Department of Biomedical Engineering, The Wallace H. Coulter, Emory University and Georgia Institute of Technology, Atlanta, GA, USA.
Department of Radiology & Imaging Sciences, Emory University, 1364 Clifton Rd, Atlanta, GA, 30322, USA.
Cardiovasc Eng Technol. 2023 Jun;14(3):476-488. doi: 10.1007/s13239-023-00667-1. Epub 2023 May 8.
Three-dimensional, ECG-gated, time-resolved, three-directional, velocity-encoded phase-contrast MRI (4D flow MRI) has been applied extensively to measure blood velocity in great vessels but has been much less used in diseased carotid arteries. Carotid artery webs (CaW) are non-inflammatory intraluminal shelf-like projections into the internal carotid artery (ICA) bulb that are associated with complex flow and cryptogenic stroke.
Optimize 4D flow MRI for measuring the velocity field of complex flow in the carotid artery bifurcation model that contains a CaW.
A 3D printed phantom model created from computed tomography angiography (CTA) of a subject with CaW was placed in a pulsatile flow loop within the MRI scanner. 4D Flow MRI images of the phantom were acquired with five different spatial resolutions (0.50-2.00 mm) and four different temporal resolutions (23-96 ms) and compared to a computational fluid dynamics (CFD) solution of the flow field as a reference. We examined four planes perpendicular to the vessel centerline, one in the common carotid artery (CCA) and three in the internal carotid artery (ICA) where complex flow was expected. At these four planes pixel-by-pixel velocity values, flow, and time average wall shear stress (TAWSS) were compared between 4D flow MRI and CFD.
An optimized 4D flow MRI protocol will provide a good correlation with CFD velocity and TAWSS values in areas of complex flow within a clinically feasible scan time (~ 10 min).
Spatial resolution affected the velocity values, time average flow, and TAWSS measurements. Qualitatively, a spatial resolution of 0.50 mm resulted in higher noise, while a lower spatial resolution of 1.50-2.00 mm did not adequately resolve the velocity profile. Isotropic spatial resolutions of 0.50-1.00 mm showed no significant difference in total flow compared to CFD. Pixel-by-pixel velocity correlation coefficients between 4D flow MRI and CFD were > 0.75 for 0.50-1.00 mm but were < 0.5 for 1.50 and 2.00 mm. Regional TAWSS values determined from 4D flow MRI were generally lower than CFD and decreased at lower spatial resolutions (larger pixel sizes). TAWSS differences between 4D flow and CFD were not statistically significant at spatial resolutions of 0.50-1.00 mm but were different at 1.50 and 2.00 mm. Differences in temporal resolution only affected the flow values when temporal resolution was > 48.4 ms; temporal resolution did not affect TAWSS values.
A spatial resolution of 0.74-1.00 mm and a temporal resolution of 23-48 ms (1-2 k-space segments) provides a 4D flow MRI protocol capable of imaging velocity and TAWSS in regions of complex flow within the carotid bifurcation at a clinically acceptable scan time.
三维、心电图门控、时分辨、三向、速度编码相位对比磁共振成像（4D 流 MRI）已广泛应用于测量大动脉中的血流速度，但在病变颈动脉中的应用较少。颈动脉网（CaW）是向颈内动脉（ICA）球内突起的非炎症性腔内架状突起，与复杂的血流和隐源性中风有关。
优化 4D 流 MRI，以测量包含 CaW 的颈动脉分叉模型中的复杂血流速度场。
使用来自伴有 CaW 的患者的 CT 血管造影（CTA）创建的 3D 打印体模，将其放置在 MRI 扫描仪内的脉动流回路中。使用五个不同的空间分辨率（0.50-2.00 毫米）和四个不同的时间分辨率（23-96 毫秒）获取体模的 4D 流 MRI 图像，并与作为参考的流场计算流体动力学（CFD）解进行比较。我们检查了与血管中心线垂直的四个平面，一个在颈总动脉（CCA），三个在颈内动脉（ICA），预计在这些平面上会出现复杂的血流。在这四个平面上，逐像素比较 4D 流 MRI 和 CFD 的速度值、流量和时间平均壁切应力（TAWSS）。
在临床可行的扫描时间（~10 分钟）内，优化的 4D 流 MRI 协议将与 CFD 速度和 TAWSS 值具有良好的相关性，适用于复杂血流区域。
空间分辨率会影响速度值、时间平均流量和 TAWSS 测量值。定性地说，0.50 毫米的空间分辨率会导致更高的噪声，而较低的 1.50-2.00 毫米的空间分辨率则不能充分分辨速度分布。0.50-1.00 毫米各向同性空间分辨率与 CFD 相比，总流量无显著差异。4D 流 MRI 和 CFD 之间的逐像素速度相关系数大于 0.75 毫米，但小于 0.5 毫米 1.50 和 2.00 毫米。4D 流 MRI 确定的局部 TAWSS 值通常低于 CFD，并且随着空间分辨率（较大的像素尺寸）的降低而降低。在 0.50-1.00 毫米的空间分辨率下，4D 流和 CFD 之间的 TAWSS 差异没有统计学意义，但在 1.50 和 2.00 毫米时则不同。时间分辨率的差异仅在时间分辨率大于 48.4 毫秒时才会影响流量值；时间分辨率不会影响 TAWSS 值。
空间分辨率为 0.74-1.00 毫米，时间分辨率为 23-48 毫秒（1-2 个 k-空间段），可在临床可接受的扫描时间内对颈动脉分叉处的复杂血流区域进行成像，提供 4D 流 MRI 协议，以测量速度和 TAWSS。
