PURPOSE 4D flow cardiovascular magnetic resonance (CMR) and the assessment of wall shear stress (WSS) are non-invasive tools to study cardiovascular risks in vivo. Major limitations of conventional triggered methods are the long measurement times needed for high-resolution data sets and the necessity of stable electrocardiographic (ECG) triggering. In this work an ECG-free retrospectively synchronized method is presented that enables accelerated high-resolution measurements of 4D flow and WSS in the aortic arch of mice. METHODS 4D flow and WSS were measured in the aortic arch of 12-week-old wildtype C57BL/6 J mice (n = 7) with a radial 4D-phase-contrast (PC)-CMR sequence, which was validated in a flow phantom. Cardiac and respiratory motion signals were extracted from the radial CMR signal and were used for the reconstruction of 4D-flow data. Rigid motion correction and a first order B0 correction was used to improve the robustness of magnitude and velocity data. The aortic lumen was segmented semi-automatically. Temporally averaged and time-resolved WSS and oscillatory shear index (OSI) were calculated from the spatial velocity gradients at the lumen surface at 14 locations along the aortic arch. Reproducibility was tested in 3 animals and the influence of subsampling was investigated. RESULTS Volume flow, cross-sectional areas, WSS and the OSI were determined in a measurement time of only 32 min. Longitudinal and circumferential WSS and radial stress were assessed at 14 analysis planes along the aortic arch. The average longitudinal, circumferential and radial stress values were 1.52 ± 0.29 N/m2, 0.28 ± 0.24 N/m2 and - 0.21 ± 0.19 N/m2, respectively. Good reproducibility of WSS values was observed. CONCLUSION This work presents a robust measurement of 4D flow and WSS in mice without the need of ECG trigger signals. The retrospective approach provides fast flow quantification within 35 min and a flexible reconstruction framework.

中文翻译：

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使用17.6 T的径向4D相衬心血管磁共振在小鼠主动脉弓中快速自导航壁切应力测量。

目的4D流心血管磁共振（CMR）和壁切应力评估（WSS）是研究体内心血管风险的非侵入性工具。传统触发方法的主要局限性是高分辨率数据集需要较长的测量时间以及稳定的心电图（ECG）触发的必要性。在这项工作中，提出了一种无ECG的回顾性同步方法，该方法可以加速对小鼠主动脉弓中的4D流和WSS进行高分辨率测量。方法在12周龄的野生型C57BL / 6 J小鼠（n = 7）的主动脉弓上测量4D血流和WSS，该小鼠具有放射状4D相衬（PC）-CMR序列，并在血流模型中进行了验证。从径向CMR信号中提取心脏和呼吸运动信号，并将其用于4D流数据的重建。刚性运动校正和一阶B0校正用于提高幅度和速度数据的鲁棒性。主动脉腔半自动分割。根据沿主动脉弓14个位置的管腔表面的空间速度梯度，计算出时间平均和时间分辨的WSS和振荡剪切指数（OSI）。在3只动物中测试了可重复性，并研究了二次采样的影响。结果体积流量，横截面积，WSS和OSI的测定时间仅为32分钟。在主动脉弓的14个分析平面上评估了纵向和周向WSS以及径向应力。纵向，圆周和径向平均应力值分别为1.52±0.29 N / m2、0.28±0.24 N / m2和-0.21±0.19 N / m2。观察到WSS值的良好再现性。结论这项工作提出了一种在不需要ECG触发信号的情况下对小鼠4D流量和WSS的可靠测量。回顾性方法可在35分钟内提供快速的流量定量，并提供灵活的重建框架。