Department of Mechanical Engineering, Hanyang University, Seoul, 04763, South Korea.
Bioimaging Research Team, Korea Basic Science Institute, Cheongju, 28119, South Korea.
Med Image Anal. 2019 Apr;53:95-103. doi: 10.1016/j.media.2019.01.009. Epub 2019 Jan 31.
Four-dimensional flow magnetic resonance imaging (4D flow MRI) is a versatile tool to obtain hemodynamic information and anatomic information simultaneously. The wall shear stress (WSS), a force exerted on a vessel wall in parallel, is one of the hemodynamic parameters available with 4D flow MRI and is thought to play an important role in clinical applications such as assessing the development of atherosclerosis. Nevertheless, the accuracy of WSS obtained with 4D flow MRI is rarely evaluated or reported in literature, especially in the in vivo studies. We propose a novel and facile criterion called Reynolds resolution to assess the accuracy of WSS estimation in 4D flow MRI studies. Reynolds resolution consists of a spatial resolution, encoding velocity, kinematic viscosity of a working fluid, and signal-to-noise ratio, which are readily accessible information in 4D flow MRI measurements. We explored the relationship between Reynolds resolution and the WSS error. To include diverse and extensive cases, we measured three circular tubing flows with a diameter of 40, 8, and 2 mm. The 40 mm tubing flow was measured by 3 Tesla (T) human MR scanner with a knee coil and spatial resolution of 0.5 mm. The 8 and 2 mm tubing flows were both measured by 4.7 T MR scanner, but the scans were performed with a conventional birdcage coil (8 mm tubing) and a custom-made solenoid coil (2 mm tubing), respectively. The spatial resolution was varied from 0.2, 0.4 or 0.8 mm for the 8 mm tubing flow, but was fixed at 0.090 mm for 2 mm tubing flow. In addition, the near-wall velocity gradient, required to be determined prior to the WSS, was calculated using two methods; these included assuming a linear velocity profile or quadratic velocity profile near wall. The accuracy of WSS obtained using each method and tubing flow was evaluated against the theoretical WSS value. As a result, we found that Reynolds resolution is in logarithmic relation to the WSS error.
四维血流磁共振成像（4D flow MRI）是一种同时获取血流动力学信息和解剖学信息的多功能工具。壁面切应力（WSS）是 4D flow MRI 可获得的血流动力学参数之一，被认为在评估动脉粥样硬化发展等临床应用中起着重要作用。然而，4D flow MRI 获得的 WSS 的准确性在文献中很少得到评估或报道，尤其是在体内研究中。我们提出了一种新颖且简单的标准，称为雷诺数分辨率，用于评估 4D flow MRI 研究中 WSS 估计的准确性。雷诺数分辨率由空间分辨率、编码速度、工作流体的运动粘度和信噪比组成，这些都是 4D flow MRI 测量中易于获得的信息。我们探讨了雷诺数分辨率与 WSS 误差之间的关系。为了包括各种广泛的情况，我们测量了三种直径为 40、8 和 2mm 的圆形管流。40mm 管流由配备膝关节线圈的 3T 人体磁共振扫描仪测量，空间分辨率为 0.5mm。8 和 2mm 管流均由 4.7T MR 扫描仪测量，但扫描分别使用传统的鸟笼线圈（8mm 管流）和定制的螺线管线圈（2mm 管流）进行。对于 8mm 管流，空间分辨率从 0.2、0.4 或 0.8mm 变化，但对于 2mm 管流，空间分辨率固定为 0.09mm。此外，壁面附近的速度梯度是 WSS 之前需要确定的，我们使用两种方法来计算这些速度梯度；这些方法包括假设壁面附近存在线性速度分布或二次速度分布。使用每种方法和管流获得的 WSS 的准确性均针对理论 WSS 值进行了评估。结果表明，雷诺数分辨率与 WSS 误差呈对数关系。
