Departement of Neuroradiology, Geneva University Hospitals, Geneva, Switzerland.
Laboratory for Hydraulic Machines (LMH), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
Magn Reson Med. 2019 Jan;81(1):560-572. doi: 10.1002/mrm.27352. Epub 2018 Jun 12.
The morphological and hemodynamic evaluations of neurovascular diseases treated with stents would benefit from noninvasive imaging techniques such as 3D time-of-flight MRI (3D-TOF) and 3D phase contrast MRI (3D-PCMRI). For this purpose, a comprehensive evaluation of the stent artifacts and their impact on the flow measurement is critical.
The artifacts of a representative sample of neurovascular stents were evaluated in vitro with 3D-TOF and 3D-PCMRI sequences. The dependency of the artifacts with respect to the orientation was analyzed for each stent design as well as the impact on the flow measurement accuracy. Furthermore, the 3D-PCMRI data of four patients carrying intracranial aneurysms treated with flow diverter stents were analyzed as illustrative examples.
The stent artifacts were mainly confined to the stent lumen therefore indicating the leading role of shielding effect. The influence of the stent design and its orientation with respect to the transmitting MR coils were highlighted. The artifacts impacted the 3D-PCMRI velocities mainly in the low magnitude domains, which were discarded from the analysis ensuring reliable near-stent velocities. The feasibility of in-stent flow measurements was confirmed in vivo on two patients who showed strong correlation between flow and geometric features. In two other patients, the consistency of out-of-stent velocities was verified qualitatively through intra-aneurysmal streamlines except when susceptibility artifacts occurred.
The present results motivate the conception of low inductance or nonconductive stent design. Furthermore, the feasibility of near-stent 3D-PCMRI measurements opens the door to clinical applications like the post-treatment follow-up of stenoses or intracranial aneurysms.
通过非侵入性成像技术（如 3D 时间飞跃 MRI（3D-TOF）和 3D 相位对比 MRI（3D-PCMRI））对神经血管疾病进行形态和血流动力学评估将受益于非侵入性成像技术。为此，对支架伪影及其对流量测量的影响进行全面评估至关重要。
使用 3D-TOF 和 3D-PCMRI 序列对代表性的神经血管支架样本的伪影进行了体外评估。分析了每个支架设计的取向对伪影的依赖性以及对流量测量精度的影响。此外，还分析了四个颅内动脉瘤患者的 3D-PCMRI 数据，这些患者接受了血流导向支架治疗。
支架伪影主要局限于支架内腔，表明屏蔽效应起主导作用。突出了支架设计及其相对于发射 MR 线圈的取向的影响。伪影主要影响低幅度域的 3D-PCMRI 速度，这些速度被从分析中丢弃，以确保支架附近的速度可靠。对两名患者进行了体内可行性研究，这些患者的流量与几何特征之间显示出很强的相关性。在另外两名患者中，通过颅内流线质心定性验证了支架外流速的一致性，除了发生磁化率伪影时。
目前的结果激发了低电感或非导电支架设计的概念。此外，支架附近 3D-PCMRI 测量的可行性为临床应用打开了大门，例如狭窄或颅内动脉瘤的治疗后随访。
