Photoacoustic tomography (PAT) is an emerging biomedical imaging modality that combines optical and ultrasonic imaging, providing overlapping fields of view. This hybrid approach allows for a natural integration of PAT and ultrasound (US) imaging in a single platform. Due to the similarities in signal acquisition and processing, the combination of PAT and US imaging creates a new hybrid imaging for novel clinical applications. Over the recent years, particular attention is paid to the development of PAT/US dual-modal systems highlighting mutual benefits in clinical cases, with an aim of substantially improving the specificity and sensitivity for diagnosis of diseases. The demonstrated feasibility and accuracy in these efforts open an avenue of translating PAT/US imaging to practical clinical applications. In this review, the current PAT/US dual-modal imaging systems are discussed in detail, and their promising clinical applications are presented and compared systematically. Finally, this review describes the potential impacts of these combined systems in the coming future.

Background: Since conjoined twins were thought to be monoamniotic in the past, diamniotic conjoined twins would be improbable theoretically. Body stalk anomaly is a severe defect of the body wall, which is rare among twins. Body stalk anomaly in monochorionic diamniotic conjoined twins has never been reported prenatally so far as we know. Case presentation: Here we present an extremely rare case of concordant body stalk anomaly in monochorionic diamniotic conjoined twins. Ultrasonography at 9 + 5 weeks revealed one chorionic and two amniotic cavities, close apposition of abdomen, limited movement, and common umbilical vessels. Follow-up ultrasonography at 11 + 6 weeks and 13 + 2 weeks showed close apposition of the lower abdominal region with cystic structures and a small bowel-like mass between the two fetuses. Three-dimensional ultrasonography assisted in observing the entire appearance of both twins in earlier first trimester, including amnioticity, conjoined region and umbilical vessels. We attribute this diamniotic conjoined twin in our case to the fusion theory. A single yolk sac was observed, challenging the idea that yolk sac number predicts amnionicity. Identification of single yolk sac and its allantois may form a common body stalk during this fusion, leading to concordant body stalk anomaly in monochorionic diamniotic twins. Conclusions: Our case may provide important insights into both ultrasonographic features and embryogenesis of this extremely rare anomaly.