Abstract
Fetal health is critically dependent on placental function, especially placental transport of oxygen from mother to fetus. When fetal growth is compromised, placental insufficiency must be distinguished from modest genetic growth potential. If placental insufficiency is present, the physician must trade off the risk of prolonged fetal exposure to placental insufficiency against the risks of preterm delivery. Current ultrasound methods to evaluate the placenta are indirect and insensitive. We propose to use Blood-Oxygenation-Level-Dependent (BOLD) MRI with maternal hyperoxia to quantitatively assess mismatch in placental function in seven monozygotic twin pairs naturally matched for genetic growth potential. In-utero BOLD MRI time series were acquired at 29 to 34 weeks gestational age. Maps of oxygen Time-To-Plateau (TTP) were obtained in the placentas by voxel-wise fitting of the time series. Fetal brain and liver volumes were measured based on structural MR images. After delivery, birth weights were obtained and placental pathological evaluations were performed. Mean placental TTP negatively correlated with fetal liver and brain volumes at the time of MRI as well as with birth weights. Mean placental TTP positively correlated with placental pathology. This study demonstrates the potential of BOLD MRI with maternal hyperoxia to quantify regional placental function in vivo.
Highlights
This study demonstrates a novel application of BOLD MRI for assessment of placental insufficiency
We investigated the utility of time-to-plateau (TTP) of the BOLD MRI time series under maternal hyperoxia as a surrogate marker for placental oxygen transport
We demonstrated that 1) placental TTP maps depict a regional perfusion pattern consistent with the known cotyledon structure; 2) placental TTP was significantly longer in placentas with moderate to severe pathology compared to normal to mild pathology; 3) placental TTP within each twin pair has a consistent tendency to be longer in the smaller twin; 4) placental TTP is significantly correlated with liver and brain volume and birth weight across all subjects, with TTP of fetuses destined to be small-for-gestational age (SGA) at birth significantly longer than those destined to be appropriate-for-gestational age (AGA)
Summary
The placenta is divided into cotyledons with varying numbers of villi and a varying vascular supply[5] Flow in both fetal capillaries and the intervillous space enables exchange of nutrients and waste products between the mother and the fetus[6]. Blood-oxygen-level-dependent (BOLD) MRI with hyperoxia is a promising alternative to gadolinium based approaches as it has been used in prior human studies to measure cerebral perfusion and blood volume[10]. In this paper we perform detailed spatiotemporal analysis of the BOLD MRI contrast generated by transient elevation of blood oxygen saturation, derive an image-based biomarker and test its performance in monochorionic diamniotic twin placentas against important clinical indicators such as fetal brain and liver volume as well as birth weight. The proposed non-invasive method for characterizing maternal placental perfusion on a regional basis with a parameter more directly related to regional placental vascularity and gas exchange represents an important step towards quantifying the relationship between in vivo placental perfusion, in vivo nutrient transport and fetal growth in humans
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