Major mouse placental compartments revealed by diffusion-weighted MRI, contrast-enhanced MRI, and fluorescence imaging

Abstract

Mammalian models, and mouse studies in particular, play a central role in our understanding of placental development. Magnetic resonance imaging (MRI) could be a valuable tool to further these studies, providing both structural and functional information. As fluid dynamics throughout the placenta are driven by a variety of flow and diffusion processes, diffusion-weighted MRI could enhance our understanding of the exchange properties of maternal and fetal blood pools-and thereby of placental function. These studies, however, have so far been hindered by the small sizes, the unavoidable motions, and the challenging air/water/fat heterogeneities, associated with mouse placental environments. The present study demonstrates that emerging methods based on the spatiotemporal encoding (SPEN) of the MRI information can robustly overcome these obstacles. Using SPEN MRI in combination with albumin-based contrast agents, we analyzed the diffusion behavior of developing placentas in a cohort of mice. These studies successfully discriminated the maternal from the fetal blood flows; the two orders of magnitude differences measured in these fluids' apparent diffusion coefficients suggest a nearly free diffusion behavior for the former and a strong flow-based component for the latter. An intermediate behavior was observed by these methods for a third compartment that, based on maternal albumin endocytosis, was associated with trophoblastic cells in the interphase labyrinth. Structural features associated with these dynamic measurements were consistent with independent intravital and ex vivo fluorescence microscopy studies and are discussed within the context of the anatomy of developing mouse placentas.robust diffusion MRI | high-field placental MRI | placental ADC maps | multimodal imaging

Real-Time Monitoring of Placental Oxygenation during Maternal Hypoxia and Hyperoxygenation Using Photoacoustic Imaging

“…This would support the oxygen reserve capacity of the placenta. Different regions within the placenta may be distinguished, according to the specific enhancements made in perfusion imaging and histological analyses [15]. Published studies have found no difference of oxygenation in these different areas [4,12].…”

Longitudinal Changes in Placental Magnetic Resonance Imaging Relaxation Parameter in Murine Pregnancy: Compartmental Analysis

“…This is conceivable since the thickness of interhemal membrane, which influences water diffusion between maternal and fetal blood spaces, also decreases with gestation [20, 55], leading to a theoretical increase in diffusion capacity (diffusion coefficient, D) with gestation [20]. Recent MR imaging based reports on the placental apparent diffusion coefficient (ADC), a measure of water diffusion in the whole placenta, however, showed no significant change with advancing gestation in both humans and mice [56, 57]. While these studies use relatively low resolution imaging and pertain to whole placental diffusion, a region-specific study of diffusion characteristics within the placenta, for example labyrinth vs. junctional, could help us in better observing their change trajectory as a function of gestational age.…”

Functional imaging of the human placenta with magnetic resonance

“…Finally, several techniques could be combined to better understand placental physiologic condition, as reported in studies of placental blood flow in mice. 49 Further extensive experimental studies are required to better define the respective roles of each fMRI method in the functional assessment of the placenta and the optimal way in which ultrasound studies can be complimented. All fMRI techniques demonstrate a potential for allowing timely recognition of placental insufficiency, thus possibly allowing for appropriate planning for follow-up examinations and timing of delivery of high-risk fetuses.…”