Functional imaging of the nonhuman primate Placenta with endogenous blood oxygen level-dependent contrast.

PURPOSE: To characterize spatial patterns of T2* in the placenta of the rhesus macaque (Macaca mulatta), to correlate these patterns with placental perfusion determined using dynamic contrast-enhanced MRI (DCE-MRI), and to evaluate the potential for using the blood oxygen level-dependent effect to quantify placental perfusion without the use of exogenous contrast reagent.
METHODS: MRI was performed on three pregnant rhesus macaques at gestational day 110. Multiecho spoiled gradient echo measurements were used to compute maps of T2*. Spatial maxima in these maps were compared with foci of early enhancement determined by DCE-MRI.
RESULTS: Local maxima in T2* maps were strongly correlated with spiral arteries identified by DCE-MRI, with mean spatial separations ranging from 2.34 to 6.11 mm in the three animals studied. Spatial patterns of R2* ( = 1/ T2*) within individual placental lobules can be quantitatively analyzed using a simple model to estimate fetal arterial oxyhemoglobin concentration [Hbo,f] and a parameter viPS/Φ, reflecting oxygen transport to the fetus. Estimated mean values of [Hbo,f] ranged from 4.25 mM to 4.46 mM, whereas viPS/Φ ranged from 2.80 × 105 cm-3 to 1.61 × 106 cm-3 .
CONCLUSIONS: Maternal spiral arteries show strong spatial correlation with foci of extended T2* observed in the primate placenta. A simple model of oxygen transport accurately describes the spatial dependence of R2* within placental lobules and enables assessment of placental function and oxygenation without requiring administration of an exogenous contrast reagent. Magn Reson Med 76:1551-1562, 2016.