Noninvasive, transcranial and localized opening of the blood-brain barrier using focused ultrasound in mice.

The feasibility of blood-brain barrier (BBB) opening in the hippocampus of wild-type mice using focused ultrasound (FUS) through the intact skull and skin was investigated. Needle hydrophone measurements through ex vivo skulls revealed minimal attenuation ( approximately 18% of the pressure amplitude), a well-focused beam pattern and minute focus displacement through the parietal bone. In experiments in vivo, the brains of three mice were sonicated transcranially. Pulsed ultrasound sonications at 1.5 MHz and acoustic pressures ranging from 0.8 to 2.7 MPa were used at 20% duty cycle. Before sonication, a bolus of 10 microL of an ultrasound contrast agents (Optison) was injected intravenously. Contrast-enhanced high-resolution magnetic resonance imaging (9.4 T) revealed BBB opening and allowed for the monitoring of the slow permeation of gadolinium in the hippocampus. The region of the brain where BBB opening occurred increased with the pressure amplitude. These findings thus demonstrated the feasibility of locally opening the BBB in mice using FUS through intact skull and skin and serve as the first step in determining and assessing feasibility of drug delivery to specific regions in the mouse brain using FUS.