Volumetric Fetal Flow Imaging with Magnetic Resonance Imaging

Fetal development relies on a complex circulatory network and accurately assessing the flow distribution is important for understanding pathologies and potential therapies. In this paper, we demonstrate a method for volumetric multidimensional imaging of fetal flow with magnetic resonance imaging (MRI). Fetal application of MRI faces several challenges such as small vascular structures, unpredictable motion, and lack of traditional cardiac gating methods. Here, orthogonal multislice stacks are acquired with accelerated multidimensional radial phase contrast (PC) MRI. Each slice is reconstructed into flow sensitive time-series images (CINEs) with retrospective intraslice motion correction and image-based fetal cardiac gating. CINEs are then combined into a dynamic 3D volume using slice-to-volume reconstruction (SVR) while accounting for interslice spatiotemporal coregistration. Validation of the technique is demonstrated in adult volunteers by comparing mean flows from SVR with 4D radial PCMRI with bias and limits of agreement being -1.1 ml/s and [-12.5 10.2] ml/s. Feasibility is demonstrated in late gestation fetuses by comparing SVR with 2D Cartesian PCMRI with bias and limits of agreement being -0.9 ml/min/kg and [-39.7 37.8] ml/min/kg for mean flows. With SVR, we also 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 side of the heart, and blood returning 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.