Occlusion of blood flow by high-intensity focused ultrasound

Abstract

This work investigates the possiblity of occluding blood flow (in vivo) using high-intensity focused ultrasound surgery (FUS). Such an effect could be used, for example, in the noninvasive treatment of foetal dysfunctions. A high-power 1.7-MHz, 150-mm focal length, piezoelectric transducer was used to expose rat femoral vessels to a free field I−SP=4660 W cm−2 for 2 s under terminal anaesthesia. Initially, eight separate exposures were used. Later experiments were aimed at determining an optimal single exposure to produce flow occlusion. Before and after exposure, magnetic resonance FISP 3-D angiograms (MRA) with submillimeter spatial resolution were acquired using a Siemens Vision MR System (1.5T) and extremity coil. In all animals, MRA showed reduced blood flow both in the treated region and distal to it. The results of single-dose optimization will be discussed. The ability to curtail blood flow using FUS allows the possibility of treating Foeto-Foetal Transfusion Syndrome by occluding the placental shunt vessels responsible for vascular inbalance in identical twins. Currently available interventional treatments (surgery or intrauterine laser therapy) have significant mortality and morbidity. The FUS has the advantage of being noninvasive. [Work was funded by the UK Medical Research Council.]