The Vasculature of Pregnancy Studied by MRI and Optoacoustic Imaging

Some of the main challenges in modern day obstetrics include the early identification of fetuses and mothers at high risk, diagnosis and quantification of placental insufficiency, and prediction of clinical outcome. In current clinical practice, screening and follow-up is largely based on ultrasound (US) assessments, however these measurements only provide an indirect estimate of several important physiological parameters, including blood flow, perfusion and oxygenation status. Development of complementary non-invasive imaging tools capable of assessing the vasculature of pregnancy and placental function could potentially serve as sensitive biomarkers for negative changes, even at early pregnancy stages, and may improve the diagnosis of pregnancy complications and potentially perinatal outcome.

Magnetic Resonance Imaging (MRI) is a versatile and powerful imaging modality, which reveals, non-invasively, both structural and functional dynamic information, with high soft-tissue contrast and high spatial resolution. MRI provides a wide range of techniques for detection of essential physiological parameters, such as blood flow, perfusion and oxygenation status. Over the past few years, a number of MRI methods were employed in animal studies and in the clinical settings to study the vasculature of pregnancy and placental function.

Photoacoustic imaging (PA) is a real-time imaging method combining laser pulse excitation and ultrasonic detection of tissue response. PA imaging allows in vivo detection of blood vasculature and spectroscopic assessment of the oxygenation of blood by exploiting the differing optical absorption spectra of deoxyhemoglobin (Hb) and oxyhemoglobin (HbO2). PA has been recently employed in rodents to obtain quantitative spectroscopic measurements of placenta oxygen-hemoglobin saturation levels.
In this talk, we will review the basis of each of these methods and examine their application, starting from preclinical small animal models, progressing to larger animal models and, finally, to human studies.