Abstract
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.