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

Abstract

Purpose To characterize spatial patterns of T2∗ in the rhesus macaque placenta, to correlate these patterns with placental perfusion determined using dynamic contrast enhanced (DCE)-MRI, and to evaluate the potential for using the blood oxygen level-dependent (BOLD) effect to quantify placental perfusion without the use of exogenous contrast reagent. Methods Magnetic resonance imaging was performed on three pregnant rhesus macaques at gestational day 110. Multi-echo 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 are 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, while 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.

28: First trimester alcohol exposure alters placental perfusion and fetal oxygen availability affecting fetal growth and development in a non-human primate model

“…In control placentas at both G110 and G135, MR image voxels proximal to spiral artery sources of oxygenated maternal blood are characterized by relatively long T 2 * values, as previously reported 14 . At greater distances from the spiral arteries, the concentration of deoxyhemoglobin is higher, due to fetal oxygen uptake, resulting in shorter T 2 * values.…”

“…Surface area of each hemisphere was measured using standard functionalities of the CARET program. Placenta MRI followed previously described procedures 14,29 . Anatomic and multiecho imaging was performed during expiratory breath holding, achieved by temporarily suspending ventilation, while DCE-MRI data were acquired during ventilated breathing.…”

“…Figure 1 shows images that reflect perfusion for a representative ethanol exposed case (1a and 1b) and for a representative control case (1c and 1d). Further, through the analysis of water T 2 * values throughout the placenta, it is possible to quantify the flow-permeability ratio, F/(vPS), which relates to spiral artery flow and oxygen delivery to the fetal blood (through the volume fraction of the intervillous space, v, and the oxygen permeability surface area product, PS) on an individual spiral artery basis 14 .…”

First trimester alcohol exposure alters placental perfusion and fetal oxygen availability affecting fetal growth and development in a non-human primate model

“…Physiological monitoring of pulse rate, arterial blood oxygen saturation, and end-tidal CO 2 partial pressure was performed throughout the imaging study, with no deviations from normal ranges observed in these parameters. Spiral artery flow from DCE-MRI data was measured as described previously in Frias et al 13 , and the flow permeability ratio, F/ ( vPS ), was determined as described in Schabel et al 14 .…”

“…However, this method cannot be used to assess blood flow within the placental intervillous space, the site of maternal-fetal oxygen and nutrient exchange. Recent work with pregnant nonhuman primates (NHP) has identified MRI based methods to characterize maternal blood flow and oxygen exchange in the placenta with the fetal vasculature 13, 14 . Maternal perfusion of the placenta can be quantified using dynamic contrast-enhanced MRI (DCE-MRI), which requires intravenous administration of an MRI contrast reagent 13 .…”