Abstract

Effects of Cavitation Induced by Low-Power Focused Ultrasound in the Presence of an US Contrast Agent: Study on Rabbit Brain in Vivo

N.Vykhodtseva, N.Mcdannold, N.Sheikov, H.Martin, K.Hynynen (Focused Ultrasound Laboratory, Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, USA)

e-mail: Natalia@bwh.harvard.edu

Objective: To study histological changes produced by pulsed focused US in the brain in the presence of an intravenous gas-based contrast agent, as a function of the US pressure amplitude. Methods: The brains of 28 rabbits were sonicated in four to eight locations, with temporal peak acoustical power of up to 25W. Two sets of sonication parameters were tested: F=1.63/1.5MHz, burst length=(10 or 100)/0.01ms, PRF=1/1000Hz. An ultrasound contrast agent was injected prior to each sonication. MRI was used to guide the procedure. Whole brain histological examination was then performed. Results: We found vascular effects ranging from no or very little damage to severe injury associated with brain tissue degeneration. These effects correlated with the pressure amplitude. With the first set of parameters, blood-brain barrier (BBB) opening was detected but was not associated with brain tissue damage at the lowest exposure levels (1MPa). With the second set, the BBB opening was observed at ~6MPa and was associated with ischemic neuronal damage. At higher pressures, the vasculature in the focal region was almost completely destroyed. Conclusions: This technique may have applications for targeted drug delivery and destruction of vasculature in brain tumors. The low powers required may avoid heating if the ultrasound is delivered through the skull.

Section : 5