Non-invasive determination of murine placental and foetal functional parameters with multispectral optoacoustic tomography

Despite the importance of placental function in embryonic development, it remains poorly understood and challenging to characterize, primarily due to the lack of non-invasive imaging tools capable of monitoring placental and foetal oxygenation and perfusion parameters during pregnancy. We developed an optoacoustic tomography approach for real-time imaging through entire ~4 cm cross-sections of pregnant mice. Functional changes in both maternal and embryo regions were studied at different gestation days when subjected to an oxygen breathing challenge and perfusion with indocyanine green. Structural phenotyping of the cross-sectional scans highlighted different internal organs, whereas multi-wavelength acquisitions enabled non-invasive label-free spectroscopic assessment of blood-oxygenation parameters in foeto-placental regions, rendering a strong correlation with the amount of oxygen administered. Likewise, the placental function in protecting the embryo from extrinsically administered agents was substantiated. The proposed methodology may potentially further serve as a probing mechanism to appraise embryo development during pregnancy in the clinical setting. A non-invasive imaging tool that reveals blood oxygen levels and perfusion in mice placentas and fetuses has potential applications for monitoring preeclampsia and other pregnancy disorders. Optoacoustic (OA) imaging involves sending laser pulses into biological tissue. The light absorption results in emission of ultrasonic waves, which are detected and used to build up images representing physiological factors such as oxygen levels. Daniel Razansky at the University of Zurich and ETH Zurich, Switzerland, and co-workers used OA imaging to non-invasively monitor placental and fetal function in pregnant mice. The team administered near-infrared contrast agent and alternate doses of 20 and 100% oxygen to the mice via breathing apparatus and monitored the resulting blood oxygenation and perfusion parameters. The images provided unprecedented detail showing how the placenta protects the embryo from excessive oxygen and extrinsically administered agents.