Purpose or Case Report: Both placental vascular density and oxygenation can indicate placenta health. MRA is a powerful tool to evaluate tissue vasculature but with limited applications because of the use of contrast agents. T₂* maps can be used to estimate the placental oxygen reserve. In this work, we acquired non-contrast enhanced MRA and T₂* maps to evaluate placental vasculature and oxygenation.
Methods & Materials: Two pregnant women were recruited for this study. One woman (Subject A, GA: 28+2/7w, fetal hydrocephalus) was studied on a 1.5T Siemens Aera system with an 8-channel body coil, and the other one (Subject B, GA: 36+2/7w, normal) was studied on a 3T Siemens Verio system with a 6-channel flex coil and a 4-channel spine coil. A 2D time-of-flight sequence and 2D multi-echo GRE sequence were run for each subject to generate the MRA and T₂* maps. The sequence parameters were: at 1.5T:1)MRA: TR/TE=23/5.6ms, in-plane resolution=0.56×0.56mm², slice thickness=3mm, BW=245Hz/px, and flip angle=50deg; and 2)T₂*mapping: TR/TE/detTE=93/5/5ms, echo number=12, in-plane resolution=1.13×2.25mm², slice thickness=3mm, BW=230Hz/px, and flip angle=20deg; while at 3T:1) MRA: TR/TE=22/4.92ms, in-plane resolution =0.66×0.82mm², slice thickness=2mm, BW=241Hz/px, and flip angle=50deg; and 2)T₂*mapping: TR/TE/detTE=70/4/4ms , echo number=12, in-plane resolution =2.97×2.97mm², slice thickness=4mm, BW=501Hz/px, and flip angle=30deg.
Results: The placenta appeared inhomogeneous in the T₂*-weighted image. Since placenta cotyledons are brighter in T₂ HASTE image, these brighter regions in both T₂* weighted images and T₂* maps were taken to correspond to the cotyledons in this data as well. For each subject, we identified one cotyledon as the target cotyledon from 20 slices of T₂* map. The T₂* value of the placenta measured from one slice was 100.6±39.2ms for Subject A and 32.2±14.2ms for Subject B. The MRA of the entire placenta were well displayed. For both subjects, it is easy to identify the umbilical vessels, chorionic vessels and stem vessels. The umbilical vein can be distinguished from umbilical arteries for Subject A. Chorionic vessels and stem vessels can be identified for both subjects in the target cotyledons. Interestingly, in Subject A, it is possible to see some stem vessels branching off the chorionic vessels.
Conclusions: Both MRA and T₂* maps can provide key information for the evaluation of placental vasculature and oxygenation and could provide a tool to investigate abnormal pregnancy and predict fetal outcome.