Application of high-intensity focused ultrasound for umbilical artery occlusion in a rabbit model

Objectives: To investigate the application of high-intensity focused ultrasound (HIFU) for fetal umbilical artery blood flow occlusion in a rabbit model. Methods: A prototype HIFU transducer in combination with an imaging probe with Doppler capability was constructed. Using this transducer, HIFU was applied at 1.4, 2.75 or 5.5 kW/cm² through the maternal abdominal skin to the fetal intra-abdominal umbilical arteries of four time-mated Japanese White rabbits (11 fetuses) on gestational day 25. Courses of 5-s HIFU exposure were performed until cessation of umbilical blood flow and cardiac arrest were confirmed by Doppler ultrasonography. Fetal necropsy was performed and exposed lesions were assessed by microscopic histological analysis. Results: The mean diameter of the fetal umbilical artery was 0.6 ± 0.2 mm and the mean peak systolic velocity of arterial blood flow was 44.7 ± 18.5 cm/s. When HIFU was applied at 5.5 kW/cm², blood flow was completely occluded within 15 courses. HIFU exposure brought about vacuolar degeneration and destruction of elastic fibers in the tunica media of the artery. Conclusions: HIFU can be used to occlude umbilical artery blood flow in fetal rabbits.