A mechanism of ultrasound balloon rupture for fetal surgery

In order to well understand process of balloon rupture by high intensity focused ultrasound (HIFU), the process was analyzed using high speed camera. The balloon, which is used in fetal endoscopic tracheal occlusion (FETO) for treatment of congenital diaphragmatic hernia (CDH), was used. A silicon tube whose inside can be seen is a model of the trachea. The balloon was placed in the silicon tube and inflated with nanodroplet that is gasified by strong ultrasound. The balloon was irradiated with HIFU on the same conditions as our animal experiment. The balloon was ruptured at the point where was different from the focus of HIFU. The volume of the balloon was increased by HIFU irradiation. We consider that the balloon rupture is strongly related with followings, 1) increase of internal pressure of the balloon which was caused by the gasification of the nanodroplets, 2) pressing of HIFU at the upper surface of the balloon, 3) stopping HIFU energy at incident point of HIFU beam by the bubbles.