Physical Property and MR Imaging of Self-expandable Metallic Stents

ABSTRACT

PURPOSE: In order to furnish basic information prior to their use, the physical properties of variousself-expandable metallic stents and their MR characteristics were evaluated. MATERIALS AND METHODS: Fourcommercially available self-expandable metallic stents - Gianturco-the R sch, Hanaro, Memotherm, and Wallstent -were used in this study. For evaluation of the physical properties of each, hoop strengths and changes in radiiaccording to the degrees of longitudinal flexion were compared. Stent characteristics seen on MR images wereevaluated by measuring magnetic torque and by comparing images obtained in the vascular phantom using SE T1WI, FSET2WI, and FMPSPGR sequences. These images were analyzed with special emphasis on artifact size and the apparantshepe of the stent. RESULTS: Hoop strength was greatest in the Gianturco-R sch stent, followed by the Memotherm,Hanaro, and Wallstent. When flexed in the longitudinal axis, the radius of the Hanaro and Memotherm stentdecreased slightly as a larger flexion angle was applied. When this was 90degree, however, the connection of theGianturco-R sch stent collapsed. In contrast, the radius of the Wallstent became larger as a larger flexion anglewas applied. At the portal of the MR imaging unit, neither the Memotherm nor Wallstent showed deflection ; exceptfor a thin hyperintense rim at both ends, their images were excellent, and the lumina of these stents were alsoclearly seen. In contrast, the Gianturco-R sch and Hanaro stent demonstrated large deflexion and showed a severeblack-hole artifact. As a result, visualization of the stents themselves and their lumina was impossible. CONCLUSION: The Gianturco-R sch stent showed greater hoop strength than the others. The Wallstent showed goodlongitudinal flexibility and was thought to be effective in tortuous vessels. For follow-up after placement,especially when the nonferromagnetic Memotherm and Wallstent are used, MR imaging appears to be safe and useful.