Poster Presentation & Flash Talk 46th Annual Meeting of the Fetal and Neonatal Physiological Society 2019

Exploring ductus venosus flow patterns in fetal sheep using 4D flow MRI (#112)

Eric M. Schrauben 1 , Brahmdeep Saini 2 3 , Jack R.T. Darby 4 , Stacey L. Holman 4 , Jia Y. Soo 4 , Mitchell C. Lock 4 , Sunthara R. Perumal 5 , Mike Seed 6 7 , Janna L. Morrison 4 , Christopher K. Macgowan 1 8
  1. Translational Medicine, Hospital for Sick Children, Toronto, Ontario, Canada
  2. Heart Centre, Hospital for Sick Children, Toronto, Ontario, Canada
  3. Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
  4. Early Origins of Adult Health Research Group, School of Pharmacy & Medical Sciences, University of South Australia, Adelaide, SA, Australia
  5. Preclinical Imaging and Research Laboratories, South Australian Health and Medical Research Institute, Adelaide, SA, Australia
  6. Division of Cardiology, Hospital for Sick Children, Toronto, Ontario, Canada
  7. Department of Paediatrics, University of Toronto, Toronto, Ontario, Canada
  8. Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

Shunting of oxygen- and nutrient-rich placental blood through the ductus venosus (DV) is paramount in the development of the fetal heart and brain. Understanding the cardiovascular changes that may occur during pregnancy complicated by various pathologies, including fetal growth restriction, requires comprehensive assessment of fetal hepatic blood flow distribution. This assessment poses difficult technical problems due to the small nature of vessels, slow blood flow within the liver, and sources of motion present in utero.

Here we couple 4D flow MRI1, which enables whole volume blood flow visualization and measurement of blood flow, with specialized animal preparation to capture 3D fetal hepatic hemodynamics in a late gestation sheep model of human pregnancy. Pregnant Merino ewes (resulting in n=13 fetal subjects; 4 females; 137-140 days gestation; term=150 days) underwent surgery to implant a vascular catheter into the fetal femoral artery for MRI triggering as previously described2. Data was collected using high resolution MRI. Whole-liver assessment followed recently published work and included segmentation, blood flow measurements, and visualization of fetal shunts with particle traces3. Average blood flow, velocity, and vessel diameter were statistically compared between  subject sex and vessels using a 2-way ANOVA (p < 0.05).

Exemplary flow visualizations using particle traces (Figure 1) display the fine detail of helical DV flow and swirling flow in the portal sinus. No statistically significant differences were observed between sex.

Here we present a technique for evaluation of fetal hepatic flow using 4D flow MRI in a large animal model, and present visualization and quantification of umbilical shunting through the DV.

 

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Figure 1. left:  Fetal ventral-oblique blood flow particle trace visualization in hepatic vessels, colored based on blood speed (A) and vessel of origin (B). C:  Gender comparison of average blood flow across 7 major vessels. UV:  umbilical vein; IVC:  inferior vena cava

  1. Markl, M., et al., 4D flow MRI. J Magn Reson Imaging, 2012. 36(5): p. 1015-36.
  2. Morrison, J.L., et al., Fetal behavioural state changes following maternal fluoxetine infusion in sheep. Brain Res Dev Brain Res, 2001. 131(1-2): p. 47-56.
  3. Schrauben, E.M., et al., Fetal hemodynamics and cardiac streaming assessed by 4D flow cardiovascular magnetic resonance in fetal sheep. J Cardiovasc Magn Reson, 2019. 21(1): p. 8.