positive predictive value.

TABLE 7-3
CCT for the Evaluation of Coronary Artery Stents
Data from Schroeder S, Achenbach S, Bengel F, et al. Cardiac computed tomography: indications, applications, limitations, and training requirements: report of a Writing Group deployed by the Working Group Nuclear Cardiology and Cardiac CT of the European Society of Cardiology and the European Council of Nuclear Cardiology. Eur Heart J. 2008;29(4):531-556.
NO. PATIENTS/STENTS NOT EVALUABLE (%) SENSITIVITY (%) SPECIFICITY (%) PPV (%) NPV (%)
482/682 12 (82/682)
95% CI: 9.7–15		 91 (105/115)
95 CI: 85–96		 93 (461/494)
95 CI: 91–95		 76 (105/138) 98 (461/471)
NPV, negative predictive value; PPV, positive predictive value.

The detail of the stent is variably, but usually fairly, defined by CCT. The metallic composition of the stent has a major effect on the brightness of the stent—for example, that of the ACS RX Multilink (Abbott Vascular, Abbott Park, IL) is 269 ± 19 HU, whereas that of the Sirius Carbostent (Sorin Biomedica Cardio, Saluggia, Italy) is 437 ± 29 HU. The metallic composition also affects the ability to image the detail of the stent. A sharp or detail reconstruction kernel often is used to minimize the blooming artifact caused by the metallic struts of a stent. This modulation of the technique is felt to increase the conspicuity of subtle neo-intimal hyperplasia within the stent. Use of a wide window (width 1500 HU; center 300 HU) is also recommended, as this, in conjunction with a sharper kernel, will minimize blooming artifact.

Restenosis or thrombosis is apparent as lower-attenuation material within the stent; visually or quantitatively, this can be referred to elsewhere in the vessel or better yet, to the ascending aorta: a reading of 0.81 predicts patency with a sensitivity of 91% and a specificity of 95%.

Expected severe artifact problems associated with imaging stents include:

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    Small vessels or small stents

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    Multiple stents at one site (overlap)

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    Stents with more metal

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    Calcium in underlying plaque

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    Artifacts from sternal wires, clips, pacemakers

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    Hypodense restenosis material in proximity to high-attenuation stent material

Some unusual stent-related problems, such as stent-induced coronary aneurysm formation, have been imaged by CCT.

Adequate CCT Imaging of Patent Stents

Figures 7-1 through 7-7 show adequate CCT imaging of patent stents.

Figure 7-1, Multiple images from a cardiac CT study in a patient with prior coronary artery stenting within the left anterior descending (LAD) coronary artery. Despite a high-quality study, the lack of any motion artifact, and high contrast density within the coronary arteries, the proximal to mid-LAD stent is virtually unassessable, due primarily to the size of the stent and its strut structure. There is no evidence of an LAD stenosis at either the proximal or the distal ends of the stent.

Figure 7-2, A 62-year-old woman with known coronary artery disease. The patient has a history of prior stent placement. Stents can be difficult to distinguish from underlying coronary artery calcification. Multiple cross-sectional images through the stent within the proximal circumflex artery demonstrate too much blooming artifact for proper evaluation.

Figure 7-3, Two images from a cardiac CT study performed to evaluate bypass graft patency demonstrate a patent left internal mammary artery (LIMA) graft with a stent just above the anastomosis of the LIMA and the left anterior descending artery (LAD). Altering the window and width levels ( B ) allows better visualization through the stent.

Figure 7-4, A graft from the saphenous vein to the second obtuse marginal branch (SVG-0M2) demonstrates moderate (50%) ostial stenosis, with five stents seen in the ongoing graft. There is no evidence of in-stent stenosis or thrombosis.

Figure 7-5, Multiple curved reformations from a cardiac CT study demonstrate no evidence of in-stent stenosis or thrombosis within a stented left anterior descending (LAD) artery or in a stented first diagonal branch. There is a mild amount of soft plaque seen proximal to the LAD stent, causing a stenosis of less than 20%.

Figure 7-6, Curved images from a cardiac CT study for stent evaluation. The proximal left anterior descending (LAD) artery with a second stent extending into the D1 branch demonstrates patency with no evidence of incident stenosis. The ongoing LAD is normal.

Figure 7-7, A, Curved reformatted view of a patent multiply-stented saphenous vein graft to the obtuse marginal branch of the left circumflex artery. B, Three-dimensional reconstruction and vessel extraction cross-sectional views of a patent multiply-stented saphenous vein graft to the obtuse marginal branch of the left circumflex artery.

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