Sound of nurturing: Advanced photoacoustic and ultrasound imaging of placental hemodynamics.

The placenta is a transient yet vital organ that regulates maternal-fetal exchange and profoundly influences pregnancy outcomes. Placental hemodynamic dysfunction is central to many major obstetric complications, including preeclampsia and fetal growth restriction. Despite advances in obstetric imaging, existing modalities such as Doppler ultrasound, magnetic resonance imaging, and X-Ray computed tomography remain limited in their ability to resolve placental microvasculature or quantify hemodynamics in vivo. Recent developments in photoacoustic (PA) and advanced ultrasound imaging have enabled assessment of placental vasculature, blood perfusion, and oxygenation with improved spatial and temporal resolution. Photoacoustic microscopy (PAM) and photoacoustic computed tomography (PACT) provide optical contrast derived from endogenous hemoglobin, offering functional insight into oxygen transport and vascular remodeling at various scales, while power Doppler (PWD), and ultrasound localization microscopy (ULM) deliver complementary blood flow and microvascular information at clinically-relevant depths. Integrating photoacoustic and ultrasound imaging allows for quantitative, multiscale visualization of placental hemodynamics from the macroscopic to the microscopic level. This review summarizes current progress in photoacoustic and ultrasound-based placental imaging, discusses different system implementations, reports important preclinical and clinical findings, and identifies remaining challenges in technical improvement and broad translation. Together, emerging photoacoustic and ultrasound imaging platforms promise to transform placental research and reproductive healthcare by enabling comprehensive, functional evaluation of maternal-fetal exchange in health and disease.