Uteroplacental and Fetal 4D Flow MRI in the Pregnant Rhesus Macaque.

Background: Pregnancy complications are often associated with poor uteroplacental vascular adaptation and standard diagnostics are unable to reliably quantify flow in all uteroplacental vessels and have poor sensitivity early in gestation.

Purpose: To investigate the feasibility of using 4D flow MRI to assess total uteroplacental blood flow in pregnant rhesus macaques as a precursor to human studies.

Study Type: Retrospective feasibility study.

Animal Model: Fifteen healthy, pregnant rhesus macaques ranging from the 1 trimester to 3 trimester of gestation.

Field Strength/sequence: Abdominal 4D flow MRI was performed on a 3.0T scanner with a radially undersampled phase contrast (PC) sequence. Reference ferumoxytol-enhanced angiograms were acquired with a 3D ultrashort echo time sequence with a center-out radial trajectory.

Assessment: Repeatability of flow measurements was assessed with scans performed same-day and on consecutive days in the uterine arteries and ovarian veins. In-flow was compared against out-flow in the uterus, umbilical cord, and fetal heart with a conservation of mass analysis. Conspicuity of uteroplacental vessels was qualitatively compared between PC angiograms derived from 4D flow data and ferumoxytol-enhanced angiograms.

Statistical Tests: Bland-Altman analysis was used to quantify same-day and consecutive-day repeatability.

Results: Same-day flow measurements showed an average difference between scans of 13% in both the uterine arteries and ovarian veins, while consecutive-day measurements showed average differences of 22% and 24%, respectively. Comparisons of in-flow and out-flow showed average differences of 15% in the uterus, 8% in fetal heart, and 15% in the umbilical cord. PC angiograms showed similar depiction of main uteroplacental vessels as high-resolution, ferumoxytol-enhanced angiograms.

Data Conclusion: 4D flow MRI could be used in the rhesus macaque for repeatable flow measurements in the uteroplacental and fetal vasculature, setting the stage for future human studies.

Level Of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:534-545.