Embryonic development, the generation of a living organism from a fertilized egg, poses some of the most intriguing challenges of biological research. Aberrations in development can arise from genetic alterations in the fetus, which can vary in the degree of penetration, and can also result from direct and indirect pathological processes affecting the fetus or the mother. Impaired fetal development is a major cause of premature morbidity and mortality. Dynamic imaging of the live fetus provides an important tool for elucidating the normal and pathological developmental changes occurring during pregnancy. In particular, as part of efforts for functional mapping of the genome using genetically modified animals, detailed analysis of fetal development in laboratory animals is central in elucidating the function of genes and the impact of alteration in gene expression. Moreover, imaging biomarkers developed in the context of basic biological research could provide the foundations for future prenatal clinical imaging. In this chapter, we will review recent developments in the use of noninvasive imaging for longitudinal monitoring of live embryos in small laboratory animals, with particular focus on in utero imaging of fetal development in the mouse.

MRI and fluorescence microscopy provide complementary information on the structure and function of placental blood vessels. Due to the highly effective fetal-maternal barrier, dynamic contrast enhanced MRI using macromolecular contrast media probes exclusively the maternal blood flow in the placenta, providing information on the rate of flow into the placenta. Arterial spin labeling follows the motion of water across the fetal-maternal barrier, and thus this approach can provide information on perfusion. Arterial spin labeling achieved by tagging water passing through the uterine versus the ovarian arterial input, provide directional information for the two blood supplies, and can also help in non invasive positioning of the embryos along the uterine horns. Fluorescence intravital and ex vivo imaging provides for faster dynamic analysis and validation of maternal blood volume respectively.

Multimodal imaging is an important part of the study of placenta structure and function, as well as embryonic development, particularly in transgenic mice. The development of novel imaging techniques can contribute significantly to enhance our understanding of placental structure, exchange within the placenta, as well as the architecture and function of the maternal and fetal vasculature system, all of which are critical in the evaluation of the dynamic relationships between the mother, placenta, and fetus during pregnancy. Recent progress of a number of imaging approaches is described herein, including non-invasive MRI, ultrasound imaging, fluorescence microscopy, and photoacoustic imaging. Applications of these techniques are used to monitor the details of blood-flow patterns in the uterine arteries, to measure placental perfusion, and to characterize angiogenesis and vascular permeability, providing insight into placental and fetal pathologies. All of these findings eventually provide a better appreciation for the unique properties of mammalian development and reproduction.