From the Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg.
Clinic for Diagnostic and Interventional Radiology, Saarland University Medical Center, Homburg/Saar, Germany.
Invest Radiol. 2020 Nov;55(11):741-746. doi: 10.1097/RLI.0000000000000692.
The aims of this study were to assess radiofrequency (RF) shielding and susceptibility-induced imaging artifacts of venous stents with different designs at 1.5 T and to analyze the relationship between stent designs, that is, cell geometry and RF shielding.
Twelve dedicated venous stents and 1 stent used for venous pathologies with 8 different designs from 5 different manufacturers were tested: Blueflow (plus medica, Düsseldorf, Germany), Sinus Obliquus, Sinus Venous, Sinus XL (Optimed, Ettlingen, Germany), Vici (Veniti, St. Louis, MO), Zilver Vena (Cook, Bjaeverskov, Denmark), and Venovo (Bard, Tempe, AZ). Two versions with different lengths were available from all stents except the Venovo. For each stent, B1 and frequency mapping was performed using the double angle method and gradient multiecho imaging. Each stent was measured in 3 different orientations: parallel, orthogonal, and at 45 degrees to B0. A correlation analysis was performed between the induced B1 field strength inside the stents and the geometries of the cells.
Radiofrequency shielding was found to be strongly varying between different stent designs. The 120-mm-long Vici stent showed the lowest mean relative B1 amplitude of (38% ± 16%) when oriented parallel to B0. The highest mean B1 amplitude was measured inside the 100-mm-long Blueflow stent with diagonal orientation (90% ± 20%). Averaged over all stents, the shielding was 18% stronger when the stents are oriented orthogonal to B0 compared with a parallel orientation and the between-stent variation was lower for the orthogonal orientation (11%) compared with the parallel orientation (20%). For laser-cut stents, a linear correlation was found between the amount of RF shielding and the length of individual cells measured perpendicular to the stents' long axes. The woven stents showed a strongly inhomogeneous intraluminal RF shielding pattern, whereas the laser-cut stents provided a more homogeneous shielding pattern. No substantial susceptibility-induced frequency shifts were measured near all stents with a maximum shift of [INCREMENT]f = 96 Hz measured in the vicinity of the 150-mm-long Sinus Obliquus stent.
Magnetic resonance imaging in the vicinity of commercially available venous stents is feasible at 1.5 T with no substantial susceptibility-induced artifacts but reduced transmit and receive B1 field strengths inside the stents. The strength and homogeneity of the intraluminal B1 depend on the stents' fabrication (woven or laser-cut) and cell geometry.
本研究旨在评估不同设计的静脉支架在 1.5T 时的射频（RF）屏蔽和感生成像伪影，并分析支架设计（即细胞几何形状和 RF 屏蔽）之间的关系。
测试了 12 个专用静脉支架和 1 个用于静脉病变的支架，这些支架来自 5 家不同制造商的 8 种不同设计：Blueflow（plus medica，杜塞尔多夫，德国）、Sinus Obliquus、Sinus Venous、Sinus XL（Optimed，埃特林根，德国）、Vici（Veniti，圣路易斯，密苏里州）、Zilver Vena（Cook，Bjaeverskov，丹麦）和 Venovo（Bard，坦佩，亚利桑那州）。除 Venovo 外，所有支架均有两种不同长度的版本。对于每个支架，使用双角度法和梯度多回波成像进行 B1 和频率映射。每个支架在 3 种不同的取向下进行测量：平行、正交和与 B0 成 45 度角。对支架内感应的 B1 场强与细胞几何形状之间进行相关性分析。
发现不同支架设计之间的射频屏蔽差异很大。当与 B0 平行取向时，120mm 长的 Vici 支架显示出最低的平均相对 B1 幅度（38%±16%）。当以对角线方向取向时，100mm 长的 Blueflow 支架内测量到的平均 B1 幅度最高（90%±20%）。在所有支架中，与平行取向相比，支架正交取向时的屏蔽强度强 18%，支架之间的变化也较小（11%比 20%）。对于激光切割支架，发现 RF 屏蔽量与垂直于支架长轴测量的单个细胞长度之间存在线性相关性。编织支架显示出腔内射频屏蔽的强烈不均匀模式，而激光切割支架则提供了更均匀的屏蔽模式。在所有支架附近测量到的磁共振成像（MRI）灵敏度诱导的频率偏移都没有实质性变化，在 150mm 长的 Sinus Obliquus 支架附近测量到的最大偏移为[增量]f=96Hz。
在 1.5T 时，使用商用静脉支架进行 MRI 是可行的，不会产生实质性的敏感性诱导伪影，但支架内的发射和接收 B1 场强会降低。腔内 B1 的强度和均匀性取决于支架的制造工艺（编织或激光切割）和细胞几何形状。
