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.
Volumetric Fetal Flow Imaging with Magnetic Resonance Imaging
