Department of Radiology, Medical Physics, University Hospital Freiburg, Germany.
Invest Radiol. 2011 May;46(5):317-25. doi: 10.1097/RLI.0b013e3182034fc2.
The purpose of this study was to characterize hemodynamic alterations and flow-derived vessel wall parameters in aortic coarctation (CoA) patients with and without operative repair by time-resolved, 3-dimensional, and 3-directional velocity sensitive, phase-contrast magnetic resonance imaging (4D PC MRI) in comparison with healthy subjects.
Twenty-four patients, 12.5 ± 6.4 years after CoA repair, 4 patients without treatment for CoA, and 19 healthy subjects were examined. The study was approved by the institutional review board and signature of written informed consent was obtained from the participants. Echocardiography was performed in patients before participation. MRI studies were conducted by applying flow-sensitive 4D phase-contrast MRI at either 1.5 T (n = 5 patients) or 3 T (all 19 healthy subjects, n = 23 patients). Blood flow visualization was used to evaluate overall aortic helicity, presence of pronounced or additional localized helix flow, and vortex development. Quantitative evaluation comprised the calculation of regional time-averaged absolute wall shear stress (WSS(mag)), peak velocities, and oscillatory shear index at 8 locations distributed along the thoracic aorta and additionally at the site of CoA. Inter- and intraobserver variabilities of calculations were determined.
Volunteers and patients demonstrated the same amount of overall aortic helicity. In contrast, the number of additional localized helix flow or vortex formation was significantly increased in patients (25/28 patients vs. 5/19 normal controls, Fisher exact test: P < 0.001). Vortices in the orifices of the supra-aortic branches were detected in 64.3% (18/28) of patients but in only 11.8% (2/19) of controls (P < 0.001). Quantitative analyses revealed a significant increase in overall aortic WSS(mag) (0.44 ± 0.17 N/m(2) in patients vs. 0.27 ± 0.08 N/m(2) in volunteers, P < 0.005) and a decrease in overall oscillatory shear index. Repeated quantitative analysis showed moderate interobserver and low intraobserver variability. Correlation with echocardiography showed good agreement with MRI which tended to underestimate peak velocities (r = 0.76; Bland-Altman analysis, limits of agreement = -0.57-2.16 m/s, mean = 0.79 m/s).
Alterations in aortic hemodynamics after CoA repair are not limited to the specific region of repair, but can be found in the entire aorta. The presented findings highlight the systemic nature of the disease and the need for a systemic diagnostic approach which can be provided by flow-sensitive 4D PC MRI. Furthermore, valuable additional insights on the hemodynamic consequences of coarctation have been shown that may help understanding secondary complications such as restenosis, aneurysm formation, and arterial hypertension.
本研究旨在通过时间分辨、三维、三维方向速度敏感的相位对比磁共振成像（4D PC MRI），对伴有和不伴有手术修复的主动脉缩窄（CoA）患者与健康受试者进行比较，以描述血流动力学改变和血流衍生的血管壁参数。
24 例患者在 CoA 修复后 12.5 ± 6.4 年，4 例未经 CoA 治疗的患者和 19 例健康受试者接受了检查。该研究得到了机构审查委员会的批准，并从参与者处获得了书面知情同意书。在参与研究之前，对患者进行了超声心动图检查。在 1.5T（n = 5 例患者）或 3T（所有 19 例健康受试者，n = 23 例患者）进行血流敏感的 4D 相位对比 MRI 研究。血流可视化用于评估整体主动脉螺旋度、存在明显或额外局部螺旋流动以及涡流发展。定量评估包括计算 8 个分布在胸主动脉和 CoA 部位的区域时均壁面切应力（WSS（mag））、峰值速度和振荡剪切指数。确定了计算的观察者间和观察者内变异性。
志愿者和患者表现出相同的整体主动脉螺旋度。相比之下，患者中额外局部螺旋流动或涡流形成的数量明显增加（28 例患者中有 25 例 vs. 19 例正常对照组中有 5 例，Fisher 确切检验：P < 0.001）。在 64.3%（28 例患者中有 18 例）的患者中检测到升主动脉分支口的涡流，但在 11.8%（19 例对照组中有 2 例）的对照组中检测到（P < 0.001）。定量分析显示整体主动脉 WSS（mag）显著增加（患者中为 0.44 ± 0.17 N/m2，志愿者中为 0.27 ± 0.08 N/m2，P < 0.005），整体振荡剪切指数降低。重复定量分析显示观察者间存在中度变异性和观察者内低变异性。与超声心动图的相关性表明，MRI 具有良好的一致性，但倾向于低估峰值速度（r = 0.76；Bland-Altman 分析，一致性界限=-0.57-2.16 m/s，平均值=0.79 m/s）。
CoA 修复后主动脉血流动力学的改变不仅局限于修复的特定区域，还可以在整个主动脉中发现。这些发现突出了疾病的系统性，并需要一种系统的诊断方法，而这种方法可以通过血流敏感的 4D PC MRI 来提供。此外，还显示了对 CoA 血流动力学后果的有价值的附加见解，这可能有助于理解再狭窄、动脉瘤形成和动脉高血压等继发性并发症。
