title: Functional imaging of the human placenta with magnetic resonance.
abstract: Abnormal placentation is responsible for most failures in pregnancy; however, an understanding of placental functions remains largely concealed from noninvasive, in vivo investigations. Magnetic resonance imaging (MRI) is safe in pregnancy for magnetic fields of up to 3 Tesla and is being used increasingly to improve the accuracy of prenatal imaging. Functional MRI (fMRI) of the placenta has not yet been validated in a clinical setting, and most data are derived from animal studies. FMRI could be used to further explore placental functions that are related to vascularization, oxygenation, and metabolism in human pregnancies by the use of various enhancement processes. Dynamic contrast-enhanced MRI is best able to quantify placental perfusion, permeability, and blood volume fractions. However, the transplacental passage of Gadolinium-based contrast agents represents a significant safety concern for this procedure in humans. There are alternative contrast agents that may be safer in pregnancy or that do not cross the placenta. Arterial spin labeling MRI relies on magnetically labeled water to quantify the blood flows within the placenta. A disadvantage of this technique is a poorer signal-to-noise ratio. Based on arterial spin labeling, placental perfusion in normal pregnancy is 176 ± 91 mL × min(-1) × 100 g(-1) and decreases in cases with intrauterine growth restriction. Blood oxygen level-dependent and oxygen-enhanced MRIs do not assess perfusion but measure the response of the placenta to changes in oxygen levels with the use of hemoglobin as an endogenous contrast agent. Diffusion-weighted imaging and intravoxel incoherent motion MRI do not require exogenous contrast agents, instead they use the movement of water molecules within tissues. The apparent diffusion coefficient and perfusion fraction are significantly lower in placentas of growth-restricted fetuses when compared with normal pregnancies. Magnetic resonance spectroscopy has the ability to extract information regarding metabolites from the placenta noninvasively and in vivo. There are marked differences in all 3 metabolites N-acetyl aspartate/choline levels, inositol/choline ratio between small, and adequately grown fetuses. Current research is focused on the ability of each fMRI technique to make a timely diagnosis of abnormal placentation that would allow for appropriate planning of follow-up examinations and optimal scheduling of delivery. These research programs will benefit from the use of well-defined sequences, standardized imaging protocols, and robust computational methods.
authors.affiliation: INSERM, U970, Sorbonne Paris Cite, Paris Cardiovascular Research Center-PARCC, Paris, France; EA FETUS and LUMIERE Unit, Université Paris-Descartes, Paris, France; Hôpital Européen Georges Pompidou, Paris, France.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Siauve
authors.affiliation: INSERM, U970, Sorbonne Paris Cite, Paris Cardiovascular Research Center-PARCC, Paris, France; EA FETUS and LUMIERE Unit, Université Paris-Descartes, Paris, France; Assistance Publique-Hôpitaux de Paris, Hôpital Necker-Enfants Malades, Paris, France.
authors.forename: Gihad E
authors.initials: GE
authors.lastname: Chalouhi
authors.affiliation: INSERM, U970, Sorbonne Paris Cite, Paris Cardiovascular Research Center-PARCC, Paris, France; EA FETUS and LUMIERE Unit, Université Paris-Descartes, Paris, France; Assistance Publique-Hôpitaux de Paris, Hôpital Necker-Enfants Malades, Paris, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Deloison
authors.affiliation: INSERM, U970, Sorbonne Paris Cite, Paris Cardiovascular Research Center-PARCC, Paris, France.
authors.forename: Marianne
authors.initials: M
authors.lastname: Alison
authors.affiliation: INSERM, U970, Sorbonne Paris Cite, Paris Cardiovascular Research Center-PARCC, Paris, France; Hôpital Européen Georges Pompidou, Paris, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Clement
authors.affiliation: EA FETUS and LUMIERE Unit, Université Paris-Descartes, Paris, France; Assistance Publique-Hôpitaux de Paris, Hôpital Necker-Enfants Malades, Paris, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Ville
authors.affiliation: INSERM, U970, Sorbonne Paris Cite, Paris Cardiovascular Research Center-PARCC, Paris, France; EA FETUS and LUMIERE Unit, Université Paris-Descartes, Paris, France; Assistance Publique-Hôpitaux de Paris, Hôpital Necker-Enfants Malades, Paris, France. Electronic address: laurentsalomon@gmail.com.
authors.forename: Laurent J
authors.initials: LJ
authors.lastname: Salomon
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000009:adverse effects; D005260:Female; D005317:Fetal Growth Retardation / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy; D010100:Oxygen / Q000494:pharmacology; D010920:Placenta / Q000187:drug effects / Q000502:physiology*; D010922:Placenta Diseases / Q000175:diagnosis*; D010929:Placentation; D011247:Pregnancy; D059629:Signal-To-Noise Ratio
chemical_list: D003287:Contrast Media; D010100:Oxygen
keywords: ASL; BOLD; DCE; IUGR; IVIM; MRI; pregnancy; spectroscopy