Le but de ce travail est d’obtenir des données non invasives sur l’oxygénation foetoplacentaire en IRM par effet BOLD (Blood Oxygenation Level Dependent). La comparaison des données sur des foetus eutrophe et d’autres en RCIU permettra de déterminer l’apport potentiel de cette technique dans le diagnostic et la prise en charge de placentas dysfonctionnels associés à un risque accru de RCIU. Les inclusions ont commencé.
L’équipe de la Maternité Necker-Enfants malades est l’auteur d’une revue des techniques d’imagerie fonctionnelle placentaire, à paraître dans un numéro spécial de l’American Journal of Obstetrics and Gynecology.
Functional Imaging of the Human Placenta with Magnetic Resonance
N. Siauve, G. Chalouhi, B. Deloison, M Alison, O Clement, Y Ville, LJ Salomon
Abnormal placentation is responsible for most failures in pregnancy, however an understanding placental functions remains largely concealed from non-invasive, in vivo investigations. Magnetic Resonance Imaging (MRI) is safe in pregnancy for magnetic fields of up to 3 Teslas and is increasingly being used 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 is derived from animal studies. fMRI could be used to further explore placental functions related to vascularization, oxygenation and metabolism in human pregnancies, by using various enhancement processes. Dynamic Contrast Enhanced MRI (DCE-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 (ASL) 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 (SNR). Based on ASL, 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 (BOLD) and Oxygen Enhanced (OE) MRI do not assess perfusion but measure the response of the placenta to changes in oxygen levels using hemoglobin (Hb) as an endogenous contrast agent. Diffusion Weighted Imaging (DWI) and Intra Voxel Incoherent Motion (IVIM) MRI do not require exogenous contrast agents, instead utilizing the movement of water molecules within tissues. The Apparent Diffusion Coefficient (ADC) and perfusion fraction (f) are significantly lower in placentas of growth-restricted fetuses when compared to normal pregnancies. Magnetic resonance spectroscopy (MRS) has the ability to extract information regarding metabolites from the placenta non-invasively and in vivo. There are marked differences in all 3 metabolites N-acetyl aspartate (NAA)/choline (Cho) levels and inositol/choline ratio between small (SGA) and adequately grown (AGA) fetuses. Current research is focused upon the ability of each fMRI technique to make a timely diagnosis of abnormal placentation that allows for appropriate planning of follow up examinations and optimal scheduling of delivery. These research programs will benefit from using well-defined sequences, standardized imaging protocols and robust computational methods.
The National Institutes of Health has announced $46 million in research awards for the Human Placenta Project, an initiative to revolutionize understanding of the placenta. The awards will fund technology development and testing to assess placental function throughout pregnancy, with the ultimate goal of improving pregnancy outcomes and lifelong health.
Many problems of pregnancy — such as preeclampsia, preterm birth, and even stillbirth — can occur because of problems with the placenta. If researchers can develop tools to monitor the placenta from the earliest stages of pregnancy, physicians may one day be able to identify problems sooner and intervene more quickly.
NIH has funded 19 projects, totaling approximately $46 million in this fiscal year. The awards will support development of safe, noninvasive methods to monitor the placenta in real time, throughout all stages of pregnancy. The funds also will support research on environmental factors that may affect placental function.
Building upon earlier work that has examined the impact of air pollution on pregnancy, Kyung Sung, Dr. Sherin Devaskar and Dr. Carla Janzen, along with Dr. Beate Ritz (not pictured), will study how exposure to pollution affects the placenta.
The National Institutes of Health has awarded UCLA a $4.2 million grant to study how environmental pollution negatively affects how the placenta develops in pregnant women, ultimately contributing to poor pregnancy outcomes.
Dr. Sherin Devaskar, the Mattel Executive Endowed Chair of the department of pediatrics at Mattel Children’s Hospital UCLA, will lead a team of researchers that will build upon earlier work that has examined the impact of air pollution on pregnancy.
The placenta is a critical organ that shuttles blood, oxygen, and nutrients from mother to fetus and clears harmful waste like carbon dioxide. It also produces hormones to help sustain the pregnancy and regulate the immune system so that mother and fetus can coexist. Many problems of pregnancy — such as preeclampsia, preterm birth, and even stillbirth — can occur because of problems with the placenta. (suite…)