Assessing Placental Health through the Lense of MRI

Abstract Authors: Oliver Wieben¹
1. Depts. Of Medical Physics and Radiology, University of Wisconsin-Madison, Madison, WI, USA

Abstract Text:

Magnetic Resonance Imaging (MRI) is a powerful, non-invasive, in-vivo imaging method that can provide structural and a wealth of functional information on tissues and organs. While MRI offers several benefits over other imaging modalities,  such as cover of the entire placenta throughout pregnancy and no need for ionizing radiation, its use in clinical routine of assessing the placenta is currently limited, e.g. to the diagnosis of placental invasion. However, recent advances in MRI methodology development and contrast agents have enabled novel research and clinical applications including quantitative biomarkers related to oxygenation, blood flow and perfusion, and placental blood volumes.  These methods have potential to provide insights into the understanding of placental development, on placental health early in pregnancy, and to guide histopathology and will be introduced with data from preclinical (rhesus macaque) and human studies.
4D Flow MRI is a technique that provides comprehensive information on the velocity field in the blood vessels of a large imaging volume. With that approach, total uterine blood flow can be assessed more accurately than with ultrasound. In addition, microscopic placental blood flow can be assessed with ASL (Arterial Spin Labeling), an approach that provides local perfusion measurements with good spatial resolution and without the need for an extrinsic contrast agent. In addition, Blood Oxygen Level Dependant (BOLD)-MRI measures placenta oxygenation by detecting T2* relaxation time changes.
Additional quantitative markers can be obtained with the use of contrast agents. The most commonly used ones in MRI are based on Gadolinium chelates, but they pose a safety risk in pregnancy as they can cross the placenta. Over the last decades, iron nanoparticles were introduced as MR contrast agents. These iron nanoparticles are FDA approved to treat anemia, including during pregnancy, and are commonly used off-label in clinical MRI. Recently, it was also used in assessing placental structure at an unprecedented level since individual functional units can be distinguished in vivo. Its use has also facilitated perfusion and flow measures based on tracer kinetics to identify local perfusion deficits and micro infarcts as well as the measurement of maternal placental blood volumes via T1 mapping.
Disclosures: This work was supported by the National Institutes of Health (grants R01 HD103443, R21 AI129308, U01 HD087216, and T32 HD041921). The University of Wiscosin-Madison receives research support from GE Healthcare. AMAG Pharmaceuticals provided ferumoxytol for preclinical MRI studies.