Effect of contrast agents on arteries occluded by exposure to HIFU

HIFU can occlude blood flow to induce hemostasis during bleeding from arteries as a treatment for anterior-venous malformation and to reduce the size of tumors by preventing blood flow from feeding arteries. We postulated that injecting ultrasound contrast agents might decrease the HIFU intensity required for arterial occlusion in addition, microbubbles because microbubbles are destroyed under ultrasound sonication; might exert a cavitation effect on the endothelium, which would damage blood vessels. This study investigates the effect of contrast agents on changes in blood flow and arterial morphology induced by HIFU. We constructed a prototype transducer which provides both color flow image and HIFU sonication. HIFU was applied through the skin for 5 seconds to nine focal spots which were aligned at intervals of 0.5 mm across the veccel on each hindpaw of Sprague-Dawley (SD) rats. Peak HIFU intensities were 530, 1080, 1550 and 2750 W/cm ². Five rats were injected with 60 mg of Levovist®, and 5 received 0.5 ml of saline (control). Blood flow was occluded by exposure to HIFU at intensities of 530, 870, 1,550 and 2,750W/cm ² in 0% (0/5), 60% (3/5), 100% (5/5) and 100% (5/5) of the rats given Levovist®, respectively. Blood flow was occluded in 0% (0/5), 0% (0/5), 0% (0/5) and 80% (4/5) of the control rats at each respective HIFU intensity. Staining with hematoxylin-eosin (HE) revealed obvious vacuolar degeneration in the tunica media and endothelium cells that had detached from the vessel walls of the rats given Levovist®. These results imply that the cavitation induced by contrast agents under HIFU exposure exerts significant effects on the vessel endothelium. Therefore, injected contrast agents might reduce the intensity of HIFU required to occlude targeted arteries.