Fetal development relies on a complex circulatory network. Accurate assessment of flow distribution is important for understanding pathologies and potential therapies. In this paper, we demonstrate a method for volumetric imaging of fetal flow with magnetic resonance imaging (MRI). Fetal MRI faces challenges: small vascular structures, unpredictable motion, and inadequate traditional cardiac gating methods. Here, orthogonal multislice stacks are acquired with accelerated multidimensional radial phase contrast (PC) MRI. Slices are reconstructed into flow sensitive time-series images with motion correction and image-based cardiac gating. They are then combined into a dynamic volume using slice-to-volume reconstruction (SVR) while resolving interslice spatiotemporal coregistration. Compared to prior methods, this approach achieves higher spatiotemporal resolution ( $1\times 1\times 1$ mm ³ , ~30 ms) with reduced scan time – important features for the quantification of flow through small fetal structures. Validation is demonstrated in adults by comparing SVR with 4D radial PCMRI (flow bias and limits of agreement: −1.1 ml/s and [−11.8 9.6] ml/s). Feasibility is demonstrated in late gestation fetuses by comparing SVR with 2D Cartesian PCMRI (flow bias and limits of agreement: −0.9 ml/min/kg and [−39.7 37.8] ml/min/kg). With SVR, we demonstrate complex flow pathways (such as parallel flow streams in the proximal inferior vena cava, preferential shunting of blood from the ductus venosus into the left atrium, and blood from the brain leaving the heart through the main pulmonary artery) for the first time in human fetal circulation. This method allows for comprehensive evaluation of the fetal circulation and enables future studies of fetal physiology.

中文翻译：

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磁共振成像的体积胎儿血流成像

胎儿发育依赖于复杂的循环网络。准确评估流量分布对于了解病理和潜在疗法非常重要。在本文中，我们展示了一种利用磁共振成像 (MRI) 对胎儿流量进行体积成像的方法。胎儿 MRI 面临挑战：血管结构小、运动不可预测以及传统的心脏门控方法不足。在这里，使用加速多维径向相衬 (PC) MRI 获得正交多层堆叠。通过运动校正和基于图像的心脏门控将切片重建为流量敏感的时间序列图像。然后使用切片到体积重建 (SVR) 将它们组合成一个动态体积，同时解决切片间时空配准问题。与之前的方法相比， $1\乘以 1\乘以 1$毫米 ³ , ~30 ms) 减少扫描时间 - 量化流经小胎儿结构的重要特征。通过比较 SVR 与 4D 径向 PCMRI（流量偏差和一致性限制：-1.1 ml/s 和 [-11.8 9.6] ml/s）在成人中验证。通过将 SVR 与 2D 笛卡尔 PCMRI（流量偏差和一致性限制：-0.9 ml/min/kg 和 [-39.7 37.8] ml/min/kg）进行比较，证明了妊娠晚期胎儿的可行性。对于 SVR，我们展示了复杂的血流通路（例如近端下腔静脉中的平行血流，血液从静脉导管优先分流到左心房，以及来自大脑的血液通过主肺动脉离开心脏）人类胎儿循环中的第一次。