BACKGROUND To date it has not been possible to obtain a comprehensive 3D assessment of fetal hemodynamics because of the technical challenges inherent in imaging small cardiac structures, movement of the fetus during data acquisition, and the difficulty of fusing data from multiple cardiac cycles when a cardiac gating signal is absent. Here we propose the combination of volumetric velocity-sensitive cardiovascular magnetic resonance imaging ("4D flow" CMR) and a specialized animal preparation (catheters to monitor fetal heart rate, anesthesia to immobilize mother and fetus) to examine fetal sheep cardiac hemodynamics in utero. METHODS Ten pregnant Merino sheep underwent surgery to implant arterial catheters in the target fetuses. Anesthetized ewes underwent 4D flow CMR with acquisition at 3 T for fetal whole-heart coverage with 1.2-1.5 mm spatial resolution and 45-62 ms temporal resolution. Flow was measured in the heart and major vessels, and particle traces were used to visualize circulatory patterns in fetal cardiovascular shunts. Conservation of mass was used to test internal 4D flow consistency, and comparison to standard 2D phase contrast (PC) CMR was performed for validation. RESULTS Streaming of blood from the ductus venosus through the foramen ovale was visualized. Flow waveforms in the major thoracic vessels and shunts displayed normal arterial and venous patterns. Combined ventricular output (CVO) was 546 mL/min per kg, and the distribution of flows (%CVO) were comparable to values obtained using other methods. Internal 4D flow consistency across 23 measurement locations was established with differences of 14.2 ± 12.1%. Compared with 2D PC CMR, 4D flow showed a strong correlation (R2 = 0.85) but underestimated flow (bias = - 21.88 mL/min per kg, p < 0.05). CONCLUSIONS The combination of fetal surgical preparation and 4D flow CMR enables characterization and quantification of complex flow patterns in utero. Visualized streaming of blood through normal physiological shunts confirms the complex mechanism of substrate delivery to the fetal heart and brain. Besides offering insight into normal physiology, this technology has the potential to qualitatively characterize complex flow patterns in congenital heart disease phenotypes in a large animal model, which can support the development of new interventions to improve outcomes in this population.

中文翻译：

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通过 4D 血流心血管磁共振评估胎羊的胎儿血流动力学和心脏血流。


背景技术迄今为止，由于对小心脏结构成像固有的技术挑战、数据采集期间胎儿的运动以及心脏检查时融合来自多个心动周期的数据的困难，迄今为止还不可能获得胎儿血流动力学的全面 3D 评估。门控信号不存在。在这里，我们建议结合体积速度敏感心血管磁共振成像（“4D 流”CMR）和专门的动物制剂（监测胎儿心率的导管、固定母亲和胎儿的麻醉）来检查子宫内胎羊心脏血流动力学。方法 对十只怀孕的美利奴羊进行手术，将动脉导管植入目标胎儿体内。麻醉母羊接受 4D 流 CMR，以 3 T 采集胎儿全心脏覆盖，空间分辨率为 1.2-1.5 毫米，时间分辨率为 45-62 毫秒。测量心脏和主要血管的流量，并使用颗粒痕迹来可视化胎儿心血管分流的循环模式。使用质量守恒来测试内部 4D 流动一致性，并与标准 2D 相衬 (PC) CMR 进行比较以进行验证。结果 可见血液从静脉导管流过卵圆孔。主要胸部血管和分流管中的血流波形显示正常的动脉和静脉模式。合并心室输出量 (CVO) 为 546 mL/min/kg，流量分布 (%CVO) 与使用其他方法获得的值相当。建立了 23 个测量位置的内部 4D 流量一致性，差异为 14.2 ± 12.1%。与 2D PC CMR 相比，4D 流量显示出很强的相关性 (R2 = 0.85)，但流量被低估（偏差 = - 21.88 mL/min/kg，p < 0.05）。 结论 胎儿手术准备和 4D 血流 CMR 相结合，能够对子宫内复杂的血流模式进行表征和量化。通过正常生理分流的可视化血流证实了底物输送到胎儿心脏和大脑的复杂机制。除了提供对正常生理学的深入了解外，该技术还有可能定性描述大型动物模型中先天性心脏病表型的复杂血流模式，这可以支持开发新的干预措施以改善该人群的结果。