Superb Microvascular Imaging Assessment of Placenta Using an 18-MHz Probe

Superb microvascular imaging (SMI) can detect low-velocity blood flow in the placenta by significantly reducing motion artifacts. Moreover, SMI using an 18-MHz probe generates a high-resolution image of the placental microvasculature in normal and abnormal placentas. In the normal placenta, the increased density of the placental microvasculature with advancing gestation was evident using SMI with an 18-MHz probe. The placental baseline between the placenta and myometrium was also clearly identified. In the first-trimester placenta with an extremely large subchorionic hematoma, decreased vascularity in the placenta adjacent to the hematoma was clearly recognized. In the circumvallate placenta, the placental microvasculature using 18-MHz-SMI was more precisely noted compared with conventional SMI. In a case of pregnancy after a previous uterine fundal incision, a high-resolution SMI with an 18-MHz probe could clearly identify the very thin uterine wall. In cases of placenta accreta spectrum (PAS) during pregnancy and in the retained placenta after birth, various types of PAS were noted, and unique microvasculature was also demonstrated using SMI with an 18-MHz probe. Superb microvascular imaging with an 18-MHz probe may become a future modality to provide novel information on the antenatal evaluation of normal and abnormal placentas, and the physiologic progress of normal placental microvascular development, and precise pathologic findings of placental abnormality in clinical practice and future research.