特集 CAS と術後評価
CT angiographyによる頚動脈ステント留置術後の評価─Wallstent使用時の撮影方法の工夫─
2017 年 45 巻 1 号 p. 7-13
詳細
2017 年 45 巻 1 号 p. 7-13
Computed tomography angiography (CTA) is useful for postoperative evaluation of restenosis and plaque protrusion after carotid artery stenting (CAS). However, stent artifacts are a common problem in the evaluation of CTA images, which are dependent on characteristics such as stent structure and raw materials. Especially Carotid Wallstent Monorail (CWS; Boston Scientific, Natick, MA, USA), which is made of cobalt-chromium alloy and tantalum, generates severe artifacts as compared with nitinol stents because of the high atomic number of tantalum. CWS is a closed-cell stent; thus, the braided wire is characteristically linear and cyclic. Therefore, we hypothesized that the effects of tantalum can be avoided by appropriate positioning of the patient in the CT scanner. In this study, we aimed to establish an optimal protocol for CTA after CAS with CWS.
Material and methods: CWS (10 × 24 mm) was used as a blood vessel model. After reconstitution of the contrast agent in diluent, CTA was performed by varying the tilt angle of the stent with respect to the Z-axis from 0° to 60°. The CT value was measured in any of the three points in the stent strut. Thirty consecutive patients who underwent CAS with CWS were examined to determine the relationship between the tilt angle and the CT value of the stent strut retrospectively.
Results: In the phantom experiment with a blood vessel model, the CWS artifacts in the curved multiplanar reconstruction (MPR) images evaluated by using Noise SD decreased with the tilt angle, especially at the tilt angle of 35–45°. Noise SD is largest at the narrowest blood vessel diameter, even at the same tilt angle. In the 30 clinical cases, a negative correlation was observed at the tilt angle of 13–40° (r = -0.73). A negative correlation was also observed between the Noise SD and minimum vessel diameter (r = -0.36).
Conclusion: CTA after CAS with CWS could be useful for evaluating the in-stent lumen with the appropriate tilt angle to reduce artifacts.
