MRI Measurement of Placental Perfusion and Fetal Blood Oxygen Saturation in Normal Pregnancy and Placental Insufficiency

The placenta is essential for successful pregnancy outcome. Inadequate placenta development leads to poor placental perfusion and placental insufficiency, responsible for one third of antenatal stillbirths. Current imaging modalities provide poor clinical assessment of placental perfusion and pregnancy outcome. In this work we propose a technique to estimate the vascular properties of retro-placenta myometrial and placental perfusion. The fetal blood saturation is a relative unknown, thus we describe a method to simultaneously estimate the fetal blood volume in addition to the fetal blood T2 relaxation time from which we can estimate this parameter. This information may prove useful for predicting if and when a placenta will fail, and thus when a small baby must be delivered to have the best neurological outcome. We report differences in vascular compartments and saturation values observed between 5 normal pregnancies, and two complicated by placental insufficiency

Investigating Perfusion of the Human Placenta

Placental insufficiency is a significant cause of morbidity and mortality, accounting for one third of antenatal stillbirths. It occurs when the maternal spiral arteries fail to remodel normally in early pregnancy, leading to inadequate maternal perfusion of the placenta. The fetus becomes hypoxic and if not delivered prematurely may ultimately die. Assessing the placenta is therefore clinically important, to diagnose placental insufficiency in vivo, and investigate poor pregnancy outcome ex vivo. Ex vivo placental assessment relies on subjective histological analysis of a small proportion of the placenta, looking for features such as oedema, inflammation and the presence of avascular villi. Regional variation and heterogeneity are not defined. In utero clinical assessment is via ultrasound Doppler measurements, looking for increased resistance in the uterine arteries, suggesting poor spiral artery remodeling, and increased resistance within the umbilical artery, suggesting inadequate development of the feto-placental microcirculation. There is therefore an urgent need to develop new ways to evaluate the perfusion of the placenta both in and ex vivo. In this thesis I investigate two imaging modalities with the potential to improve our understanding of placental perfusion. Ex vivo I develop a placental perfusion and micro-CT imaging technique, to directly visualise the feto-placental microcirculation, before applying the technique to investigate heterogeneity within a cohort of normal term placentae. I investigate differences in vascular density through the placenta at multiple scales. In vivo I investigate a novel Magnetic Resonance Imaging model of placental perfusion, that combines diffusion weighted imaging with T2 relaxometry, to estimate maternal and fetal placental perfusion. I develop this technique, exploring MRI parameters relating to perfusion in normally grown and growth restricted pregnancies. This work is important as the techniques developed improve our ability to investigate and understand placental perfusion, and provide potential new parameters of placental function in vivo