Department of Radiology and Neuroradiology, University Medical Center Schleswig-Holstein (UKSH), Section Biomedical Imaging, Molecular Imaging North Competence Center (MOIN CC), Kiel University, 24105 Kiel, Germany.
Department of Fluid Dynamics and Technical Flows, Research Campus STIMULATE, Magdeburg University, 39106 Magdeburg, Germany.
Tomography. 2022 Feb 10;8(1):457-478. doi: 10.3390/tomography8010038.
Four-dimensional (4D) flow MRI allows quantifying flow in blood vessels-non invasively and in vivo. The clinical use of 4D flow MRI in small vessels, however, is hampered by long examination times and limited spatial resolution. Compressed SENSE (CS-SENSE) is a technique that can accelerate 4D flow dramatically. Here, we investigated the effect of spatial resolution and CS acceleration on flow measurements by using 4D flow MRI in small vessels in vitro at 3 T. We compared the flow in silicon tubes (inner diameters of 2, 3, 4, and 5 mm) measured with 4D flow MRI, accelerated with four CS factors (CS = 2.5, 4.5, 6.5, and 13) and three voxel sizes (0.5, 1, and 1.5 mm) to 2D flow MRI and a flow sensor. Additionally, the velocity field in an aneurysm model acquired with 4D flow MRI was compared to the one simulated with computational fluid dynamics (CFD). A strong correlation was observed between flow sensor, 2D flow MRI, and 4D flow MRI (rho > 0.94). The use of fewer than seven voxels per vessel diameter (nROI) resulted in an overestimation of flow in more than 5% of flow measured with 2D flow MRI. A negative correlation (rho = -0.81) between flow error and nROI were found for CS = 2.5 and 4.5. No statistically significant impact of CS factor on differences in flow rates was observed. However, a trend of increased flow error with increased CS factor was observed. In an aneurysm model, the peak velocity and stagnation zone were detected by CFD and all 4D flow MRI variants. The velocity difference error in the aneurysm sac did not exceed 11% for CS = 4.5 in comparison to CS = 2.5 for all spatial resolutions. Therefore, CS factors from 2.5-4.5 can appear suitable to improve spatial or temporal resolution for accurate quantification of flow rate and velocity. We encourage reporting the number of voxels per vessel diameter to standardize 4D flow MRI protocols.
四维（4D）流磁共振成像可无创、在体量化血管内的血流。然而，由于检查时间长和空间分辨率有限，4D 流磁共振成像在小血管中的临床应用受到阻碍。压缩感知（CS-SENSE）是一种可以显著加速 4D 流的技术。在这里，我们在 3T 体外研究了空间分辨率和 CS 加速对小血管 4D 流测量的影响。我们比较了使用 4D 流磁共振成像、使用四个 CS 因子（CS = 2.5、4.5、6.5 和 13）和三个体素大小（0.5、1 和 1.5 毫米）加速测量的硅管（内径为 2、3、4 和 5 毫米）内的流动，与 2D 流磁共振成像和流量传感器的结果。此外，还比较了用 4D 流磁共振成像获得的动脉瘤模型的速度场与用计算流体动力学（CFD）模拟的速度场。流量传感器、2D 流磁共振成像和 4D 流磁共振成像之间观察到很强的相关性（rho > 0.94）。对于每个血管直径使用少于七个体素（nROI），会导致超过 5%的 2D 流磁共振成像测量的流量被高估。对于 CS = 2.5 和 4.5，发现流量误差与 nROI 之间存在负相关（rho = -0.81）。没有观察到 CS 因子对流量率差异的统计学显著影响。然而，观察到随着 CS 因子的增加，流量误差增加的趋势。在动脉瘤模型中，用 CFD 和所有 4D 流磁共振成像变体检测到了峰值速度和停滞区。与 CS = 2.5 相比，所有空间分辨率下 CS = 4.5 在动脉瘤囊中检测到的速度差误差均不超过 11%。因此，CS 因子从 2.5-4.5 可以提高空间或时间分辨率，从而准确量化流量和速度。我们鼓励报告每个血管直径的体素数量，以标准化 4D 流磁共振成像协议。
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