New insights in magnetic resonance imaging evaluation of aortic valve hemodynamics

主动脉瓣狭窄(AS)是指主动脉瓣的病理性狭窄。在欧洲和北美，它是继全身性高血压和冠心病之后最常见的心脏瓣膜病和最常见的心血管疾病。目前，心导管和多普勒超声心动图是最常用的判断主动脉瓣狭窄严重程度的方法。然而，心导管技术有很大的技术局限性，它是一种侵入性技术，可能会使患者面临不必要的风险，而多普勒超声心动图有几个实际和理论上的限制，限制了它在大约20%的主动脉狭窄患者中的适用性。在最近的一项体外研究中，我们利用粒子图像测速仪(PIV)开发了一种根据速度场准确判断主动脉狭窄严重程度的新方法。虽然这种方法非常有希望，但由于PIV需要透明的结构，其在体内的适用性受到限制。然而，这不是磁共振相位对比(MR PC)的情况。事实上，MR PC是一种强大的非侵入性、非电离技术，能够通过人体心脏瓣膜研究速度场。因此，本研究的目的是在体外和体内确定我们的新方法应用于MR PC测量的速度场的可行性和准确性。此外，我们还将研究MR PC计算主动脉狭窄下游湍流特性的能力。我们预计，该项目的结果将对临床评估主动脉瓣狭窄的严重程度产生重大影响。

Aortic stenosis (AS) is defined as the pathological narrowing of the aortic valve. It is the most frequent valvular heart disease and the most frequent cardiovascular disease after systemic hypertension and coronary artery disease in Europe and North America. Currently, cardiac catheterization and Doppler echocardiography are the most frequently used methods for the determination of aortic stenosis severity. However, cardiac catheterization has significant technical limitations and it is an invasive technique that may place the patient at unnecessary risk while Doppler echocardiography has several practical and theoretical limitations that limit its applicability in around 20% of the patients with aortic stenosis. In a recent in vitro study, we developed, using particle image velocimetry (PIV), a new accurate method to determine the severity of aortic stenosis from the velocity field. Although very promising, the applicability of this method was limited in vivo because PIV requires transparent structures. However, this is not the case for magnetic resonance phase contrast (MR PC). In fact, MR PC is a powerful non-invasive, non-ionizing technique, able to investigate the velocity field through human heart valves. The objective of the present study is, therefore, to determine in vitro and in vivo the feasibility and the accuracy of our new method applied to the velocity field measured by MR PC. Furthermore, we will investigate the ability of MR PC to compute turbulence characteristics downstream of an aortic stenosis. We expect that the results of this project will have a significant impact on the clinical evaluation of the severity of aortic stenosis.